Characterization of Apt- cell lines exhibiting cross-resistance to glucocorticoid- and Fas-mediated apoptosis

Apoptosis induction by staurosporine, ceramide, and Fas stimulation was inv estigated in the mouse thymoma cell line W7.2 and a panel of dexamethasone (dex)-resistant W7.2 mutant cell lines, Apt3.8, Apt4.8 and Apt5.8, and a Bc l-2 transfected W7.2 cell line (Wbcl2), While W7.2 cells were found to be s ensitive to these apoptosis inducers, the Apt- mutants and Wbcl2 cells were shown to be resistant to some or all of the treatments. Specifically, all three Apt- mutants and Wbcl2 cells were found to be resistant to ceramide a nd Fas-mediated apoptosis, whereas, Apt4.8 and Apt5.8 were sensitive to sta urosporine-induced apoptosis under conditions in which Apt3.8 and Wbcl2 cel ls were resistant, Measurements of caspase activity and cytochrome c releas e in cytosolic extracts of dex and staurosporine-treated cells indicated th at the recessive Apt- mutations effect steps upstream of mitochondrial dysf unction, Steady-state RNA levels of apoptosis-associated gene transcripts s howed that the observed differential resistance of the Apt- cell lines coul d not be explained by altered expression of numerous Bcl-2 or Pas related g enes. Transient transfection of human Fas gene coding sequences into the Ap t- mutants and Wbcl2 cells did not induce apoptosis, even though these same cell lines were sensitive to ectopic expression of the FADD and caspase 8 genes. Taken together, these data provide genetic evidence for the existenc e of shared components in the dex- and Fas-mediated apoptotic pathways in W 7.2 cells.