Degradation of phospholipids and protein kinase C activation for the control of neuronal functions.

Abstract

Protein kinase C (PKC) has been postulated to play key roles in several neuronal processes such as transmitter release, ion channel modulation, receptor downregulation, cross-talk with other signaling systems, neuronal development and regeneration, and long-term potentiation (LTP). The hydrolysis of inositol phospholipids catalyzed by phospholipase C was initially thought to be the sole mechanism for the activation of PKC. Subsequent studies, however, have shown that the receptor-mediated hydrolysis of phosphatidylcholine (PC) may also be involved in the transmembrane signaling (for a review, see Exton, 1990). In addition, in synergy with diacylglycerol (DG), unsaturated free fatty acids (FFAs) such as arachidonic, oleic, linoleic, linolenic, and docosahexaenoic acids dramatically activate some members of the PKC family at the basal level of Ca2+ concentration. It is plausible that phospholipase C, phospholipase A2 and possibly phospholipase D as well are all involved in the activation of PKC. Presumably, this enzyme activation is integrated into the signal-induced membrane phospholipid degradation cascade, prolonging the activation of PKC. The sustained activation of this enzyme appears to be of importance for the long-term cellular responses such as neuronal plasticity and gene activation. This article will briefly discuss a possible link between signal-induced degradation of various membrane phospholipids and PKC activation, and the implications of such a linkage in the control of neuronal functions.