Orphan Nuclear Receptor Small Heterodimer Partner Represses Hepatocyte Nuclear Factor 3/Foxa Transactivation via Inhibition of Its DNA Binding

Abstract

Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor and acts as a coregulator of various nuclear receptors. Herein, we examined a novel cross talk between SHP and a forkhead transcription factor HNF3 (hepatocyte nuclear factor 3/Foxa. Transient transfection assay demonstrated that SHP inhibited the transcriptional activity of all three isoforms of HNF3, HNF3alpha, beta, and gamma. In vivo and in vitro protein interaction studies showed that SHP physically interacted with HNF3. Adenovirus-mediated overexpression of SHP significantly decreased the mRNA levels of glucose-6-phosphase (G6Pase), cholesterol 7-alpha-hydroxylase (CYP7A1), and phosphoenolpyruvate carboxykinase (PEPCK) in HepG2 cells and rat primary hepatocytes. Moreover, the mRNA level of G6Pase was notably increased by down-regulation of SHP with small interfering RNA. Interestingly, HNF3 transactivity was still repressed by SHPDelta128-139 that fails to repress nuclear receptors. Mapping of interaction domain revealed that SHP interacted with forkhead DNA binding domain of HNF3alpha. Gel mobility shift and chromatin immunoprecipitation assays demonstrated that SHP inhibits DNA binding of HNF3. These results suggest that SHP is involved in the regulation of G6Pase, CYP7A1, and PEPCK gene expression via novel mechanism of inhibition of HNF3 activity and expand the role of SHP as a coregulator of other family of transcription factors in addition to nuclear receptors.

Metformin Inhibits Hepatic Gluconeogenesis Through AMP-Activated Protein Kinase–Dependent Regulation of the Orphan Nuclear Receptor SHP

“…Bile acid is an endogenous ligand of the farnesoid X receptor, which can profoundly activate SHP transcription (34), and SHP decreased the expression of CYP7A1 via the inhibition of LRH-1 activity (19,35). Additionally, bile acid-induced SHP can downregulate PEPCK and G6Pase expression by the repression of the transcriptional activity of HNF-4␣, FoxO1, and FoxA2 (23)(24). However, the correlation between SHP expression and type 2 diabetes, and/or antidiabetic agent, has not been previously elucidated.…”

“…SHP represses the transcriptional activity of a number of nuclear receptors (15)(16)(17)(18)(19)(20)(21)(22), as well as hepatocyte nuclear factor (HNF)-4␣ (NR2A1), FoxO1 (also known as FKHR) (23), and the forkhead transcription factor FoxA2 (also referred to as HNF-3␤) (24), which are the primary transcription factors that regulate PEPCK and/or G6Pase expression. Recent evidence suggests that SHP may perform a function in glucose homeostasis by the regulation of hepatic gluconeogenesis.…”

“…Yamagata et al (23) showed that the expressions of hepatic gluconeogenic genes, including PEPCK, G6Pase, and fructose 1,6-bis phosphatase (FBP1), are inhibited by bile acids in a SHP-dependent manner. In our previous study, it was shown that SHP inhibits PEPCK, G6Pase, and CYP7A1 expression via the repression of FoxA2-mediated transcriptional activity (24). However, no study has examined whether SHP expression is induced by pharmacological agents, such as the AMPK activators that suppress hepatic gluconeogenic genes, or whether metformin-induced suppression of hepatic gluconeogenic gene expression is mediated by SHP.…”

The Orphan Nuclear Receptor SHP Attenuates Renal Fibrosis

“…11 In this study, we found that adenovirus-mediated overexpression of SHP successfully inhibited TGF-␤-stimulated PAI-1 and matrix protein expression in cultured kidney cell lines. Although the mechanism of repression by SHP is not clearly understood, previous reports have suggested that SHP represses transcription factor-mediated transactivation by inhibition of DNA binding, 22,38,39 recruitment of unknown corepressors, 40 -42 and interfering the interaction with coactivator p300. 25 In this study, we found that that SHP repressed Smad3 transactivation by inhibition of DNA binding.…”

Orphan nuclear receptor small heterodimer partner inhibits angiotensin II-stimulated PAI-1 expression in vascular smooth muscle cells

“…Previous reports have demonstrated the mechanisms by which SHP regulates target gene transcription without directly binding to target promoter sequences. SHP represses transcription factor-mediated transactivation by inhibiting DNA binding (Seol et al, 1996;Ourlin et al, 2003;Kim et al, 2004), by recruiting unknown corepressors (Johansson et al, 2000;Lee et al, 2000Lee et al, , 2002 and by interfering with the interaction with coactivator (Suh et al, 2006). Fiorucci et al (2004) showed that the inhibitory effect on AP-1 activity is mediated by a physical interaction between AP-1 and SHP that decreases AP-1 DNA binding.…”