Effects of the simultaneous application of dibutyryl, cAMP and phorbol ester on morphological differentiation in ng108-15 cells

Abstract

The simultaneous application of dibutyryl cAMP and 12- o-tetradecanoyl-phorbol 13-acetate (TPA) markedly induced neurite outgrowth in NG108-15 cells compared to treatment with each agent alone. Neurites induced by both drugs remained after withdrawal of the drugs, although the neurites elongated by dibutyryl cAMP or TPA alone disappeared after the withdrawal. [ 3H]Thymidine incorporation reached a peak at 24 and 44 h after cultivation in control cells. This incorporation was partially inhibited by dibutyryl cAMP or TPA, and blocked by combination of both drugs. Staurosporine or K-252a inhibited neurite outgrowth induced by the combination. Staurosporine also inhibited TPA-induced transient activation of protein kinase C (PKC). These results suggest that PKC activation is involved in the neurite elongation. However, inhibition of PKC seems to be involved in the neurite elongation since: (1) the proportion of neurite-elongated cells was in accord with grade of decrease in PKC activity: (2) exposure of both dibutyryl cAMP and TPA for 24 h followed by their removal (when PKC activity was still kept) failed to induce neurite elongation: and (3) for neurite extension it took at least 2 days exposure to both drugs when PKC activity was completely decreased. It is suggested that: (1) modulation of the activity of both cAMP-dependent protein kinase (PKA) and PKC is required to induce irreversible neurite outgrowth and (2) inhibition as well as activation of PKC could be involved in neurite elongation in NG108-15 cells.