Role of Protein Tyrosine Phosphorylation in Etoposide-Induced Apoptosis and NF-κB Activation

When a human myeloid cell line, U937, was incubated with etoposide (10 mu g/mL), morphologically apoptotic cells first appeared at 3 hr and increased with time to 50% at 5 hr. Pretreatment of U937 cells for 30 min with a potent tyrosine kinase inhibitor, herbimycin A (10 mu M), significantly suppressed the appearance of apoptotic morphological changes. Concomitantly, herbimycin A pretreatment prevented both high molecular weight and internucleosomal DNA fragmentation induced by etoposide. Two major bands at 30 and 66 kDa with enhanced tyrosine phosphorylation inhibited by herbimycin A were detectable after 30 min of incubation with etoposide. In addition, herbimycin A prevented etoposide-induced NF-kappa B activation. The expressions of Bcl-2 and Bar, on the other hand, were not affected by herbimycin A pretreatment. Herbimycin A was also found to inhibit 1-beta-D-arabinofuranosylcytosine-induced apoptotic changes and NF-kappa B activation. These results suggest that activation of tyrosine kinase(s) may play an important role in apoptotic processes induced by a variety of anti-cancer drugs. (C) 1998 Elsevier Science Inc.