Fas-associated phosphatase-1 promotes Fas-mediated apoptosis in human colon cancer cells: Novel function of FAP-1

Background and Aim: Fas-associated phosphatase-1 (FAP-1) has been thought as an inhibitor in Fas-mediated apoptosis. Here, we investigated the role of FAP-1 in Fas-mediated apoptosis of human colon cancer cells. Method: The viability of four colon cancer cell lines treated with agonistic anti-Fas antibody was determined using WST-1 assay and cell death detection ELISA. pRc/CMV-FAP-1 was transfected to a FAP-1-negative, Fas-resistant colon cancer cell line SW480 by lipofection and the clones expressing FAP-1 protein were selected by limiting dilution. In the clones, expression of 550 genes was analyzed by cDNA microarrays. Protein expression of FAP-1 and molecules related to apoptosis was examined by western blot. Results: We obtained two FAP-1 overexpressed clones which were much more susceptible to Fas-mediated apoptosis than control cells. In the clones, caspase 8 and caspase 3 were fully activated by agonistic anti-Fas antibody treatment. Bcl-2 family proteins were not related to the high susceptibility of these clones, because caspase 9 was not activated. Transfection of FAP-1 did not suppress the survival actions of insulin-like growth factor (IGF-1) which enhanced survival signal through Akt phosphorylation. Upregulation in 21 genes and downregulation in 29 genes was revealed by cDNA arrays. We confirmed protein expression of p21 and phosphorylated p21 were much more enhanced in the clones than in control cells. Conclusions: Overexpression of FAP-1 enhanced susceptibility to Fas-mediated apoptosis in SW480 and upregulation of p21 may contribute to this phenomenon. Our results indicate a novel function of FAP-1 in Fas-mediated apoptosis of human colon cancer cells.