Naturally occurring mutations of the luteinizing-hormone receptor: lessons learned about reproductive physiology and G protein-coupled receptors

Effect of LHCGR and FSHR gene polymorphisms on fertility traits and milk yield of cross-bred dairy cows in Sri Lanka

Single nucleotide polymorphism (SNP) analysis of fertility genes will be useful in improving the genetic potential of dairy cows. A population of 142 cross-bred dairy cows was screened for SNPs in bovine luteinizing hormone choriogonadotropin receptor (LHCGR) and bovine follicle stimulating hormone receptor (FSHR) genes. The effect of reported SNPs on selected fertility traits (average calving interval, average number of services per conception and age at first calving) and milk yield was determined. Altogether six SNPs were detected in animals screened under the present study. Among them, four SNPs (rs41256848, rs41256850, rs465790244, and rs45463781) were located in the exon 11 region of the LHCGR gene and two SNPs (rs43676359 and G-278-A (GU253337) were located in the five upstream region of the FSHR gene. Minor alleles identified for SNPs in the FSHR gene in the studied small population of cows differed from those reported in other research. In this study, only rs45463781 SNP at exon 11 of the LHCGR gene significantly affected the average milk yield in cross-bred cows. The nucleotide change from "G" to "A" negatively affected the average milk yield. Further investigations are needed to confirm the reported association with a larger sample size.

Olfactory marker protein elevates basal cAMP concentration

Olfactory marker protein (OMP), which is expressed abundantly in mature olfactory receptor neurons, operates as a cAMP-binding protein. OMP captures phasic cAMP surges induced by sensory stimuli and punctuates the downstream signalling in the cilia. On the other hand, OMP is also abundant in the soma. At equilibrium, OMP should exhibit association/dissociation reactions with cAMP. To examine the steady-state function of OMP, we expressed OMP in an HEK293 heterologous expression system and measured the activity of cAMP-dependent protein kinase (PKA) using a cAMP response element/luciferase reporter assay. In the presence of OMP, the basal activity level of PKA was elevated to approximately twice as much as that in the absence of OMP. Upon tonic stimulation by membrane-permeable cAMP, the PKA activity increased in a dose-dependent manner and was greater in the presence of OMP at all doses until saturation. These results indicate that OMP, a cytosolic cAMP-binding protein, operates as a cAMP reservoir by increases the basal cAMP concentration and enhances tonic cAMP actions. Together with the previous finding that OMP acutely sequesters cAMP-related responses, these results indicate that OMP can buffer acute surges in cAMP and tonic production, which stabilizes the basal cAMP pool in the long run.

Constitutive luteinizing hormone receptor signaling causes sexual dysfunction and Leydig cell adenomas in male mice

The luteinizing hormone receptor (LHCGR) is necessary for fertility, and genetic mutations cause defects in reproductive development and function. Activating mutations in LHCGR cause familial male-limited precocious puberty (FMPP). We have previously characterized a mouse model (KiLHRD582G) for FMPP that exhibits the same phenotype of precocious puberty, Leydig cell hyperplasia, and elevated testosterone as boys with the disorder. We observed that KiLHRD582G male mice became infertile by 6 months of age, although sperm count and motility were normal. In this study, we sought to determine the reason for the progressive infertility and the long-term consequences of constant LHCGR signaling. Mating with superovulated females showed that infertile KiLHRD582G mice had functional sperm and normal accessory gland function. Sexual behavior studies revealed that KiLHRD582G mice mounted females, but intromission was brief and ejaculation was not achieved. Histological analysis of the reproductive tract showed unique metaplastic changes resulting in pseudostratified columnar epithelial cells with cilia in the ampulla and chondrocytes in the penile body of the KiLHRD582G mice. The infertile KiLHRD582G exhibited enlarged sinusoids and a decrease in smooth muscle content in the corpora cavernosa of the penile body. However, collagen content was unchanged. Leydig cell adenomas and degenerating seminiferous tubules were seen in 1-year-old KiLHRD582G mice. We conclude that progressive infertility in KiLHRD582G mice is due to sexual dysfunction likely due to functional defects in the penis.

Endocrine, Paracrine, and Autocrine Signaling Pathways That Regulate Ovulation

The central role of luteinizing hormone (LH) and its receptor (LHCGR) in triggering ovulation has been recognized for decades. Because the LHCGR is present in the mural (outermost) granulosa cell layer of preovulatory follicles (POFs), the LH-initiated signal has to be transmitted to another somatic cell type (cumulus granulosa cells) and the oocyte to release a fertilizable oocyte. Recent studies have shown that activation of the LHCGR initiates vectorial transfer of information among the two somatic cell types and the oocyte and the molecules and signaling pathways involved are now better understood. This review summarizes the newer developments on the complex signaling pathways that regulate ovulation.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

The LH/CG receptor activates canonical signaling pathway when expressed in Drosophila

G-protein coupled receptors (GPCRs) and their ligands provide precise tissue regulation and are therefore often restricted to specific animal phyla. For example, the gonadotropins and their receptors are crucial for vertebrate reproduction but absent from invertebrates. In mammals, LHR mainly couples to the PKA signaling pathway, and CREB is the major transcription factor of this pathway. Here we present the results of expressing elements of the human gonadotropin system in Drosophila. Specifically, we generated transgenic Drosophila expressing the human LH/CG receptor (denoted as LHR), a constitutively active form of LHR, and an hCG analog. We demonstrate activation-dependent signaling by LHR to direct Drosophila phenotypes including lethality and specific midline defects; these phenotypes were due to LHR activation of PKA/CREB pathway activity. That the LHR can act in an invertebrate demonstrates the conservation of factors required for GPCR function among phylogenetically distant organisms. This novel gonadotropin model may assist the identification of new modulators of mammalian fertility by exploiting the powerful genetic and pharmacological tools available in Drosophila.

Genetic Models for the Study of Luteinizing Hormone Receptor Function

The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is essential for fertility in men and women. LHCGR binds luteinizing hormone (LH) as well as the highly homologous chorionic gonadotropin. Signaling from LHCGR is required for steroidogenesis and gametogenesis in males and females and for sexual differentiation in the male. The importance of LHCGR in reproductive physiology is underscored by the large number of naturally occurring inactivating and activating mutations in the receptor that result in reproductive disorders. Consequently, several genetically modified mouse models have been developed for the study of LHCGR function. They include targeted deletion of LH and LHCGR that mimic inactivating mutations in hormone and receptor, expression of a constitutively active mutant in LHCGR that mimics activating mutations associated with familial male-limited precocious puberty and transgenic models of LH and hCG overexpression. This review summarizes the salient findings from these models and their utility in understanding the physiological and pathological consequences of loss and gain of function in LHCGR signaling.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Precocious puberty and Leydig cell hyperplasia in male mice with a gain of function mutation in the LH receptor gene

The LH receptor (LHR) is critical for steroidogenesis and gametogenesis. Its essential role is underscored by the developmental and reproductive abnormalities that occur due to genetic mutations identified in the human LHR. In males, activating mutations are associated with precocious puberty and Leydig cell hyperplasia. To generate a mouse model for the human disease, we have introduced an aspartic acid to glycine mutation in amino acid residue 582 (D582G) of the mouse LHR gene corresponding to the most common D578G mutation found in boys with familial male-limited precocious puberty (FMPP). In transfected cells, mouse D582G mLHR exhibited constitutive activity with a 23-fold increase in basal cAMP levels compared with the wild-type receptor. A temporal study of male mice from 7 days to 24 weeks indicated that the knock-in mice with the mutated receptor (KiLHR(D582G)) exhibited precocious puberty with elevated testosterone levels as early as 7 days of age and through adulthood. Leydig cell-specific genes encoding LHR and several steroidogenic enzymes were up-regulated in KiLHR(D582G) testis. Leydig cell hyperplasia was detected at all ages, whereas Sertoli and germ cell development appeared normal. A novel finding from our studies, not previously reported in the FMPP cases, is that extensive hyperplasia is commonly found around the periphery of the testis. We further demonstrate that the hyperplasia is due to premature proliferation and precocious differentiation of adult Leydig cells in the KiLHR(D582G) testis. The KiLHR(D582G) mice provide a mouse model for FMPP, and we suggest that it is a useful model for studying pathologies associated with altered LHR signaling.

Structure, function and regulation of gonadotropin receptors - a perspective

Luteinizing hormone receptor and follicle stimulating hormone receptor play a crucial role in female and male reproduction. Significant new information has emerged about the structure, mechanism of activation, and regulation of expression of these receptors. Here we provide an overview of the current information on those aspects with an in-depth discussion of the recent developments in the post-transcriptional mechanism of LH receptor expression mediated by a specific LH receptor mRNA binding protein, designated as LRBP. LRBP was identified by electrophoretic gel mobility shift assay using cytosolic fractions from ovaries in the down regulated state. LRBP was purified, its binding site on LH receptor mRNA was identified and characterized. During ligand-induced down regulation, LRBP expression is increased through the cAMP/PKA and ERK signaling pathway, is translocated to translating ribosomes, binds LH receptor mRNA and forms an untranslatable ribonucleoprotein complex. This complex is then routed to the mRNA degradation machinery resulting in diminished levels of both LHR mRNA and cell surface expression of LH receptor. The studies leading to these conclusions are presented.

Revisiting and questioning functional rescue between dimerized LH receptor mutants

The glycoprotein hormone receptors are G protein-coupled receptors containing a large extracellular domain fused to a prototypical serpentine domain. cis-activation occurs when binding of hormone to the extracellular domain stabilizes the serpentine domain in an active conformation. Studies by others suggested that these receptors can also signal by trans-activation, where hormone binding to one receptor protomer activates the serpentine domain of an associated protomer, as documented by the partial rescue of hormone-dependent signaling when a binding defective mutant is coexpressed with a signaling defective mutant. However, our characterizations of several LH receptor (LHR) mutants used in previous studies differ markedly from those originally reported. Also, when examining a pair of LHR mutants previously shown to functionally rescue in vitro as well as in vivo, in addition to finding that the properties of the individual mutants differ significantly from those originally described, we determined that when this pair of mutants was coexpressed in vitro, quantitative analyses did not indicate functional rescue. Additional data are presented that provide a plausible alternate explanation for the apparent in vivo trans-activation that was reported. Finally, using LHR mutants that we have documented to be expressed at the cell surface but to lack human chorionic gonadotropin binding activity or to be severely impaired in their ability to activate Gs, we did not observe functional rescue of human chorionic gonadotropin-stimulated cAMP when the mutants were coexpressed, even though bioluminescence resonance energy transfer analyses confirmed that the coexpressed mutants formed dimers. Taken altogether, our data substantively question the concept of functional rescue between LHR mutants.

LH receptor gene expression in cumulus cells in women entering an ART program

PURPOSE

Luteinizing hormone (LH) exerts its actions through its receptor (LHR), which is mainly expressed in theca cells and to a lesser extent in oocytes, granulosa and cumulus cells. The aim of the present study was the investigation of a possible correlation between LHR gene and LHR splice variants expression in cumulus cells and ovarian response as well as ART outcome.

METHODS

Forty patients undergoing ICSI treatment for male factor infertility underwent a long luteal GnRH-agonist downregulation protocol with a fixed 5-day rLH pre-treatment prior to rFSH stimulation and samples of cumulus cells were collected on the day of egg collection. RNA extraction and cDNA preparation was followed by LHR gene expression investigation through real-time PCR. Furthermore, cumulus cells were investigated for the detection of LHR splice variants using reverse transcription PCR.

RESULTS

Concerning LHR expression in cumulus cells, a statistically significant negative association was observed with the duration of ovarian stimulation (odds ratio = 0.23, p = 0.012). Interestingly, 6 over 7 women who fell pregnant expressed at least two specific types of LHR splice variants (735 bp, 621 bp), while only 1 out of 19 women that did not express any splice variant achieved a pregnancy.

CONCLUSIONS

Consequently, the present study provide a step towards a new role of LHR gene expression profiling as a biomarker in the prediction of ovarian response at least in terms of duration of stimulation and also a tentative role of LHR splice variants expression in the prediction of pregnancy success.

Regulatory processes governing the cell surface expression of LH and FSH receptors

The LH receptor (LHR) and FSH receptor (FSHR), collectively termed the gonadotropin receptors, are members of the Family A of GPCRs. The gonadotropin receptors each contain N-linked carbohydrates that are not directly involved in hormone binding, but contribute to the proper folding, and therefore, cell surface expression of the receptor. Loss-of-function mutations of an LHR or FSHR results in decreased target cell responsiveness. Most inactivating mutations cause receptor misfolding, resulting in the retention of the mutant in its immature form in the endoplasmic reticulum. A membrane-permeable allosteric agonist of the LHR has been shown to serve as a pharmacological chaperone for misfolded and intracellularly retained LHRs by promoting their cell surface expression. Wild-type LHR and FSHR each form homodimers and heterodimers while in the ER. Therefore, when wild-type receptor is co-expressed with a misfolded mutant, the misfolded receptor dimerizes with immature wild-type receptor in the ER, causing a dominant-negative effect on cell surface expression of the mature wild-type receptor. Notably, the propensity for homodimerization is not affected by the activation status of the receptor. However, within a receptor dimer, the activity of one protomer may allosterically regulate the other protomer. Therefore, the dimerization of the gonadotropin receptors appears to be an obligate process that is part of the normal itinerary for trafficking to the cell surface and, once there, the dimerized receptors allow for additional modulations of cell signaling.

Constitutive activity of the lutropin receptor and its allosteric modulation by receptor heterodimerization

The lutropin receptor (LHR) is a G protein-coupled receptor (GPCR) that mediates the actions of pituitary LH in males and females and that of placental hCG in pregnant women and, therefore, plays an essential role in reproductive physiology. Mutations of the lhcgr gene that result in constitutive activation of the LHR have been shown to be causative of gonadotropin-independent precocious puberty in young boys. Studies on constitutively active mutants (CAMs) of the LHR have been extremely informative in elucidating the roles of the LHR in reproductive physiology as well as in understanding the molecular basis underlying activation of this GPCR. The constitutive activities of hLHR CAMs can be attenuated by introducing mutations into the CAMs that stabilize the resting state of the hLHR or by coexpressing the hLHR CAMs with an hLHR mutant that is stabilized in the resting state, allowing the two forms of the hLHR to heterodimerize. This chapter describes the experimental methods and strategies underlying studies of hLHR CAMs.

Bicalutamide and third-generation aromatase inhibitors in testotoxicosis

Testotoxicosis, a form of gonadotropin-independent precocious puberty, results from an activating mutation of the luteinizing hormone receptor expressed in testicular Leydig cells. Affected males experience early testosterone secretion, virilization, advancing bone age, and resultant short stature. Recently, the use of combination therapy with a potent antiandrogen agent (bicalutamide) and a third-generation aromatase inhibitor (anastrozole or letrozole) was reported to yield encouraging short-term results. We present here the results of longer-term treatment (4.5 and 5 years) with this combination therapy in 2 boys who demonstrated that it is well tolerated, slows bone-age advancement in the face of continued linear growth, and prevents progression of virilization.

Follicle stimulating hormone receptor mutations and reproductive disorders

The follicle stimulating hormone receptor (FSHR) plays a critical role in reproductive function. In the males, FSH supports spermatogenesis, whereas in females, FSH is absolutely required for ovarian follicle growth. In females, inactivating mutations in the FSHR result in ovarian dysgenesis with amenorrhea and infertility. The few males reported with severe inactivating mutations exhibited varying spermatogenic defects, but not azoospermia. While these findings may potentially suggest that FSH action is not absolutely required for spermatogenesis, it cannot be ruled out that these individuals have some residual FSHR activity. Gain-of-function mutations in the FSHR cause spontaneous ovarian hyperstimulation syndrome in females due to the inappropriate stimulation of the mutant FSHR by human choriogonadotropin.

A cell surface inactive mutant of the human lutropin receptor (hLHR) attenuates signaling of wild-type or constitutively active receptors via heterodimerization

The D405N and Y546F mutations of the human lutropin receptor (hLHR) have previously been shown to partially attenuate hCG-stimulated cAMP synthesis despite normal cell surface expression and hCG binding affinity (Min, L. and Ascoli, M. Mol. Endocrinol. 14:1797-1810, 2000). We now show that these mutations each stabilize a resting state of the hLHR. A combined mutant D405N,Y546F is similarly expressed at the cell surface and exhibits normal ligand-binding, but is profoundly signaling impaired. Introduction of hLHR(wt) into cells stably expressing the signaling inactive D405N,Y546F resulted in the attenuation of hCG-stimulated cAMP production by hLHR(wt) even if excess Gs is co-expressed. Similarly, co-expression of D405N,Y546F with hLHR constitutively active mutants (CAMs) attenuated their constitutive activity. Quantitative bioluminescence resonance energy transfer (BRET) analyses demonstrated that D405N,Y546F formed heterodimers with both wt and CAM hLHR. In contrast hLHR(D405N,Y546F) did not heterodimerize with the melanocortin 3 receptor (MC3R) and agonist-stimulated cAMP production through the MC3R was not attenuated when these two receptors were co-expressed. Taken altogether, our data demonstrate that a signaling inactive hLHR mutant (that is trafficked normally to the plasma membrane) attenuates the signaling of the cell surface localized wt or the constitutively active hLHR due to receptor heterodimerization. Our studies, therefore, suggest a novel ramification of GPCR signaling resulting from receptor dimerization.

Mother-to-son transmission of a luteinizing hormone receptor activating mutation in a prepubertal child with testotoxicosis

AIM

To identify the LHR gene mutation in a prepubertal child with testotoxicosis.

METHODS

Standard RIA procedure was used for estimating LH, FSH and testosterone levels. Molecular analysis was done by standard PCR using different sets of primers and reaction conditions specific for the LHR gene. Direct sequencing was done using the ABI Prism Dye terminator sequencing kit and the ABI 310 sequencing apparatus.

RESULTS

We found a heterozygous mutation of the LHR gene in exon 11 of the second transmembrane region, Met-->Thr at the 398 position (M398T). The same mutation was also found in the proband's mother.

CONCLUSION

To our knowledge, this is the first molecular characterization of maternally inherited testotoxicosis in a 5 1/2-year-old boy from the Indian subcontinent.

Bioluminescence resonance energy transfer studies reveal constitutive dimerization of the human lutropin receptor and a lack of correlation between receptor activation and the propensity for dimerization

Previous studies from our laboratory using co-immunoprecipitation techniques suggested that the human lutropin receptor (hLHR) constitutively self-associates into dimers/oligomers and that agonist treatment of cells either increased hLHR dimerization/oligomerization and/or stabilized hLHR dimers/oligomers to detergent solubilization (Tao, Y. X., Johnson, N. B., and Segaloff, D. L. (2004) J. Biol. Chem. 279, 5904-5914). In this study, bioluminescence resonance energy transfer (BRET(2)) analyses confirmed that the hLHR constitutively self-associates in living cells. After subcellular fractionation, hLHR dimers/oligomers were detected in both the plasma membrane and endoplasmic reticulum (ER). Further evidence supporting the constitutive formation of hLHR dimer/oligomers in the ER is provided by data showing homodimerization of misfolded hLHR mutants that are retained in the ER. These mutants, when co-expressed with wild-type receptor, are shown by BRET(2) to heterodimerize, accounting for their dominant-negative effects on cell surface receptor expression. Hormone desorption assays using intact cells demonstrate allosterism between hLHR protomers, indicating functional cell surface hLHR dimers. However, quantitative BRET(2) analyses in intact cells indicate a lack of effect of agonist on the propensity of the hLHR to dimerize. Using purified plasma membranes, human chorionic gonadotropin was similarly observed to have no effect on the BRET(2) signal. An examination of the propensity for constitutively active and signaling inactive hLHR mutants to dimerize further showed no correlation between dimerization and the activation state of the hLHR. Taken altogether, our data suggest that hLHR dimers/oligomers are formed early in the biosynthetic pathway in the ER, are constitutively expressed on the plasma membrane, and are not affected by the activation state of the hLHR.

Constitutive activation of G protein-coupled receptors and diseases: insights into mechanisms of activation and therapeutics

The existence of constitutive activity for G protein-coupled receptors (GPCRs) was first described in 1980s. In 1991, the first naturally occurring constitutively active mutations in GPCRs that cause diseases were reported in rhodopsin. Since then, numerous constitutively active mutations that cause human diseases were reported in several additional receptors. More recently, loss of constitutive activity was postulated to also cause diseases. Animal models expressing some of these mutants confirmed the roles of these mutations in the pathogenesis of the diseases. Detailed functional studies of these naturally occurring mutations, combined with homology modeling using rhodopsin crystal structure as the template, lead to important insights into the mechanism of activation in the absence of crystal structure of GPCRs in active state. Search for inverse agonists on these receptors will be critical for correcting the diseases cause by activating mutations in GPCRs. Theoretically, these inverse agonists are better therapeutics than neutral antagonists in treating genetic diseases caused by constitutively activating mutations in GPCRs.

Long-term treatment of familial male-limited precocious puberty (testotoxicosis) with cyproterone acetate or ketoconazole

BACKGROUND

Familial male-limited precocious puberty (FMPP) or testotoxicosis is a rare gonadotrophin-independent form of sexual precocity caused by constitutively activating mutations of the LH receptor. Several clinical therapeutic approaches have been reported for this disorder, but with a paucity of long-term outcome data.

OBJECTIVE

To evaluate the long-term treatment of testotoxicosis with cyproterone acetate or ketoconazole.

DESIGN

A multicentric retrospective clinical study.

PATIENTS

Ten boys from eight unrelated Brazilian families who carried known LH-receptor activating mutations were treated with 70 mg/m(2) cyproterone acetate (n = 5) or 10 mg/kg ketoconazole (n = 5) for a mean period of 5 and 8 years, respectively.

MEASUREMENTS

Chronological and bone ages, bone age/chronological age ratio, target height (TH) range, adult height, basal and GnRH-stimulated gonadotrophin levels and basal testosterone levels were assessed.

RESULTS

Growth velocity decreased significantly during treatment with cyproterone acetate or ketoconazole when compared to pretreatment value in each group (P < 0.05). Bone age/chronological age ratio decreased significantly after cyproterone acetate or ketoconazole therapy. Basal testosterone levels were significantly lower in patients undergoing ketoconazole compared to cyproterone acetate treatment [0.6 +/- 0.3 nmol/l (42 +/- 21 ng/dl) vs. 5.6 +/- 4.0 nmol/l (392 +/- 280 ng/dl); P < 0.05], as expected. Secondary gonadotrophin-dependent precocious puberty occurred at a similar frequency (40%) in both groups. Five patients have attained adult height and two patients have already reached 90% of their adult height. Two of them achieved their TH range and one patient, for whom TH was not available, had an adult height of 0.3 SDS. Four boys (two in each group) did not attain their TH range.

CONCLUSION

Long-term treatment with cyproterone acetate or ketoconazole resulted in similar outcomes without important side-effects in boys with testotoxicosis. However, both therapies showed limited efficacy in attaining normal adult height.

An intracellular loop (IL2) residue confers different basal constitutive activities to the human lutropin receptor and human thyrotropin receptor through structural communication between IL2 and helix 6, via helix 3

The human lutropin receptor (hLHR) and human TSH receptor (hTSHR) are G protein-coupled receptors that play key roles in reproductive and thyroid physiology, respectively. We show using a quantitative assessment of cAMP production as a function of cell surface receptor expression that the hTSHR possesses greater basal constitutive activity than the hLHR. Further studies were undertaken to test the hypothesis that different potential Gs-coupling motifs identified in IL2 of the hTSHR and hLHR contribute to their different basal constitutive activities. Although mutating the receptors to interchange their potential Gs-coupling motifs reversed their relative activities, we show this to be due to the swapping of one IL2 residue (Q476 in the hLHR; R531 in the hTSHR). Molecular dynamics simulations show that the effect of the hLHR(Q476R) mutation, switching the structural features of the hLHR toward those of the hTSHR, is greater than the switching effect of the hTSHR(R531Q) mutant toward the hLHR. The structural model of the hLHR(Q476R) mutant can be considered as a hybrid of wild-type (wt) hTSHR and constitutively active mutant hLHR forms. In this hLHR(Q476R) mutant, IL2 adopts a structure similar to IL2 of the wt hTSHR, but it shares with the hLHR constitutively active mutant the solvent exposure and the reciprocal arrangement of helices 3, 5, and 6, including the weakening of the wt native R3.50-D6.30 interaction. Our results suggest a H3-mediated structural connection between IL2 and the cytosolic extension of H6. Thus, IL2 contributes significantly to the inactive and active state ensembles of these G protein-coupled receptors.

The role of chorionic gonadotropin and Notch1 in implantation

PURPOSE

Failed implantation is a major limiting factor in infertility and early pregnancy loss. In primates, human chorionic gonadotropin mediated inhibition of stromal cell apoptosis and their subsequent differentiation into decidual cells is critical for successful embryo implantation. A major regulator of cell survival and differentiation is the Notch receptor, which transduces extracellular signals responsible for cell fate determination during development. Proteolytic cleavage of full-length Notch1 releases an active intracellular peptide, which later translocates to the nucleus and activates gene transcription. Induction of Notch1 during the window of uterine receptivity in stromal fibroblasts in response to chorionic gonadotropin upregulates anti- apoptotic genes and induces alpha-smooth muscle actin, enabling stromal cells to proliferate and differentiate into a decidualized phenotype. As such, prior to implantation the embryonic signal, chorionic gonadotropin, rescues stromal fibroblasts from normal regression at the end of each ovarian cycle.

CONCLUSION

We are suggesting that chorionic gonadotropin and Notch1 coordinately regulate decidualization by preventing apoptosis of endometrial stromal fibroblasts, averting uterine sloughing, and promoting cell survival and differentiation into the decidualized phenotype, which is critical for the maintenance of pregnancy.

A Select Set of Opioid Ligands Induce Up-Regulation by Promoting the Maturation and Stability of the Rat κ-Opioid Receptor in Human Embryonic Kidney 293 Cells

Ligand-induced regulation of the rat kappa-opioid receptor (rKOR) was investigated in human embryonic kidney 293 cells stably expressing the FLAG-tagged rKOR. Incubation of rKOR cells with naltrexone for 24 h increased the B(max) >3-fold, with no change in the affinity of [(3)H]diprenorphine. Two immunoreactive receptor species were present in cell lysates: naltrexone treatment caused a >3-fold increase in the 52-kDa species while decreasing the level of the 42-kDa species. Dynorphin(1-13), U69,593 [(5alpha,7alpha,8beta)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4,5]dec-8-yl)benzeneacetamide], or salvinorin A [2S,4aR,6aR,7R,9S,10aS, 10bR)-9-(acetyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1c]pyran-7-carboxylic acid methyl ester] treatment did not alter the level of immunoreactive rKOR protein, whereas etorphine, cyclazocine, naloxone, and naloxone methiodide increased the 52-kDa and decreased the 42-kDa rKOR bands. Receptor up-regulation was associated with an increase in the number of cell surface receptors and a 2-fold increase in the E(max) for guanosine 5'-O-(3-[(35)S]thio)triphosphate binding. Glycosidase digestion indicated that the 52- and 42-kDa receptors contained complex and high-mannose N-glycans, respectively, Pulse-chase analysis and glycosidase digestion sensitivities suggested that the 42-kDa rKOR species was a precursor of the 52-kDa species. Naltrexone did not alter rKOR mRNA levels or translational efficiency, and rKOR up-regulation was not inhibited by cycloheximide. Brefeldin A caused accumulation of intracellular rKOR intermediates, and coincubation with naltrexone increased the levels of the brefeldin-induced species significantly. These results suggest that select opioid ligands up-regulate rKOR by enhancing the rate of receptor folding and maturation and by protecting the receptor from degradation, resulting in an increase in the number of rKOR binding sites, immunoreactive protein, and functional receptors.

Intrinsic differences in the response of the human lutropin receptor versus the human follitropin receptor to activating mutations

In contrast to the human lutropin receptor (hLHR), very few naturally occurring activating mutations of the structurally related human follitropin receptor (hFSHR) have been identified. The present study was undertaken to determine if one aspect underlying this discrepancy might be a general resistance of the hFSHR to mutation-induced constitutive activity. Five different mutations were introduced into both the hLHR and hFSHR (four based on activating mutations of the hLHR gene, one based on an activating mutation of the hFSHR gene). Our results demonstrate that hFSHR constitutively activating mutants (CAMs) were not as active as hLHR CAMs containing the comparable mutation. Furthermore, although all hFSHR CAMs exhibited strong promiscuous activation by high concentrations of the other glycoprotein hormone receptors, hLHR CAMs showed little or no promiscuous activation. Our in vitro findings are consistent with in vivo observations of known pathophysiological conditions associated with hLHR CAMs, but not hFSHR CAMs, and with promiscuous activation of hFSHR CAMs, but not hLHR CAMs. Computational experiments suggest that the mechanisms through which homologous mutations increase the basal activity of the hLHR and the hFSHR are similar. This is particularly true for the strongest CAMs like L460(3.43)R. Disparate properties of the hLHR versus hFSHR CAMs may, therefore, be due to differences in shape and electrostatics features of the solvent-exposed cytosolic receptor domains involved in the receptor-G protein interface rather than to differences in the nature of local perturbation at the mutation site or in the way local perturbation is transferred to the putative G protein binding domains.

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

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.

Insights learned from L457(3.43)R, an activating mutant of the human lutropin receptor

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.

Molecular analysis of the neuropeptide Y1 receptor gene in human idiopathic gonadotropin-dependent precocious puberty and isolated hypogonadotropic hypogonadism

OBJECTIVE

To investigate the role of mutations or polymorphisms in the NPY-Y1R gene in human idiopathic central pubertal disorders.

DESIGN

Molecular studies.

SETTING

University hospital.

PATIENT(S)

Thirty-three patients with gonadotropin-dependent precocious puberty, 22 with hypogonadotropic hypogonadism, and 50 controls.

INTERVENTION(S)

Genomic DNA extraction, NPY-Y1R gene sequence analysis, cell-surface expression, and functional activity of an identified receptor variant.

MAIN OUTCOME MEASURE(S)

Results of sequencing, cell-surface receptor expression, and receptor function.

RESULT(S)

A heterozygous substitution of lysine (K) by threonine (T) at position 374 in the carboxyl terminal region of NPY-Y1R was identified in a girl with familial GDPP. Her mother, who had pubertal developmental at appropriate age, carried the same genetic variant. Introduction of the K374T variant into an expression vector containing the human NPY-Y1R complementary DNA led to a partial reduction in cell-surface expression of NPY-Y1R in transiently transfected HEK293 cells. This mutation did not lead to a significant reduction in NPY-stimulated activity of the receptor in this heterologous expression system. No other allelic variants of the NPY-Y1R gene were identified in patients or controls.

CONCLUSION(S)

We have identified an inherited heterozygous variant of the NPY-Y1R gene in a girl with precocious puberty; however, this most likely did not contribute to her phenotype. Mutations of the highly conserved NPY-Y1R gene do not appear to represent a frequent mechanism underlying human idiopathic central pubertal disorders.

[Leydig cell hypoplasia]

The Leydig cell hypoplasia is a rare and well defined form of male pseudohermaphroditism with autosomal recessive inheritance pattern. An inadequate fetal testicular Leydig cell differentiation and, consequently a low androgenic production during intra uterine and post natal periods, result in absence or incomplete virilization in patients with 46,XY karyotype. These patients exhibit a wide clinical spectrum, ranging from complete female external genitalia to male external genital with micropenis, low serum testosterone levels associated with high LH levels. Inactivating mutations of the LH/hCG receptor gene have been identified in affected families in the last decade. However, the low frequency of inactivating mutations in this gene, and the lack of segregation of intragenic polymorphisms among affected members from families with typical phenotype of Leydig cell hypoplasia, suggest the genetic heterogeneity of this condition.

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

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.

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

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.

N-linked glycosylation facilitates processing and cell surface expression of rat luteinizing hormone receptor

The extracellular domain of the luteinizing hormone (LH) receptor has six potential N-linked glycosylation sites. Although previous studies have shown that mutation of the first three sites results in decreased ligand binding at the cell surface, the role of glycosylation in LH receptor processing is not understood. In the present study, we examined whether mutation of the first three sites has any affect on receptor synthesis, processing, and degradation of the mutant receptors. The data show that mutation of N77, N152, or N173 did not affect receptor synthesis, but did significantly reduce processing of the receptor precursor to the mature, cell surface form. Furthermore, defective processing was due to increased degradation of the precursor rather than increased turnover of cell surface receptors. Thus, lack of glycosylation decreases LH receptor processing and targets the receptors for degradation thereby leading to decreased cell surface expression. These results show that glycosylation of the LH receptor plays an important role in receptor processing and cell surface expression.

Gonadotropin receptors: role of post-translational modifications and post-transcriptional regulation

This review focuses on the post-translational modifications of LH and FSH receptors and recent studies on the regulation of LH receptor expression mediated by an RNA binding protein. Both LH and FSH receptors undergo extensive post-translational modifications. N-linked glycosylation occurs co-translationally and plays a role in the maturation and processing of the receptor, while palmitoylation is involved in receptor endocytosis and post-endocytic trafficking. A third type of post-translational modification is phosphorylation and its function has been reviewed. Finally, the regulation of LH receptor at the mRNA level by an RNA binding protein is discussed in the context of ovarian function.

Leydig cell hypoplasia due to inactivation of luteinizing hormone receptor by a novel homozygous nonsense truncation mutation in the seventh transmembrane domain

Inactivating mutations in the LH receptor are the predominant cause for male pseudohermaphroditism in subjects with Leydig cell hypoplasia (LCH). The severity of the mutations, correlates with residual receptor activities. Here, we detail the clinical presentation of one subject with complete male pseudohermaphroditism and LCH. We identify within the proband and her similarly afflicted sibling a homozygous T to G transversion at nucleotide 1836 in exon 11 of the LH/CGR gene. This causes conversion of a tyrosine codon into a stop codon at codon 612 in the seventh transmembrane domain, resulting in a truncated receptor that lacks a cytoplasmic tail. In vitro, in contrast to cells expressing a normal LHR, cells transfected with the mutant cDNA exhibit neither surface binding of radiolabeled hCG nor cAMP generation. In vitro expression under the control of the LHR signal peptide of either a wild type or mutant LHR-GFP fusion protein shows no differences in receptor cellular localization. In conclusion, the in vitro studies suggest that residues in the seventh transmembrane domain and cytoplasmic tail are important for receptor binding and activation without playing a major role in receptor cellular trafficking.

Constitutive and Agonist-dependent Self-association of the Cell Surface Human Lutropin Receptor

The human lutropin receptor (hLHR) is a G protein-coupled receptor (GPCR) that plays an essential role in reproductive physiology. The present studies were undertaken to determine whether the hLHR self-associates. We show that high molecular weight complexes of the hLHR can be co-immunoprecipitated from 293 cells transfected with differentially tagged hLHRs. These complexes are detected only in extracts from cells that have been co-transfected and not in extracts combined from cells expressing only one form of tagged hLHR, confirming the in vivo self-association of the receptor. In transiently transfected cells, in which a small percentage of cells overexpress hLHR and most of the hLHR is located intracellularly in the ER, the self-associated hLHR is composed predominantly of immature hLHR. When cells were transiently co-transfected with wild-type hLHR and a misfolded mutant of the hLHR, a physical association of the ER-localized misfolded mutant with the immature hLHR was observed, resulting in a decreased cell surface expression of the wild-type receptor. In contrast, in stably transfected cells, where the majority of cells express receptor and there is much less intracellular accumulation of hLHR, the self-associated forms of the hLHR are composed predominantly of cell surface receptor. The abundance of cell surface hLHR dimers and oligomers, as detected on SDS gels, is increased further upon human choriogonadotropin treatment of the stably transfected cells. In addition to documenting the self-association of cell surface hLHR, our results underscore the importance of the cellular distribution of recombinant GPCR as it relates to the nature of the GPCR dimerization and oligomerization.

Clinical and molecular analysis of human reproductive disorders in Brazilian patients

Several genes that influence the development and function of the hypothalamic-pituitary-gonadal-axis (HPG) have been identified. These genes encode an array of transcription factors, matrix proteins, hormones, receptors, and enzymes that are expressed at multiple levels of the HPG. We report the experience of a single Endocrinology Unit in the identification and characterization of naturally occurring mutations in families affected by HPG disorders, including forms of precocious puberty, hypogonadism and abnormal sexual development due to impaired gonadotropin function. Eight distinct genes implicated in HPG function were studied: KAL, SF1, DAX1, GnRH, GnRHR, FSHbeta, FSHR, and LHR. Most mutations identified in our cohort are described for the first time in literature. New mutations in SF1, DAX1 and GnRHR genes were identified in three Brazilian patients with hypogonadism. Eight boys with luteinizing hormone- (LH) independent precocious puberty due to testotoxicosis were studied, and all have their LH receptor (LHR) defects elucidated. Among the identified LHR molecular defects, three were new activating mutations. In addition, these mutations were frequently associated with new clinical and hormonal aspects, contributing significantly to the knowledge of the molecular basis of reproductive disorders. In conclusion, the naturally occurring genetic mutations described in the Brazilian families studied provide important insights into the regulation of the HPG.

Le syndrome des ovaires polykystiques en période péri-pubertaire : polymorphisme clinique, biologique, métabolique et génétique

Polycystic ovary syndrome (PCOS) is a common cause of hyperandrogenism in adolescent girls. In its complete post menarchal expression, the syndrome is characterized by the association of typical clinical, biological, and ultrasonographic findings. Many factors have contributed to our knowledge of different clinical forms of PCOS in adolescent girls. They are helpful for clarifying misleading situations in a period of life when diagnosis of PCOS implies a treatment for many years and may interfere with gynecological outcome. During the last 3 years, we had the opportunity to manage in our unit 45 adolescent girls with ovarian hyperandrogenism: 32 of them had PCOS and the other 13 functional ovarian hyperandrogenism defined by clinical and biological hyperandrogenism without ultrasonographic abnormality. In this review, we report, from our personal experience as well as from recent literature data, the different clinical expressions of PCOS in the pubertal period: the classical post menarchal form, the exceptional pre menarchal form, the post precocious pubarche and the post precocious puberty forms, the familial expression as well as the dominant metabolic expression.

The lutropin/choriogonadotropin receptor-induced phosphorylation of the extracellular signal-regulated kinases in leydig cells is mediated by a protein kinase a-dependent activation of ras

The pathways involved in activation of the ERK1/2 cascade in Leydig cells were examined in MA-10 cells expressing the recombinant human LH receptor (hLHR) and in primary cultures of rat Leydig cell precursors. In MA-10 cells expressing the recombinant hLHR, human choriogonadotropin-induced activation of ERK1/2 is effectively inhibited by overexpression of a cAMP phosphodiesterase (a manipulation that blunts the human choriogonadotropin-induced cAMP response), by addition of H89 (a selective inhibitor of protein kinase A), or by overexpression of the heat-stable protein kinase A inhibitor, but not by overexpression of an inactive mutant of this inhibitor. Stimulation of hLHR did not activate Rap1, but activated Ras in an H89-sensitive fashion. Addition of H89 to MA-10 cells that had been cotransfected with a guanosine triphosphatase-deficient mutant of Ras almost completely inhibited the hLHR-mediated activation of ERK1/2. We also show that 8-bromo-cAMP activates Ras and ERK1/2 in MA-10 cells and in primary cultures of rat Leydig cells precursors in an H89-sensitive fashion, whereas a cAMP analog 8-(4-chloro-phenylthio)-2'-O-methyl-cAMP (8CPT-2Me-cAMP) that is selective for cAMP-dependent guanine nucleotide exchange factor has no effect. Collectively, our results show that the hLHR-induced phosphorylation of ERK1/2 in Leydig cells is mediated by a protein kinase A-dependent activation of Ras.

Functional characterization of melanocortin-4 receptor mutations associated with childhood obesity

The melanocortin-4 receptor (MC4R) is a member of the rhodopsin-like G protein-coupled receptor family. The binding of alpha-MSH to the MC4R leads to increased cAMP production. Recent pharmacological and genetic studies have provided compelling evidence that MC4R is an important regulator of food intake and energy homeostasis. Allelic variants of MC4R were reported in some children with early-onset severe obesity. However, few studies have been performed to confirm that these allelic variants result in an impairment of the receptor's function. In this study, we expressed wild-type and variant MC4Rs in HEK293 cells and systematically studied ligand binding, agonist-stimulated cAMP, and cell surface expression. Six of the 11 mutants examined had either decreased (S58C, N62S, Y157S, C271Y) or no (P78L, G98R) ligand binding, with proportional impairments in [Nle4, d-Phe7]-alpha-MSH-stimulated cAMP production. Confocal microscopy confirmed that the observed decreases in hormone binding by these mutants are associated with decreased cell surface expression due to intracellular retention of the mutants. The other five allelic variants (D37V, P48S, V50M, I170V, N274S) were found to be expressed at the cell surface and to bind agonist and respond with increased cAMP production normally. The data on these latter five variants raise the question as to whether they are indeed causative of the obesity or not and, if so, by what mechanism. Our data, therefore, stress the importance of characterizing the properties of MC4R variants associated with early-onset severe obesity. We further propose a classification scheme for mutant MC4Rs based upon their properties.

A constitutively active somatic mutation of the human lutropin receptor found in Leydig cell tumors activates the same families of G proteins as germ line mutations associated with Leydig cell hyperplasia

Using a Leydig tumor cell line (MA-10) transiently transfected with the human lutropin receptor (hLHR) and mutants thereof, we examined the identity of the G proteins activated by the agonist-engaged hLHR-wild type (wt) and by three of its naturally occurring constitutively active mutants. Two of the mutants examined, L457R in transmembrane helix 3 and D578Y in transmembrane helix 6, are germ-line mutations found in boys with Leydig cell hyperplasia and precocious puberty. The third, D578H, is a somatic mutation found in Leydig cell tumors in boys with precocious puberty. We show that the hLHR-wt and the three mutants activate the G(s), G(i/o), and G(q/11), but not the G(12/13), families of G proteins. The activation of these G proteins by the hLHR-wt occurs only when engaged by agonist, but their activation by the L457R, D578Y, and D578H mutants occurs independently of agonist stimulation. We conclude that the G proteins activated by constitutively active mutants of the hLHR associated with Leydig cell hyperplasia or tumors are identical and are the same as those activated by the agonist-engaged hLHR-wt. If there was preferential activation of some G protein families by the somatic D578H mutation found in Leydig cell tumors as opposed to the germ line mutations found in Leydig cell hyperplasia, then one could envision mechanisms by which the D578H mutant would be oncogenic. The data presented here suggest that such mechanisms do not need to be considered.