THE CYCLIN-DEPENDENT KINASE INHIBITOR P21(WAF1) IS REQUIRED FOR SURVIVAL OF DIFFERENTIATING NEUROBLASTOMA-CELLS

We are employing recent advances in the understanding of the cell cycl e to study the inverse relationship between proliferation and neuronal differentiation. Nerve growth factor and aphidicolin, an inhibitor of DNA polymerases, synergistically induce neuronal differentiation of S H-SY5Y neuroblastoma cells and the expression of p21(WAF1), an inhibit or of cyclin-dependent kinases. The differentiated cells continue to e xpress p21(WAF1) even after removal of aphidicolin from the culture me dium. The p21(WAF1), protein coimmunoprecipitates with cyclin E and in hibits cyclin E-associated protein kinase activity. Each of three anti sense oligonucleotides complementary to p21(WAF1) mRNA partially block s expression of p21(WAF1) and promotes programmed cell death. These da ta indicate that p21(WAF1) expression is required for survival of thes e differentiating neuroblastoma cells. Thus, the problem of neuronal d ifferentiation can now be understood in the context of negative regula tors of the cell cycle.