FAP-1 in pancreatic cancer cells: functional and mechanistic studies on its inhibitory role in CD95-mediated apoptosis

In this study we investigated the functional role of FAP-1 as a potential i nhibitor of CD95 (Fas, APO-1)-mediated apoptosis in pancreatic cancer cells . Stable transfection of the CD95-sensitive, FAP-1-negative cell line Capan -1 with an FAP-1 cDNA resulted in a strongly decreased sensitivity to CD95- induced apoptosis, as measured by DNA fragmentation and caspase-3 activity. Inhibition of cellular protein tyrosine phosphatases with orthovanadate do se-dependently increased CD95-induced apoptosis in CD95-resistant FAP-1-pos itive Panc89 and Capan-1-FAP-1 cells almost to the level seen in wild-type Capan-1 cells. Blocking the CD95/FAP-1 interaction in Panc89 cells by cytop lasmic microinjection of a synthetic tripeptide mimicking the C terminus of CD95 resulted in a mean 5.5-fold increase in apoptosis compared to cells t hat received a control peptide. Using confocal laser scanning microscopy we show that in Panc89 cells FAP-1 is mainly associated with the Golgi comple x and with peripheral vesicles. FAP-1 displayed enhanced colocalization wit h CD95 upon CD95 stimulation in the Golgi complex but not in surface-associ ated vesicles. This correlated with a decrease in plasma membrane staining for CD95 as determined by FACS analysis. Inhibition of Golgi anterograde tr ansport by brefeldin A abolished the anti-CD95-induced colocalization of FA P-1 and CD95 as well as the decrease in cell-surface-associated CD95. Final ly, we demonstrate by immunohistochemistry that FAP-1 is strongly expressed in tumor cells from pancreatic carcinoma tissues. Taken together, these re sults show that FAP-1 can protect pancreatic carcinoma cells from CD95-medi ated apoptosis, probably by preventing anti-CD95-induced translocation of C D95 from intracellular stores to the cell surface.