INDUCTION OF P53-INDEPENDENT APOPTOSIS ASSOCIATED WITH G2M ARREST FOLLOWING DNA-DAMAGE IN HUMAN COLON-CANCER CELL-LINES

The tumor suppressor p53 protein induces apoptosis in response to vari ous kinds of DNA damage in normal cells, but it is still unclear wheth er or not apoptosis induced by DNA damage correlates with the p53 stat us in tumor cells, We determined the status of p53 by functional analy sis of separated alleles in yeast in five human colon cancer cell line s, SW-480, SW-620, DLD-1, COLO320 and LS174T and investigated whether p53 is necessary for apoptosis and cell cycle arrest after treatment o f the cells with a DNA-damaging agent, etoposide (VP-16), or gamma-irr adiation. Of these cell lines, only LS174T expresses a functional p53, Apoptosis was detected in SW-480 and COLO320 cell lines, but not in t he other cell lines, including LS174T cell line with a normal p53 func tion. Furthermore, cell cycle analysis revealed accumulation in the G( 2)M phase preceding induction of apoptosis in SW-480 and COLO320 cells , but not in the other cells, These results suggest that apoptotic ind uction by DNA damage is not necessarily related to p53 status and that induction of p53-independent apoptosis following DNA damage may corre late with G2M arrest in the cell cycle, at least in the colon cancer c ell lines used in this study.