ACTIVATION OF PHOSPHOLIPASE C-GAMMA BY THE CONCERTED ACTION OF TAU-PROTEIN AND ARACHIDONIC-ACID

Phospholipase C-gamma (PLC-gamma) isozymes are thought to be activated by receptor-induced tyrosine phosphorylation. Proteins that activate PLC-gamma 1 have now been purified from bovine brain and identified as members of the tan family of microtubule-associated proteins. Activat ion of PLC-gamma by tau was enhanced in the presence of unsaturated fa tty acids such as arachidonic acid, saturated fatty acids being ineffe ctive. Maximal (15-20-fold) activation was apparent in the presence of 0.15 mu M tau and 25 mu M arachidonic acid (AA). The effect of tau an d AA was specific to PLC-gamma isozymes in the presence of submicromol ar concentrations of Ca2+ and was markedly inhibited by phosphatidylch oline. These results suggest that in cells that express tau, receptor to cytosolic phospholipase A, may activate PLC-gamma isozymes indirect ly in the absence of tyrosine phosphorylation through the hydrolysis o f phosphatidylcholine to generate AA.