MicroRNA 21 (miR-21) - Function, Cancer & Biomarker
MicroRNA 21 (miR-21) is a small non-coding RNA molecule that regulates gene expression and plays a key role in cancer, inflammation, and cardiovascular disease.
Things worth knowing about "MicroRNA 21"
MicroRNA 21 (miR-21) is a small non-coding RNA molecule that regulates gene expression and plays a key role in cancer, inflammation, and cardiovascular disease.
What is MicroRNA 21?
MicroRNA 21 (abbreviated miR-21) is a small, non-coding ribonucleic acid (RNA) molecule approximately 22 nucleotides in length. It belongs to the family of microRNAs (miRNAs), a class of regulatory RNA molecules that do not encode proteins but instead control the activity of other genes. miR-21 is one of the most extensively studied and best-characterized microRNA molecules in the human body.
MicroRNAs such as miR-21 bind to the 3' untranslated region (3'-UTR) of messenger RNA (mRNA) molecules, thereby inhibiting the translation of these mRNAs into proteins or promoting their degradation. In this way, a single miRNA molecule can influence the expression of hundreds of different target genes.
Biological Function
miR-21 is expressed in virtually all human tissues and plays central regulatory roles in several cellular processes:
- Cell proliferation: miR-21 promotes cell growth by silencing tumor suppressor genes.
- Apoptosis: By inhibiting pro-apoptotic genes, miR-21 can suppress programmed cell death.
- Cell migration and invasion: miR-21 influences the ability of cells to migrate, which is relevant to cancer metastasis.
- Inflammation regulation: miR-21 modulates inflammatory signaling pathways, including the NF-κB pathway.
- Fibrosis: miR-21 plays a role in excessive connective tissue formation (fibrosis) in various organs.
Role in Disease
Cancer (Oncology)
miR-21 is the only microRNA molecule found to be overexpressed in virtually all cancer types studied to date. For this reason, it is referred to as an oncomiR. Key target genes of miR-21 include well-known tumor suppressors such as PTEN, PDCD4, and RECK. By silencing these genes, miR-21 promotes tumor growth, metastasis, and resistance to chemotherapy. Elevated miR-21 expression has been demonstrated in numerous cancer types, including:
- Breast cancer
- Lung cancer
- Colorectal cancer
- Pancreatic cancer
- Gastric (stomach) cancer
- Hepatocellular carcinoma (liver cancer)
- Glioblastoma (brain tumor)
Cardiovascular Disease
miR-21 is involved in the development and progression of several heart conditions. It influences cardiac fibrosis -- the scarring of heart tissue -- as well as hypertrophy (enlargement) of the heart muscle. Studies have shown that miR-21 is upregulated in cardiac tissue following myocardial infarction (heart attack) and contributes to structural remodeling of the heart (cardiac remodeling).
Inflammatory Diseases
Through its role in regulating inflammatory signaling pathways, miR-21 is also relevant to chronic inflammatory conditions, including rheumatoid arthritis, inflammatory bowel diseases, and various forms of organ fibrosis (e.g., pulmonary fibrosis, renal fibrosis).
Kidney Disease
miR-21 is overexpressed in chronic kidney disease and promotes renal fibrosis, contributing to the progressive loss of kidney function.
Diagnostic Significance as a Biomarker
miR-21 is detectable in blood, urine, and other body fluids, making it a promising liquid biopsy biomarker. Elevated miR-21 levels in blood serum may indicate the presence of certain malignancies and are being investigated as a potential diagnostic and prognostic marker. When found circulating freely in the bloodstream or packaged within exosomes, it is referred to as circulating miR-21.
- Diagnosis: Elevated miR-21 levels may provide early indication of cancer.
- Prognosis: High miR-21 expression is associated with a worse clinical outcome and shorter survival in various cancers.
- Treatment response: Changes in miR-21 levels may serve as indicators of response to or failure of cancer therapy.
Therapeutic Approaches
Given its central role in so many pathological processes, miR-21 is an attractive target for novel therapeutic strategies. Several approaches are currently under investigation:
- Antagomirs: Synthetic, chemically modified oligonucleotides designed to specifically inhibit miR-21 (anti-miR-21 strategies).
- miRNA sponges: Artificial RNA constructs that sequester miR-21 and neutralize its activity.
- Nanoparticle-based drug delivery: Delivery of miR-21 inhibitors directly into tumor cells via nanocarriers.
Most of these approaches are still in the preclinical or early clinical research stage.
References
- Iorio, M. V. & Croce, C. M. (2012). MicroRNA dysregulation in cancer: diagnostics, monitoring and therapeutics. A comprehensive review. EMBO Molecular Medicine, 4(3), 143-159. DOI: 10.1002/emmm.201100209
- Dong, H. et al. (2013). MicroRNA: function, detection, and bioanalysis. Chemical Reviews, 113(8), 6207-6233. DOI: 10.1021/cr300362f
- Kumarswamy, R., Volkmann, I. & Thum, T. (2011). Regulation and function of miRNA-21 in health and disease. RNA Biology, 8(5), 706-713. DOI: 10.4161/rna.8.5.16154
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