COMPARISON OF PROTEIN-PHOSPHORYLATION PATTERNS PRODUCED IN ADRENAL-CELLS BY ACTIVATION OF CAMP-DEPENDENT PROTEIN-KINASE AND CA-DEPENDENT PROTEIN-KINASE

Bovine adrenal fasciculata cells, exposed to either ACTH or AII, synth esize glucocorticoids at an enhanced rate. It is generally accepted th at the signaling pathways triggered by these two peptides are not iden tical. ACTH presumably acts via a cAMP-dependent protein kinase (PKA) and AII, via a calcium-dependent protein kinase. We have found that ei ther peptide hormone stimulates synthesis of a mitochondrial phosphopr otein pp37, leading to accumulation of its proteolytically processed p roducts pp30 and pp29. On the basis of a number of criteria, this 37 k Da protein is the bovine homolog of the 37 kDa protein that we have ch aracterized in rodent steroidogenic tissue (Epstein L. F. and Orme-Joh nson N. R.: J. Biol. Chem 266 (1991) 19,739-19,745). Further, bovine p p37 is phosphorylated when PKA or protein kinase C (PKC) is activated directly by (Bu)(2) cAMP or PMA, respectively. These studies indicate that either pp37 is a common substrate for PKA and PKC in these cells or there is a common downstream kinase, which is activated by exposure to either ACTH or AII. Rat adrenal glomerulosa cells, exposed to eith er ACTH or AII, show an enhanced rate of mineralocorticoid synthesis. As for bovine fasciculata cells, it is thought that the signaling path way triggered by ACTH differs from that triggered by All. As we found for bovine fasciculata, pp37 is phosphorylated when the rat cells are exposed to either peptide hormone. However, in contrast to the finding for bovine fasciculata, while exposure of the rat glomerulosa cells t o (Bu)(2) cAMP does cause the synthesis of pp37, exposure of the cells to PMA does not. Taken together, these findings provide further evide nce that the subcellular signaling events, triggered by the action of AII on bovine adrenal fasciculata and rat adrenal glomerulosa cells, d iffer. Further, the fact, that pp37 is phosphorylated only when the ra te of steroidogenesis is enhanced, reaffirms its potential involvement in the signaling pathway that causes stimulation of steroid hormone b iosynthesis.