Regulation of p53-Dependent Apoptosis in Human Neuroblastoma Cells by Isoquinolines

Abstract

We have studied staurosporine and a few other isoquinolines, which are known protein kinases inhibitors, for their ability in regulating the apoptosis in human neuroblastoma cells. Staurosporine and a subset of isoquinolinesulphonamides, including H-7 ([1-(5-Isoquinolinesulfonyl)-2-methylpiperazine]), were found to be able to induce widespread apoptosis, characterized by DNA fragmentation and nuclear condensation, in human neuroblastoma cells, SH-SY5Y, within 24 hours. Surprisingly, exposure of the cells to the H-7, but not staurosporine, caused a dramatic nuclear accumulation of p53. The kinetics of nuclear accumulation of p53 correlates well with the kinetics of induction of apoptosis. The effect of H-7 was further assessed in a group of human cell lines. Only cell lines harbouring the wild-type p53 gene were responsive to the stimulatory effect of H-7 on nuclear accumulation of p53. Furthermore, cell lines carrying a mutated p53 gene were resistant to the cytotoxic effect of H-7. The ability of the compound in mediating the apoptotic response in the SH-SY5Y line expressing a dominant negative mutant of p53 was significantly reduced. These data strongly suggest that a p53-dependent mechanism contributes to the cytoxicity of the H-7 in human neuroblastoma cells. Other PKC inhibitors failed to mediate apoptosis in neuroblastoma cells through the p53 pathway further suggest that a unique H-7 sensitive pathway which is different from the known PKC pathway is responsible for mediating the effect. Thus, the experimental paradigm of apoptosis triggered by H-7 in neuroblastoma cells is likely to be useful for gaining a further understanding of the pathways and mechanisms underlying the apoptotic function of p53.