MicroRNA-200b targets protein kinase Cα and suppresses triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with poor prognosis and lacks effective targeted therapies. The microRNA-200 (miR-200) family is found to inhibit or promote breast cancer metastasis; however, the underlying mechanism is not well understood. This study was performed to investigate the effect and mechanism of miR-200b on TNBC metastasis and identify targets for developing more efficient treatment for TNBC. We found that miR-200 family expression levels are significantly lower in highly migratory TNBC cells and metastatic TNBC tumors than other types of breast cancer cells and tumors. Ectopically expressing a single member (miR-200b) of the miR-200 family drastically reduces TNBC cell migration and inhibits tumor metastasis in an orthotopic mouse mammary xenograft tumor model. We identified protein kinase C alpha (PKC alpha) as a new direct target of miR-200b and found that PKC alpha protein levels are inversely correlated with miR-200b levels in 12 kinds of breast cancer cells. Inhibiting PKC alpha activity or knocking down PKC alpha levels significantly reduces TNBC cell migration. In contrast, forced expression of PKC alpha impairs the inhibitory effect of miR-200b on cell migration and tumor metastasis. Further mechanistic studies revealed that PKC alpha downregulation by miR-200b results in a significant decrease of Rac1 activation in TNBC cells. These results show that loss of miR-200b expression plays a crucial role in TNBC aggressiveness and that miR-200b suppresses TNBC cell migration and tumor metastasis by targeting PKC alpha. Our findings suggest that miR-200b and PKC alpha may serve as promising therapeutic targets for metastatic TNBC.