(47) INCREASED EXPRESSION OF FAS ON CELL SURFACE BY DEPOLARIZING MITOCHONDRIA

Bharathi Laxman, Laurie Miller and Bertrand C. Liang
Human Medical Genetics Unit, Department of Medicine, University Of Vermont College Of Medicine, Burlington, VT 05401

The involvement of mitochondria /mtDNA in tumorigenicity and apoptosis is well documented with changes in mitochondria/mtDNA linked to the tumorigenic phenotype. Earlier studies have shown altered susceptibility of cells in culture to drug induced apoptosis upon depletion of mtDNA; in addition, the sensitivity of cells to undergo programmed cell death is related to the cellular surface expression of Fas. We therefore investigated the relationship of mitochondria to Fas expression.

It has been demonstrated that the mitochondrial membrane is depolarized and the electron transport complex is uncoupled during the cell death program. We used an uncoupler of the mitochondrial membrane potential (AG17) at non-toxic and non-growth inhibitory doses to determine the effects of modification of the potential on Fas. Human glioblastoma (DKMG) and human breast cancer (MCF-7) cells were treated with 0.25 uM AG17 for 7 days. The expression of Fas on the surface and intracellular levels were analyzed by FACScan flow cytometer using FITC-labeled anti-Fas antibody. The sensitivity of these cells to anti-Fas antibody was determined by morphological assessment of apoptosis and to cis-diamminedichloroplatinum and etoposide by low density plating and colony counting. We report an increased expression of Fas (2-6 fold) on the cell surface of these tumor cells with a concomitant decrease (6-16 fold) in the intracellular levels of Fas and increased sensitivity to Fas/drug induced cell death upon mitochondrial membrane potential uncoupling using AG17. Mitochondrial alteration may provide a target to increase the sensitivity of tumor cells to cytotoxic agents and Fas mediated apoptotic death as these cells are known to harbor mechanisms that alter the death pathway resulting in escape from cellular death and drug resistance.