Roles of type I and type II isoenzymes of cyclic AMP-dependent protein kinase in steroidogenesis in rat adrenal cells

Abstract

The role played by cyclic AMP (cAMP)-dependent protein kinases (PKAs) in rat adrenal steroidogenesis has been investigated using cAMP analogues which show partial selectivity for the type I and type II PKA isoenzymes. These were aminohexylamino-cAMP (AHA-cAMP; selective for site 1 on type I PKA), N6-benzoyl-cAMP (BZ-cAMP; selective for site 2 on PKA types I and II) and 8-thiomethyl-cAMP (TM-cAMP; selective for site 1 on type II PKA). Positive cooperativity exists between the two nucleotide-binding sites, thus the presence of type I PKA was inferred when synergistic increases in corticosteroid production were obtained with AHA-cAMP plus BZ-cAMP and that of type II PKA when synergistic increases were obtained with TM-cAMP plus BZ-cAMP. The effects of AHA-cAMP, TM-cAMP and BZ-cAMP (10-100 mumol/l) on aldosterone production by glomerulosa cell preparations and corticosterone production by fasciculata/reticularis cell preparations were compared. Dose-related stimulation of steroid production was obtained with each cAMP analogue in both types of cell preparation. Experiments were performed using the cAMP analogues in combination at doses which gave minimal stimulation individually. Cells were incubated with AHA-cAMP (66 and 100 mumol/l) or TM-cAMP (15, 30 and 45 mumol/l) in the presence and absence of 15 mumol BZ-cAMP/l. Synergistic responses were obtained with both analogue pairs in both cell types.(ABSTRACT TRUNCATED AT 250 WORDS)