DIFFERENTIAL GROWTH-REGULATION BY ALL-TRANS-RETINOIC ACID IS DETERMINED BY PROTEIN-KINASE-C-ALPHA IN HUMAN PANCREATIC-CARCINOMA CELLS

We have investigated the pole of protein kinase C (PKC) isoenzymes in the differential growth regulation of human pancreatic carcinoma cell lines by all-trans retinoic acid (RA). RA treatment results in dose-de pendent stimulation of anchorage-independent growth in AsPc1 cells and growth inhibition in Capan 2 cells. Both cell lines express an identi cal pattern of nuclear RA and retinoid X receptors as determined by RT -PCR. Western blotting using monospecific antibodies revealed that bot h cell lines express PHC isoenzymes alpha and zeta, whereas beta, gamm a, delta, and epsilon were not detected. Incubation with RA in the gro wth-stimulated AsPc1 cell line resulted in induction of PKC alpha expr ession, whereas PKC alpha expression was decreased by RA in the growth -inhibited Capan 2 cell line, In contrast, PKC zeta expression was not affected by RA in either cell line. Incubation of AsPc1 cells with th e phorbol eater 12-O-tetradecanoyl phorbol 13-acetate resulted in a ti me- and dose-dependent selective down-regulation of PKC alpha but not zeta. The dose-dependent decrease of intracellular PKC alpha concentra tion correlated well with the anchorage-independent growth rate of AsP c1 cells. Furthermore, selective down-regulation of PKC alpha blocks s ubsequent growth stimulation by RA in AsPc1 cells. When PKC alpha conc entration was decreased by stably transfecting AsPc1 cells with a PKC alpha complementary DNA antisense construct, RA-stimulated growth coul d also be partially blocked. These data, therefore, suggest that diffe rential regulation of PKC alpha expression plays a central role in det ermining the bidirectional effects of RA on growth in pancreatic carci noma cells.