[Hsa_circ_0000670 promoted the progression of gastric cancer through the miR-515-5p/SIX1 molecular axis]

Objective: To explore whether hsa_circ_0000670 promotes the progression of gastric cancer by regulating the miR-515-5p/SIX1 molecular axis. Methods: The gastric cancer and adjacent normal tissues of 35 gastric cancer patients admitted to Rugao Hospital Affiliated to Nantong University from 2014 to 2015 were collected. The expression levels of circ_0000670, miR-515-5p and Sine oculis homeobox 1 (SIX1) in gastric cancer tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The correlations between circ_0000670 and miR-515-5p, miR-515-5p and SIX1, circ_0000670 and SIX1 were analyzed by the Pearson method. Patients were divided into low circ_0000670 expression group (17 cases) and high circ_0000670 expression group (18 cases) based on the median of circ_0000670 expression level, and Kaplan-Meier was used to analyze the 5-year survival of patients. Cell proliferation was assessed via clone formation assay. Cell cycle and apoptosis were detected by flow cytometry. Wound healing and Transwell assays were used to detect cell migration and invasion ability. The targeting relationship between miR-515-5p and circ_0000670 or SIX1 was confirmed by the dual luciferase reporter assay. Nude mice were injected into HGC-27 cells transfected with sh-NC or sh-circ_0000670, and the volume and weight of the transplanted tumor were measured, also, the levels of circ_0000670, miR-515-5p and SIX1 in the transplanted tumor tissue were detected. Results: The expression levels of circ_0000670 and SIX1 in gastric cancer tissues and cell lines were significantly increased (P<0.05), while the expression levels of miR-515-5p were significantly decreased (P<0.05). The survival rate of patients in the low circ_0000670 expression group (82.4%) was significantly higher than that in the high circ_0000670 expression group (28.7%, P=0.034). Circ_0000670 was negatively correlated with miR-515-5p (r=-0.846, P<0.001), and miR-515-5p was negatively correlated with SIX1 (r=-0.615, P<0.001), but circ_0000670 was positively correlated with SIX1 (r=0.814, P<0.001). Transfection of si-circ_0000670 or miR-515-5p mimic could significantly reduce the number of clone-forming cells, migration distance, migration and invasion cells (P<0.05), and increase the ratio of G(0)/G(1) phase cells, apoptosis rate and the protein level of E-cadherin (P<0.05), decreased the proportion of S-phase cells and the protein level of Vimentin (P<0.05). The dual luciferase report assay confirmed that circ_0000670 could target miR-515-5p, and miR-515-5p could bind to SIX1. Co-transfection of si-circ_0000670 and miR-515-5p inhibitor could significantly attenuate the effects of si-circ_0000670 on cell proliferation, migration, invasion, cell cycle and apoptosis (P<0.05). Co-transfection of miR-515-5p mimic and pcDNA-SIX1 could significantly reduce the effects of miR-515-5p mimic on cell proliferation, migration, invasion, cell cycle and apoptosis (P<0.05). Compared with the sh-NC group [volume=(596.20±125.46) mm(3) and weight=(538.00±114.39) g], the volume and weight of transplanted tumors in the sh-circ_0000670 group [volume=(299.20±47.58) mm 3 and weight=(289.80±48.73 g)] were significantly reduced (P<0.05), the expression levels of circ_0000670 and SIX1 were significantly reduced (P<0.05), and the expression level of miR-515-5p was significantly increased (P<0.05). Conclusion: Knockdown of circ_0000670 could inhibit cell proliferation, migration, invasion of gastric cancer cells, induce cell cycle arrest in G(0)/G(1) phase and promote cell apoptosis by regulating the miR-515-5p/SIX1 axis.