MicroRNA-320b promotes colorectal cancer proliferation and invasion by competing with its homologous microRNA-320a.

Colorectal cancer metastasis is believed to be associated with microRNA dysregulation. However, little is known as to how microRNAs regulate colorectal cancer proliferation, invasion and metastasis. In the present study, we compared the microRNA expression profiles between patients of colorectal cancer at diagnosis with and without liver metastasis. MicroRNA-320b was found to be among those up-regulated in the patient group with metastasis. We subsequently found that microRNA-320b, opposite of its homolog, microRNA-320a that differs by only a single nucleotide, functions in promoting colorectal cancer cell proliferation and invasion. Moreover, we found that overexpression of exogenous microRNA-320b can up-regulate the target genes of microRNA-320a including β-catenin, Neuropilin-1 and Rac-1, which are all known to promote tumor proliferation, invasion and metastasis. These results suggest that microRNA-320b may function in competing with microRNA-320a. Thus, our study has proposed one novel mechanism for controlling colorectal cancer proliferation and invasion through homologous competition between microRNAs. This mechanism may be important for colorectal cancer metastasis.