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
Clark
B J
BJ
Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, KY 40292, USA. bjclark@louisville.edu
Ranganathan
V
V
Combs
R
R
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