microRNA 21 also known as hsa-mir-21 or miRNA21 is a mammalian microRNA that is encoded by the MIR21gene.[1]
MIRN21 was one of the first mammalian microRNAs identified. The mature miR-21 sequence is strongly conserved throughout evolution. The human microRNA-21 gene is located on plus strand of chromosome 17q23.2 (55273409–55273480) within a coding gene TMEM49 (also called vacuole membrane protein). Despite being located in intronic regions of a coding gene in the direction of transcription, it has its own promoter regions and forms a ~3433-nt long primary transcript of miR-21 (known as pri-miR-21) which is independently transcribed. The stem–loop precursor of miR-21(pre-miR-21) resides between nucleotides 2445 and 2516 of pri-miR-21.
Gene ID: 406991: "microRNAs (miRNAs) are short (20-24 nt) non-coding RNAs that are involved in post-transcriptional regulation of gene expression in multicellular organisms by affecting both the stability and translation of mRNAs. miRNAs are transcribed by RNA polymerase II as part of capped and polyadenylated primary transcripts (pri-miRNAs) that can be either protein-coding or non-coding. The primary transcript is cleaved by the Drosha ribonuclease III enzyme to produce an approximately 70-nt stem-loop precursor miRNA (pre-miRNA), which is further cleaved by the cytoplasmic Dicer ribonuclease to generate the mature miRNA and antisense miRNA star (miRNA*) products. The mature miRNA is incorporated into a RNA-induced silencing complex (RISC), which recognizes target mRNAs through imperfect base pairing with the miRNA and most commonly results in translational inhibition or destabilization of the target mRNA."[2]
Mature miR-21
Pri-miR-21 is cut by the endonuclease Drosha in the nucleus to produce pre-miR-21, which is exported into the cytosol. This pre-miR-21 is then cut into a short RNA duplex by Dicer in the cytosol. Although abundance of both strands is equal by transcription, only one strand (miR-21) is selected for processing as mature microRNA based on the thermodynamic stability of each end of the duplex, while the other strand (designated with an asterisk; miR-21*) is generally degraded. Mature microRNA is then loaded into microRNA ribonucleoprotein complex RISC (RNA-induced silencing complex) and guided to target mRNAs with near perfect complimentarily at 3’UTR.
Targets
A number of targets for microRNA-21 have been experimentally validated and most of them are tumor suppressors, Notable targets include:
miR-21 is one of the most frequently upregulated miRNAs in solid tumours, and its high levels were first described in B cell lymphomas. Overall, miR-21 is considered to be a typical 'onco-miR', which acts by inhibiting the expression of phosphatases, which limit the activity of signalling pathways such as AKT and MAPK.
As most of the targets of miR-21 are tumor suppressors, miR-21 is associated with a wide variety of cancers including that of breast,[19]ovaries,[20]cervix,[21]colon,[11]lung,[22]liver,[12]brain,[23]esophagus,[24]prostate,[22]pancreas,[22] and thyroid.[25] A 2014 meta-analysis of 36 studies evaluated circulating miR-21 as a biomarker of various carinomas, finding it has potential as a tool for early diagnosis.[26] miR-21 expression was associated with survival in 53 triple negative breast cancer patients.[27] Moreover, it has been demonstrated as an independent prognostic factor in patients with pancreatic neuroendocrine neoplasms.[28]
Cardiac disease
miR-21 has been shown to play important role in development of heart disease. It is one of the microRNAs whose expression is increased in failing murine and human hearts.[17][29] Further, inhibition of microRNAs in mice using chemically modified and cholesterol-conjugated miRNA inhibitors (antagomirs) was shown to inhibit interstitial fibrosis and improve cardiac function in a pressure- overload cardiac disease mice model.[17] Surprisingly, miR-21 global knock-out mice did not show any overt phenotype when compared with wild type mice with respect to cardiac stress response. Similarly, short (8-nt) oligonucleotides designed to inhibit miR-21 could not inhibit cardiac hypertrophy or fibrosis.[30] In another study with a mouse model of acute myocardial infarction, miR-21 expression was found to be significantly lower in infarcted areas and overexpression of miR-21 in those mice via adenovirus-mediated gene transfer decreased myocardial infarct size.[31]
miR-21 has been hypothesized to be an intermediary in the effects of air pollution that lead to endothelial dysfunction and eventually to cardiac disease. Expression of miR-21 is negatively associated with exposure to PM10 air pollution and may mediate its effect on small blood vessels.[32]
References
↑Lagos-Quintana M, Rauhut R, Lendeckel W, Tuschl T (Oct 2001). "Identification of novel genes coding for small expressed RNAs". Science. 294 (5543): 853–8. doi:10.1126/science.1064921. PMID11679670.
↑RefSeq (September 2009). "MIR21 microRNA 21 [ Homo sapiens (human) ]". 8600 Rockville Pike, Bethesda MD, 20894 USA: National Center for Biotechnology Information, U.S. National Library of Medicine. Retrieved 23 November 2019.
↑Liu M, Wu H, Liu T, Li Y, Wang F, Wan H, Li X, Tang H (Jul 2009). "Regulation of the cell cycle gene, BTG2, by miR-21 in human laryngeal carcinoma". Cell Research. 19 (7): 828–37. doi:10.1038/cr.2009.72. PMID19546886.
↑Zheng J, Xue H, Wang T, Jiang Y, Liu B, Li J, Liu Y, Wang W, Zhang B, Sun M (Mar 2011). "miR-21 downregulates the tumor suppressor P12 CDK2AP1 and stimulates cell proliferation and invasion". Journal of Cellular Biochemistry. 112 (3): 872–80. doi:10.1002/jcb.22995. PMID21328460.
↑ 6.06.16.2Papagiannakopoulos T, Shapiro A, Kosik KS (Oct 2008). "MicroRNA-21 targets a network of key tumor-suppressive pathways in glioblastoma cells". Cancer Research. 68 (19): 8164–72. doi:10.1158/0008-5472.CAN-08-1305. PMID18829576.
↑Iorio MV, Ferracin M, Liu CG, Veronese A, Spizzo R, Sabbioni S, Magri E, Pedriali M, Fabbri M, Campiglio M, Ménard S, Palazzo JP, Rosenberg A, Musiani P, Volinia S, Nenci I, Calin GA, Querzoli P, Negrini M, Croce CM (Aug 2005). "MicroRNA gene expression deregulation in human breast cancer". Cancer Research. 65 (16): 7065–70. doi:10.1158/0008-5472.CAN-05-1783. PMID16103053.
↑Iorio MV, Visone R, Di Leva G, Donati V, Petrocca F, Casalini P, Taccioli C, Volinia S, Liu CG, Alder H, Calin GA, Ménard S, Croce CM (Sep 2007). "MicroRNA signatures in human ovarian cancer". Cancer Research. 67 (18): 8699–707. doi:10.1158/0008-5472.CAN-07-1936. PMID17875710.
↑Lui WO, Pourmand N, Patterson BK, Fire A (Jul 2007). "Patterns of known and novel small RNAs in human cervical cancer". Cancer Research. 67 (13): 6031–43. doi:10.1158/0008-5472.CAN-06-0561. PMID17616659.
↑Chan JA, Krichevsky AM, Kosik KS (Jul 2005). "MicroRNA-21 is an antiapoptotic factor in human glioblastoma cells". Cancer Research. 65 (14): 6029–33. doi:10.1158/0008-5472.CAN-05-0137. PMID16024602.
↑Tetzlaff MT, Liu A, Xu X, Master SR, Baldwin DA, Tobias JW, Livolsi VA, Baloch ZW (2007). "Differential expression of miRNAs in papillary thyroid carcinoma compared to multinodular goiter using formalin fixed paraffin embedded tissues". Endocrine Pathology. 18 (3): 163–73. doi:10.1007/s12022-007-0023-7. PMID18058265.
↑Wu K, Li L, Li S (Mar 2015). "Circulating microRNA-21 as a biomarker for the detection of various carcinomas: an updated meta-analysis based on 36 studies". Tumour Biology. 36 (3): 1973–81. doi:10.1007/s13277-014-2803-2. PMID25527152.
↑Lánczky, András; Nagy, Ádám; Bottai, Giulia; Munkácsy, Gyöngyi; Szabó, András; Santarpia, Libero; Győrffy, Balázs (2016-12-01). "miRpower: a web-tool to validate survival-associated miRNAs utilizing expression data from 2178 breast cancer patients". Breast Cancer Research and Treatment. 160 (3): 439–446. doi:10.1007/s10549-016-4013-7. ISSN1573-7217. PMID27744485.
↑Louwies T, Vuegen C, Panis LI, Cox B, Vrijens K, Nawrot TS, De Boever P (2016). "miRNA expression profiles and retinal blood vessel calibers are associated with short-term particulate matter air pollution exposure". Environmental Research. 147: 24–31. doi:10.1016/j.envres.2016.01.027. PMID26836502.
Further reading
Cardin S, Guasch E, Luo X, Naud P, Le Quang K, Shi Y, Tardif JC, Comtois P, Nattel S (Oct 2012). "Role for MicroRNA-21 in atrial profibrillatory fibrotic remodeling associated with experimental postinfarction heart failure". Circulation: Arrhythmia and Electrophysiology. 5 (5): 1027–35. doi:10.1161/CIRCEP.112.973214. PMID22923342.
Zhong Z, Dong Z, Yang L, Gong Z (Oct 2012). "miR-21 induces cell cycle at S phase and modulates cell proliferation by down-regulating hMSH2 in lung cancer". Journal of Cancer Research and Clinical Oncology. 138 (10): 1781–8. doi:10.1007/s00432-012-1287-y. PMID22806311.