Background: Gastric cancer (GC) is one of the most common aggressive cancers and is characterized by high mortality. Increasing evidence has shown that microRNA-665 (miRNA-665) serves as inhibiting-miRNA in cancers. However, the role of miR-665 in GC is yet unclear.
Methods: miR-665 was first analyzed using bioinformatics. Subsequent quantitative real-time PCR was used to detect miR-665 expression levels in different GC cell lines and tissues. The function of miR-665 in GC cells was determined via Cell Counting Kit 8, colony formation, wound healing, and transwell assays. Furthermore, Western blotting was utilized to measure the expression level of epithelial–mesenchymal transition (EMT)-related proteins. The target prediction and luciferase reporter assays were performed to confirm the binding between miR-665 and 3ʹ-UTR of the CRIM1  gene. In addition, rescue assays were used to determine whether CRIM1  upregulation abolished the inhibitory effect of miR-665.
Results: The expression of miR-665 was significantly decreased in GC patients and GC cell lines. Clinical and pathological analyses showed that the low expression of miR-665 was significantly associated with high TNM stage (P = 0.007), distant metastasis (P = 0.031), and poor differentiation (P = 0.029). Endogenic mimics of miR-665 remarkably suppressed GC cell proliferation, migration, invasion, and EMT in in vitro experiments. Inhibition of miR-665 expression induced the opposite effects. The results of the bioinformatics analysis and dual-luciferase assay showed that miR-665 targeted the 3ʹ-UTR of the CRIM1  gene. Rescue assays revealed that overexpression of CRIM1  attenuated the inhibitory effects of miR-665 in GC progression and EMT.
Conclusion: The overall study results demonstrated that miR-665 inhibits tumor progression and EMT in GC by targeting CRIM1 , indicating that miR-665 might be a potential therapeutic target in the treatment of GC patients.
Keywords: gastric cancer, prognosis, miR-665, CRIM1 , epithelial–mesenchymal transition