The inhibitory role of Mir-29 in growth of breast cancer cells.

Mir-29 microRNA families are involved in regulation of various types of cancers. Although Mir-29 was shown to play an inhibitory role in tumorigenesis, the role of Mir-29 in breast cancer still remains obscure. In this study, we showed that Mir-29a is the dominant isoform in its family in mammary cells and expression of Mir-29a was down-regulated in different types of breast cancers. Furthermore, over-expression of Mir-29a resulted in significant slower growth of breast cancer cells and caused higher percentage of cells at G0/G1 phase. Consistent with this over-expression data, knockdown of Mir-29a in normal mammary cells lead to higher cell growth rate, and higher percentage of cells entering S phase. We further found that Mir-29a negatively regulated expression of B-Myb, which is a transcription factor associated with tumorigenesis. The protein levels of Cyclin A2 and D1 are consistent with the protein level of B-Myb. Taken together, our data suggests Mir-29a plays an important role in inhibiting growth of breast cancer cells and arresting cells at G0/G1 phase. Our data also suggests that Mir-29a may suppress tumor growth through down-regulating B-Myb.