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 de velopment of T-cells and prevention of oncogenesis, Here, we establish ed Chinese hamster ovary (CHO) cell lines which stably express Fas ant igen, and analyzed apoptosis induced by anti-fas IgM. While Fas-transf ected hamster cells did not undergo apoptosis when stimulated with ant i-Fas antibody in the presence of medium containing 10% serum, in redu ced serum concentrations, anti-Pas antibody caused these cells to roun d up and detach from the culture dish. Analysis of the DNA content by a now 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 apoptotic cells was inhibited by an apo pain (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 includi ng insulin-like growth factor-I in fetal bovine serum protect CHO cell s from apopain-dependent apoptosis mediated by Fas-antigen stimulation .