Phorbol ester-induced conventional protein kinase C (PKC
, -
/
, and -
) isozyme activitiesare potentiated by 1,2-diacyl-
sn-glycerol. This has been attributed to a "cooperative" interaction of thetwo activators with two discrete sites termed the low- and high-affinity phorbol ester binding sites,respectively [
Slater, S.
J., Milano, S. K., Stagliano, B. A., Gergich, K. J., Ho, C., Mazurek, A., Taddeo,F. J., Kelly, M. B., Yeager, M. D., and Stubbs, C. D. (1999)
Biochemistry 38, 3804-3815]. Here, wereport that the 1-
O-alkyl ether diglyceride, 1-
O-hexadecyl-2-acetyl-
sn-glycerol (HAG), like its 1,2-diacylcounterpart, 1-oleoyl-2-acetyl-
sn-glycerol (OAG), also potentiated PKC
, -
I/II, and -
activities inducedby the phorbol ester 4
-12-
O-tetradecanoylphorbol-13-acetate (TPA). Similar to OAG, HAG was foundto bind to the low-affinity phorbol ester binding site and to enhance high-affinity phorbol ester binding,and to decrease the level of Ca
2+ required for phorbol ester-induced activity, while being without effecton the Ca
2+ dependence of membrane association. Thus, similar to OAG, HAG may also potentiate phorbolester-induced activity by interacting with the low-affinity phorbol ester binding site, leading to a reducedlevel of Ca
2+ required for the activating conformational change. However, HAG was found not to behavelike a 1,2-diacyl-
sn-glycerol in that alone it did not induce PKC activity, and also in that it enhancedOAG-induced activity. The results reveal HAG to be a member of a new class of "nonactivating"compounds that modulate PKC activity by interacting with the low-affinity phorbol ester binding site.