NEURITE OUTGROWTH FROM N18TG2 NEUROBLASTOMA INDUCED BY H-7, A PROTEIN-KINASE INHIBITOR, IN THE PRESENCE OF COLCHICINE

Our previous studies have demonstrated that the protein kinase inhibitor H-7 promotes neurite outgrowth from mouse neuroblastoma N18TG2 cells as well as from primary cerebellar cells, and also that the neurites induced by H-7 were more tolerant of colchicine (COL) than those induced by dibutyryl cAMP (dB-cAMP). In the present study, we tested the effects of H-7 and dB-cAMP on neurite growth from N18TG2 cells in the presence of COL. We found that only H-7 promoted neurite formation in the presence of COL. The percentage of cells with neurites induced by H-7 in the presence of COL (H-7+COL) was similar to that induced by H-7 alone. The neurites induced by H-7+COL grew straight. They were very thin (less than 1 mum in diameter) and had round varicosities, as did the neurites induced by H-7 alone. By transmission electron microscopy, the neurites induced by H-7+COL were found to contain longitudinally arranged intermediate filaments (IF). Microtubules (MT) were not observed within the neurites. We also examined the effect of cytochalasin B (CB) on the neurites induced by H-7+COL and by H-7 alone. The neurites induced by H-7+COL were tolerant to CB, but those induced by H-7 were resorbed completely within 24 h after CB was applied. Neurites tolerant to CB contained longitudinally IF. Simultaneous application of CB with H-7+COL or with H-7 alone did not induce neurite formation. The present findings suggest that the neurite growth from N18TG2 cells induced by H-7 is independent of MT formation, although that induced by dB-cANP is closely related to MT. In addition, actin filaments play a crucial roles in H-7-induced neurite formation in N18TG2 cells, and IF enhanced the mechanical strength of the neurites.