Bcl-x and Bcl-2 inhibit TNF and Fas-induced apoptosis and activation of phospholipase A2 in breast carcinoma cells.

Data suggest an involvement of PLA2 in both TNF- and Fas-mediated cytotoxicity and a novel mechanism of action for b cl-2 and bcl-x, i.e. inhibition of arachidonic acid metabolism, by which they may, in addition of apoptosis, modulate inflammation.

Abstract

Tumor necrosis factor (TNF) induces cel death in several tumor cell lines by undefined mechanisms. Using a cDNA expression cloning strategy we identified two cDNAs that completely inhibit the TNF-induced death pathway in MCF7 breast carcinoma cells. These cDNAs encoded for Bcl-2 and Bcl-x. To compare the cytotoxic signal transduction pathway induced by the TNF receptor versus that induced by Fas, we transfected MCF7 cells with a Fas expression construct. The resulting cell line, MCF-Fas, was highly sensitive to cytotoxicity induced by TNF or anti-Fas. Expression of either bcl-2 or bcl-x in these cells rendered them completely resistant to lysis induced by either TNF or Fas. Interestingly, exposure of MCF-Fas cells to anti-Fas or TNF induced activation of phospholipase A2 (PLA2), while only TNF activated NF-kappa B. Activation of PLA2 was completely blocked whereas activation of NF-kappa B was unaffected by overexpression of either bcl-x or bcl-2. Moreover, PLA2-inhibitors, quinacrine and dexamethasone, partially inhibited cytotoxicity induced by either TNF or anti-Fas. These data suggest an involvement of PLA2 in both TNF- and Fas-mediated cytotoxicity and a novel mechanism of action for bcl-2 and bcl-x, i.e. inhibition of arachidonic acid metabolism, by which they may, in addition of apoptosis, modulate inflammation.