Role and mechanism of circular RNA-vimentin in the proliferation and apoptosis of colorectal cancer cells

Objective To investigate the role and mechanism of circular RNA-vimentin (circ-VIM) in the proliferation and apoptosis of colorectal cancer cells. Methods From December 2016 to December 2017, at Department of General Surgery of The First Affiliated Hospital of Zhengzhou University, the clinical data of 100 patients who underwent radical resection of colorectal cancer and were confirmed by pathological examination after operation were collected. The tumor tissues and corresponding paracancerous tissues (negative control) were also collected. The expression of circ-VIM in the colorectal cancer tissues was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The proliferation of HCT-116 and HT29 colorectal cancer cells was detected by cell counting kit-8 assay. The ratio of apoptosis of HCT-116 and HT29 cells was measured by annexin Ⅴ/propidium iodide double staining assay. The mitochondrial membrane potential of HCT-116 and HT29 cells was examined by 5, 5′, 6, 6′-tetrachloro-1, 1′, 3, 3′-tetraethyl-imidacarbocyanine iodide (JC-1) assay. The expression changes of protein kinase B and mammalian target of rapamycin were tested by Western blotting. The target miRNA of circ-VIM was predicted by miRDB software. T-test and chi-square test were performed for statistical analysis. Results The expression of circ-VIM in colorectal cancer tissues was 2.387±0.536, which was higher than that in corresponding paracancerous tissues (1.110±0.134), and the difference was statistically significant (t=23.096, P<0.01). And the expression levels of circ-VIM were significantly different in patients with different tumor size, TNM stage and lymph node metastasis (all P<0.05). The proliferation of HCT-116 cells and HT29 cells in lenti-circ-VIM group was 0.737±0.023 and 0.835±0.025, respectively, which were both higher than those in control group (0.449±0.020 and 0.531±0.019), and the differences were statistically significant (t=20.706 and -15.374, both P<0.01). The proliferation of HCT-116 cells and HT29 cells in lenti-circ-VIM-shRNA group was 0.236±0.027 and 0.243±0.019, which were lower than those in control group, and the differences were statistically significant (t=24.557 and -23.197, both P<0.01). The ratio of apoptosis of HCT-116 cells and HT29 cells in lenti-circ-VIM-shRNA group was (18.00±1.82)% and (20.80±0.61)%, which was higher than those in control group ((6.64±2.01)% and (7.35±1.36)%), and the differences were statistically significant (t=8.826 and 17.454, both P<0.01). The fluorescence intensity ratio of JC-1 aggregate and JC-1 monomer of HCT-116 cells and HT29 cells in lenti-circ-VIM-shRNA group was 2.21±0.12 and 1.40±0.11, which was lower than those in control group (14.54±1.00 and 9.24±1.18), and the differences were statistically significant (t=-19.558 and -15.685, both P<0.01), which indicated mitochondrial membrane potential decreased. After treated with lenti-circ-VIM-shRNA, the expression of phosphorylated protein kinase B, phosphorylated mammalian target of rapamycin, B-cell lymphoma-2 and mitochondrial cytochrome C at protein level were all down-regulated, however the expression of cytoplasmic cytochrome C, B-cell lymphoma-2 associated X protein and cleaved caspase-3 at protein level were all up-regulated. When the expression of circ-VIM was up-regulated, the expression of miRNA-147b, miRNA-4447 and miRNA-3656 was down-regulated. When the expression of circ-VIM was down-regulated, the expression of miRNA-147b, miRNA-4447 and miRNA-3656 was up-regulated. Conclusion The expression of circ-VIM in colorectal cancer is abnormally increased, which is involved in the proliferation and apoptosis of colorectal cancer cells. Key words: Colorectal neoplasms; Cell proliferation; Apoptosis; circ-VIM