Effects of angiotensin II and adrenocorticotropic hormone myristoylated alanine-rich C-kinase substrate phosphorylation in glomerulosa cells

Angiotensin II (AngII) is thought to stimulate aldosterone secretion from b ovine adrenal glomerulosa cells in part via activation of protein kinase C (PKC), while adrenocorticotropic hormone (ACTH) functions through increases in intracellular cAMP levels and calcium influx. Rather than using invasiv e homogenization techniques as in previous studies, we chose to monitor PKC activity in intact glomerulosa cells in situ by measuring the phosphorylat ion of the endogenous PKC substrate, myristoylated alanine-rich C-kinase su bstrate (MARCKS). AngII enhanced MARCKS phosphorylation in a rapid, sustain ed manner; whereas ACTH induced a rapid and sustained inhibition of MARCKS phosphorylation. Studies using pharmacological agents to mimic various sign als indicated that the AngII-induced MARCKS phosphorylation was due to PKC activation, and the ACTH-elicited decrease was mediated by increases in cal cium influx rather than cAMP production. We propose that changes in the pho sphorylation state of MARCKS, an actin-binding protein, may contribute to c ytoskeletal rearrangements involved in steroidogenesis. (C) 1999 Elsevier S cience Ireland Ltd. All rights reserved.