[Clinical significance and mechanism of TBX5 gene in colorectal cancer]

Objective: To examine the expression of T-box5 (TBX5) in colorectal cancer tissues and its clinical significance, and explore the effects of TBX5 on the invasion and metastasis of colorectal cancer cells and its mechanism. Methods: The expressions of TBX5 in cancer and adjacent normal tissues were tested by immunohistochemistry (IHC), and the relationship between TBX5 and clinicopathological features and prognosis of colorectal cancer was analyzed. Real-time quantitative PCR (RT-qPCR) and western blot were used to detect the expressions of TBX5 in different colorectal cancer cell lines. TBX5 overexpression plasmid was constructed and transfected into human colorectal cancer cell line HT-29, and cell counting kit-8 (CCK-8) was used to detect the activities of transfection HT-29 cells. Cell scratch test and Transwell assay were used to detect the migration and invasion abilities of cells, while RT-qPCR and western blot were used to detect the mRNA and protein expressions of PCNA, p21, p16, p27, MMP-2, MMP-7 and TIMP-1. Results: The positive rate of TBX5 protein in colorectal cancer tissues was 24.44% (22/90), significantly lower than 65.56% of adjacent normal tissues (P<0.001). The expression of TBX5 was significantly related to lymph node metastasis, depth of invasion and nerve invasion (P<0.05). The survival period of 22 patients with positive TBX5 expression was (60.2±2.4) months, better than (44.3±2.8) months of 68 patients with negative TBX5 expression (P<0.05). Among human colon cancer cell lines of HT29, SW620, SW480, LOVO and HCT116, the expression of TBX5 in HT29 cells was the weakest. After transfection, the expression of TBX5 in transfection group was significantly higher than those in control group and blank group (P=0.043 and P<0.001). Cell viability in transfection group was significantly lower than those in control group and blank group (both P<0.001). The ratio of cells in G(0)/G(1) phase was increased (P=0.009), while in G(2)/M phase was decreased (P<0.001). Cells' abilities of migration and invasion in transfection group were also significantly decreased (both P<0.001). Overexpression of TBX5 downregulated the expressions of PCNA, MMP-2 and MMP-7, while upregulated the expressions of p21, p16, p27 (P<0.05 for all). TBX5 had marginal effect on the expression of TIMP-1 (P>0.05). Conclusions: Downregulation of TBX5 is a marker of poor prognosis in patients with colorectal cancer. TBX5 may inhibit the progression of colorectal cancer by inhibiting proliferation, invasion and metastasis related genes.