1
|
Shizu R, Nishiguchi H, Tashiro S, Sato T, Sugawara A, Kanno Y, Hosaka T, Sasaki T, Yoshinari K. Helix 12 stabilization contributes to basal transcriptional activity of PXR. J Biol Chem 2021; 297:100978. [PMID: 34284062 PMCID: PMC8390552 DOI: 10.1016/j.jbc.2021.100978] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 07/12/2021] [Accepted: 07/16/2021] [Indexed: 11/19/2022] Open
Abstract
Pregnane X receptor (PXR) plays an important role in xenobiotic metabolism. While ligand binding induces PXR-dependent gene transcription, PXR shows constitutive transcriptional activity in the absence of ligands when expressed in cultured cells. This constitutive activity sometimes hampers investigation of PXR activation by compounds of interest. In this study, we investigated the molecular mechanism of PXR activation. In the reported crystal structures of unliganded PXR, helix 12 (H12), including a coactivator binding motif, was stabilized, while it is destabilized in the unliganded structures of other nuclear receptors, suggesting a role for H12 stabilization in the basal activity of PXR. Since Phe420, located in the loop between H11 and H12, is thought to interact with Leu411 and Ile414 to stabilize H12, we substituted alanine at Phe420 (PXR-F420A) and separately inserted three alanine residues directly after Phe420 (PXR-3A) and investigated their influence on PXR-mediated transcription. Reporter gene assays demonstrated that the mutants showed drastically reduced basal activity and enhanced responses to various ligands, which was further enhanced by coexpression of the coactivator peroxisome proliferator-activated receptor gamma coactivator 1α. Mutations of both Leu411 and Ile414 to alanine also suppressed basal activity. Mammalian two-hybrid assays showed that PXR-F420A and PXR-3A bound to corepressors and coactivators in the absence and presence of ligands, respectively. We conclude that the intramolecular interactions of Phe420 with Leu411 and Ile414 stabilize H12 to recruit coactivators even in the absence of ligands, contributing to the basal transcriptional activity of PXR. We propose that the generated mutants might be useful for PXR ligand screening.
Collapse
Affiliation(s)
- Ryota Shizu
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
| | - Hikaru Nishiguchi
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Sarii Tashiro
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Takumi Sato
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Ayaka Sugawara
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Yuichiro Kanno
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Takuomi Hosaka
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Takamitsu Sasaki
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Kouichi Yoshinari
- Laboratory of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
| |
Collapse
|
2
|
Shiizaki K, Yoshikawa T, Takada E, Hirose S, Ito-Harashima S, Kawanishi M, Yagi T. Development of yeast reporter assay for screening specific ligands of retinoic acid and retinoid X receptor subtypes. J Pharmacol Toxicol Methods 2014; 69:245-52. [PMID: 24530888 DOI: 10.1016/j.vascn.2014.01.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 01/28/2014] [Indexed: 11/18/2022]
Abstract
INTRODUCTION Retinoic acids are essential for embryonic development, tissue organization, and homeostasis and act via retinoic acid receptors (RARs) that form heterodimers with retinoid X receptors (RXRs). Human RARs and RXRs include the three subtypes α, β, and γ, which have varying distributions and physiological functions among human tissues. Recent reports show that subtype-specific binding of several chemicals to RARs or RXRs may lead to endocrine disruption. To evaluate these ligand-like chemicals, convenient assay systems for each receptor subtype are required. METHODS We developed reporter assay yeasts to screen ligands for RXR subtype receptor homodimers. To screen RAR ligands, yeasts were engineered to express RAR subtypes with defective RXRα, which fails to bind to coactivators because of its shortened c-terminus. RESULTS These assay yeasts were validated using known RXR- and RAR-specific ligands and subtype-specific responses were clearly shown. Subtype-specific ligand activities of the suspected chemical RAR or RXR ligands o-t-butylphenol, triphenyltin chloride, tributyltin chloride, and 4-nonylphenol were determined. DISCUSSION The present assay yeasts may be valuable tools for subtype-specific assessments of unidentified environmental ligand chemicals and receptor-specific pharmaceuticals.
Collapse
Affiliation(s)
- Kazuhiro Shiizaki
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Tomoya Yoshikawa
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Eiji Takada
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Shizuma Hirose
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Sayoko Ito-Harashima
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Masanobu Kawanishi
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan
| | - Takashi Yagi
- Department of Biology, Graduate School of Science, Osaka Prefecture University, Osaka, Japan; Department of Life Science, Dongguk University, Seoul, Republic of Korea.
| |
Collapse
|
3
|
Manna PR, Slominski AT, King SR, Stetson CL, Stocco DM. Synergistic activation of steroidogenic acute regulatory protein expression and steroid biosynthesis by retinoids: involvement of cAMP/PKA signaling. Endocrinology 2014; 155:576-91. [PMID: 24265455 PMCID: PMC3891939 DOI: 10.1210/en.2013-1694] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Both retinoic acid receptors (RARs) and retinoid X receptors (RXRs) mediate the action of retinoids that play important roles in reproductive development and function, as well as steroidogenesis. Regulation of steroid biosynthesis is principally mediated by the steroidogenic acute regulatory protein (StAR); however, the modes of action of retinoids in the regulation of steroidogenesis remain obscure. In this study we demonstrate that all-trans retinoic acid (atRA) enhances StAR expression, but not its phosphorylation (P-StAR), and progesterone production in MA-10 mouse Leydig cells. Activation of the protein kinase A (PKA) cascade, by dibutyrl-cAMP or type I/II PKA analogs, markedly increased retinoid-responsive StAR, P-StAR, and steroid levels. Targeted silencing of endogenous RARα and RXRα, with small interfering RNAs, resulted in decreases in 9-cis RA-stimulated StAR and progesterone levels. Truncation of and mutational alterations in the 5'-flanking region of the StAR gene demonstrated the importance of the -254/-1-bp region in retinoid responsiveness. An oligonucleotide probe encompassing an RXR/liver X receptor recognition motif, located within the -254/-1-bp region, specifically bound MA-10 nuclear proteins and in vitro transcribed/translated RXRα and RARα in EMSAs. Transcription of the StAR gene in response to atRA and dibutyrl-cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of cAMP response-element binding protein (CREB). Chromatin immunoprecipitation studies revealed the association of phosphorylation of CREB, CREB binding protein, RXRα, and RARα to the StAR promoter. Further studies elucidated that hormone-sensitive lipase plays an important role in atRA-mediated regulation of the steroidogenic response that involves liver X receptor signaling. These findings delineate the molecular events by which retinoids influence cAMP/PKA signaling and provide additional and novel insight into the regulation of StAR expression and steroidogenesis in mouse Leydig cells.
Collapse
Affiliation(s)
- Pulak R Manna
- Department of Cell Biology and Biochemistry (P.R.M., S.R.K., D.M.S.), Department of Dermatology and Pathology (C.L.S.), Texas Tech University Health Sciences Center, Lubbock, Texas 79430; and Department of Pathology and Laboratory Medicine (A.T.S.), University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | | | | | | | | |
Collapse
|
4
|
Khurana S, Chakraborty S, Lam M, Liu Y, Su YT, Zhao X, Saleem MA, Mathieson PW, Bruggeman LA, Kao HY. Familial focal segmental glomerulosclerosis (FSGS)-linked α-actinin 4 (ACTN4) protein mutants lose ability to activate transcription by nuclear hormone receptors. J Biol Chem 2012; 287:12027-35. [PMID: 22351778 DOI: 10.1074/jbc.m112.345421] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Mutations in α-actinin 4 (ACTN4) are linked to familial forms of focal segmental glomerulosclerosis (FSGS), a kidney disease characterized by proteinuria due to podocyte injury. The mechanisms underlying ACTN4 mutant-associated FSGS are not completely understood. Although α-actinins are better known to cross-link actin filaments and modulate cytoskeletal organization, we have previously shown that ACTN4 interacts with transcription factors including estrogen receptor and MEF2s and potentiates their transcriptional activity. Nuclear receptors including retinoic acid receptor (RAR) have been proposed to play a protective role in podocytes. We show here that ACTN4 interacts with and enhances transcriptional activation by RARα. In addition, FSGS-linked ACTN4 mutants not only mislocalized to the cytoplasm, but also lost their ability to associate with nuclear receptors. Consequently, FSGS-linked ACTN4 mutants failed to potentiate transcriptional activation by nuclear hormone receptors in podocytes. In addition, overexpression of these mutants suppressed the transcriptional activity mediated by endogenous wild-type ACTN4 possibly by a cytoplasmic sequestration mechanism. Our data provide the first link between FSGS-linked ACTN4 mutants and transcriptional activation by nuclear receptor such as RARα and peroxisome proliferator-activated receptor γ.
Collapse
Affiliation(s)
- Simran Khurana
- Department of Biochemistry, School of Medicine, Case Western Reserve University and Research Institute of University Hospitals of Cleveland, Cleveland, Ohio 44106, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Dawson MI, Xia Z. The retinoid X receptors and their ligands. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:21-56. [PMID: 22020178 DOI: 10.1016/j.bbalip.2011.09.014] [Citation(s) in RCA: 258] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2011] [Revised: 08/23/2011] [Accepted: 09/23/2011] [Indexed: 12/12/2022]
Abstract
This chapter presents an overview of the current status of studies on the structural and molecular biology of the retinoid X receptor subtypes α, β, and γ (RXRs, NR2B1-3), their nuclear and cytoplasmic functions, post-transcriptional processing, and recently reported ligands. Points of interest are the different changes in the ligand-binding pocket induced by variously shaped agonists, the communication of the ligand-bound pocket with the coactivator binding surface and the heterodimerization interface, and recently identified ligands that are natural products, those that function as environmental toxins or drugs that had been originally designed to interact with other targets, as well as those that were deliberately designed as RXR-selective transcriptional agonists, synergists, or antagonists. Of these synthetic ligands, the general trend in design appears to be away from fully aromatic rigid structures to those containing partial elements of the flexible tetraene side chain of 9-cis-retinoic acid. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
Collapse
Affiliation(s)
- Marcia I Dawson
- Cancer Center, Sanford-Burn Medical Research Institute, 10901 North Torrey Pines Rd., La Jolla, CA 93207, USA.
| | | |
Collapse
|
6
|
Li CW, Dinh GK, Chen JD. Preferential physical and functional interaction of pregnane X receptor with the SMRTalpha isoform. Mol Pharmacol 2008; 75:363-73. [PMID: 18978041 DOI: 10.1124/mol.108.047845] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The silencing mediator for retinoid and thyroid hormone receptors (SMRT) serves as a platform for transcriptional repression elicited by several steroid/nuclear receptors and transcription factors. SMRT exists in two major splicing isoforms, alpha and tau, with SMRTalpha containing only an extra 46-amino acid sequence inserted immediately downstream from the C-terminal corepressor motif. Little is known about potential functional differences between these two isoforms. Here we show that the pregnane X receptor (PXR) interacts more strongly with SMRTalpha than with SMRTtau both in vitro and in vivo. It is interesting that the PXR-SMRTalpha interaction is also resistant to PXR ligand-induced dissociation, in contrast to the PXR-SMRTtau interaction. SMRTalpha consistently inhibits PXR activity more efficiently than does SMRTtau in transfection assays, although they possess comparable intrinsic repression activity and association with histone deacetylase. We further show that the mechanism for the enhanced PXR-SMRTalpha interaction involves both the 46-amino acid insert and the C-terminal corepressor motif. In particular, the first five amino acids of the SMRTalpha insert are essential and sufficient for the enhanced binding of SMRTalpha to PXR. Furthermore, we demonstrate that Tyr2354 and Asp2355 residues of the SMRTalpha insert are most critical for the enhanced interaction. In addition, expression data show that SMRTalpha is more abundantly expressed in most human tissues and cancer cell lines, and together these data suggest that SMRTalpha may play a more important role than SMRTtau in the negative regulation of PXR.
Collapse
Affiliation(s)
- Chia-Wei Li
- Department of Pharmacology,University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA
| | | | | |
Collapse
|
7
|
Reineke EL, Liu H, Lam M, Liu Y, Kao HY. Aberrant association of promyelocytic leukemia protein-retinoic acid receptor-alpha with coactivators contributes to its ability to regulate gene expression. J Biol Chem 2007; 282:18584-18596. [PMID: 17475621 DOI: 10.1074/jbc.m700330200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The aberrant association of promyelocytic leukemia protein-retinoic acid receptor-alpha (PML-RARalpha) with corepressor complexes is generally thought to contribute to the ability of PML-RARalpha to regulate transcription. We report here that PML-RARalpha acquires aberrant association with coactivators. We show that endogenous PML-RARalpha interacts with the histone acetyltransferases CBP, p300, and SRC-1 in a hormoneindependent manner, an association not seen for RARalpha. This hormone-independent coactivator binding activity requires an intact ligand-binding domain and the NR box of the coactivators. Confocal microscopy studies demonstrate that exogenous PML-RARalpha sequesters and colocalizes with coactivators. These observations correlate with the ability of PML-RARalpha to attenuate the transcription activation of the Notch signaling downstream effector, CBF1, and of the glucocorticoid receptor. This includes attenuation of the glucocorticoid-induced leucine zipper (GILZ) and FLJ25390 target genes of the endogenous glucocorticoid receptor. Furthermore, treatment of NB4 cells with all-trans-retinoic acid, which promotes PML-RARalpha degradation, resulted in increased activation of GILZ. On the basis of these findings, we propose a model in which the hormone-independent association between PML-RARalpha and coactivators contributes to its ability to regulate gene expression.
Collapse
Affiliation(s)
- Erin L Reineke
- Department of Biochemistry, School of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44106
| | - Heng Liu
- Department of Biochemistry, School of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44106
| | - Minh Lam
- Research Institute of University Hospitals of Cleveland and the Comprehensive Cancer Center of Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106
| | - Yu Liu
- Department of Biochemistry, School of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44106
| | - Hung-Ying Kao
- Department of Biochemistry, School of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44106.
| |
Collapse
|