Upregulation of SNTB1 Correlates with Poor Prognosis and Promotes Cell Growth in Colorectal Cancer

Abstract

\n Background: Colorectal cancer (CRC) is one of the most highly malignant tumors and has a complicated pathogenesis. A preliminary study identified syntrophin beta 1 (SNTB1) as a potential oncogene in CRC. However, the clinical significance, biological function, and underlying mechanisms of SNTB1 in CRC are unknown. Thus, the present study aimed to investigate the function of SNTB1 in CRC.Methods: The expression profile of SNTB1 in CRC samples was evaluated by database analysis, cDNA array, tissue microarray, Quantitative real-time PCR (qPCR), and immunohistochemistry. SNTB1 expression in human CRC cells was silenced using short hairpin RNAs and its mRNA and protein levels were assessed by qPCR and western blotting, respectively. Cell proliferation, colony formation, cell cycle and apoptosis were determined by the cell counting, colony formation, and flow cytometry assays, respectively. A xenograft nude mouse model of CRC was established for validating the roles of SNTB1 in vivo. Immunohistochemistry was used to score the expression of SNTB1 in tissue samples. The isobaric tags for relative and absolute quantification (iTRAQ) was used to analyze the differentially expressed proteins after knockdown of SNTB1 in CRC cells.Results: SNTB1 expression was increased in CRC tissue compared with adjacent noncancerous tissues and the increased expression was associated with shorter overall survival of CRC patients. Silencing of SNTB1 suppressed cell viability and survival, induced cell cycle arrest and apoptosis in vitro, and inhibited the growth of CRC cells in vivo. Further elucidation of the regulation of STNB on CRC growth by iTRAQ analysis identified 210 up-regulated and 55 down-regulated proteins in CRC cells after SNTB knockdown. A PPI network analysis identified protein kinase N2 (PKN2) as a hub protein and was up-regulated in CRC cells after SNTB1 knockdown. Western-blot analysis further confirmed that SNTB1 knockdown significantly up-regulated PKN2 protein expression in CRC cells and decreased the phosphorylation of both ERK1/2 and AKT. Conclusion: These findings indicate that SNTB1 is overexpressed in CRC. Elevated SNTB1 levels are correlated with shorter patient survival. Importantly, SNTB1 promoted tumor growth and progression of CRC, possibly by reducing the expression of PKN2 and activating the ERK and AKT signaling pathway. Our study highlights the potential of SNTB1 as a new prognostic predictor and therapeutic target for CRC.