REGULATION BY PHORBOL ESTERS OF AMYLOID PRECURSOR PROTEIN RELEASE FROM SWISS 3T3 FIBROBLASTS OVEREXPRESSING PROTEIN KINASE-C-ALPHA

Release of large soluble NH2-terminal fragments of the amyloid precurs or protein (APP) of Alzheimer's disease was measured in two Swiss 3T3 fibroblast cell lines (designated SF1.4 and SF3.2), overexpressing the alpha subtype of protein kinase C, and in two control cell lines (SC1 and SC2) (Eldar, H., Zisman, Y., Ullrich, A., and Livneh, E. (1990) J . Biol. Chem. 265, 13290-13296). Basal release of APP was significantl y increased in SF1.4 cells, but not in SF3.2 cells, relative to contro ls. Phorbol 12-myristate 13-acetate, an activator of protein kinase C, elicited a concentration-dependent increase in APP release in all fou r cell lines. However, the estimated EC50 for this effect was lower in the two cell lines overexpressing protein kinase C-alpha (7 and 6 nM, in SF1.4 and SF3.2 cells, respectively) than in control SC1 and SC2 c ells (56 and 22 nM, respectively). The absolute amount of APP released by maximal concentrations of phorbol ester was not altered by overexp ression of protein kinase Calpha. The protein kinase C inhibitor H-7 ( 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride) signifi cantly reduced the response to phorbol esters in control (SC1) cells b ut not in cells (SF1.4) that overexpress protein kinase Calpha. Levels of cell-associated APP were slightly elevated, and rates of APP turno ver were unchanged, in SF1.4 cells relative to controls. However, cell -associated APP levels were lower in SF3.2 cells than in controls. The results demonstrate that protein kinase Calpha regulates APP release in Swiss 3T3 fibroblasts, and perhaps in other tissues, including brai n, and may be the isozyme that mediates receptor-evoked release of APP .