Alleviation of apoptosis by serum in Chinese hamster ovary cells ectopically expressing human Fas antigen

Fas-mediated apoptosis is an important regulatory mechanism for the development of T-cells and prevention of oncogenesis. Here, we establish Chinese hamster ovary (CHO) cell lines which stably express Fas antigen, and analyzed apoptosis induced by anti-Fas IgM. While Fas-transfected hamster cells did not undergo apoptosis when stimulated with anti-Fas antibody in the presence of medium containing 10% serum, in reduced serum concentrations, anti-Fas antibody caused these cells to round up and detach from the culture dish. Analysis of the DNA content by a flow cytometry demonstrated a significant increase of cells with sub-G1 amount of DNA upon Fas stimulation in the low serum concentrations. The increase in the number of apoptosis cells was inhibited by an apopain (CPP32, caspase 3) inhibitor or insulin-like growth factor-I. In contrast, apoptosis in a Fas-transfected mouse T-cell line occurred in the presence of 10% serum. these results suggest that factors including insulin-like growth factor-I in fetal bovine serum protect CHO cells from apopain-dependent apoptosis mediated by Fas-antigen stimulation.