Alteration in the expression of microRNA-21 regulated target genes: Role in breast cancer

Breast cancer, also recognized as the principal cause of cancer-related deaths among women, is the second most familiar and prevalent form of cancer. New diagnostic and prognostic biomarkers that are highly specific are urgently needed for its early prognosis. MicroRNAs (miRNAs), a class of non-coding RNAs, are known to control the biological processes involving transcription, post-transcriptional and covalent modifications, splicing, translation, cell differentiation, proliferation, apoptosis, cancer progression, and invasion. Any dysregulation in miRNA expression, demonstrating their oncogenic and tumor-suppressive functions, contributes to cancer progression. MicroRNA-21 (miR-21), an 'onco-miR' in breast cancer, is involved in tumor progression and metastasis by suppressing the activity of the target gene via its interaction with the 3'UTR of the target gene. The upregulation of miR-21 is observed in many instances of breast cancer. Our review aims to summarize the current understanding of miR-21 in the regulation of important cellular functions via regulation of its target genes. We discuss its biosynthesis, oncogenic function in breast cancer, and different methods used for its detection. This will increase the current understanding of the role of miR-21 in breast cancer tumorigenesis, which will offer a perception of using miR-21 as an early detection molecular prognostic and diagnostic biomarker and as a therapeutic target in breast cancer care.