BCL-2 OVEREXPRESSION IN THE HACAT CELL-LINE IS ASSOCIATED WITH A DIFFERENT MEMBRANE FATTY-ACID COMPOSITION AND SENSITIVITY TO OXIDATIVE STRESS

Different mechanisms have been proposed for the activity of the Bcl-2 proto-oncogene product. A bona fide antioxidant activity and a pro-oxi dant setting up of the cell have been suggested using different experi mental models, yet many uncertainties exist about the biochemical mech anism of Bcl-2 action. In the present paper, we report the characteriz ation of the cellular response to mild oxidative stress of a cultured cell line of immortalized keratinocytes (HaCaT), overexpressing the Bc l-2 oncogene product. A sublethal oxidative stress was induced by 1 h treatment with 200 mu M tert-butyl-hydroperoxide (t-BOOH). Following p eroxide treatment, the formation of reactive oxygen species was lower in Bcl-2 expressing cells, suggesting a better capacity to counter oxi dative stress. Total Superoxide Dismutase activity was induced by oxid ative t-BOOH treatment in bcl-2 transfected cells, which also accumula ted less damage to membrane lipids and proteins, as assessed by TBA-RS and carbonyl formation respectively. On the other hand, the formation of 4-hydroxy-nonenal, a more specific marker of peroxidative damage t o polyunsaturated fatty acids, was higher in bcl-2 transfected cells t han in control cells. Bcl-2 over-expression was also associated with s ignificant changes in the fatty acid composition of cell membranes. Tr ansfected cells presented a higher proportion of mono-unsaturated fatt y acids and omega 6 poly unsaturated fatty acids and a lower proportio n of penta-enoic PUFA, thus resulting in a higher unsaturation index w ith respect to control cells. Changes in Protein kinase C activity wer e also associated to bcl-2 expression, possibly resulting from the dif ferences in membrane fatty acid composition. These data may be an impo rtant background for the understanding of Bcl-2 involvement in the con trol of apoptotic response as well as in the induction of antioxidant cell defenses against oxidative stress. (C) 1997 Elsevier Science Inc.