MiR-221 promotes trastuzumab-resistance and metastasis in HER2-positive breast cancers by targeting PTEN

HER2-overexpressing breast cancers are characterized by frequent distant metastasis and often develop resistance after short-term effective treatment with the monoclonal antibody drug, trastuzumab. Here, we found that the oncogenic miRNA, miR-221, inhibited apoptosis, induced trastuzumab resistance and promoted metastasis of HER2-positive breast cancers. The tumor suppressor PTEN was identified as a miR-221 target; overexpression of PTEN abrogated the aforementioned miR-221-induced malignant phenotypes of the cells. These findings indicate that miR-221 may promote trastuzumab resistance and metastasis of HER2-positive breast cancers by targeting PTEN, suggesting its role as a potential biomarker for progression and poor prognosis, and as a novel target for trastuzumab-combined treatment of breast cancers. [BMB Reports 2014; 47(5): 268-273].