1 Mir-17-5p Regulates Breast Cancer Cell Proliferation by Inhibiting Translation of AIB1 mRNA

2 MicroRNAs are an extensive family of ~22-nucleotide-long noncoding RNAs expressed in a wide range of eukaryotes, including humans, and they are important in development and disease. We found that microRNA Mir-17-5p has extensive complementarity to the mRNA of amplified in breast cancer-1 (AIB1). Cell culture experiments showed that AIB1 expression was downregulated by Mir-17-5p, primarily through translational inhibition. Expression of Mir-17-5p was low in breast cancer cell lines. We also found that downregulation of AIB1 by Mir-17-5p resulted in decreased estrogen receptor-mediated as well as estrogen receptor-independent gene expression and decreased proliferation of breast cancer cells. Mir-17-5p also completely abrogated the IGF-1-mediated, anchorage-independent growth of breast cancer cells. Our results reveal that Mir-17-5p has a role as a tumor suppressor in breast cancer cells. AC