Comprehensive Mass Spectrometry Analysis Identifies a Novel Therapeutic Target in the Wnt Signaling Pathway

Abstract

The great majority of colorectal cancers carry somatic mutations in one of two genes involved in the canonical Wnt/β-catenin signaling pathway: the adenomatous polyposis coli (APC) and β-catenin (CTNNB1) genes. Either type of genetic alteration results in accumulation of β-catenin and mimics the activation of Wnt signaling. Numerous attempts have therefore been made to develop therapeutics targeting the Wnt/β-catenin pathway. In colorectal cancer, however, due to the genetic inactivation of APC, only the molecules downstream of APC can be considered as therapeutic targets. We have therefore been searching for druggable target molecules downstream of APC, especially in the nucleus. We examined nuclear proteins of colorectal cancer cell lines immunoprecipitated with anti-TCF-4 or anti-β-catenin antibody by mass spectrometry and identified Traf2- and Nck-interacting kinase (TNIK) as an essential regulator of the TCF-4 or anti-β-catenin transcriptional complex. TNIK phosphorylated the conserved serine 154 residue of TCF4. Small interfering RNA (siRNA) targeting TNIK inhibited the proliferation of colorectal cancer cells and the growth of tumors produced by injecting colorectal cancer cells subcutaneously into immunodeficient mice. Several ATP-competing kinase inhibitors have been applied to cancer treatment and have shown significant activity. TNIK regulates Wnt signaling in the most downstream part of the pathway, and its inhibition is expected to block the signal even in colorectal cancer cells with APC gene mutation. TNIK is considered to be a feasible target of pharmacological intervention for manipulation of the aberrant Wnt signaling pathway in colorectal cancer.