BOMBESIN, PLATELET-DERIVED GROWTH-FACTOR, AND DIACYLGLYCEROL INDUCE SELECTIVE-MEMBRANE ASSOCIATION AND DOWN-REGULATION OF PROTEIN-KINASE-C ISOTYPES IN SWISS 3T3-CELLS

Swiss 3T3 cells contain protein kinase C (PKC) isotypes alpha, delta, epsilon and zeta (Olivier, A. R., and Parker, P. J. (1992) J. Cell. Ph ysiol. 152, 240-244). Acute stimulation of quiescent cells with the ne uropeptide bombesin decreases the mobility of PKC-delta and PKC-epsilo n on SDS-polyacrylamide gels. These slower migrating forms of PKC-delt a and PKC-epsilon rapidly (within 1 s) and selectively are found assoc iated with the Triton X-100-soluble membrane fraction. No change in th e mobility or distribution of PKC-alpha or PKC-zeta is detected. Long- term treatment of cells with bombesin induces selective membrane assoc iation and down-regulation of PKC-delta and PKC-epsilon (decreasing 70 and 65%, respectively). No change in the long-term distribution of PK C-alpha and PKC-zeta was detected. Bombesin did, however, increase PKC -alpha protein levels by 60% compared to control cells. PKC-zeta level s remained unchanged. Both the shift in mobility and down-regulation o f PKC-delta and PKC-epsilon were only induced by mitogenic doses of bo mbesin. The potent mitogen platelet-derived growth factor induced simi lar effects on the PKC isotypes delta and epsilon. PKC-alpha and PKC-z eta levels were unaffected. Repeated doses of the synthetic diglycerid e 1-oleoyl-2-acetyl-sn-glycerol induced PKC-delta and PKC-epsilon down -regulation and stimulated the cells to divide. Again PKC-alpha and PK C-zeta levels were unaffected. These results show a correlation betwee n the membrane association and down-regulation of PKC-delta and PKC-ep silon and the entry of cells into S phase.