PGC-1α Coactivates SF-1 To Regulate The Synthesis Of Luteinizing Hormone And Aldosterone

Peroxisome proliferators-activated receptor y coactivator-la (PGC-la) is capable of coactivating a number of nuclear receptors and other transcription factors involved in the regulation of multiple metabolic processes. The orphan nuclear receptor steroidogenic factor 1 (SF-1) is highly expressed in the pituitary, gonad and adrenal gland. To date, it is the only transcription factor demonstrated to play the key roles at all levels of the hypothalamic-pituitary-steroidogenic tissue axis.In the present study, we demonstrated that PGC-la interacts with and coactivates SF-1 to induce LHβand aGSU gene expression, subsequently leading to the increased secrection of LH in pituitary gonadotrope-derivedαT3-1 cells. PGC-la-induced activation of LHβexpression occurs at its transcription level that is mediated by an SF-1 binding element (GSE) mapped in the promoter region of LHβgene. Our ChIP assays confirm the binding of SF-1 to PGC-la-responsive element and that PGC-la is presumably recruited to LHβpromoter region through interaction with SF-1. Mammalian two-hybrid and coimmunoprecipitation (CoIP) assays demonstrated PGC-la interaction with SF-1 in vivo. Furthermore, GST pull-down experiments indicated PGC-la interacts with SF-1 through its N-terminal fragment (1-180 amino acid) containing containing LXXLL domain and that SF-1 interacts with PGC-1αthrough its C-terminal fragment (187-462 amino acid) containing proximal activation domain and AF-2 domain. Additionally, PGC-1αalso stimulates the expression of Cyp11b2, Cyp11b1 and P450scc, as well as synthesis of aldosterone in adrenal cortex-derived Y-1 cells. In addition to coactivation of SF-1, PGC-1αwas demonstrated to induce SF-1 gene expression in αT3-1 and Y-1 cells.Based on these data, we proposed a model of mechanism of PGC-1αaction on LH synthesis and steroidogenesis in cells. PGC-la coactivates ERRs or other factors to induce SF-1 gene expression, meanwhile, it interacts directly with and coactivates SF-1 to stimulate its target genes. Given that SF-1 is a key regulator of endocrine function within hypothalamic-pituitary-gonadal reproductive axis and adrenal cortex, it is reasonable to propose that PGC-la may play important roles in steroidogenesis, gonad development and sex differentiation in these tissues through SF-1. Our studies revealed the potential role of PGC-1αand suggested PGC-1αhas much broader effects in endocrine system, more than energy metabolism, glucose and fatty acid metabolism. Peroxisome proliferator-activated receptor coactivator-1α(PGC-1α) is a key regulator of cellular energy metabolism, and regulates processes such as adaptive thermogenesis, hepatic gluconeogenesis, fatty acid oxidation and mitochondrial biogenesis by coactivating numerous nuclear receptors and transcription factors. Here, we demonstrate the presence of ERRa binding site in the regulatory sequence of the glucokinase gene and that PGC-1αcoactivates ERRαto stimulate the transcription of glucokinase. Simultaneous over-expression of PGC-1αand ERRa potently induced the glucokinase gene expression and its enzymatic activity in primary hepatocytes; however, expression of either PGC-1αor ERRαalone had no significant effect. Electrophoretic mobility shift and chromatin immuno-precipitation assays revealed the interaction of ERRαwith the glucokinase promoter. Finally, the knockdown of endogenous ERRαwith specific siRNA (siERRα) or pharmacological inhibition of ERRαwith XCT790 attenuated insulin-induced glucokinase expression. Taken together, this research identifies glucokinase as a novel target of PGC-1α/ERRα, and underscores the regulatory function of ERRαin insulin-dependent enzyme regulation.