MiRNA-125a-3p is a negative regulator of the RhoA-actomyosin pathway in A549 cells.

MicroRNAs (miRNAs) function as genetic modulators that regulate gene expression, and are, thus, involved in a wide range of biological roles, including tumor cell migration and invasion. MiR-125a-3p is a mature form of miR-125a, derived from the 3'-end of pre-miR-125a. Our group has previously reported that miR-125a-3p functions as a tumor suppressor gene that inhibits the migration and invasion of lung cancer cells. Here, we report the discovery of a new regulatory layer of the RhoA-actomyosin pathway through which miR-125a-3p controls tumor cell migration. Overexpression of miR-125a-3p by transfection of sense‑miR‑125a-3p resulted in decreased RhoA protein levels, while the levels of RhoA mRNA remained constant. The concentrations of both RhoA-GTP protein and actin filaments decreased after miR-125a-3p overexpression in the A549 lung cancer cell line. Conversely, knockdown of miR-125a-3p by transfection of antisense-miR-125a-3p resulted in increased RhoA protein levels while the levels of RhoA mRNA remained unchanged. However, the concentration of both RhoA-GTP protein and actin filaments increased. To further demonstrate that RhoA is a potential target of miR‑125a-3p, luciferase reporter constructs containing the RhoA 3'UTR demonstrated reduced reporter activity after ectopic expression of miR-125a-3p. Moreover, luciferase reporter constructs containing the RhoA 3'UTR mutant did not show significantly changed reporter activity. Furthermore, A549 cells demonstrated reduced migratory capacity after treatment with the Rho inhibitor CT04. Our results indicate that the loss of miR-125a‑3p-controlled regulation of the RhoA-actomyosin pathway can lead to increased migration of tumor cells because of the upregulation of RhoA expression. In particular, an increased intracellular concentration of RhoA-GTP protein in A549 cells leads to the accumulation of actin filaments. These results provide new insights into the role of the miR-125a family in lung cancer.