STIMULATION OF A CA2+-DEPENDENT PROTEIN-KINASE BY GM1 GANGLIOSIDE IN NERVE GROWTH FACTOR-TREATED PC12 CELLS

We have investigated the ability of exogenous gangliosides to modulate nerve growth factor (NGF) signal transduction in PC12 cells. The effects of exogenous ganglioside G(M1) on multiple protein kinase activities were assayed by analyzing site-specific serine phosphorylation of tyrosine hydroxylase (TyrOHase) by two-dimensional phosphopeptide mapping. In the presence of NGF, exogenous G(M1) (1-10-mu-M) increased P-32 incorporation into TyrOHase phosphopeptide T2, a Ca2+/calmodulin-dependent protein kinase substrate whose phosphorylation is not normally affected by NGF treatment. In the absence of NGF, G(M1) treatment had no significant effects on TyrOHase phosphorylation. The removal of extracellular Ca2+ or blockade of dihydropyridine-sensitive Ca2+ channels prevented the G(M1)-induced increases in P-32 incorporation into phosphopeptide T2. Exogenous G(M1) also potentiated K+ depolarization-induced increases in the phosphorylation of TyrOHase. These results suggest that the stimulatory effects of exogenous G(M1) ganglioside on NGF actions may be due to its ability to potentiate a Ca2+-dependent signaling pathway.