StAR expression: Integration of Transcription with regulation via the mRNA 3'UTR

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Cortisol synthesis in the adrenal cortex plays a central role in stress responses, in dietary control, and in cardiovascular regulation. Aberrations in this control of the hypothalamic pituitary adrenal axis play an important part in the Metabolic Syndrome that is often associated with Type 2 diabetes. ACTH stimulation of cortisol synthesis starts with the conversion of cholesterol to pregnenolone by mitochondrial cytochrome P450 11A1. Activation of this step depends on new synthesis of the steroidogenesis acute regulator (StAR) and its phosphorylation by protein kinase A (PKA). StAR deficiency causes hyperlipidemic adrenal insufficiency. This research focuses on the finding that StAR expression is stimulated in very different ways by PKA and by protein kinase C (PKC). We will show how these processes are clearly distinguished by essential contributions from, respectively, histone de-acetylatases and Erk kinase. We will characterize these processes for different contributions from nuclear factors, including the differentiation regulator, SF-1. This includes time-dependent modifications that cycle up and down during transcription (phosphorylation/de-phosphorylation and acetylation/de- acetylation). Evidence will be developed that PKA can also enhance a late stage in the PKC process, thus producing strong synergy in StAR transcription. Posttranscriptional regulation of StAR provides another point of distinction between PKA and PKC regulation. A novel regulator, the Zn finger protein, TIS11b, targets specific sequences in the extended 3'untranslated region of the 3.5 kb StAR mRNA. TIS11b is rapidly stimulated by PKA, but suppressed by PKC. We will identify specific TIS11b recognition sites at the end of the StAR 3.5 kb mRNA and show that this interaction can enhance StAR protein translation, while increasing mRNA degradation. We will test whether TIS11b is co-transcribed with StAR due to shared transcription factors, including SF-1. We will determine how these mechanisms interplay during ACTH stimulation, including in primary adrenal cell lines and in adrenals in vivo. The promoter and mRNA sequences that specify SF-1 and TIS11b interactions during StAR expression are substantially conserved from mouse to humans. We will test whether these mouse mechanisms are retained in human adrenal H295 cells. Our research shows that TIS11b interaction with StAR and predominance of an extended StAR mRNA are conserved in primary bovine adrenal cells and respond to ACTH. This work will bring together several laboratories to provide a first look at the interplay between PKA, SF-1, and TIS11b (or factors related to each), which is likely to occur in multiple steroidogenic tissues. Cortisol synthesis in the adrenal cortex plays a central role in stress responses, in dietary control, and in cardiovascular regulation. ACTH, which is elevated by stress, stimulates cortisol synthesis through enhanced conversion of cholesterol to pregnenolone. This step depends on new synthesis of the steroidogenesis acute regulator (StAR). The proposed research addresses a novel process, whereby ACTH stimulates not only transcription of StAR, but also a protein called TIS11b, which separately regulates StAR protein translation and mRNA degradation. We make a detailed analysis of regulatory processes that control StAR and TIS11b transcription in order to understand their potential coordination. TIS11b may accelerate the response time to stress, while also aiding in the removal of StAR when the ACTH stimulus is removed. TIS11b regulation is present in other tissues that make steroids (testis). Deficiency in this mRNA regulator may lead to more sluggish responses to ACTH and stress as well as abnormal cortisol output.