The cyclin-dependent kinase inhibitor p21 super(WAF1) is required for survival of differentiating neuroblastoma cells

We are employing recent advances in the understanding of the cell cycle 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 SH-SY5Y neuroblastoma cells and the expression of p21 super(WAF1), an inhibitor of cyclin-dependent kinases. The differentiated cells continue to express p21 super(WAF1), even after removal of aphidicolin from the culture medium. The p21 super(WAF1) protein coimmunoprecipitates with cyclin E and inhibits cyclin E-associated protein kinase activity. Each of three antisense oligonucleotides complementary to p21 super(WAF1) mRNA partially blocks expression of p21 super(WAF1) and promotes programmed cell death. These data indicate that p21 super(WAF1) expression is required for survival of these differentiating neuroblastoma cells. Thus, the problem of neuronal differentiation can now be understood in the context of negative regulators of the cell cycle.