INCREASED NEURITE OUTGROWTH INDUCED BY INHIBITION OF PROTEIN-TYROSINEKINASE-ACTIVITY IN PC12 PHEOCHROMOCYTOMA CELLS

Genistein and other inhibitors of protein tyrosine kinases were examin ed for effects on neurite elongation and growth cone morphology in the rat PC12 pheochromocytoma cell line. Genistein increased the rate of neurite elongation in PC 12 cells grown on a collagen/polylysine subst ratum after priming with nerve growth factor (NGF), but had no effect on undifferentiated cells. Steady-state levels of phosphotyrosine-modi fied proteins (105, 59, 52, and 46 kDa) were reduced in NGF-primed cel ls by genistein treatment. The target of genistein action did not appe ar to be the NGF receptor/trk tyrosine kinase because the presence of NGF in cultures of NGF-primed cells was not necessary for genistein-st imulated neurite outgrowth. The tyrosine kinase inhibitors tyrphostin RG508964 and herbimycin A also increased the rate of neurite elongatio n in NGF-primed PC 12 cells. Video-enhanced differential interference contrast microscopy revealed that growth cones of genistein-treated ce lls had less complex morphologies and were less dynamic than untreated cells, with short filopodia restricted to the leading edge, unlike un treated cells whose growth cones exhibited longer, more numerous filop odia and lamellipodia, which remodeled continuously. These results sug gest that protein tyrosine kinase activity in PC 1 2 cells negatively regulates neurite outgrowth and directly or indirectly affects growth cone morphology.