Breast cancer is the most common cancer diagnosed in women. Although there were noteworthy advances in the early diagnosis and treatment during the past several decades, breast cancer still stands as the leading cause of cancer death in women worldwide [1, 2]. The underlying mechanism for breast cancer development and metastasis is far from being completely understood. The high prevalence of this disease calls for more mechanistic insights for the development of new generation diagnostic and therapeutic strategies. Recently (after 2005), there is a growing interest in the roles of a new class of small non-coding RNAs, microRNAs (miRNAs) in breast cancer development [3, 4].
MicroRNAs are ubiquitously expressed small RNAs which exert negative regulatory effects on gene expression at a post-transcriptional level . Given the fact that microRNAs theoretically target any mRNA, it is likely that microRNAs possess a very broad functional spectrum which includes cell cycle regulation, cell growth, apoptosis, cell differentiation and stress response [5–9]. Consistent with this notion, it is no surprise that microRNAs are extensively involved in human cancer development . To date, there are over 1000 miRNAs that have been discovered in human, among which MiR-29 stands as one of the most intriguing miRNA families which may play pivotal roles in cancer biology [8, 11].
Composed of three mature members (MiR-29a, b and c), this family has been shown to be down-regulated in many different types of cancers and have been attributed predominantly tumor-suppressing properties. In lung cancers, MiR-29 family was reported to regulate specific genes associated with tissue invasion and metastasis in lung adenocarcinoma . In hematologic neoplasms, MiRNA-29 expression levels are inversely correlated with prognosis of Mantle cell lymphoma (MCL) . In addition, MiR-29 reduces cell growth and induces apoptosis in primary acute myeloid leukemia (AML) cells and related cell lines . Moreover, it has been reported that by inhibiting MMP2 activity, MiR-29 plays an important inhibitory role in APOBEC3G induced colon cancer migration and invasion . Finally, consistent with the data from studies on other types of cancer, MiR-29 family inhibits ovarian cancer development by targeting DNA methyltransferases 3A and 3B .
Unfortunately, there is relatively lack of information on the role of MiR-29 in breast cancer. Study from JK Richer’s group demonstrated that Mir-29a has an inhibitory role in tumor growth in vivo . However, in another paper, the authors showed that MiR-29a may promote metastasis through facilitating epithelial-to-mesenchymal transition . Thus, the function of Mir-29 in tumorigenesis and metastasis of breast cancer still remains unclear. In the current study, we are endeavored to further elucidate the roles of MiR-29 in breast cancers, which highlights MiR-29 as a potential new biomarker and therapeutic target for breast cancer.