Cyclin-A2 is a protein that in humans is encoded by the CCNA2gene.[1] It is one of the two types of cyclin A: cyclin A1 is expressed during meiosis and embryogenesis while cyclin A2 is expressed in dividing somatic cells.[2]
Cyclin A2 belongs to the cyclin family, whose members regulate cell cycle progression by interacting with CDK kinases. Cyclin A2 is unique in that it can activate two different CDK kinases; it binds CDK2 during S phase, and CDK1 during the transition from G2 to M phase.[3]
Cyclin A2 is synthesized at the onset of S phase and localizes to the nucleus, where the cyclin A2-CDK2 complex is implicated in the initiation and progression of DNA synthesis. Phosphorylation of CDC6 and MCM4 by the cyclin A2-CDK2 complex prevents re-replication of DNA during the cell cycle.[2]
Cyclin A2 is involved in the G2/M transition but it cannot independently form a maturation promoting factor (MPF).[4] Recent studies have shown that the cyclin A2-CDK1 complex triggers cyclin B1-CDK1 activation which results in chromatin condensation and the breakdown of the nuclear envelope.[5]
The levels of cyclin A2 are tightly synchronized with the progression of the cell cycle.[6] Transcription initiates in late G1, peaks and plateaus in mid-S, and declines in G2.[6][2]
Cyclin A2 transcription is mostly regulated by the transcription factor E2F and begins in G1, after the R point.[6][2] Absence of cyclin A2 before the R point is due to the E2F inhibition by hypophosphorylated retinoblastoma protein (pRb). After the R point, pRb is phosphorylated and can no longer bind E2F, leading to cyclin A2 transcription.[7][8] The cyclin A2-CDK2 complex eventually phosphorylates E2F, turning off cyclin A2 transcription.[6] E2F promotes cyclin A2 transcription by de-repressing the promoter.[6][7]
Cyclin A2 (Ccna2) is a key protein involved in the direction of mammalian cardiac myocytes to grow and divide, and has been shown to induce cardiac repair following myocardial infarction.[17] Normally, Ccna2 is silenced postnatally in mammalian cardiac myocytes. Because of this gene silencing, adult heart muscle cells cannot divide readily to repair and regenerate after a heart attack.[17]
Ccna2 has been found to induce cardiac repair in small-animal models following myocardial infarction.[17] Preclinical trials involving injections of adenovirus which contained the Ccna2 gene into infarcted porcine (pig) hearts has shown to be protective of MI in pig hearts.[17] Ccna2 mediated cardiac repair showed both a decrease in fibrosis in the peri-infarct tissue and a greater number of cardiomyocytes at the sites of injection.[17] Delivery of Ccna2 into cardiac tissue invokes a regenerative response and markedly enhances cardiac function.[17][18][19]
Increased expression of cyclin A2 has been observed in many types of cancer such as breast, cervical, liver, and lung among others.[2][20][21][22][23] While it is not clear whether increased expression of cyclin A2 is a cause or result of tumorigenesis, it is indicative of prognostic values such as predictions of survival or relapse.[2]
Overexpression of cyclin A2 in mammalian cells can result in the delayed onset of metaphase and anaphase.[24] It is also possible that cyclin A2-CDK contributes to tumorigenesis by the phosphorylation of oncoproteins or tumor suppressors like p53.[25]
↑ 7.07.1Woo RA, Poon RY (Jul–Aug 2003). "Cyclin-dependent kinases and S phase control in mammalian cells". Cell Cycle. 2 (4): 316–24. doi:10.4161/cc.2.4.468. PMID12851482.
↑Henneke G, Koundrioukoff S, Hübscher U (July 2003). "Phosphorylation of human Fen1 by cyclin-dependent kinase modulates its role in replication fork regulation". Oncogene. 22 (28): 4301–13. doi:10.1038/sj.onc.1206606. PMID12853968.
↑Ohtoshi A, Maeda T, Higashi H, Ashizawa S, Yamada M, Hatakeyama M (January 2000). "beta3-endonexin as a novel inhibitor of cyclin A-associated kinase". Biochem. Biophys. Res. Commun. 267 (3): 947–52. doi:10.1006/bbrc.1999.2007. PMID10673397.
↑Joaquin M, Bessa M, Saville MK, Watson RJ (November 2002). "B-Myb overcomes a p107-mediated cell proliferation block by interacting with an N-terminal domain of p107". Oncogene. 21 (52): 7923–32. doi:10.1038/sj.onc.1206001. PMID12439743.
↑Rosner M, Hengstschläger M (November 2004). "Tuberin binds p27 and negatively regulates its interaction with the SCF component Skp2". J. Biol. Chem. 279 (47): 48707–15. doi:10.1074/jbc.M405528200. PMID15355997.
↑Marti A, Wirbelauer C, Scheffner M, Krek W (May 1999). "Interaction between ubiquitin-protein ligase SCFSKP2 and E2F-1 underlies the regulation of E2F-1 degradation". Nat. Cell Biol. 1 (1): 14–9. doi:10.1038/8984. PMID10559858.
↑ 17.017.117.217.317.417.5Shapiro SD, Ranjan AK, Kawase Y, Cheng RK, Kara RJ, Bhattacharya R, Guzman-Martinez G, Sanz J, Garcia MJ, Chaudhry HW (2014). "Cyclin A2 induces cardiac regeneration after myocardial infarction through cytokinesis of adult cardiomyocytes". Sci Transl Med. 6 (224): 224ra27. doi:10.1126/scitranslmed.3007668. PMID24553388.
↑Woo YJ, Panlilio CM, Cheng RK, Liao GP, Suarez EE, Atluri P, Chaudhry HW (2007). "Myocardial regeneration therapy for ischemic cardiomyopathy with cyclin A2". J. Thorac. Cardiovasc. Surg. 133 (4): 927–33. doi:10.1016/j.jtcvs.2006.07.057. PMID17382628.
↑Bukholm IR, Bukholm G, Nesland JM (Jul 2001). "Over-expression of cyclin A is highly associated with early relapse and reduced survival in patients with primary breast carcinomas". Int. J. Cancer. 93 (2): 283–7. doi:10.1002/ijc.1311. PMID11410878.
↑Kanai M, Shiozawa T, Xin L, Nikaido T, Fujii S (May 1998). "Immunohistochemical detection of sex steroid receptors, cyclins, and cyclin-dependent kinases in the normal and neoplastic squamous epithelia of the uterine cervix". Cancer. 82 (9): 1709–19. doi:10.1002/(sici)1097-0142(19980501)82:9<1709::aid-cncr18>3.0.co;2-8. PMID9576293.
↑Ohashi R, Gao C, Miyazaki M, Hamazaki K, Tsuji T, Inoue Y, Uemura T, Hirai R, Shimizu N, Namba M (Jan–Feb 2001). "Enhanced expression of cyclin E and cyclin A in human hepatocellular carcinomas". Anticancer Res. 21 (1B): 657–62. PMID11299822.
↑Wang Y, Prives C (Jul 1995). "Increased and altered DNA binding of human p53 by S and G2/M but not G1 cyclin-dependent kinases". Nature. 376 (6535): 88–91. doi:10.1038/376088a0. PMID7596441.
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Faha B, Ewen ME, Tsai LH, Livingston DM, Harlow E (1992). "Interaction between human cyclin A and adenovirus E1A-associated p107 protein". Science. 255 (5040): 87–90. doi:10.1126/science.1532458. PMID1532458.
Bandara LR, Adamczewski JP, Hunt T, La Thangue NB (1991). "Cyclin A and the retinoblastoma gene product complex with a common transcription factor". Nature. 352 (6332): 249–51. doi:10.1038/352249a0. PMID1830372.
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