Role of tyrosine kinase and protein kinase C in the steroidogenic actions of angiotensin II, α-melanocyte-stimulating hormone and corticotropin in the rat adrenal cortex

Abstract

The role of protein kinases in the steroidogenic actions of alpha-melanocyte-stimulating hormone (alpha-MSH), angiotensin II (AngII) and corticotropin (ACTH) in the rat adrenal zona glomerulosa was examined. Ro31-8220, a potent selective inhibitor of protein kinase C (PKC), inhibited both AngII- and alpha-MSH-stimulated aldosterone secretion but had no effect on aldosterone secretion in response to ACTH. The effect of Ro31-8220 on PKC activity was measured in subcellular fractions. Basal PKC activity was higher in cytosol than in membrane or nuclear fractions. Incubation of the zona glomerulosa with either alpha-MSH or AngII resulted in significant increases in PKC activity in the nuclear and cytosolic fractions and decreases in the membrane fraction. These effects were all inhibited by Ro31-8220. ACTH caused a significant increase in nuclear PKC activity only, and this was inhibited by Ro31-8220 without any significant effect on the steroidogenic response to ACTH, suggesting that PKC translocation in response to ACTH may be involved in another aspect of adrenal cellular function. Tyrosine phosphorylation has not previously been considered to be an important component of the response of adrenocortical cells to peptide hormones. Both AngII and alpha-MSH were found to activate tyrosine kinase, but ACTH had no effect, observations that have not been previously reported. Tyrphostin 23, a specific antagonist of tyrosine kinases, inhibited aldosterone secretion in response to AngII and alpha-MSH, but not ACTH. These data confirm the importance of PKC in the adrenocortical response to AngII and alpha-MSH, and, furthermore, indicate that tyrosine kinase may play a critical role in the steroidogenic actions of AngII and alpha-MSH in the rat adrenal zona glomerulosa.

The role of tyrosine kinases in capacitative calcium influx-mediated aldosterone production in bovine adrenal zona glomerulosa cells

“…Tyrosine kinase inhibitors also decreased Ang II-stimulated aldosterone production in rat adrenal capsules and cultured bovine glomerulosa cells (Bodart et al 1995, Kapas et al 1995. In fact, Ang II can activate tyrosine kinase activity in rat adrenal capsules (Kapas et al 1995). However, in none of these studies, a functional link with Ca 2+ influx was demonstrated.…”

“…Thus, for example, in longitudinal strips from guinea pig gastric smooth muscle, tyrosine kinase inhibitors selectively and completely blocked Ang IImediated contraction (Yang et al 1993). Tyrosine kinase inhibitors also decreased Ang II-stimulated aldosterone production in rat adrenal capsules and cultured bovine glomerulosa cells (Bodart et al 1995, Kapas et al 1995. In fact, Ang II can activate tyrosine kinase activity in rat adrenal capsules (Kapas et al 1995).…”

The melanocortin system

“…However, MCR signaling has also been associated with increases in intracellular Ca 2ϩ concentration secondary to activation of inositol trisphosphate (25), influx of extracellular Ca 2ϩ (24), and activation of the MAP kinase (15), janus kinase/signal transducer and activator of transcription (7), and PKC pathways (23). Importantly, the five MCRs have differing affinities for the melanocortins and the endogenous antagonists agouti and AGRP (Table 1).…”

Evidence That Tyrphostins AG10 and AG18 Are Mitochondrial Uncouplers That Alter Phosphorylation-dependent Cell Signaling

“…Tyrphostins have been used to implicate tyrosine kinases in various cell signaling and biological events, such as sodium pump (15) and chloride channel (16) activation in epithelial cells, mitogenactivated protein kinase activation (17,18), and aldosterone secretion in rat cortex (19). In initial experiments with parotid acinar cells, the QO 2 was not increased by carbachol in cells exposed to AG18.…”