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

Genistein and other inhibitors of protein tyrosine kinases were examined 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 substratum after priming with nerve growth factor (NGF), but had no effect on undifferentiated cells. Steady-state levels of phosphotyrosine-modified proteins (105, 59, 52, and 46 kDa) were reduced in NGF-primed cells by genistein treatment. The target of genistein action did not appear to be the NGF receptor/trk tyrosine kinase because the presence of NGF in cultures of NGF-primed cells was not necessary for genistein-stimulated neurite outgrowth. The tyrosine kinase inhibitors tyrphostin RG508964 and herbimycin A also increased the rate of neurite elongation in NGF-primed PC 12 cells. Video-enhanced differential interference contrast microscopy revealed that growth cones of genistein-treated cells had less complex morphologies and were less dynamic than untreated cells, with short filopodia restricted to the leading edge, unlike untreated cells whose growth cones exhibited longer, more numerous filopodia and lamellipodia, which remodeled continuously. These results suggest that protein tyrosine kinase activity in PC 1 2 cells negatively regulates neurite outgrowth and directly or indirectly affects growth cone morphology.