LXXLL motifs and AF-2 domain mediate SHP (NR0B2) homodimerization and DAX1 (NR0B1)-DAX1A heterodimerization

Inhibition of GLI Transcriptional Activity and Prostate Cancer Cell Growth and Proliferation by DAX1

The Hedgehog (Hh) signaling pathway plays an essential role in the initiation and progression of prostate cancer. This is mediated by transcriptional factors belonging to the GLI (glioma-associated oncogene) family, which regulate downstream targets to drive prostate cancer progression. The activity of GLI proteins is tightly controlled by a range of mechanisms, including molecular interactions and post-translational modifications. In particular, mitogenic and oncogenic signaling pathways have been shown to regulate GLI protein activity independently of upstream Hh pathway signaling. Identifying GLI protein regulators is critical for the development of targeted therapies that can improve patient outcomes. This study aimed to identify a novel protein that directly regulates the activity of GLI transcription factors in prostate cancer. We performed gene expression, cellular analyses, and reporter assays to demonstrate that DAX1 (dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on X chromosome, gene 1) interacts with GLI1 and GLI2, the master regulators of Hh signaling. Interestingly, DAX1 overexpression significantly inhibited Hh signaling by reducing GLI1 and GLI2 activity, prostate cancer cell proliferation, and viability. Our results shed light on a novel regulatory mechanism of Hh signaling in prostate cancer cells. The interaction between DAX1 and GLI transcription factors provides insight into the complex regulation of Hh signaling in prostate cancer. Given the importance of Hh signaling in prostate cancer progression, targeting DAX1-GLI interactions may represent a promising therapeutic approach against prostate cancer. Overall, this study provides new insights into the regulation of the Hh pathway and its role in prostate cancer progression. The findings suggest that DAX1 could serve as a potential therapeutic target for the treatment of prostate cancer.

Inhibition of β-catenin dependent WNT signalling upregulates the transcriptional repressor NR0B1 and downregulates markers of an A9 phenotype in human embryonic stem cell-derived dopaminergic neurons: Implications for Parkinson's disease

In this study we investigate how β-catenin-dependent WNT signalling impacts midbrain dopaminergic neuron (mDA) specification. mDA cultures at day 65 of differentiation responded to 25 days of the tankyrase inhibitor XAV969 (XAV, 100nM) with reduced expression of markers of an A9 mDA phenotype (KCNJ6, ALDH1A1 and TH) but increased expression of the transcriptional repressors NR0B1 and NR0B2. Overexpression of NR0B1 and or NR0B2 promoted a loss of A9 dopaminergic neuron phenotype markers (KCNJ6, ALDH1A1 and TH). Overexpression of NR0B1, but not NR0B2 promoted a reduction in expression of the β-catenin-dependent WNT signalling pathway activator RSPO2. Analysis of Parkinson’s disease (PD) transcriptomic databases shows a profound PD-associated elevation of NR0B1 as well as reduced transcript for RSPO2. We conclude that reduced β-catenin-dependent WNT signalling impacts dopaminergic neuron identity, in vitro, through increased expression of the transcriptional repressor, NR0B1. We also speculate that dopaminergic neuron regulatory mechanisms may be perturbed in PD and that this may have an impact upon both existing nigral neurons and also neural progenitors transplanted as PD therapy.

Characterization, expression, and regulatory effects of nr0b1a and nr0b1b in spotted scat (Scatophagus argus)

Nuclear receptor subfamily 0 group B member 1 (Nr0b1) belongs to the nuclear receptor (NR) superfamily. It plays critical roles in sex determination, sex differentiation, and gonadal development in mammals. In this study, the duplicated genes nr0b1a and nr0b1b were identified in spotted scat (Scatophagus argus). Phylogenetic and synteny analyses revealed that, unlike nr0b1a, nr0b1b was retained in several species of teleosts after an nr0b1 gene duplication event but was secondarily lost in other fish species, amphibians, reptiles, birds, and mammals. In a sequence analysis, only 1.5 LXXLL-related repeat motifs were identified in spotted scat Nr0b1a, Nr0b1b, and non-mammalian Nr0b1a/Nr0b1, different from the 3.5 repeat motifs in mammalian Nr0b1. By qPCR, nr0b1a and nr0b1b were highly expressed in testes from stages IV to V and in ovaries from stages II to IV, respectively. Male-to-female sex reversal was induced in XY spotted scat by the administration of exogenous E2. A qPCR analysis showed that nr0b1b mRNA expression was higher in sex-reversed XY fish than in control XY fish, with no difference in nr0b1a. A luciferase assay showed that spotted scat Nr0b1a and Nr0b1b did not individually activate cyp19a1a gene transcription. As in mammals, spotted scat Nr0b1a suppressed Nr5a1-mediated cyp19a1a expression, despite containing only 1.5 LXXLL-related repeat motifs in its N-terminal region, while Nr0b1b stimulated Nr5a1-mediated cyp19a1a transcription. These results demonstrated that nr0b1a and nr0b1b in spotted scat have distinct expression patterns and regulatory effects and further indicate that nr0b1b might be involved in ovarian development by regulating Nr5a1-mediated cyp19a1a expression.

Small heterodimer partner 1 directly interacts with NS5A viral protein and has a key role in HCV related liver cell transformation

HCV life cycle is strictly correlated with the hepatocyte lipid metabolism; moreover, the progression of HCV chronic hepatitis is accelerated by the presence of liver steatosis. Among the steatogenic genes deregulated during the HCV infection one of the most attractive is the Small Heterodimer Protein 1 (SHP1; NR0B2), that is involved in a remarkable number of metabolic functions. HCV NS5A is an essential and integral component of the HCV membranous-web replicon complex (RC) and plays an essential role to transfer the viral genome from the RCs to the surface of the lipid droplets (LDs) that, in turn, play a key function during HCV life cycle.

With the help of a HCV infection model, we demonstrate a functional interaction between SHP1 and HCV NS5A protein. SHP1 silencing (siSHP1) reversed the pro-oncogenic effects of HCV infection, inducing a significant decrease in liver lipid accumulation and in NS5A protein expression. Moreover, siSHP1 causes a strong modulation of some genes involved in HCV-related EMT, such as: HNF4, a central regulators of hepatocyte differentiation, E-Cadherin, SNAILs.

Our data suggest that SHP1 results not only to be strictly connected to the pathogenesis of HCV-related liver steatosis, but also to its progression towards the liver transformation.

Molecular cloning, expression analysis and transcript localization of testicular orphan nuclear receptor 2 in the male catfish, Clarias batrachus

Testicular receptor 2 (TR2; also known as Nr2c1) is one of the first orphan nuclear receptors identified and known to regulate various physiological process with or without any ligand. In this study, we report the cloning of full length nr2c1 and its expression analysis during gonadal development, seasonal testicular cycle and after human chorionic gonadotropin (hCG) induction. In addition, in situ hybridization (ISH) was performed to localize nr2c1 transcripts in adult testis and whole catfish (1day post hatch). Tissue distribution and gonadal ontogeny studies revealed high expression of nr2c1 in developing and adult testis. Early embryonic stage-wise expression of nr2c1 seems to emphasize its importance in cellular differentiation and development. Substantial expression of nr2c1 during pre-spawning phase and localization of nr2c1 transcripts in sperm/spermatids were observed. Significant upregulation after hCG induction indicate that nr2c1 is under the regulation of gonadotropins. Whole mount ISH analysis displayed nr2c1 expression in notochord indicating its role in normal vertebrate development. Taken together, our findings suggest that nr2c1 may have a plausible role in the testicular and embryonic development of catfish.

A pleiotropic role for the orphan nuclear receptor small heterodimer partner in lipid homeostasis and metabolic pathways

Nuclear receptors (NRs) comprise one of the most abundant classes of transcriptional regulators of metabolic diseases and have emerged as promising pharmaceutical targets. Small heterodimer partner (SHP; NR0B2) is a unique orphan NR lacking a DNA-binding domain but contains a putative ligand-binding domain. SHP is a transcriptional regulator affecting multiple key biological functions and metabolic processes including cholesterol, bile acid, and fatty acid metabolism, as well as reproductive biology and glucose-energy homeostasis. About half of all mammalian NRs and several transcriptional coregulators can interact with SHP. The SHP-mediated repression of target transcription factors includes at least three mechanisms including direct interference with the C-terminal activation function 2 (AF2) coactivator domains of NRs, recruitment of corepressors, or direct interaction with the surface of NR/transcription factors. Future research must focus on synthetic ligands acting on SHP as a potential therapeutic target in a series of metabolic abnormalities. Current understanding about the pleiotropic role of SHP is examined in this paper, and principal metabolic aspects connected with SHP function will be also discussed.

Identification of common and cell type specific LXXLL motif EcR cofactors using a bioinformatics refined candidate RNAi screen in Drosophila melanogaster cell lines

Background

During Drosophila development, titers of the steroid ecdysone trigger and maintain temporal and tissue specific biological transitions. Decades of evidence reveal that the ecdysone response is both unique to specific tissues and distinct among developmental timepoints. To achieve this diversity in response, the several isoforms of the Ecdysone Receptor, which transduce the hormone signal to the genome level, are believed to interact with tissue specific cofactors. To date, little is known about the identity of these cofactor interactions; therefore, we conducted a bioinformatics informed, RNAi luciferase reporter screen against a subset of putative candidate cofactors identified through an in silico proteome screen. Candidates were chosen based on criteria obtained from bioinformatic consensus of known nuclear receptor cofactors and homologs, including amino acid sequence motif content and context.

Results

The bioinformatics pre-screen of the Drosophila melanogaster proteome was successful in identifying an enriched putative candidate gene cohort. Over 80% of the genes tested yielded a positive hit in our reporter screen. We have identified both cell type specific and common cofactors which appear to be necessary for proper ecdysone induced gene regulation. We have determined that certain cofactors act as co-repressors to reduce target gene expression, while others act as co-activators to increase target gene expression. Interestingly, we find that a few of the cofactors shared among cell types have a reversible roles to function as co-repressors in certain cell types while in other cell types they serve as co-activators. Lastly, these proteins are highly conserved, with higher order organism homologs also harboring the LXXLL steroid receptor interaction domains, suggesting a highly conserved mode of steroid cell target specificity.

Conclusions

In conclusion, we submit these cofactors as novel components of the ecdysone signaling pathway in order to further elucidate the dynamics of steroid specificity.

Role of nuclear receptor SHP in metabolism and cancer

Small heterodimer partner (SHP, NR0B2) is a unique member of the nuclear receptor (NR) superfamily that contains the dimerization and ligand-binding domain found in other family members, but lacks the conserved DNA-binding domain. The ability of SHP to bind directly to multiple NRs is crucial for its physiological function as a transcriptional inhibitor of gene expression. A wide variety of interacting partners for SHP have been identified, indicating the potential for SHP to regulate an array of genes in different biological pathways. In this review, we summarize studies concerning the structure and target genes of SHP and discuss recent progress in understanding the function of SHP in bile acid, cholesterol, triglyceride, glucose, and drug metabolism. In addition, we review the regulatory role of SHP in microRNA (miRNA) regulation, liver fibrosis and cancer progression. The fact that SHP controls a complex set of genes in multiple metabolic pathways suggests the intriguing possibility of developing new therapeutics for metabolic diseases, including fatty liver, dyslipidemia and obesity, by regulating SHP with small molecules. To achieve this goal, more progress regarding SHP ligands and protein structure will be required. Besides its metabolic regulatory function, studies by us and other groups provide strong evidence that SHP plays a critical role in the development of cancer, particularly liver and breast cancer. An increased understanding of the fundamental mechanisms by which SHP regulates the development of cancers will be critical in applying knowledge of SHP in diagnostic, therapeutic or preventive strategies for specific cancers. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Phosphorylation-dependent interaction of SATB1 and PIAS1 directs SUMO-regulated caspase cleavage of SATB1

Special AT-rich sequence-binding protein 1 (SATB1) is a tissue-restricted genome organizer that provides a key link between DNA loop organization, chromatin modification/remodeling, and transcription factor association at matrix attachment regions (MARs). The SUMO E3 ligase PIAS1 enhances SUMO conjugation to SATB1 lysine-744, and this modification regulates caspase-6 mediated cleavage of SATB1 at promyelocytic leukemia nuclear bodies (PML NBs). Since this regulated caspase cleavage occurs on only a subset of SATB1, and the products are relatively stable, proteolysis likely mediates cellular processes other than programmed cell death. However, the mechanism for the spatial and temporal regulation of SATB1 sumoylation and caspase cleavage is not known. Here we report that these processes are controlled by SATB1 phosphorylation; specifically, PIAS1 interaction with SATB1 is inhibited by phosphorylation. Mutagenesis studies identified interaction of the PIAS SAP (scaffold attachment factor-A/B/acinus/PIAS) motif with SATB1 N-terminal sequences. Notably, phosphorylation of SATB1 at threonine-188 regulates its interaction with PIAS1. Sequences near this phosphorylation site, LXXLL (residues 193 to 197), appear to be conserved among a subset of SUMO substrate proteins. Thus, this motif may be commonly involved in interaction with the PIAS SAP, and phosphorylation may similarly inhibit some of these substrates by preventing their interaction with the ligase.

Dax-1 and steroid receptor RNA activator (SRA) function as transcriptional coactivators for steroidogenic factor 1 in steroidogenesis

The nuclear receptor steroidogenic factor 1 (SF-1) is essential for adrenal development and steroidogenesis. The atypical orphan nuclear receptor Dax-1 binds to SF-1 and represses SF-1 target genes. Paradoxically, however, loss-of-function mutations of Dax-1 also cause adrenal hypoplasia, suggesting that Dax-1 may function as an SF-1 coactivator under some circumstances. Indeed, we found that Dax-1 can function as a dosage-dependent SF-1 coactivator. Both SF-1 and Dax-1 bind to steroid receptor RNA activator (SRA), a coactivator that functions as an RNA. The coactivator TIF2 also associates with Dax-1 and synergistically coactivates SF-1 target gene transcription. A naturally occurring Dax-1 mutation inhibits this transactivation, and the mutant Dax-1-TIF2 complex mislocalizes in living cells. Coactivation by Dax-1 is abolished by SRA knockdown. The expression of the steroidogenic gene products steroidogenic acute regulatory protein (StAR) and melanocortin 2 receptor is reduced in adrenal Y1 cells following the knockdown of endogenous SRA. Similarly, the knockdown of endogenous Dax-1 downregulates the expression of the steroidogenic gene products CYP11A1 and StAR in both H295R adrenal and MA-10 Leydig cells. These findings reveal novel functions of SRA and Dax-1 in steroidogenesis and adrenal biology.