Transmembrane and coiled-coil domain 1 impairs the AKT signaling pathway in urinary bladder urothelial carcinoma: a characterization of a tumor suppressor

Purpose: Urinary bladder urothelial carcinoma (UBUC) is a common malignant disease in developed countries. Cell cycle dysregulation resulting in uncontrolled cell proliferation has been associated with UBUC development. This study aimed to explore the roles of TMCO1 in UBUCs. Experimental Design: Data mining, branched DNA assay, immunohistochemistry, xenograft, cell culture, quantitative RT-PCR, immunoblotting, stable and transient transfection, lentivirus production and stable knockdown, cell cycle, cell viability and proliferation, soft agar, wound healing, transwell migration and invasion, co-immunoprecipitation, immunocytochemistry, AKT serine/threonine kinase (AKT) activity assays and site-directed mutagenesis were used to study TMCO1 involvement in vivo and in vitro. Results: Data mining identified that the TMCO1 transcript was downregulated during the progression of UBUCs. In distinct UBUC-derived cell lines, changes in TMCO1 levels altered the cell-cycle distribution, cell viability, cell proliferation, colony formation and modulated the AKT pathway. TMCO1 recruited the PH domain and leucine rich repeat protein phosphatase 2 (PHLPP2) to dephosphorylate pAKT1(serine 473) (S473). Mutagenesis at S60 of the TMCO1 protein released TMCO1-induced cell cycle arrest and restored the AKT pathway in BFTC905 cells. Stable TMCO1 (wild-type) overexpression suppressed, while T33A and S60A mutants recovered, tumor size in xenograft mice. Conclusions: Clinical associations, xenograft mice and in vitro indications provide solid evidence that the TMCO1 gene is a novel tumor suppressor in UBUCs. TMCO1 dysregulates cell cycle progression via suppression of the AKT pathway, and S60 of the TMCO1 protein is crucial for its tumor suppressor roles.

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