Abstract 1224: TNIK is a protein kinase essential for Wnt signaling and colorectal carcinogenesis

Abstract

Abstract Aberrant transactivation of a certain set of target genes of T-cell factor-4 (TCF4), a member of the TCF/lymphoid enhancer factor (LEF) family of transcription factors, by Wnt signaling has been considered crucial in colorectal carcinogenesis. Through a comprehensive proteome approach we identified Traf2- and Nck-interacting kinase (TNIK) as a novel activator for TCF4. Here we report the functional involvement of TNIK in Wnt signaling and human colon cancer growth in vitro and in vivo. Methods: Proteins of two colorectal cancer cell lines, HCT-116 and DLD1, were immunoprecipitated with anti-TCF-4 antibody and analyzed directly by nano-flow liquid chromatography and mass spectrometry. Results: TNIK was detected in the immunoprecipitates with anti-TCF4 or anti-β-catenin antibody, but not with control IgG. Conversely, β-catenin and TCF4 proteins were immunoprecipitated with anti-TNIK antibody, indicating that TCF4, β-catenin, and TNIK proteins form a complex in colorectal cancer cells. TCF4 protein was phosphorylated by TNIK, but not by the catalytically inactive mutant of TNIK with substitution (K54R) of the conserved lysine 54 residue in the ATP-binding pocket of the kinase domain. Knockdown of TNIK by siRNA against TNIK suppressed the TCF/LEF transcriptional activity and proliferation of DLD1 and HCT-116 cells. The expression of known target genes of the β-catenin and TCF/LEF complexes, such as axis inhibitor-2 (AXIN2), c-myc (MYC), c-jun (JUN), and matrilysin (MMP7), except for cyclin D1 (CCND1), was significantly reduced by transient transfection with siRNA against TNIK. siRNA targeting TNIK inhibited the growth of tumors produced by injecting colorectal cancer cells subcutaneously into immunodeficient mice, and the growth inhibition was abolished by restoring the catalytic domain of TNIK. Conclusions: Wnt signaling is a major force driving colorectal carcinogenesis. More than 80% of colorectal cancers show mutation of the APC gene, resulting in accumulation of β-catenin and constitutive activation of Wnt signaling. Because restoration of the loss of function resulting from mutation of the APC gene is not a realistic approach, we have been searching for molecules involved in Wnt signaling downstream of APC, especially in the nucleus, that could be potential drug targets. We identified TNIK as the activating kinase of the TCF4 and β-catenin transcriptional complex. Several ATP-competing kinase inhibitors have been applied to cancer treatment and have shown significant activity. A new drug targeting TNIK might be effective for suppressing aberrant Wnt signaling and colorectal cancer growth.