Steroidogenic acute regulatory protein expression is dependent upon post-translational effects of cAMP-dependent protein kinase A.
Tropic hormones acutely stimulate adrenal and gonadal steroidogenesis by activation of the cAMP-dependent protein kinase A (PKA) signaling pathway and subsequent induction of Steroidogenic Acute Regulatory (StAR) protein (StAR) expression. We present a comparative study of StAR regulation in mouse adrenocortical Y1 and the derived PKA mutant Kin-8 cell lines to evaluate the PKA requirement for StAR expression. A parallel increase in StAR steady-state mRNA and protein was observed in Y1 cells. StAR mRNA was induced in 8-Br-cAMP-treated Kin-8 cells with maximal expression levels approx. 50% of that observed in Y1 cells. However, a corresponding increase in StAR protein, as detected by Western analysis, was absent in the Kin-8 cells. A similar distribution of StAR mRNA in active polysome fractions was observed for both 8-Br-cAMP-treated Y1 and Kin-8 cells, as well as a 2-fold increase in incorporation of [35S]methionine into StAR, which indicated translation was not blocked in Kin-8 cells. Together these data indicate that PKA functions at the post-translational level to regulate StAR expression and we propose that phosphorylation of StAR by PKA contributes to protein stability
Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, KY 40292, USA. bjclark@louisville.edu
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D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000098682:Steroidogenic Acute Regulatory Protein
D007546:Isoquinolines; D010750:Phosphoproteins; D012333:RNA, Messenger; D000098682:Steroidogenic Acute Regulatory Protein; D015124:8-Bromo Cyclic Adenosine Monophosphate; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D002786:Cholesterol Side-Chain Cleavage Enzyme; D017868:Cyclic AMP-Dependent Protein Kinases