Dissociation of CDK2 from cyclin A in response to the topoisomerase II inhibitor etoposide in v-src-transformed but not normal NIH 3T3 cells

Our previous work has demonstrated that treatment of NIB 3T3 cells with eto poside (VP16), an inhibitor of DNA topoisomerase II and widely used antican cer agent, results in G2/M-phase arrest, whereas treatment of cells transfo rmed by v-src, v-ras, or v-raf results in an S-phase blockage. The present studies describe the mechanistic aspects of this selective S-phase arrest i n the v-src-transformed cells. The S-phase arrest in these cells was found to be coupled with depletion of cyclin A-dependent kinase activity. This de crease could not be explained by changes in the overall level of cyclin A, CDK2, p27, or p21 proteins. Rather, it was associated with a time-dependent reduction of CDK2 protein complexed with cyclin A following VP16 treatment , It was further shown that the decrease of cyclin A-associated CDK2 was li nked to an increase of CDK2 protein in cyclin E immunocomplexes, which sugg ests that CDK2 might become redistributed following treatment with VP16. Th us, oncogenic transformation by v-src can trigger separation of CDK2 protei n from cyclin A in response to VP16. This might contribute to the depletion of cyclin A-dependent kinase activity and the selective S-phase arrest by VP16 in v-src-transformed cells. (C) 1999 Academic Press.