TIPE2 (tumor necrosis factor-a-induced protein-8-like 2, TNFAIP8-like 2) is reported to be a negative regulator of immune cell function, required for preventing hyperresponsiveness and maintaining immune homeostasis.1 TIPE2 targets the Ras signaling pathway to provide a molecular bridge from inflammation to cancer.2 TIPE2 is downregulated in patients with chronic inflammatory diseases such as systemic lupus erythematosus3 and hepatitis,4 the low expression level of TIPE2 in tumor tissue suggests that TIPE2 may perform a function in the carcinogenesis. TIPE2 suppresses hepatocellular carcinoma metastasis5 and gastic cancer cell proliferation,6 so we hypothesize that TIPE2 plays a key role in CRC (colorectal carcinoma, CRC) growth and explore the mechanism by which TIPE2 induces of apoptosis and inhibits proliferation.Methods:
Viability of HCT116, HT29 and Hela cells transfected with Ad-empty and Ad-TIPE2 was tested by MTT. TIPE2 mRNA was suppressed by shRNA transfection and the transfection efficiency was proved by westernblot, and use flow cytometry analysis to keep a tally of apoptotic cells. In order to elucidate the effect of TIPE2 on autophagy of colon cancer cells, HCT116 cells were transfected with TIPE2 and GFP-LC3, the autophagosome formation was observed by fluorescence microscopy, and LC3-I, LC3-II and p62 protein expression was detected by westernblot. Implantation of TIPE2-expression-HCT116 stable cell line was performed subcutaneously into nude mice, measure the volume of the tumor every other day, and resected tumors were examined by immunohistochemistry.Results:
Recombinant adenovirus-expressing TIPE2 effectively inhibited the proliferation of several kinds of tumor cells. TIPE2 expression was knocked down successfully by shRNA transfection, which resulted in the decrease of apoptosis. TIPE2 overexpression induced autophagosome formation, increased the ratio of LC3-II/LC3-I and decreased p62 expression in HCT116 cells. In nude mice, marked tumor growth was observed after empty-expression-HCT116 stable cell line subcutaneous implantation while TIPE2-expression-HCT116 stable cell line failed to induce CRC.Conclusions:
TIPE2 can inhibit the proliferation of tumor cells and promotes apoptosis. In addition, TIPE2 induces autophagy of colon cancer cells, which provides one new therapeutic target for clinical treatment schedule.