Vitamin E succinate (VES) induces Fas sensitivity in human breast cancer cells: Role for M-r 43,000 Fas in VES-triggered apoptosis

Fas (CD95/APO-1) is an important mediator of apoptosis. We show that Fas-re sistant MCF-7, MDA-MB-231, and MDA-MB-435 human breast cancer cells become responsive to anti-Fas (CD95) agonistic antibody-triggered apoptosis after pretreatment or cotreatment with vitamin E succinate (VES; RRR-alpha-tocoph eryl succinate). In contrast, no enhancement of anti-Fas agonistic antibody -triggered apoptosis was observed following VES pretreatment or cotreatment with Fas-sensitive primary cultures of human mammary epithelial cells, imm ortalized MCF-10A cells, or T47D human breast cancer cells. Although VES is itself a potent apoptotic triggering agent, the 6-h pretreatment procedure for Fas sensitization did not initiate VES-mediated apoptosis. The combina tion of VES plus anti-Fas in pretreatment protocols was synergistic, induci ng 2.8-, 3.0-, and 6.3-fold enhanced apoptosis in Fas-resistant MCF-7, MDA- MB-231, and MDA-MB-435 cells, respectively. Likewise, cotreatment of Fas-re sistant MCF-7, MDA-MB-231, and MDA-MB-435 cells with VES plus anti-Fas enha nced apoptosis 1.9-, 2.0-, and 2.6-fold, respectively. Functional knockout of Fas-mediated signaling with tither Fas-neutralizing antibody (MCF-7-, MD A-MB-231-, and MDA-MB-435-treated cells) or Fas antisense oligomers (MDA-MB -435-treated cells only), reduced VES-triggered apoptosis by similar to 50% . Analyses of whole cell extracts from Fas-sensitive cells revealed high co nstitutive expression of M-r 43,000 Fas, whereas Fas-resistant cells expres sed low levels that were confined to the cytosolic fraction. VES treatment of the Fas-resistant cells caused a depletion of cytosolic M-r 43,000 Fas w ith a concomitant increase in M-r 43,000 membrane Fas. These data show that VES can convert Fas-resistant human breast cancer cells to a Fas-sensitive phenotype, perhaps by translocation of cytosolic M-r 43,000 Fas to the mem brane and show that VES-mediated apoptosis involves M-r 43,000 Fas signalin g.