CCK ACTIVATES P90(RSK) IN RAT PANCREATIC ACINI THROUGH PROTEIN-KINASE-C

The presence of the 90-kDa ribosomal 86 protein kinase (p90(rsk)) in i solated rat pancreatic acini was demonstrated by Western blotting and immunoprecipitation with anti-p90(rsk). Cholecystokinin (CCK) activate d p90(rsk) activity in a time- and dose-dependent manner and increased its phosphorylation. The threshold concentration of CCK was 10 pM and the maximal effect was seen at 1 nM. An increase in p90(rsk) was obse rved 1 min after 1 nM CCK stimulation, reaching a maximum at 10 min, w hen p90(rsk) activity was increased 5.4-fold. Carbachol and bombesin, but not vasoactive intestinal peptide, also activated p90(rsk). CCK-in duced activation of p90(rsk) appears to be mediated by protein kinase C (PKC), since 12-O-tetradecanoylphorbol-13-acetate increased p90(rsk) activity 5.3-fold. GF-109293X, a potent inhibitor of PKC, strongly in hibited CCK-evoked p90(rsk) activity, Treatment of acini with ionomyci n or ,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid had no ef fect, indicating that mobilization of intracellular Ca2+ by CCK is not important in p90(rsk) activation. Although there were some quantitati ve differences in the extent of inhibition, the specific inhibitors [r apamycin, wortmannin, mitogen-activated protein kinase (MAPK) kinase i nhibitor PD98059, and GF-109293X] had parallel effects on p90(rsk) and p42(mapk) activities, consistent with a model in which p90(rsk) can b e regulated in acini by MAPK.