The TNF-like weak inducer of apoptosis (TWEAK) can induce diverse cellular responses, including cell death, inflammation, migration, and proliferation in various transformed cell lines. We investigated TWEAK sensitivity, TWEAK effects on nuclear factor-kappaB activation, and expression of TWEAK in the HT-29, LS180, SK-CO-1 and SW480 human colonic adenocarcinoma cell lines, all of which express the TWEAK receptor (Fn14). TWEAK alone induced cell death in SW480 cells and induced cell death of HT-29 cells after addition of IFN-gamma, actinomycin D or cycloheximide. TWEAK did not affect cell viability of LS-180 or SK-CO-1 cells. Activation of NF-kappaB was not obviously influenced by TWEAK in any of the cell lines. All four human colonic adenocarcinoma cell lines constitutively expressed TWEAK mRNA, protein and membrane-bound TWEAK antigen, as detected by RT-PCR, Western blotting and flow cytometry. Stimulation by an anticancer drug (camptothecin) augmented cell surface expression of TWEAK and all human colonic adenocarcinoma tissue samples studied (n=59) demonstrated positive staining for TWEAK antigen. Soluble TWEAK was detected in culture medium of these cell lines by ELISA and conditioned medium from SW480 cells incubated with anti-TWEAK antibody significantly inhibited endothelial cell tube formation in Matrigels. Thus, functional expression of TWEAK from human colonic adenocarcinoma cells may contribute to neovascularization.