Reciprocal control of apoptosis and proliferation in cultured rat hepatomaARL-6 cells: Roles of nutrient supply, serum, and oxidative stress

In order to understand how cancer cells accumulate, rat hepatoma ARL-6 cell s were cultured for 8 d to identify factors involved in spontaneous cell pr oliferation and apoptosis. With increasing time in culture, the proportion of cells in the proliferative phases of the cell cycle and the rate of deox yribonucleic acid (DNA) synthesis decreased. The waning of proliferation wa s associated with a gradual reduction of cell viability, and this was tempo rally related to the appearance of typical apoptotic morphology and DNA lad dering. Medium replacement or supplementation with fetal calf serum (FCS) s uppressed apoptosis, while medium change, but not fetal calf serum alone, e nhanced cell proliferation. Apoptosis was also suppressed by dimethyl sulfo xide (DMSO), but supplementary glutathione was without effect. Expression o f poly(adenosine diphosphate[ADP]-ribose)polymerase peaked on days 3-4 of c ulture, and was followed by a progressive decrease thereafter, consistent w ith proteolytic cleavage. This decrease was prevented to varying extents by complete medium replacement, FCS and DMSO, indicating a close temporal rel ationship between poly(ADP-ribose)polymerase activation and apoptosis. Expr ession of Fas and Bcl-2 did not change appreciably over the 8-d culture, bu t there was a gradual increase in Bar expression; medium change, FCS and DM SO all partly inhibited Bar expression. These data indicate that spontaneou s apoptosis in cultured ARL-6 cells is inversely related to cell proliferat ion, and that nutrient supply, and to a lesser extent, serum-derived factor s and oxidative stress modulate apoptosis in this system. Proteolytic cleav age of poly(ADP-ribose)polymerase and expression of Bar are likely to be me chanistically involved with the control of spontaneous apoptosis in ARL-6 c ells, whereas changes in the levels of Fas and Bcl-2 do not play a role.