Cell cycle specificity of Fas-mediated apoptosis in WIL-2 cells.

Antibodies to Fas/APO1 receptor induce effective apoptosis in WIL-2 cells of the human B-lymphoid line. Quantitative assessment of the extent of the death in cells synchronized by thymidine block revealed a significant increase in their sensitivity to the cytocidal effect mediated by Fas/APO1 during the G1 phase of the cell cycle. Western analysis of the content of the p53 antigen in the cytoplasm and nuclei of the cells showed that the Fas/APO1-induced death is accompanied by massive translocation of the p53 from the cytoplasm to the nucleus. These findings suggest that cell vulnerability to the Fas/APO1-mediated apoptosis is subjected to regulation by cell cycle-dependent mechanisms, one of which is probably the function of the p53 antigen.