351
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Shiraishi K, Ascoli M. Lutropin/choriogonadotropin stimulate the proliferation of primary cultures of rat Leydig cells through a pathway that involves activation of the extracellularly regulated kinase 1/2 cascade. Endocrinology 2007; 148:3214-25. [PMID: 17412805 PMCID: PMC2085235 DOI: 10.1210/en.2007-0160] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Primary cultures of progenitor and immature rat Leydig cells were established from the testes of 21- and 35-d-old rats, respectively. The cell population remained homogeneous after 4-6 d in culture as judged by staining for 3beta-hydroxysteroid dehydrogenase, but the cells were unable to bind 125I-human chorionic gonadotropin (hCG) or to respond to hCG with classical LH receptor (LHR)-mediated responses, including cAMP and inositol phosphate accumulation, steroid biosynthesis, or the phosphorylation of ERK1/2. Infection of primary cultures with recombinant adenovirus coding for beta-galactosidase showed that approximately 65% of the cells are infected. Infection with adenovirus coding for the human LHR (hLHR) allowed for expression of the hLHR at a density of approximately 25,000 receptors per cell and allowed the cells to respond to hCG with increases in cAMP and inositol phosphate accumulation, steroid biosynthesis, and the phosphorylation of ERK1/2. Although progenitor and immature cells were able to respond to hCG with an increase in progesterone, only the immature cells responded with an increase in testosterone. In addition to these classical LHR-mediated responses, the primary cultures of progenitor or immature rat Leydig cells expressing the recombinant hLHR proliferated robustly when incubated with hCG, and this proliferative response was sensitive to an inhibitor of ERK1/2 phosphorylation. These studies establish a novel experimental paradigm that can be used to study the proliferative response of Leydig cells to LH/CG. We conclude that activation of the LHR-provoked Leydig cell proliferation requires activation of the ERK1/2 cascade.
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Affiliation(s)
- Koji Shiraishi
- Department of Pharmacology, Carver College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA
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352
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Gromoll J, Lahrmann L, Godmann M, Müller T, Michel C, Stamm S, Simoni M. Genomic checkpoints for exon 10 usage in the luteinizing hormone receptor type 1 and type 2. Mol Endocrinol 2007; 21:1984-96. [PMID: 17505059 DOI: 10.1210/me.2006-0506] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Alternative splicing is a hallmark of glycoprotein hormone receptor gene regulation, but its molecular mechanism is unknown. The LH receptor (LHR) gene possesses 11 exons, but exon 10 is constitutively skipped in the New World monkey lineage (LHR type 2), whereas it is constitutively spliced in the human (LHR type 1). This study identifies the regulatory elements of exon 10 usage. Sequencing of genomic marmoset DNA revealed that the cryptic LHR exon 10 is highly homologous to exon 10 from other species and displays intact splice sites. Functional studies using a minigene approach excluded the contribution of intronic, marmoset-specific long interspersed nucleotide-1 elements to exon 10 skipping. Sequencing of the genomic regions surrounding exon 10 from several primate lineages, sequence comparisons including the human and mouse LHR gene, revealed the presence of unique nucleotides at 3'-intronic position -19 and -10 and at position +26 within exon 10 of the marmoset LHR. Exon trap experiments and in vitro mutagenesis of these nucleotides resulted in the identification of a composite regulatory element of splicing consisting of cis-acting elements represented by two polypyrimidine tracts and a trans-acting element within exon 10, which affect the secondary RNA structure. Changes within this complex resulted either in constitutive exon inclusion, constitutive skipping, or alternative splicing of exon 10. This work delineates the molecular pathway leading to intronization of exon 10 in the LHR type 2 and reveals, for the first time, the essential function of regulatory and structural elements involved in glycoprotein hormone receptor splicing.
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Affiliation(s)
- Jörg Gromoll
- Institute of Reproductive Medicine, University Hospital, D-48129 Münster, Germany.
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353
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Wilken JA, Bedows E. A novel four-amino acid determinant defines conformational freedom within chorionic gonadotropin beta-subunits. Biochemistry 2007; 46:4417-24. [PMID: 17358049 PMCID: PMC2597539 DOI: 10.1021/bi602449d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
On the basis of apparent molecular mass heterogeneity following reducing versus nonreducing SDS-PAGE, we determined that the beta-subunit of macaque (Macaca fascicularis) chorionic gonadotropin (mCG-beta) is more conformationally constrained than the beta-subunit of human chorionic gonadotropin (hCG-beta). The amino acid sequences of these two subunits are 81% identical. To determine the conformational variance source, which was not due to glycosylation differences, we generated a series of hCG-beta-mCG-beta chimeras and identified domains that contributed to CG-beta conformational freedom. We discovered that the CG-beta 54-101 domain contained a small subdomain, residues 74-77, that regulated the conformational freedom of the beta-subunit; i.e., when residues 74-77 were of macaque origin (PGVD), the mutated hCG-beta subunit displayed macaque-like conformational rigidity, and when residues 74-77 were of human origin (RGVN), the mutated mCG-beta subunit displayed human-like conformational freedom and microheterogeneity. Additionally, CG-beta N-terminal domain residues (8, 18, 42, and 46-48) were also found to influence CG-beta conformational freedom when residues 74-77 were of human but not macaque origin. The biological significance of the CG-beta conformational variance was tested using a biological assay that showed that the hCG-alpha-hCG-beta heterodimer facilitated human CG receptor-mediated cAMP-driven luciferase reporter gene activity in HEK cells nearly 1 order of magnitude more effectively than the hCG-alpha-mCG-beta chimera. Together, these data demonstrate that two essential amino acid residues within a four-amino acid subdomain regulated CG-beta conformational freedom and that a conformational difference between hCG-beta and mCG-beta was recapitulated in the context of receptor-mediated CG heterodimer signal transduction activation.
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MESH Headings
- Algorithms
- Amino Acid Sequence
- Animals
- Biological Assay
- Cell Line
- Chorionic Gonadotropin/chemistry
- Chorionic Gonadotropin/genetics
- Chorionic Gonadotropin/metabolism
- Chorionic Gonadotropin, beta Subunit, Human/chemistry
- Chorionic Gonadotropin, beta Subunit, Human/genetics
- Chorionic Gonadotropin, beta Subunit, Human/isolation & purification
- Chorionic Gonadotropin, beta Subunit, Human/metabolism
- Cyclic AMP/metabolism
- Dimerization
- Disulfides/chemistry
- Genes, Reporter
- Humans
- Kinetics
- Luciferases/metabolism
- Macaca fascicularis
- Models, Molecular
- Molecular Sequence Data
- Mutation
- Polymerase Chain Reaction
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Protein Subunits/chemistry
- Protein Subunits/genetics
- Protein Subunits/isolation & purification
- Protein Subunits/metabolism
- Recombinant Proteins/chemistry
- Recombinant Proteins/metabolism
- Signal Transduction
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Affiliation(s)
- Jason A Wilken
- Department of Biochemistry and Molecular Biology and the Eppley Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198
| | - Elliott Bedows
- Department of Biochemistry and Molecular Biology and the Eppley Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198
- * To whom correspondence should be addressed: School of Allied Health Professions, College of Medicine, 984300 Nebraska Medical Center, Omaha, NE 68198-4300 Tel.: 402-559-6074 Fax: 402-559-8112 E-mail:
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354
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Kern A, Agoulnik AI, Bryant-Greenwood GD. The low-density lipoprotein class A module of the relaxin receptor (leucine-rich repeat containing G-protein coupled receptor 7): its role in signaling and trafficking to the cell membrane. Endocrinology 2007; 148:1181-94. [PMID: 17158203 DOI: 10.1210/en.2006-1086] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The relaxin receptor (LGR7, relaxin family peptide receptor 1) is a member of the leucine-rich repeat containing G protein-coupled receptors subgroup C. This and the LGR8 (relaxin family peptide receptor 2) receptor are unique in having a low-density lipoprotein class A (LDL-A) module at their N termini. This study was designed to show the role of the LDL-A in LGR7 expression and function. Point mutants for the conserved cysteines (Cys(47) and Cys(53)) and for calcium binding asparagine (Asp(58)), a mutant with deleted LDL-A domain and chimeric LGR7 receptor with LGR8 LDL-A all showed no cAMP response to human relaxins H1 or H2. We have shown that their cell surface delivery was uncompromised. The mutation of the putative N-linked glycosylation site (Asn(36)) decreased cAMP production and reduced cell surface expression to 37% of the wild-type LGR7. All point mutant, chimeric, and wild-type receptor proteins were expressed as the two forms. The immature or precursor form of the receptor was 80 kDa, whereas the mature receptor, delivered to the cell surface was 95 kDa. The glycosylation mutant was also expressed as two forms with appropriately smaller molecular masses. Deletion of the LDL-A module resulted in expression of the mature receptor only. These data suggest that the LDL-A module of LGR7 influences receptor maturation, cell surface expression, and relaxin-activated signal transduction.
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Affiliation(s)
- András Kern
- Pacific Biosciences Research Center, University of Hawaii, 651 Ilalo Street, Honolulu, HI 96813, USA.
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355
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Halls ML, van der Westhuizen ET, Bathgate RAD, Summers RJ. Relaxin family peptide receptors--former orphans reunite with their parent ligands to activate multiple signalling pathways. Br J Pharmacol 2007; 150:677-91. [PMID: 17293890 PMCID: PMC2013861 DOI: 10.1038/sj.bjp.0707140] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The relaxin family peptides, although structurally closely related to insulin, act on a group of four G protein-coupled receptors now known as Relaxin Family Peptide (RXFP) Receptors. The leucine-rich repeat containing RXFP1 and RXFP2 and the small peptide-like RXFP3 and RXFP4 are the physiological targets for relaxin, insulin-like (INSL) peptide 3, relaxin-3 and INSL5, respectively. RXFP1 and RXFP2 have at least two binding sites--a high-affinity site in the leucine-rich repeat region of the ectodomain and a lower-affinity site in an exoloop of the transmembrane region. Although they respond to peptides that are structurally similar, RXFP3 and RXFP4 demonstrate distinct binding properties with relaxin-3 being the only peptide that can recognize these receptors in addition to RXFP1. Activation of RXFP1 or RXFP2 causes increased cAMP and the initial response for both receptors is the resultant of Gs-mediated activation and G(oB)-mediated inhibition of adenylate cyclase. With RXFP1, an additional delayed increase in cAMP involves betagamma subunits released from G(i3). In contrast, RXFP3 and RXFP4 inhibit adenylate cyclase and RXFP3 causes ERK1/2 phosphorylation. Drugs acting at RXFP1 have potential for the treatment of diseases involving tissue fibrosis such as cardiac and renal failure, asthma and scleroderma and may also be useful to facilitate embryo implantation. Activators of RXFP2 may be useful to treat cryptorchidism and infertility and inhibitors have potential as contraceptives. Studies of the distribution and function of RXFP3 suggest that it is a potential target for anti-anxiety and anti-obesity drugs.
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MESH Headings
- Amino Acid Sequence
- Animals
- Conserved Sequence
- Evolution, Molecular
- Female
- Humans
- Ligands
- Male
- Models, Biological
- Models, Molecular
- Molecular Sequence Data
- Protein Isoforms/chemistry
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- Receptors, G-Protein-Coupled/chemistry
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Receptors, Peptide/chemistry
- Receptors, Peptide/genetics
- Receptors, Peptide/metabolism
- Relaxin/metabolism
- Sequence Homology, Amino Acid
- Signal Transduction/physiology
- Tissue Distribution
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Affiliation(s)
- M L Halls
- Department of Pharmacology, Monash University, Clayton Victoria, Australia
| | | | - R A D Bathgate
- Howard Florey Institute, University of Melbourne Victoria, Australia
| | - R J Summers
- Department of Pharmacology, Monash University, Clayton Victoria, Australia
- Author for correspondence:
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356
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Yang EJ, Nasipak BT, Kelley DB. Direct action of gonadotropin in brain integrates behavioral and reproductive functions. Proc Natl Acad Sci U S A 2007; 104:2477-82. [PMID: 17284605 PMCID: PMC1893001 DOI: 10.1073/pnas.0608391104] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Essential roles for gonadotropins in gonadal development and reproduction are well established. Over the past decade, however, the expression of luteinizing hormone receptor (LHR) has also been reported in the brain of various mammals and birds. Although suggestive, it has not yet been determined whether this expression pattern supports a novel function for gonadotropins. Here, we demonstrate a CNS-mediated role of gonadotropins in a reproductive behavior: the courtship songs of the South African clawed frog, Xenopus laevis. Male advertisement calling in this species depends on a nongonadal action of gonadotropin. To determine whether this effect is due to action on the CNS, we administered gonadotropin intracerebroventricularly (ICV) or systemically to intact or castrated males with or without concomitant androgen replacement. In intact and androgen-replaced gonadectomized males, gonadotropin significantly increased calling within 1 h after ICV injection. The effective dosage via ICV injections was less than one hundredth of the effective systemic dose. In situ hybridization with a cloned fragment of Xenopus LHR revealed strong expression in ventral forebrain areas important for vocal control. Further, gonadotropin treatment of brain in vitro up-regulates immunoreactivity for the LHR downstream target, egr-1, specifically in these vocal forebrain areas. Up-regulation occurs even when synaptic transmission is suppressed by incubation in Ca2+ free/high magnesium saline. These results demonstrate a neural role for gonadotropin in the control of calling behavior, potentially mediated via LHRs in forebrain vocal nuclei. Gonadotropin may play a novel integrative role in modulating both reproductive physiology and behavior.
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Affiliation(s)
- Eun-Jin Yang
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
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357
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Abstract
The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.
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Affiliation(s)
- Carlos Stocco
- Department of Obstetrics, Gynecology and Reproductive Science, Yale University School of Medicine, New Haven, CT 06510, USA
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358
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Mazzuco TL, Chabre O, Feige JJ, Thomas M. Aberrant GPCR expression is a sufficient genetic event to trigger adrenocortical tumorigenesis. Mol Cell Endocrinol 2007; 265-266:23-8. [PMID: 17250952 DOI: 10.1016/j.mce.2006.12.034] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aberrant expression of G protein-coupled receptors (GPCR) in the adrenal cortex is observed in some cases of ACTH-independent macronodular adrenal hyperplasias and adenomas associated with Cushing syndrome (CS). Although there is clinical evidence for the implication of these receptors in abnormal regulation of cortisol secretion, whether this aberrant expression also directly causes the development of a benign adrenocortical tumor is an open question. Cell transplantation provides a way to study genes that may be important in human tumor development. The system we developed uses genetically modified adrenocortical cells transplanted into adrenalectomized immunodeficient mice, which form a functional tissue structure. We observed that enforcing expression of the gastric inhibitory polypeptide (GIP) receptor or the luteinizing hormone (LH) receptor genes (taken as canonical examples of aberrantly expressed GPCRs) in adrenocortical cells resulted in the formation of hyperplastic tissues and the development of Cushing syndrome features in transplanted mice.
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Affiliation(s)
- T L Mazzuco
- Institut National de la Santé et de la Recherche Médicale, Unité 878, Grenoble, France
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359
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Puett D, Li Y, DeMars G, Angelova K, Fanelli F. A functional transmembrane complex: the luteinizing hormone receptor with bound ligand and G protein. Mol Cell Endocrinol 2007; 260-262:126-36. [PMID: 17059864 PMCID: PMC1866297 DOI: 10.1016/j.mce.2006.05.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Accepted: 05/11/2006] [Indexed: 02/08/2023]
Abstract
The luteinizing hormone receptor (LHR) is one of eight members in a cluster of the rhodopsin family of the large G protein-coupled receptor (GPCR) superfamily that contains some 800-900 genes in the human genome. LHR, along with its paralogons, follicle stimulating hormone receptor (FSHR) and thyroid stimulating hormone receptor, form one of the three classes in this cluster; the two other classes contain the relaxin-binding GPCRs and orphan GPCRs. These GPCRs are characterized by a relatively large ectodomain (ECD) containing leucine-rich-repeats (LRRs); in the class of glycoprotein hormone receptors, the LRR region is capped by N-terminal and C-terminal cysteine-rich regions. Binding of human chorionic gonadotropin (hCG) or luteinizing hormone to the LHR-ECD triggers a conformational change of the transmembrane region of the receptor facilitating binding and activation of Gs, followed by effector enzyme activation and subsequent intracellular signaling. Viewing LHR as a transmembrane anchoring protein that sequentially binds hCG and Gs to give the hCG-LHR-Gs complex, numerous interactions and conformational changes must be considered. There is, unfortunately, a paucity of structural data on LHR, but crystal structures exist for hCG, the homologous FSH-FSHR-ECD (N-terminal fragment) complex, rhodopsin (in the inactive state), an active form of Galphas (transducin), and the betagamma heterodimer. Using a combined experimental (site-directed mutagenesis followed by characterization in transfected cells) and computational (homology modeling and molecular dynamics simulations) approach, good working models are being developed for the protein-protein interaction faces and, in some cases, the ensuing conformational changes induced by complex formation. hCG binding to the LHR-ECD appears to involve several LRRs; LHR activation can be described in terms of disrupting a network of H-bonds in the cytosolic halves of helices 1-3, 6, and 7; and binding of LHR to Gs involves, in large part, intracellular loop 2 binding, presumably to Gsalpha at its C-terminus. Major gaps exist in our understanding at the molecular level of the six-polypeptide chain complex, hCG-LHR-Gs, but considerable progress has been made in the past few years.
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Affiliation(s)
- D Puett
- Department of Biochemistry & Molecular Biology, Life Sciences Building, University of Georgia, 120 Green Street, Athens, GA 30602-7229, USA.
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360
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Meehan TP, Narayan P. Constitutively active luteinizing hormone receptors: consequences of in vivo expression. Mol Cell Endocrinol 2007; 260-262:294-300. [PMID: 17045736 PMCID: PMC1800889 DOI: 10.1016/j.mce.2006.03.045] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Accepted: 03/02/2006] [Indexed: 11/17/2022]
Abstract
Activating mutations in the luteinizing hormone receptor (LHR) gene are one of the most common mutations found in the gonadotropin receptor genes. Human males with these mutations exhibit precocious puberty while females do not have an obvious phenotype. To better understand the pathophysiology of premature LHR activation, transgenic mice have been generated with an activating mutation in LHR and a genetically engineered ligand-activated LHR. This review will summarize the major findings obtained with these two genetically modified mouse models and briefly discuss the similarities and differences between them and with the human phenotype.
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Affiliation(s)
| | - Prema Narayan
- * Corresponding author: Department of Physiology,
School of Medicine, Southern Illinois University, Life Science III, Mailcode
6523, Carbondale IL, 62901, USA, Tel: 618-453-1567, Fax: 618-453-1517,
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361
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Jeoung M, Lee C, Ji I, Ji TH. Trans-activation, cis-activation and signal selection of gonadotropin receptors. Mol Cell Endocrinol 2007; 260-262:137-43. [PMID: 17055146 PMCID: PMC1831837 DOI: 10.1016/j.mce.2005.09.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2005] [Accepted: 09/13/2005] [Indexed: 10/24/2022]
Abstract
It has been thought that when a hormone binds to a receptor, the liganded receptor activates itself and generates hormone signals, such as the cAMP signal and the inositol phosphate signal (cis-activation). We describe that a liganded LH receptor or FSH receptor molecule is capable of intermolecularly activating nonliganded receptors (trans-activation). Particularly, intriguing is the possibility that a pair of compound heterozygous mutants, one defective in binding and the other defective in signaling, may cooperate and rescue signaling. Furthermore, trans-activation of the binding deficient receptors examined in our studies generates either the cAMP signal or the IP signal, but not both. Trans-activation and selective signal generation have broad implications on signal generation mechanisms, and suggest new therapeutic approaches.
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Affiliation(s)
| | | | | | - Tae H. Ji
- *Correspondence should be sent to Tae H, Ji, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055. , Tel: 859-257-3163, Fax:859-257-3229
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362
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Latronico AC, Segaloff DL. Insights learned from L457(3.43)R, an activating mutant of the human lutropin receptor. Mol Cell Endocrinol 2007; 260-262:287-93. [PMID: 17055147 PMCID: PMC1785107 DOI: 10.1016/j.mce.2005.11.053] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Accepted: 11/21/2005] [Indexed: 11/15/2022]
Abstract
The L457(3.43)R mutation of the hLHR was initially identified in a Brazilian boy with gonadotropin-independent precocious puberty. As would be expected, L457(3.43)R, when expressed in 293 cells, caused a marked elevation in basal cAMP levels. Interestingly, in spite of the fact that the elevated basal levels of cAMP elicited by L457R were not as great as those elicited by the wild-type hLHR when stimulated with hCG, L457(3.43)R cells were unresponsive to further hormonal stimulation. We have since determined that the L457(3.43)R mutant, as well as other constitutively active mutants of the hLHR, causes an increase in phosphodiesterase activity that attenuates the target cell to hormonal stimulation of the wild-type hLHR or other Gs-coupled GPCRs. We have also shown that the constitutive activity and lack of hormonal responsiveness of L457(3.43)R are due to the formation of a salt bridge between the introduced arginine in the mid portion of helix 3 with D578(6.44) in the mid portion of helix 6. The formation of this salt bridge results in the disruption of interactions between the cytoplasmic ends of helices 3 and 6 that are associated in general with activation of the hLHR. As such, this mutant has provided novel insights into the properties of target cells expressing activating hLHR mutants and into the structural basis for hLHR activation.
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Affiliation(s)
- Ana Claudia Latronico
- Developmental Endocrinology Unit, Hormone and Molecular Genetics Laboratory, Clinical Hospital, Sao Paulo University Medical School, Sao Paulo, Brazil
| | - Deborah L. Segaloff
- Department of Physiology and Biophysics, The Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, IA, USA
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363
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Fan QR, Hendrickson WA. Assembly and structural characterization of an authentic complex between human follicle stimulating hormone and a hormone-binding ectodomain of its receptor. Mol Cell Endocrinol 2007; 260-262:73-82. [PMID: 17045735 PMCID: PMC2012943 DOI: 10.1016/j.mce.2005.12.055] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2005] [Accepted: 12/22/2005] [Indexed: 10/24/2022]
Abstract
Follicle stimulating hormone (FSH) is secreted from the pituitary gland to regulate reproduction in vertebrates. FSH signals through a G-protein coupled receptor (FSHR) on the target cell surface. We describe here the strategy to produce a soluble FSH-FSHR complex that involves the co-secretion of a truncated FSHR ectodomain (FSHR(HB)) and a covalently linked FSHalphabeta heterodimer from baculovirus-infected insect cells. FSH binds to FSHR(HB) with a high affinity comparable to that for the full-length receptor. The crystal structure of the FSH-FSHR(HB) complex provides explanations for the high affinity and specificity of FSH interaction with FSHR, and it shows an unexpected dimerization of these complexes. Here we also compare the crystal structure with theoretical models of the FSH-FSHR-binding mode. We conclude that the FSH-FSHR(HB) structure gives an authentic representation of FSH binding to intact FSHR.
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MESH Headings
- Animals
- Baculoviridae
- Chorionic Gonadotropin/chemistry
- Chromatography, Gel
- Crystallization
- Dimerization
- Follicle Stimulating Hormone, beta Subunit/analysis
- Follicle Stimulating Hormone, beta Subunit/chemistry
- Follicle Stimulating Hormone, beta Subunit/metabolism
- Glycoprotein Hormones, alpha Subunit/analysis
- Glycoprotein Hormones, alpha Subunit/chemistry
- Glycoprotein Hormones, alpha Subunit/metabolism
- Glycosylation
- Humans
- Models, Molecular
- Protein Structure, Quaternary
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, FSH/analysis
- Receptors, FSH/chemistry
- Receptors, FSH/metabolism
- Solubility
- Structure-Activity Relationship
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Affiliation(s)
- Qing R. Fan
- Department of Biochemistry and Molecular Biophysics, Columbia University, 630 West 168th Street, New York, NY 10032
| | - Wayne A. Hendrickson
- Department of Biochemistry and Molecular Biophysics, Columbia University, 630 West 168th Street, New York, NY 10032
- Howard Hughes Medical Institute, Columbia University, 630 West 168th Street, New York, NY 10032
- * Corresponding author. Tel.: +1 212 305 3456; Fax: 212-305-7379. Email address: (W. A. Hendrickson)
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364
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Ascoli M. Potential Leydig cell mitogenic signals generated by the wild-type and constitutively active mutants of the lutropin/choriogonadotropin receptor (LHR). Mol Cell Endocrinol 2007; 260-262:244-8. [PMID: 17055151 PMCID: PMC1761117 DOI: 10.1016/j.mce.2005.09.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2005] [Accepted: 09/23/2005] [Indexed: 11/21/2022]
Affiliation(s)
- Mario Ascoli
- Department of Pharmacology, 2-319B BSB, 51 Newton Road, The University of Iowa, Iowa City, IA 52242-1109, United States.
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365
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Piersma D, Verhoef-Post M, Berns EMJJ, Themmen APN. LH receptor gene mutations and polymorphisms: an overview. Mol Cell Endocrinol 2007; 260-262:282-6. [PMID: 17030087 DOI: 10.1016/j.mce.2005.11.048] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Accepted: 11/07/2005] [Indexed: 11/30/2022]
Affiliation(s)
- Djura Piersma
- Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
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366
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Saint-Dizier M, Malandain E, Thoumire S, Remy B, Chastant-Maillard S. Expression of follicle stimulating hormone and luteinizing hormone receptors during follicular growth in the domestic cat ovary. Mol Reprod Dev 2007; 74:989-96. [PMID: 17219419 DOI: 10.1002/mrd.20676] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In order to better understand the pituitary regulation of follicular growth in the domestic cat, follicle stimulating hormone (FSH) and luteinizing hormone (LH) receptors (R) were localized and quantified in relation to follicle diameter and atresia using in situ ligand binding on ovarian sections. Expression of FSHR was homogeneous and restricted to follicle granulosa cells from the early antral stage onwards, whereas expression of LHR was heterogeneous on theca cells of all follicles from the early antral stage onward, and homogeneous on granulosa cells of healthy follicles larger than 800 microm in diameter and in corpora lutea. LHR were also widely expressed as heterogeneous aggregates in the ovarian interstitial tissue. Atretic follicles exhibited significantly reduced levels of both FSHR and LHR on granulosa cells, compared with healthy follicles whatever the follicular diameter, whereas levels of LHR on theca cells were lower only for atretic follicles larger than 1,600 microm in diameter. In healthy follicles, levels of FSHR and LHR in all follicular compartments increased significantly with diameter. Although generally comparable to that observed in other mammals, the expression pattern of gonadotropin receptors in the cat ovary is characterized by an early acquisition of LHR on granulosa cells of growing follicles and islets of LH binding sites in the ovarian interstitial tissue.
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Affiliation(s)
- Marie Saint-Dizier
- UMR 1198 INRA/ENVA/CNRS, Biologie du Développement et Reproduction, Ecole Nationale Vétérinaire d'Alfort, Maisons-Alfort Cedex, France.
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367
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Kleinau G, Claus M, Jaeschke H, Mueller S, Neumann S, Paschke R, Krause G. Contacts between Extracellular Loop Two and Transmembrane Helix Six Determine Basal Activity of the Thyroid-stimulating Hormone Receptor. J Biol Chem 2007; 282:518-25. [PMID: 17079233 DOI: 10.1074/jbc.m606176200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A number of alanine mutations in extracellular loop two (ECL2) of the thyroid-stimulating hormone receptor (TSHR) were found to increase or decrease basal activity when compared with the wild type receptor. K565A was identified as a mutant with decreased basal activity, and strongly impaired hormone induced signaling activity. To gain insights into how ECL2 mutants affect basal activity, we focused on constitutively activating pathogenic mutant I568V in ECL2, which exhibits elevated basal activity. Because our molecular model suggests that Ile-568 is embedded in an environment of hydrophobic residues provided by transmembrane helix bundle, we tested mutants in this region to identify potential interaction partner(s) for Ile-568. Indeed, the double mutant I568V/I640L (ECL2/TMH6) suppresses the increased basal activity exhibited by I568V alone. We suggest a spatial and functional relationship between ECL2 and TMH6 in which side chain interaction between Ile-568 and Ile-640 constrains the receptor in a conformation with low basal activity. Although the single mutant I640L exhibits basal activity lower than wild type, its differently branched and bulkier side chain complements the reduced side chain bulk in I568V, restoring wild type basal activity to the double mutant. This scenario is confirmed by the reciprocal double mutant I640V/I568L. The combination of basally increased activity of I640V and basally decreased activity of mutant I568L also restores basal activity of wild type TSHR. These and other mutant phenotypes reported here support a dynamic interface between TMH6 and ECL2. Disruption of this critical interface for signaling by introduction of mutations in TSHR can either increase or decrease basal activity.
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Affiliation(s)
- Gunnar Kleinau
- Leibniz-Institut für molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, D-13125 Berlin, Germany
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368
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Bonomi M, Busnelli M, Persani L, Vassart G, Costagliola S. Structural Differences in the Hinge Region of the Glycoprotein Hormone Receptors: Evidence from the Sulfated Tyrosine Residues. Mol Endocrinol 2006; 20:3351-63. [PMID: 16901970 DOI: 10.1210/me.2005-0521] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Tyrosine sulfation is a late posttranslational modification of proteins that takes place in the Golgi network. In the past few years, this process has been identified as an important modulator of protein-protein interactions. Sulfated tyrosine residues have recently been identified in the C-terminal, so-called hinge region of the ectodomain of glycoprotein hormone receptors [TSH, LH/chorionic gonadotropin (CG), and FSH receptors] and were shown to play an important role in the interaction with their natural ligands. The position of two sulfated tyrosine residues in a Y-D/E-Y motif appears perfectly conserved in the alignment of TSH and LH receptors from different species, and site-directed mutagenesis experiments demonstrated that sulfation of the first residue of this motif was responsible for the functional effect on hormone binding. In contrast, the corresponding motif is not conserved in the FSH receptor, in which the first tyrosine residue is missing: the Y-D/E-Y motif is replaced by F(333)DY(335). We extend here our previous observation that, in this case, it is sulfation of the second sole tyrosine residue in the motif that is functionally important. An LH/CG receptor harboring an F(331)DY(333) motif (i.e. displaying decreased sensitivity to human CG) was used as a backbone in which short portions of the FSH receptor were substituted. Segments from the FSH receptor capable of restoring sensitivity to human CG were identified by transfection of the chimeras in COS-7 cells. These experiments identified key amino acid residues in the hinge region of the FSH receptor associated with the functional role of the second sulfated tyrosine residue in a Y-D/E-Y motif, allowing for efficient hormone binding. The experiments represent strong evidence that structural differences in the hinge regions of FSH and LH/CG receptors play a significant role in hormone-receptor-specific recognition.
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Affiliation(s)
- Marco Bonomi
- Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire, Université Libre de Bruxelles, Belgium.
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369
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Kleinau G, Brehm M, Wiedemann U, Labudde D, Leser U, Krause G. Implications for molecular mechanisms of glycoprotein hormone receptors using a new sequence-structure-function analysis resource. Mol Endocrinol 2006; 21:574-80. [PMID: 17110401 DOI: 10.1210/me.2006-0309] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Comparison between wild-type and mutated glycoprotein hormone receptors (GPHRs), TSH receptor, FSH receptor, and LH-chorionic gonadotropin receptor is established to identify determinants involved in molecular activation mechanism. The basic aims of the current work are 1) the discrimination of receptor phenotypes according to the differences between activity states they represent, 2) the assignment of classified phenotypes to three-dimensional structural positions to reveal 3) functional-structural hot spots and 4) interrelations between determinants that are responsible for corresponding activity states. Because it is hard to survey the vast amount of pathogenic and site-directed mutations at GPHRs and to improve an almost isolated consideration of individual point mutations, we present a system for systematic and diversified sequence-structure-function analysis (http://www.fmp-berlin.de/ssfa). To combine all mutagenesis data into one set, we converted the functional data into unified scaled values. This at least enables their comparison in a rough classification manner. In this study we describe the compiled data set and a wide spectrum of functions for user-driven searches and classification of receptor functionalities such as cell surface expression, maximum of hormone binding capability, and basal as well as hormone-induced Galphas/Galphaq mediated cAMP/inositol phosphate accumulation. Complementary to known databases, our data set and bioinformatics tools allow functional and biochemical specificities to be linked with spatial features to reveal concealed structure-function relationships by a semiquantitative analysis. A comprehensive discrimination of specificities of pathogenic mutations and in vitro mutant phenotypes and their relation to signaling mechanisms of GPHRs demonstrates the utility of sequence-structure-function analysis. Moreover, new interrelations of determinants important for selective G protein-mediated activation of GPHRs are resumed.
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MESH Headings
- Animals
- Databases, Protein
- Humans
- Models, Molecular
- Mutation
- Protein Conformation
- Receptors, FSH/chemistry
- Receptors, FSH/genetics
- Receptors, FSH/physiology
- Receptors, LH/chemistry
- Receptors, LH/genetics
- Receptors, LH/physiology
- Receptors, Thyrotropin/chemistry
- Receptors, Thyrotropin/genetics
- Receptors, Thyrotropin/physiology
- Signal Transduction
- Structure-Activity Relationship
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Affiliation(s)
- Gunnar Kleinau
- Leibniz-Institut für Molekulare Pharmakologie, Robert-Rössle-Strasse 10, D-13125 Berlin, Germany
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370
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Cameo P, Szmidt M, Strakova Z, Mavrogianis P, Sharpe-Timms KL, Fazleabas AT. Decidualization Regulates the Expression of the Endometrial Chorionic Gonadotropin Receptor in the Primate1. Biol Reprod 2006; 75:681-9. [PMID: 16837644 DOI: 10.1095/biolreprod.106.051805] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Chorionic gonadotropin (CG) plays an important role in establishing a receptive endometrium by directly modulating the function of both endometrial stromal and epithelial cells in the baboon. The focus of this study was to characterize changes in CG receptor (LHCGR, also known as CG-R) expression during the menstrual cycle and early pregnancy, particularly during decidualization. LHCGR was localized by using a peptide-specific antibody generated against the extracellular domain. Immunostaining was absent in any of the cell types during the proliferative phase of the cycle. In contrast, during the secretory phase, both luminal and glandular epithelial cells stained positively. Stromal staining was confined to the cells around spiral arteries (SAs) and in the basalis layer. This stromal staining pattern persisted at the implantation site between Days 18 and 25 of pregnancy and after CG infusion. However, as pregnancy progressed (Days 40 to 60), staining for LHCGR was dramatically decreased in the stromal cells. These data were confirmed by nonisotopic in situ hybridization. To confirm whether the loss of LHCGR was associated with a decidual response, stromal fibroblasts were decidualized in vitro, and cell lysates obtained after 3, 6, and 12 days of culture were analyzed by Western blotting. LHCGR protein decreased with the onset of decidualization in vitro, confirming the in vivo results. Addition of CG to decidualized cells resulted in the reinduction of LHCGR in the absence of dbcAMP. We propose that CG acting via its R on stromal cells modulates SA in preparation for pregnancy and trophoblast invasion. As pregnancy progresses, further modification of SA by migrating endovascular trophoblasts and subsequent decidualization results in the downregulation of LHCGR. This inhibition of LHCGR expression also coincides with the decrease of measurable CG in peripheral circulation.
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Affiliation(s)
- Paula Cameo
- Department of Obstetrics and Gynecology, University of Illinois at Chicago, Chicago, Illinois 60212-7313, USA
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371
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Berndt S, Perrier d'Hauterive S, Blacher S, Péqueux C, Lorquet S, Munaut C, Applanat M, Hervé MA, Lamandé N, Corvol P, van den Brûle F, Frankenne F, Poutanen M, Huhtaniemi I, Geenen V, Noël A, Foidart JM. Angiogenic activity of human chorionic gonadotropin through LH receptor activation on endothelial and epithelial cells of the endometrium. FASEB J 2006; 20:2630-2. [PMID: 17065221 DOI: 10.1096/fj.06-5885fje] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Successful embryo development requires an extensive endometrial angiogenesis in proximity of implantation site. The glycoprotein hCG is produced even before implantation by trophoblast in normal pregnancy. In this manuscript, we demonstrate an angiogenic effect of hCG in several in vivo (chick chorioallantoïc membrane, matrigel plug assay, aortic ring assay) and in vitro experimental models. In contrast, human placental lactogen (hPL) did not display angiogenic properties. LH/hCG receptor was detected in endothelial cells by reverse-transcriptase polymerase chain reaction (RT-PCR) and by Western blotting. In mice aortic ring assay, angiostimulation by hCG was abrogated by deletion of LH/hCG receptor (LuRKO mice). Use of recombinant hCG and anti-hCG antibody (Ab) further confirmed the specificity of this angiogenic activity. By using dibutyryl cAMP, adenylate cyclase, or protein kinase A inhibitors, we demonstrate that hCG-mediated angiogenesis involves adenylyl-cyclase-protein kinase A activation. Addition of hCG to endometrial epithelial epithelial cells, but not to cultured endothelial cells, stimulated vascular endothelial growth factor (VEGF). VEGF and hCG also displayed additive activities. Altogether, these data demonstrate that peritrophoblastic angiostimulation may result from a paracrine dialogue between trophoblast, epithelial, and endothelial cells through hCG and VEGF.
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Affiliation(s)
- Sarah Berndt
- Laboratory of Tumor and Development Biology, Centre de recherche en cancérologie expérimentale, Université de Liège, Liège, Belgium
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372
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Fanelli F, De Benedetti PG. Inactive and active states and supramolecular organization of GPCRs: insights from computational modeling. J Comput Aided Mol Des 2006; 20:449-61. [PMID: 17009093 DOI: 10.1007/s10822-006-9064-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Accepted: 08/04/2006] [Indexed: 10/24/2022]
Abstract
Herein we make an overview of the results of our computational experiments aimed at gaining insight into the molecular mechanisms of GPCR functioning either in their normal conditions or when hit by gain-of-function or loss-of-function mutations. Molecular simulations of a number of GPCRs in their wild type and mutated as well as free and ligand-bound forms were instrumental in inferring the structural features, which differentiate the mutation- and ligand-induced active from the inactive states. These features essentially reside in the interaction pattern of the E/DRY arginine and in the degree of solvent exposure of selected cytosolic domains. Indeed, the active states differ from the inactive ones in the weakening of the interactions made by the highly conserved arginine and in the increase in solvent accessibility of the cytosolic interface between helices 3 and 6. Where possible, the structural hallmarks of the active and inactive receptor states are translated into molecular descriptors useful for in silico functional screening of novel receptor mutants or ligands. Computational modeling of the supramolecular organization of GPCRs and their intracellular partners is the current challenge toward a deep understanding of their functioning mechanisms.
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Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy.
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373
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Andric N, Ascoli M. A delayed gonadotropin-dependent and growth factor-mediated activation of the extracellular signal-regulated kinase 1/2 cascade negatively regulates aromatase expression in granulosa cells. Mol Endocrinol 2006; 20:3308-20. [PMID: 16973759 PMCID: PMC1665466 DOI: 10.1210/me.2006-0241] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Human chorionic gonadotropin and human FSH (hFSH) elicit a transient increase in ERK1/2 phosphorylation lasting less than 60 min in immature granulosa cells expressing a low density of gonadotropin receptors. In cells expressing a high density of receptors, human chorionic gonadotropin and human FSH elicit this fast transient increase in ERK1/2 phosphorylation and also a delayed and more sustained increase that is detectable after 6-9 h. Both the early and delayed increases in ERK1/2 phosphorylation can be blocked with inhibitors of protein kinase A, the epidermal growth factor receptor kinase, metalloproteases, and MAPK kinase. The delayed effect, but not the early effect, can also be blocked with an inhibitor of protein kinase C. Because the delayed increase in ERK1/2 phosphorylation correlates with low aromatase expression in response to gonadotropins, we tested the effects of these inhibitors on aromatase expression. These inhibitors had little or no effect on gonadotropin-induced aromatase expression in cells expressing a low density of receptors, but they enhanced gonadotropin-induced aromatase expression in cells expressing a high density of receptors. Phorbol esters also induced a prolonged increase in ERK1/2 phosphorylation and, when added together with hFSH, blocked the induction of aromatase expression by hFSH in cells expressing a low density of hFSH receptor. A MAPK kinase inhibitor reversed the inhibitory effect of the phorbol ester on aromatase induction. We conclude that the effects of gonadotropins on ERK1/2 phosphorylation are mediated by epidermal growth factor-like growth factors and that the delayed effect is partially mediated by protein kinase C and acts as a negative regulator of aromatase expression.
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Affiliation(s)
| | - Mario Ascoli
- Address correspondence to: Mario Ascoli, Ph.D. Department of Pharmacology, 2-319B BSB, 51 Newton Road, The University of Iowa, Iowa City, IA 52242, Email , Voice 319-335-9907, Fax 319-335-8930
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374
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Wang Y, Song L, Hong X, Cui L, Zhang Z, Xiao H, Zhou J, Wang X. Low concentrations mono-butyl phthalate stimulates steroidogenesis by facilitating steroidogenic acute regulatory protein expression in mouse Leydig tumor cells (MLTC-1). Chem Biol Interact 2006; 164:15-24. [PMID: 16999944 DOI: 10.1016/j.cbi.2006.08.022] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Revised: 08/14/2006] [Accepted: 08/17/2006] [Indexed: 11/27/2022]
Abstract
Di-n-butyl phthalate (DBP) is one of the most dominant phthalate esters and is widely distributed environmental contaminant. Although previous studies have demonstrated that DBP led to a variety of male reproductive abnormalities similar to those caused by androgen receptor antagonists, DBP and its active metabolite, mono-butyl phthalate (MBP), have been demonstrated no affinity for the androgen receptor, but rather exert anti-androgenic effect by altering testosterone biosynthesis. Furthermore, all these results were obtained from very high administrations of DBP or MBP. The purpose of this study was to determine the onset and the site of action of relatively low concentration of MBP on steroidogenesis in vitro. The mouse Leydig tumor cells (MLTC-1) was employed as a cellular model to investigate the effect of MBP on steroidogenesis. Various concentrations of MBP (1, 10, 100 and 1000nmol/l) and its solvent dimethyl sulfoxide (DMSO) were added to the medium for 24h followed by stimulation of some compounds such as human chorionic gonadotrophin (hCG), cholera toxin (CT), forskolin, cAMP analog 8-Br-cAMP, 22(R)-hydroxycholesterol (22R-HC) and pregnenolone. Progesterone in the medium and amounts of intracellular cAMP were measured by RIA. Expression of steroidogenic acute regulatory protein (StAR) was monitored by real-time PCR and Western blotting. The results revealed that the increases of progesterone production in the presence of hCG, CT, forskolin and 8-Br-cAMP were augmented by MBP. In contrast, the levels of intracellular cAMP exhibited no statistical significance when MLTC-1 cells were treated as above. These results implied that the site in the steroid biosynthesis pathway affected by MBP occurs after PKA activation in MLTC-1 cells. Moreover, supplementing the medium with 22R-HC and pregnenolone as progesterone precursors for P450 side chain cleavage enzyme (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), respectively, resulted in no rise in progesterone production, making clear that MBP did not influence the P450scc and 3beta-HSD but on the rate-limiting step, cholesterol transportation into mitochondria. In fact, the above results were confirmed by the upgraded StAR expression in MBP-treated cells. These data support that MBP promotes steroid hormone production by facilitating StAR expression in MLTC-1 cells.
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Affiliation(s)
- Yubang Wang
- Key Laboratory of Reproductive Medicine of Jiangsu Province, Institute of Toxicology, Nanjing Medical University, Nanjing 210029, PR China
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375
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Shiraishi K, Ascoli M. Activation of the lutropin/choriogonadotropin receptor in MA-10 cells stimulates tyrosine kinase cascades that activate ras and the extracellular signal regulated kinases (ERK1/2). Endocrinology 2006; 147:3419-27. [PMID: 16614081 PMCID: PMC1482736 DOI: 10.1210/en.2005-1478] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We show that activation of the recombinant lutropin/choriogonadotropin receptor (LHR) in mouse Leydig tumor cells (MA-10 cells) leads to the tyrosine phosphorylation of Shc (Src homology and collagen homology) and the formation of complexes containing Shc and Sos (Son of sevenless), a guanine nucleotide exchange factor for Ras. Because a dominant-negative mutant of Shc inhibits the LHR-mediated activation of Ras and the phosphorylation of ERK1/2, we conclude that the LHR-mediated phosphorylation of ERK1/2 is mediated, at least partially, by the classical pathway used by growth factor receptors. We also show that the endogenous epidermal growth factor receptor (EGFR) present in MA-10 cells is phosphorylated upon activation of the LHR. The LHR-mediated phosphorylation of the EGFR and Shc, the activation of Ras, and the phosphorylation of ERK1/2 are inhibited by expression of a dominant-negative mutant of Fyn, a member of the Src family kinases (SFKs) expressed in MA-10 cells and by PP2, a pharmacological inhibitor of the SFKs. These are also inhibited, but to a lesser extent, by AG1478, an inhibitor of the EGFR kinase. We conclude that the SFKs are responsible for the LHR-mediated phosphorylation of the EGFR and Shc, the formation of complexes containing Shc and Sos, the activation of Ras, and the phosphorylation of ERK1/2.
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Affiliation(s)
- Koji Shiraishi
- Department of Pharmacology, 2-319B BSB, 51 Newton Road, The University of Iowa, Iowa City, 52242-1109, USA
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376
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Galet C, Ascoli M. A constitutively active mutant of the human lutropin receptor (hLHR-L457R) escapes lysosomal targeting and degradation. Mol Endocrinol 2006; 20:2931-45. [PMID: 16803865 PMCID: PMC1626098 DOI: 10.1210/me.2006-0138] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Using biochemical and imaging approaches, we examined the postendocytotic fate of the complex formed by human choriogonadotropin (hCG) and a constitutively active mutant of the human lutropin receptor (hLHR-L457R) found in a boy with precocious puberty and Leydig cell hyperplasia. After internalization, some of the complex formed by the hLHR-wild type (hLHR-wt) and hCG recycles to the cell surface, and some is found in lysosomes where the hormone is degraded. In contrast, the complex formed by the hLHR-L457R and hCG is not routed to the lysosomes, most of it is recycled to the cell surface and hormone degradation is barely detectable. For both, hLHR-wt and -L457R, there is an hCG-induced loss of cell surface receptors that accompanies internalization but this loss cannot be prevented by leupeptin. The removal of recycling motifs of the hLHR by truncation of the C-terminal tail at residue 682 greatly enhances the lysosomal accumulation of the hormone-receptor complexes formed by the hLHR-wt or the L457R mutant, the degradation of the internalized hormone, and the loss of cell surface receptors. The degradation of the hormone internalized by these mutants as well as the loss of cell surface receptors is largely prevented by leupeptin. These results highlight a previously unrecognized complexity in the postendocytotic trafficking of the hLHR and document a clear difference between the properties of the constitutively active mutant and the agonist-activated hLHR-wt. This lack of lysosomal degradation of the L457R mutant could contribute to its constitutive activity by prolonging the duration of signaling.
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Affiliation(s)
- Colette Galet
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, 2-319B Bowen Science Building, 51 Newton Road, Iowa City, Iowa 52242-1109, USA
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377
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Andersen CY, Humaidan P, Ejdrup HB, Bungum L, Grøndahl ML, Westergaard LG. Hormonal characteristics of follicular fluid from women receiving either GnRH agonist or hCG for ovulation induction. Hum Reprod 2006; 21:2126-30. [PMID: 16682403 DOI: 10.1093/humrep/del119] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND A recent prospective randomized study from our group compared GnRH agonist (0.5 mg buserelin) and hCG (10,000 IU) for triggering of ovulation following a flexible antagonist protocol. The agonist group showed a poor reproductive outcome despite luteal phase support with progesterone and estradiol (E(2)). In the present prospective observational study, the health status of follicles from the above study was monitored by analysing the hormonal content of frozen/thawed follicular fluid samples. The aim was to test whether the poor reproductive outcome could be related to a defective pre-ovulatory follicular maturation resulting in oocytes with a compromised developmental competence. METHODS Hormone concentrations were measured in two individual follicular fluid samples from each of 32 women receiving buserelin and 37 receiving hCG, thus representing a subset of the follicles retrieved. RESULTS Follicular fluid levels of LH in the agonist group as compared with the hCG group was 11.1 +/- 0.5 versus 3.6 +/- 0.3 IU/l (mean +/- SEM; P < 0.001); FSH, 6.3 +/- 0.6 versus 3.3 +/- 0.2 IU/l (P < 0.001); hCG, not determined versus 139+/-8 IU/l; E(2), 1.9 +/- 0.2 versus 1.8 +/- 0.2 micromol/l (P > 0.10); progesterone, 70 +/- 4 versus 93 +/- 6 micromol/l (P < 0.001); inhibin-A, 36.9 +/- 3.1 versus 37.1 +/- 2.5 ng/ml (P > 0.10) and inhibin-B, 35.6 +/- 2.8 versus 40.1 +/- 3.1 ng/ml (P > 0.10). Thus, pronounced hormonal differences exist in follicular fluid, and the collective concentration of all three gonadotropins and the follicular fluid concentration of progesterone were much higher in the group of women receiving hCG for ovulation induction. CONCLUSION The study suggests that GnRH agonist results in proper pre-ovulatory follicular maturation, but the ovulatory signal--probably in synergy with the resulting pituitary down-regulation--is too low to support appropriate corpus luteum (CL) function.
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Affiliation(s)
- C Yding Andersen
- Laboratory of Reproductive Biology, University Hospital of Copenhagen, Rigshospitalet, Copenhagen, Denmark.
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378
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Apaja PM, Tuusa JT, Pietilä EM, Rajaniemi HJ, Petäjä-Repo UE. Luteinizing hormone receptor ectodomain splice variant misroutes the full-length receptor into a subcompartment of the endoplasmic reticulum. Mol Biol Cell 2006; 17:2243-55. [PMID: 16495341 PMCID: PMC1446094 DOI: 10.1091/mbc.e05-09-0875] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Revised: 02/06/2006] [Accepted: 02/13/2006] [Indexed: 11/11/2022] Open
Abstract
The luteinizing hormone receptor (LHR) is a G protein-coupled receptor that is expressed in multiple RNA messenger forms. The common rat ectodomain splice variant is expressed concomitantly with the full-length LHR in tissues and is a truncated transcript corresponding to the partial ectodomain with a unique C-terminal end. Here we demonstrate that the variant alters the behavior of the full-length receptor by misrouting it away from the normal secretory pathway in human embryonic kidney 293 cells. The variant was expressed as two soluble forms of M(r) 52,000 and M(r) 54,000, but although the protein contains a cleavable signal sequence, no secretion to the medium was observed. Only a very small fraction of the protein was able to gain hormone-binding ability, suggesting that it is retained in the endoplasmic reticulum (ER) by its quality control due to misfolding. This was supported by the finding that the variant was found to interact with calnexin and calreticulin and accumulated together with these ER chaperones in a specialized juxtanuclear subcompartment of the ER. Only proteasomal blockade with lactacystin led to accumulation of the variant in the cytosol. Importantly, coexpression of the variant with the full-length LHR resulted in reduction in the number of receptors that were capable of hormone binding and were expressed at the cell surface and in targeting of immature receptors to the juxtanuclear ER subcompartment. Thus, the variant mediated misrouting of the newly synthesized full-length LHRs may provide a way to regulate the number of cell surface receptors.
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Affiliation(s)
- Pirjo M Apaja
- Biocenter Oulu, University of Oulu, FI-90014 Oulu, Finland
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379
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Van Durme J, Horn F, Costagliola S, Vriend G, Vassart G. GRIS: glycoprotein-hormone receptor information system. Mol Endocrinol 2006; 20:2247-55. [PMID: 16543405 DOI: 10.1210/me.2006-0020] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The glycoprotein-hormone receptor information system (GRIS) presents a comprehensive view on all available molecular data for the lutropin/choriogonadotropin receptor, follitropin receptor, and thyrotropin receptor G protein-coupled receptors. It features a mutation database presently containing 696 point mutations, combined with all sequences and the associated homology models. The mutation information was automatically extracted from the literature and manually augmented with respect to constitutivity, surface expression, sensitivity to hormones, and binding affinity. All information in this integrated system is presented in a G protein-coupled receptor specialist-friendly way. A series of interactive tools such as rotamer analysis, mutation prediction, or cavity visualization aids with the design and interpretation of experiments. A universal residue numbering system has been introduced to ease database searches as well as the use of the information in conjunction with literature data from diverse origins. Users can upload new mutations. GRIS is freely accessible at http://gris.ulb.ac.be/.
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Affiliation(s)
- Joost Van Durme
- Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire, Université Libre de Bruxelles, Campus Erasme, Route de Lennik 808, B-1070 Brussels, Belgium
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380
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Jäschke H, Neumann S, Moore S, Thomas CJ, Colson AO, Costanzi S, Kleinau G, Jiang JK, Paschke R, Raaka BM, Krause G, Gershengorn MC. A low molecular weight agonist signals by binding to the transmembrane domain of thyroid-stimulating hormone receptor (TSHR) and luteinizing hormone/chorionic gonadotropin receptor (LHCGR). J Biol Chem 2006; 281:9841-4. [PMID: 16488885 DOI: 10.1074/jbc.c600014200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Many cognate low molecular weight (LMW) agonists bind to seven transmembrane-spanning receptors within their transmembrane helices (TMHs). The thienopyrimidine org41841 was identified previously as an agonist for the luteinizing hormone/chorionic gonadotropin receptor (LHCGR) and suggested to bind within its TMHs because it did not compete for LH binding to the LHCGR ectodomain. Because of its high homology with LHCGR, we predicted that thyroid-stimulating hormone receptor (TSHR) might be activated by org41841 also. We show that org41841 is a partial agonist for TSHR but with lower potency than for LHCGR. Analysis of three-dimensional molecular models of TSHR and LHCGR predicted a binding pocket for org41841 in common clefts between TMHs 3, 4, 5, 6, and 7 and extracellular loop 2 in both receptors. Evidence for this binding pocket was obtained in signaling studies with chimeric receptors that exhibited improved responses to org41841. Furthermore, a key receptor-ligand interaction between the highly conserved negatively charged E3.37 and the amino group of org41841 predicted by docking of the ligand into the three-dimensional TSHR model was experimentally confirmed. These findings provide the first evidence that, in contrast to the ectodomain binding of cognate ligands, a LMW agonist can bind to and activate glycoprotein hormone receptors via interaction with their transmembrane domain.
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Affiliation(s)
- Holger Jäschke
- Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 50 South Drive, Bethesda, MD 20892, USA
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381
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Manna PR, Chandrala SP, King SR, Jo Y, Counis R, Huhtaniemi IT, Stocco DM. Molecular Mechanisms of Insulin-like Growth Factor-I Mediated Regulation of the Steroidogenic Acute Regulatory Protein in Mouse Leydig Cells. Mol Endocrinol 2006; 20:362-78. [PMID: 16166197 DOI: 10.1210/me.2004-0526] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Growth factors are known to play diverse roles in steroidogenesis, a process regulated by the mitochondrial steroidogenic acute regulatory (StAR) protein. The mechanism of action of one such growth factor, IGF-I, was investigated in mouse Leydig tumor (mLTC-1) cells to determine its potential role in the regulation of StAR expression. mLTC-1 cells treated with IGF-I demonstrated temporal and concentration-dependent increases in StAR expression and steroid synthesis. However, IGF-I had no effect on cytochrome P450 side-chain cleavage or 3beta-hydroxysteroid dehydrogenase protein levels. IGF-I was capable of augmenting N,O'-dibutyrl-cAMP-stimulated steroidogenic responsiveness in these cells. The steroidogenic potential of IGF-I was also confirmed in primary cultures of isolated mouse Leydig cells. IGF-I increased phosphorylation of ERK1/2, an event inhibited by the MAPK/ERK inhibitors, PD98059 and U0126. Interestingly, inhibition of ERK activity enhanced IGF-I-mediated StAR protein expression, but phosphorylation of StAR was undetectable, an observation in contrast to that seen with N,O'-dibutyrl-cAMP signaling. Further studies demonstrated that these events were tightly correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 and scavenger receptor class B type 1. Whereas both protein kinase A and protein kinase C signaling were involved in the IGF-I-mediated steroidogenic response, the majority of the effects of IGF-I were found to be mediated by the protein kinase C pathway. Transcriptional activation of the StAR gene by IGF-I was influenced by several transcription factors, its up-regulation being dependent on phosphorylation of the cAMP response element-binding protein (CREB) and the activator protein 1 family member, c-Jun. Conversely, StAR gene transcription was markedly inhibited by expression of nonphosphorylatable CREB (Ser(133)Ala), dominant negative A-CREB, and dominant negative c-Jun (TAM-67) mutants. Collectively, the present studies identify molecular events in IGF-I signaling that may influence testicular growth, development, and the Leydig cell steroidogenic machinery through autocrine/paracrine regulation.
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Affiliation(s)
- Pulak R Manna
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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382
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Hughes IA, Martin H, Jääskeläinen J. Genetic mechanisms of fetal male undermasculinization: a background to the role of endocrine disruptors. ENVIRONMENTAL RESEARCH 2006; 100:44-9. [PMID: 16271714 DOI: 10.1016/j.envres.2005.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Revised: 06/23/2005] [Accepted: 07/12/2005] [Indexed: 05/05/2023]
Abstract
Fetal male sex development proceeds along an orderly sequence of events coordinated by an interplay of genetic and hormonal events. These operate in a time- and concentration-dependent manner. Once a testis is formed (the female sex being constitutive in nature), differentiation of the internal and external male genitalia is androgen dependent. A number of genetic syndromes of sex reversal are well characterized at the biochemical and molecular levels. They fall into three principal categories: defects in formation of the testis, defects in production of androgens, and defects in the action of androgens. In many instances, the precise cause is not established, although the investigative evidence points in the direction of one of the three stated classifications. Polymorphic variants in several of the genes involved in male development are associated with certain degrees of male undermasculinization. While the genetic background is essentially static, it is plausible that the effect of endocrine disruptors during fetal life acting through epigenetic mechanisms may partly explain the observed changing trends in male reproductive tract disorders.
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Affiliation(s)
- Ieuan A Hughes
- Department of Paediatrics, University of Cambridge, Addenbrooke's Hospital, Box 116, Level 8, Hills Road, Cambridge CB2 2QQ, UK.
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383
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Abstract
Our previous studies have identified a luteinizing hormone receptor (LHR) mRNA-binding protein (LRBP) that binds to the coding region (LBS) of rat LHR mRNA. The identity of LRBP was later established as mevalonate kinase (MVK). The present study examined if LRBP binding to LHR mRNA impairs translation. A full-length FLAG-tagged rat LHR mRNA was synthesized and translated in vitro. The translation product was immunoprecipitated and analyzed on SDS-PAGE. The addition of LRBP inhibited LHR mRNA translation. This inhibitory effect was reversed by an excess of wild type (wt) LBS. To determine whether this reversal of the inhibitory effect of LRBP was indeed due to the sequestration of LRBP by the wtLBS, a translation reaction was performed in the presence of mutated LBS in which all the cytidine in the wtLBS was mutated to uridine. This mutation of LBS has been shown to render it incapable of interacting with LRBP. Unlike wtLBS, the mutated LBS was unable to reverse the inhibitory effect of LRBP on LHR mRNA translation. The addition of mevalonate, which has been shown to compete for LHR mRNA binding to LRBP, also reduced the extent of translation inhibition by LRBP. Endogenous association of LHR mRNA with MVK was assessed by immunoprecipitation of the ribonucleoprotein complex with MVK antibody followed by reverse transcription-PCR of the RNA associated with the immune complex. Amplification of LHR mRNA, if any, associated with the immunoprecipitate obtained from ovarian ribonucleoprotein complex with gene-specific primers confirmed the association of LHR mRNA with MVK. Collectively, the present data support the novel function of LRBP as a translational inhibitor of LHR mRNA in the ovary.
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Affiliation(s)
- Anil K Nair
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0617, USA
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384
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Mizutani T, Shiraishi K, Welsh T, Ascoli M. Activation of the lutropin/choriogonadotropin receptor in MA-10 cells leads to the tyrosine phosphorylation of the focal adhesion kinase by a pathway that involves Src family kinases. Mol Endocrinol 2005; 20:619-30. [PMID: 16293639 PMCID: PMC1382007 DOI: 10.1210/me.2005-0277] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We show that activation of the endogenous or recombinant lutropin/choriogonadotropin receptor (LHR) in mouse Leydig tumor cells (MA-10 cells) leads to the tyrosine phosphorylation of the focal adhesion kinase (FAK) and one of its substrates (paxillin). Using specific antibodies to the five tyrosine residues of FAK that become phosphorylated, we show that activation of the LHR increases the phosphorylation of Tyr576 and Tyr577, but it does not affect the phosphorylation of Tyr397, Tyr861, or Tyr925. Because FAK is a prominent substrate for the Src family of tyrosine kinases (SFKs) we tested for their involvement in the LHR-mediated phosphorylation of FAK-Tyr576. Src is not detectable in MA-10 cells, but two other prominent members of this family (Fyn and Yes) are present. The LHR-mediated phosphorylation of FAK-Tyr576 is readily inhibited by PP2 (a pharmacological inhibitor of SFKs) and by dominant-negative mutants of SKFs. Moreover, activation of the LHR in MA-10 cells results in the stimulation of the activity of Fyn and Yes, and overexpression of either of these two tyrosine kinases enhances the LHR-mediated phosphorylation of FAK-Tyr576. Studies involving activation of other G protein-coupled receptors, overexpression of the different Galpha-subunits, and the use of second messenger analogs suggest that the LHR-induced phosphorylation of FAK-Tyr576 in MA-10 cells is mediated by SFKs, and that this family of kinases is, in turn, independently or cooperatively activated by the LHR-induced stimulation of Gs and Gq/11-mediated pathways.
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Affiliation(s)
| | | | | | - Mario Ascoli
- Address correspondence to: Dr. Mario Ascoli, Department of Pharmacology, 2-319B BSB, 51 Newton Road, The University of Iowa, Iowa City, IA 52242-1109, Phone = 319-335-9907, Fax = 319-335-8930, Email =
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385
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Favre N, Fanelli F, Missotten M, Nichols A, Wilson J, di Tiani M, Rommel C, Scheer A. The DRY motif as a molecular switch of the human oxytocin receptor. Biochemistry 2005; 44:9990-10008. [PMID: 16042376 DOI: 10.1021/bi0509853] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The human oxytocin receptor is known to exhibit promiscuous activity by coupling to both Galpha(q) and Galpha(i) G proteins to activate distinct signaling pathways. A single-amino acid substitution within the highly conserved E/DRY motif at the cytosolic extension of helix 3 [i.e., D136(3.49)N] increased the rate of both basal and agonist-stimulated inositol phosphate (IP(3)) accumulation of the receptor. Furthermore, like for a typical constitutively active receptor, the partial agonist arginine vasopressin behaved as a full agonist for the D136(3.49)N mutant. Subsequently, both oxytocin and arginine vasopressin showed an increased potency in stimulating IP3 accumulation as compared to the wild-type receptor. Very interestingly, our experiments provide strong evidence that the D136(3.49)N mutant inhibits receptor signaling via Galpha(i)-mediated pathways while increasing the activity through the Galpha(q)-mediated pathways. Molecular simulations of the free and OT-bound forms of wild-type OTR and of the D136(3.49)N constitutively active mutant suggest that the receptor portions close to the E/DRY and NPxxY motifs are particularly susceptible to undergoing structural modification in response to activating mutations and agonist binding. Furthermore, computational modeling suggests that the OT-bound form of wild-type OTR is able to explore more states than the OT-bound form of the D136(3.49)N constitutively active mutant, consistent with its G protein promiscuity. Taken together, these observations emphasize the important role of the E/DRY motif not only in receptor activation but also in the promiscuity of G protein coupling. Knowledge of the mechanism of selective G protein coupling could aid drug discovery efforts to identify signaling specific therapies.
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Affiliation(s)
- Nicolas Favre
- Serono Pharmaceutical Research Institute, 14, Ch. des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
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386
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387
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Robert NM, Martin LJ, Tremblay JJ. The orphan nuclear receptor NR4A1 regulates insulin-like 3 gene transcription in Leydig cells. Biol Reprod 2005; 74:322-30. [PMID: 16237153 DOI: 10.1095/biolreprod.105.044560] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Insulin-like 3 (INSL3) is a hormone produced by fetal and adult Leydig cells of the testis and by theca and luteal cells of the adult ovary. In males, INSL3 regulates testicular descent during fetal life, whereas in adults, it acts as a germ cell survival factor. In the ovary, INSL3 regulates oocyte maturation. Despite its importance for male sex differentiation and reproductive function in both sexes, very little is known regarding the molecular mechanisms that regulate Insl3 expression. So far, the nuclear receptor NR5A1 is the only transcription factor known to regulate the mouse Insl3 promoter in Leydig cells. NR5A1 by itself, however, cannot explain the spatiotemporal expression pattern of the Insl3 gene. In the present study, we have identified the orphan nuclear receptor NR4A1 as a novel regulator of INSL3 transcription in Leydig cells. Using RT-PCR, we found that Nr4a1 is coexpressed with Insl3 in purified Leydig cells and in several Leydig cell lines. Through detailed analyses of the mouse and human INSL3 promoter in Leydig cells, we have mapped a novel regulatory element located at -100 bp that is essential and sufficient to confer NR4A1 responsiveness. Consistent with a role for NR4A1 in Insl3 transcription, chromatin immunoprecipitation assays revealed that endogenous NR4A1 binds to the proximal Insl3 promoter in vivo. Finally, we found that NR4A1 is also implicated in cAMP-induced Insl3 transcription in Leydig cells. Taken together, our identification of NR4A1 as an important regulator of mouse and human INSL3 promoter activity helps us to better define the tissue-specific regulation of the INSL3 gene in gonadal cells.
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Affiliation(s)
- Nicholas M Robert
- Ontogeny-Reproduction Research Unit, CHUL Research Centre, Ste-Foy, Québec, Canada G1V 4G2
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388
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Donadeu FX, Ascoli M. The differential effects of the gonadotropin receptors on aromatase expression in primary cultures of immature rat granulosa cells are highly dependent on the density of receptors expressed and the activation of the inositol phosphate cascade. Endocrinology 2005; 146:3907-16. [PMID: 15919743 PMCID: PMC1262674 DOI: 10.1210/en.2005-0403] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Signaling pathways mediating the divergent effects of FSH and LH on aromatase in immature rat granulosa cells were studied by infecting cells with increasing amounts of adenoviral vectors for the human LH receptor (hLHR) or FSH receptor (hFSHR). Increasing amounts of Ad-hLHR, used at a multiplicity of infection (MOI) of 20 or 200 viable viral particles/cell, increased human chorionic gonadotropin (hCG) binding and hCG-induced cAMP and Akt phosphorylation, but inositol phosphates only increased in response to hCG in cells infected with 200 MOI Ad-hLHR. In contrast, hCG increased aromatase expression in cells infected with 20, but not in cells infected with 200, MOI Ad-hLHR. Cells infected with 20 or 200 MOI Ad-hFSHR showed increased hFSH binding and hFSH-induced Akt phosphorylation, but the hFSH-induced cAMP response was unchanged relative to control cells. However, hFSH was able to stimulate the inositol phosphate cascade in the Ad-hFSHR-infected cells, and the hFSH induction of aromatase was abolished. We also found that activation of C kinase or expression of a constitutively active form of Galphaq inhibited the induction of aromatase by hFSH or 8Br-cAMP. We conclude that the differential effects of FSH and LH on aromatase in immature granulosa cells are highly dependent on gonadotropin receptor density and on the signaling pathways activated. We propose that aromatase is induced by common signals generated by activation of the FSHR and LHR (possibly cAMP and Akt) and that the activation of the inositol phosphate cascade in cells expressing a high density of LHR or FSHR antagonizes this induction.
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Affiliation(s)
| | - Mario Ascoli
- Address correspondence to: Dr. Mario Ascoli, Department of Pharmacology, Carver College of Medicine, 2-319B BSB, 51 Newton Road, The University of Iowa, Iowa City, IA 52242, Phone 319-335-9907, Fax 319-335-8930, Email
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389
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Bielinska M, Genova E, Boime I, Parviainen H, Kiiveri S, Leppäluoto J, Rahman N, Heikinheimo M, Wilson DB. Gonadotropin-induced adrenocortical neoplasia in NU/J nude mice. Endocrinology 2005; 146:3975-84. [PMID: 15919738 DOI: 10.1210/en.2004-1643] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In response to prepubertal gonadectomy certain inbred mouse strains, including DBA/2J, develop sex steroid-producing adrenocortical neoplasms. This phenomenon has been attributed to a lack of gonadal hormones or a compensatory increase in gonadotropins. To assess the relative importance of these mechanisms, we created a new inbred model of adrenocortical neoplasia using female NU/J nude mice. These mice developed adrenocortical neoplasms in response to either gonadectomy or gonadotropin elevation from xenografts of human chorionic gonadotropin (hCG)-secreting Chinese hamster ovary cells. In each instance the adrenal tumors resembled the neoplasms found in gonadectomized DBA/2J mice and were composed of spindle-shaped A cells and lipid-laden B cells. Both cell populations were defined by ectopic expression of GATA-4 and an absence of the adrenocortical markers melanocortin-2-receptor and steroid 21-hydroxylase, but only B cells expressed the gonadal steroidogenic markers inhibin-alpha, LH receptor, P450c17, and P450c19. Expression of sex steroidogenic markers was attenuated in the neoplastic adrenal cortex of hCG-treated vs. gonadectomized mice. Whereas neoplastic adrenals were an obvious source of estradiol in gonadectomized mice, ovaries appeared to be the major source of this hormone in hCG-treated mice. Gonadectomy and hCG treatment elicited comparable increases in serum estradiol, but testosterone levels increased significantly only in hCG-treated mice. We conclude that chronic gonadotropin elevation, caused by either gonadectomy or hCG administration, signals a population of cells in the adrenal subcapsular region of permissive mice to undergo differentiation along a gonadal rather than an adrenal lineage. Thus, NU/J nude mice can be used as a model to study both neoplasia and adrenogonadal lineage specification.
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Affiliation(s)
- Malgorzata Bielinska
- Department of Pediatrics, Box 8208, Washington University School of Medicine, St. Louis Children's Hospital, 660 South Euclid Avenue, St. Louis, MO 63110, USA
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390
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Fanelli F, De Benedetti PG. Computational Modeling Approaches to Structure−Function Analysis of G Protein-Coupled Receptors. Chem Rev 2005; 105:3297-351. [PMID: 16159154 DOI: 10.1021/cr000095n] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute and Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
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391
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Apaja PM, Aatsinki JT, Rajaniemi HJ, Petäjä-Repo UE. Expression of the mature luteinizing hormone receptor in rodent urogenital and adrenal tissues is developmentally regulated at a posttranslational level. Endocrinology 2005; 146:3224-32. [PMID: 15860556 DOI: 10.1210/en.2005-0073] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The LH receptor (LHR) is a G protein-coupled receptor involved in the regulation of ovarian and testicular functions. In this study we demonstrate novel and unexpected patterns of receptor expression and regulation in fetal and adult rodent urogenital and adrenal tissues. Two rat LHR promoter fragments (approximately 2 and 4 kb) were shown to direct expression of the lacZ reporter in transgenic mice to gonads, adrenal glands, and kidneys, starting at 14.5 d post coitum, and to genital tubercles, starting at 11.5 d post coitum. These tissues were also found to express the full-length LHR mRNA and protein during rat fetal development, but, importantly, only immature receptors carrying unprocessed N-linked glycans were detected. After birth, the receptor gene activity ceased, except in the gonads, which started to express the mature receptor carrying fully processed N-linked glycans. Surprisingly, both LHR mRNA and mature protein levels were up-regulated substantially in pregnant female adrenal glands and kidneys at a time that coincides with differentiation of fetal urogenital tissues. Taken together, these results indicate that the LHR protein is expressed constitutively in gonadal and nongonadal urogenital tissues as well in adrenal glands, but its final functional maturation at the posttranslational level appears to be developmentally and physiologically regulated.
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Affiliation(s)
- Pirjo M Apaja
- Biocenter Oulu and Department of Anatomy and Cell Biology, University of Oulu, FI-90014 Oulu, Finland.
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392
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Abstract
Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.
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Affiliation(s)
- Stephen J Marx
- Metabolic Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases/NIH, Building 10, Room 9C-101, 10 Center Drive, MSC 1802, Bethesda, MD 20892-1802, USA.
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393
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Ascoli M. Learning new tricks from an old dog: the processing of the intracellular precursor of the luteinizing hormone receptor (LHR) into the mature cell-surface LHR is a regulated process. Endocrinology 2005; 146:3221-3. [PMID: 16009970 DOI: 10.1210/en.2005-0590] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Mario Ascoli
- Department of Pharmacology, Carver College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA.
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394
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Conti M, Hsieh M, Park JY, Su YQ. Role of the epidermal growth factor network in ovarian follicles. Mol Endocrinol 2005; 20:715-23. [PMID: 16051667 DOI: 10.1210/me.2005-0185] [Citation(s) in RCA: 266] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The LH surge causes major remodeling of the ovarian follicle in preparation for the ovulatory process. These changes include reprogramming of granulosa cells to differentiate into luteal cells, changes in cumulus cell secretory properties, and oocyte maturation. This review summarizes published data in support of the concept that LH stimulation of ovarian follicles involves activation of a local epidermal growth factor (EGF) network. A model describing this property of LH signaling and its branching to other signaling modules is discussed. According to this model, LH activation of mural granulosa cells stimulates cAMP signaling, which, in turn, induces the expression of the EGF-like growth factors epiregulin, amphiregulin, and betacellulin. These growth factors function by activating EGF receptors in either an autocrine/juxtacrine fashion within the mural layer, or they diffuse to act on cumulus cells. Activation of EGF receptor signaling in cumulus cells, together with cAMP priming, triggers oocyte nuclear maturation and acquisition of developmental competence as well as cumulus expansion. This model has important implications for ovarian physiology and for the development of new strategies for the pharmacological control of ovulation and for gamete maturation in vitro.
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Affiliation(s)
- Marco Conti
- Division of Reproductive Biology, Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, California 94305-5317, USA.
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395
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Van Schoore G, Mendive F, Pochet R, Vassart G. Expression pattern of the orphan receptor LGR4/GPR48 gene in the mouse. Histochem Cell Biol 2005; 124:35-50. [PMID: 16028069 DOI: 10.1007/s00418-005-0002-3] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2005] [Indexed: 10/25/2022]
Abstract
Leucine-rich G-protein-coupled Receptors (LGR) constitute a subfamily of receptors related to glycoprotein hormone receptors. Amongst them, LGR4, LGR5 and LGR6 form a cluster for which natural agonists are still unknown. By an extensive gene trapping approach, Leighton et al. (2001) obtained a mouse line in which the LGR4 gene is disrupted by a trap vector carrying two biological markers, beta-geo (a fusion between bacterial beta-galactosidase and neomycin phosphotransferase) and a placental alkaline phosphatase (PLAP). Due to perinatal lethality, characterization of adult mice homozygous for this insertion has been impaired. In the present study we have investigated LacZ and PLAP activity patterns in heterozygous mice as a marker for LGR4 natural expression at both macroscopic and histological levels. We present a detailed atlas of LGR4 expression, which displays very wide expression with particularly strong activity in cartilages, kidneys, reproductive tracts and nervous system cells.
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Affiliation(s)
- Grégory Van Schoore
- Université Libre de Bruxelles, Campus Erasme, 808 route de Lennik, 1070 Brussels, Belgium
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396
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Pietilä EM, Tuusa JT, Apaja PM, Aatsinki JT, Hakalahti AE, Rajaniemi HJ, Petäjä-Repo UE. Inefficient Maturation of the Rat Luteinizing Hormone Receptor. J Biol Chem 2005; 280:26622-9. [PMID: 15901736 DOI: 10.1074/jbc.m413815200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Increasing evidence suggests that the folding and maturation of monomeric proteins and assembly of multimeric protein complexes in the endoplasmic reticulum (ER) may be inefficient not only for mutants that carry changes in the primary structure but also for wild type proteins. In the present study, we demonstrate that the rat luteinizing hormone receptor, a G protein-coupled receptor, is one of these proteins that matures inefficiently and appears to be very prone to premature degradation. A substantial portion of the receptors in stably transfected human embryonic kidney 293 cells existed in immature form of M(r) 73,000, containing high mannose-type N-linked glycans. In metabolic pulse-chase studies, only approximately 20% of these receptor precursors were found to gain hormone binding ability and matured to a form of M(r) 90,000, containing bi- and multiantennary sialylated N-linked glycans. The rest had a propensity to form disulfide-bonded complexes with a M(r) 120,000 protein in the ER membrane and were eventually targeted for degradation in proteasomes. The number of membrane-bound receptor precursors increased when proteasomal degradation was inhibited, and no cytosolic receptor forms were detected, suggesting that retrotranslocation of the misfolded/incompletely folded receptors is tightly coupled to proteasomal function. Furthermore, a proteasomal blockade was found to increase the number of receptors that were capable of hormone binding. Thus, these results raise the interesting possibility that luteinizing hormone receptor expression at the cell surface may be controlled at the ER level by regulating the number of newly synthesized proteins that will mature and escape the ER quality control and premature degradation.
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Affiliation(s)
- E Maritta Pietilä
- Biocenter Oulu and Department of Anatomy and Cell Biology, University of Oulu, Finland
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397
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Banerjee S, Smallwood A, Chambers AE, Papageorghiou A, Loosfelt H, Spencer K, Campbell S, Nicolaides K. A link between high serum levels of human chorionic gonadotrophin and chorionic expression of its mature functional receptor (LHCGR) in Down's syndrome pregnancies. Reprod Biol Endocrinol 2005; 3:25. [PMID: 15969756 PMCID: PMC1190215 DOI: 10.1186/1477-7827-3-25] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Accepted: 06/21/2005] [Indexed: 11/26/2022] Open
Abstract
Human chorionic gonadotrophin (hCG) is released from placental trophoblasts and is involved in establishing pregnancy by maintaining progesterone secretion from the corpus luteum. Serum hCG is detected in the maternal circulation within the first 2-3 wks of gestation and peaks at the end of the first trimester before declining. In Down's syndrome (DS) pregnancies, serum hCG remains significantly high compared to gestation age-matched uncompromised pregnancies. It has been proposed that increased serum hCG levels could be due to transcriptional hyper-activation of the CGB (hCG beta) gene, or an increased half life of glycosylated hCG hormone, or both. Another possibility is that serum hCG levels remain high due to reduced availability of the hormone's cognate receptor, LHCGR, leading to lack of hormone utilization. We have tested this hypothesis by quantifying the expression of the hCG beta (CGB) RNA, LHCGR RNA and LHCGR proteins in chorionic villous samples. We demonstrate that chorionic expression of hCG beta (CGB) mRNA directly correlates with high serum hCG levels. The steady-state synthesis of LHCGR mRNA (exons 1-5) in DS pregnancies was significantly higher than that of controls, but the expression of full-length LHCGR mRNA (exons 1-11) in DS was comparable to that of uncompromised pregnancies. However, the synthesis of high molecular weight mature LHCGR proteins was significantly reduced in DS compared to uncompromised pregnancies, suggesting a lack of utilization of circulating hCG in DS pregnancies.
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MESH Headings
- Animals
- Antibodies, Monoclonal/analysis
- Antibody Specificity
- Blotting, Western
- Chorionic Gonadotropin, beta Subunit, Human/blood
- Chorionic Gonadotropin, beta Subunit, Human/genetics
- Chorionic Gonadotropin, beta Subunit, Human/metabolism
- Chorionic Villi/metabolism
- Down Syndrome/embryology
- Down Syndrome/genetics
- Female
- Glycoprotein Hormones, alpha Subunit/blood
- Glycoprotein Hormones, alpha Subunit/genetics
- Glycoprotein Hormones, alpha Subunit/metabolism
- Humans
- Mice
- Pregnancy
- Protein Isoforms/metabolism
- RNA, Messenger/metabolism
- Receptors, LH/chemistry
- Receptors, LH/genetics
- Receptors, LH/metabolism
- Trisomy
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Affiliation(s)
- Subhasis Banerjee
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
| | - Alan Smallwood
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
| | - Anne E Chambers
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
| | - Aris Papageorghiou
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
| | - Hugues Loosfelt
- INSERM U135, Biochimie hormonale, CHU de Kremlin-Bicêtre, Bat Paul Broca, 3e niveau 78 avenue du général Leclerc, 94275 Le Kremlin-Bicêtre, France
| | - Kevin Spencer
- Endocrine Unit, Clinical Biochemistry Department, Harold Wood Hospital, Gubbins Lane, Romford RM3 0BE, UK
| | - Stuart Campbell
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
| | - Kypros Nicolaides
- Harris Birthright Research Centre for Fetal Medicine, King's College Hospital Medical School, Denmark Hill, London SE5 9RS, UK
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398
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Sayasith K, Lussier JG, Sirois J. Role of upstream stimulatory factor phosphorylation in the regulation of the prostaglandin G/H synthase-2 promoter in granulosa cells. J Biol Chem 2005; 280:28885-93. [PMID: 15927963 DOI: 10.1074/jbc.m413434200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
To investigate the role of USF phosphorylation in the regulation of the PGHS-2 promoter in granulosa cells, promoter activity assays were performed in primary cultures of bovine granulosa cells transfected with the chimeric PGHS-2 promoter/luciferase (LUC) construct -149/-2PGHS-2.LUC. Transfections were done in the absence or presence of forskolin; the protein kinase A (PKA) inhibitor H-89; or an expression vector encoding USF1, USF2, the catalytic subunit of PKA (cPKA), or a PKA inhibitor protein (PKI). Electrophoretic mobility shift assays were performed to study USF/DNA interactions using granulosa cell nuclear extracts and a 32P-labeled proximal PGHS-2 promoter fragment containing the E-box element. The results show that forskolin stimulation and cPKA overexpression caused a marked and significant increase in USF-dependent DNA binding and PGHS-2 promoter activities (p < 0.05). In contrast, both activities were decreased by H-89 treatment or PKI overexpression. Reverse transcription-PCR analyses revealed that these treatments had similar effects on endogenous PGHS-2 mRNA levels in granulosa cells. Cotransfection studies with a USF2 mutant lacking N-terminal activation domains (U2Delta1-220) repressed forskolin-, cPKA-, and USF-dependent PGHS-2 promoter activities. Electrophoretic mobility shift assays showed that U2Delta1-220 was able to compete with full-length USF proteins and to saturate the E-box element. Immunoprecipitation/Western blot analyses revealed an increase in the levels of phosphorylated USF1 and USF2 after forskolin treatment, whereas chromatin immunoprecipitation assays showed that binding of USF proteins to the endogenous PGHS-2 promoter was stimulated by forskolin. Site-directed mutagenesis of a consensus PKA phosphorylation site within USF proteins abolished their transactivating capacity. Collectively, these results characterize the role of USF phosphorylation in PGHS-2 expression and identify the phosphorylation-dependent increase in USF binding to the E-box as a putative molecular basis for the increase in PGHS-2 promoter transactivation in granulosa cells.
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Affiliation(s)
- Khampoune Sayasith
- Centre de Recherche en Reproduction Animale and the Département de Biomédecine Vétérinaire, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec J2S 7C6, Canada
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399
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Zhang M, Mizrachi D, Fanelli F, Segaloff DL. The formation of a salt bridge between helices 3 and 6 is responsible for the constitutive activity and lack of hormone responsiveness of the naturally occurring L457R mutation of the human lutropin receptor. J Biol Chem 2005; 280:26169-76. [PMID: 15908694 PMCID: PMC1237128 DOI: 10.1074/jbc.m502102200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human lutropin receptor (hLHR) plays a pivotal role in reproductive endocrinology. A number of naturally occurring mutations of the hLHR have been identified that cause the receptor to become constitutively active. To gain further insights into the structural basis for the activation of the hLHR by activating mutations, we chose to examine a particularly strong constitutively activating mutation of this receptor, L457R, in which a leucine that is highly conserved among rhodopsin-like G protein-coupled receptors in helix 3 has been substituted with arginine. Using both disruptive as well as reciprocal mutagenesis strategies, our studies demonstrate that the ability of L457R to stabilize an active form of the hLHR is because of the formation of a salt bridge between the replacing amino acid and Asp-578 in helix 6. Such a lock between the transmembrane portions of helices 3 and 6 is concurrent with weakening the connections between the cytosolic ends of the same helices, including the interaction found in the wild-type receptor between Arg-464, of the (E/D)R(Y/W) motif, and Asp-564. This structural effect is properly marked by the increase in the solvent accessibility of selected amino acids at the cytosolic interfaces between helices 3 and 6. The integrity of the conserved amino acids Asn-615 and Asn-619 in helix 7 is required for the transfer of the structural change from the activating mutation site to the cytosolic interface between helices 3 and 6. The results of in vitro and computational experiments further suggest that the structural trigger of the constitutive activity of the L457R mutant may also be responsible for its lack of hormone responsiveness.
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Affiliation(s)
- Meilin Zhang
- From the Department of Physiology and Biophysics, The University of Iowa, Iowa City, Iowa 52242 and
| | - Dario Mizrachi
- From the Department of Physiology and Biophysics, The University of Iowa, Iowa City, Iowa 52242 and
| | - Francesca Fanelli
- the Dulbecco Telethon Institute and Department of Chemistry, University of Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - Deborah L. Segaloff
- From the Department of Physiology and Biophysics, The University of Iowa, Iowa City, Iowa 52242 and
- ** To whom correspondence should be addressed: Dept. of Physiology and Biophysics, 5–470 Bowen Science Bldg., The University of Iowa, IA City, IA 52242. Tel.: 319-335-7850; Fax: 319-335-7330; E-mail:
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400
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Yamashita S, Nakamura K, Omori Y, Tsunekawa K, Murakami M, Minegishi T. Association of human follitropin (FSH) receptor with splicing variant of human lutropin/choriogonadotropin receptor negatively controls the expression of human FSH receptor. Mol Endocrinol 2005; 19:2099-111. [PMID: 15890674 DOI: 10.1210/me.2005-0049] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
A splice variant of human lutropin (LH)/choriogonadotropin (CG)-receptor [hLHR(exon 9)] that lacks exon 9 was previously cloned in the corpus luteum of a woman with a normal menstrual cycle. Supported by a detergent-soluble binding assay and a receptor biotinylation experiment, the receptor binding assay shows hLHR(exon 9) is neither expressed at the cell surface nor has the capability of binding to hCG. In addition, hLHR(exon 9) was confirmed in the endoplasmic reticulum (ER) by endoglycosidase H treatment. A coimmunoprecipitation experiment clearly showed that hLHR(exon 9) and constitutively inactivate mutant-LHRs, which stay in the ER, form an association with the human follitropin (FSH)-receptor (hFSHR). This suggests that in the presence of mutant-LHR, hFSHR, which is trapped in the ER and associated with hLHR(exon 9), is unable to come up to the plasma membrane. This phenomenon is specific among gonadotropin receptors because human TSH receptor failed to be coimmunoprecipitated. Furthermore, this receptor complex attenuated the hFSHR receptor protein level within the cells, which impaired cAMP production. To elucidate the mechanism underlying the decrease in hFSHR protein by this receptor complex, we performed a Percoll fractionation experiment, which indicated that the receptor complex drove hFSHR to the lysosome instead of the plasma membrane. These results reveal a novel mechanism of FSHR expression regulation.
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Affiliation(s)
- Soichi Yamashita
- Department of Obstetrics and Gynecology, School of Medicine, Gunma University, Gunma 371-8511, Japan
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