Post-translational regulation of steroidogenic acute regulatory protein by cAMP-dependent protein kinase A.
Adrenal steroid production is stimulated by adrenocorticotropin hormone activation of the cAMP-dependent protein kinase A (PKA) signaling pathway and subsequent induction of Steroidogenic Acute Regulatory (StAR) protein expression. Herein we have compared StAR mRNA and protein levels in 8-Br-cAMP-treated mouse adrenocortical Y1 and the derived PKA mutant Kin-8 cell lines to evaluate the PKA requirement in StAR expression. StAR mRNA was induced by 8-Br-cAMP-treatment of both Y1 and Kin-8 cells with maximal expression levels in Kin-8 cells approximately 50% of that observed in Y1 cells. StAR protein levels, as detected by Western analysis, were concomitantly increased in Y1 cells but were not detected in the Kin-8 cells. StAR mRNA colocalized with the active polysome fractions in both 8-Br-cAMP-treated Y1 and Kin-8 cells, indicating translation was not blocked in Kin-8 cells. Consistent with this data, a 2-fold increase in incorporation of [35S]methionine into StAR was also observed after 8-Br-cAMP treatment of both cell lines. Since StAR protein levels were not sufficient to detect by Western analysis, 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, Kentucky 40292, USA. bjclark@louisville.edu
Ranganathan
V
V
Combs
R
R
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000302:Adrenal Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D008715:Methionine / Q000378:metabolism; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D000098682:Steroidogenic Acute Regulatory Protein
D010750:Phosphoproteins; D012333:RNA, Messenger; D000098682:Steroidogenic Acute Regulatory Protein; D015124:8-Bromo Cyclic Adenosine Monophosphate; D008715:Methionine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases