Tumor Suppressive Role of ARHGAP17 in Colon Cancer Through Wnt/β-Catenin Signaling.

BACKGROUND/AIMS: A few Rho GTPase activating proteins (RhoGAPs) have been identified as tumor suppressors in a variety of human cancers. ARHGAP17, a member of RhoGAPs, has been reported to be involved in the maintenance of tight junction and epithelial barrier. The present study aimed to explore its expression in colon cancer and the possible function in colonic carcinogenesis.

METHODS: The mRNA and protein expression was assessed by realtime PCR and immunoblotting, respectively. Cell Counting Kit-8 (CCK-8) and Transwell assays were performed to evaluate cell proliferation and invasion, respectively.

RESULTS: We found that ARHGAP17 expression was obviously lower in colon cancer specimens than in normal colonic mucosa. ARHGAP17 expression was associated with tumor stage, size and differentiation. In vitro analysis demonstrated that ARHGAP17 overexpression inhibited cell growth and invasion of HCT-8 and HCT-116 cells. In addition, an in vivo experimental metastasis model showed that ARHGAP17 overexpression restricted cancer metastasis to the lung. Mechanically, we found that Wnt signaling contributed to the functions of ARHGAP17 in colon cancer cells. Gene set enrichment analysis (GSEA) in The Cancer Genome Atlas dataset showed that the Wnt signaling pathway was negatively associated with ARHGAP17 expression. The mRNA expression of β-catenin (an important signaling transducer of canonical Wnt signaling) gene (CTNNB1) was negatively correlated with ARHGAP17 expression. Immunoblot analysis of downstream effectors of β-catenin (c-Myc/p27 and MMP7) in ARHGAP17 overexpressing colon cancer cells and metastatic tumors within the lung also validated the GSEA result. ARHGAP17 overexpression increased the phosphorylation of glycogen synthetase kinase 3β, and decreased β-catenin nuclear localization and transcriptional activity. Furthermore, inhibition of Wnt signaling by Wnt Inhibitor Factor-1 (WIF-1) in HIEC cells with ARHGAP17 knockdown significantly attenuated the promotion effects of ARHGAP17 knockdown on cell proliferation, invasion and the activation of β-catenin.

CONCLUSION: these results suggest that ARHGAP17 might serve as a tumor suppressor in colon cancer progression and metastasis through Wnt/β-catenin signaling pathway.