The protein encoded by this gene is a member of the cyclin-dependent protein kinase (CDK) family. CDK8 and cyclin C associate with the mediator complex and regulate transcription by several mechanisms. CDK8 binds to and/or phosphorylates several transcription factors, which can have an activating or inhibitory effect on transcription factor function.[3][4] CDK8 phosphorylates the Notch intracellular domain,[5]SREBP,[6] and STAT1 S727.[7] CDK8 also inhibits transcriptional activation by influencing turnover of subunits in the mediator complex tail module.[8][9] In addition, CDK8 influences binding of RNA polymerase II to the mediator complex.[10][11]
Clinical significance
CDK8 is a colorectal cancer oncogene: the CDK8 gene is amplified in human colorectal tumors, activating β-catenin-mediated transcription that drives colon tumorigenesis.[12] However, CDK8 may not be oncogenic in all cell types, and indeed may act as a tumor suppressor in the notch and EGFR signaling pathways. Specifically, CDK8 promotes turnover of the notch intracellular domain,[5] and inhibits EGFR signaling-driven cell fates in C. elegans.[9] Thus, CDK8 may be an oncogene in cancers driven by Wnt/β-catenin signaling, but could instead be a tumor suppressor gene in cancers driven by notch or EGFR signaling. In addition, CDK8 promotes transcriptional activation mediated by the tumor suppressor protein p53, indicating that it may have an important role in tumor suppression [13] Further research is needed to delineate the effects of CDK8 inhibition in different tissues, so for the time being, drugs targeting CDK8 for cancer treatment remain untested in humans.
As a potential drug target
The natural product cortistatin A is a potent and selective inhibitor of CDK8 and CDK19.[14] Inhibition of CDK8 and CDK19 with cortistatin A suppresses AML cell growth and has anticancer activity in animal models of AML by causing selective and disproportionate up regulation of super-enhancer-associated genes including the cell identity genes CEBPA and IRF8.
Interactions
Cyclin-dependent kinase 8 has been shown to interact with:
↑Nemet J, Jelicic B, Rubelj I, Sopta M (Feb 2014). "The two faces of Cdk8, a positive/negative regulator of transcription". Biochimie. 97: 22–7. doi:10.1016/j.biochi.2013.10.004. PMID24139904.
↑ 5.05.15.2Fryer CJ, White JB, Jones KA (Nov 2004). "Mastermind recruits CycC:CDK8 to phosphorylate the Notch ICD and coordinate activation with turnover". Molecular Cell. 16 (4): 509–20. doi:10.1016/j.molcel.2004.10.014. PMID15546612.
↑Zhang Y, Iratni R, Erdjument-Bromage H, Tempst P, Reinberg D (May 1997). "Histone deacetylases and SAP18, a novel polypeptide, are components of a human Sin3 complex". Cell. 89 (3): 357–64. doi:10.1016/s0092-8674(00)80216-0. PMID9150135.
↑ 19.019.119.219.319.419.519.619.7Ito M, Yuan CX, Malik S, Gu W, Fondell JD, Yamamura S, Fu ZY, Zhang X, Qin J, Roeder RG (Mar 1999). "Identity between TRAP and SMCC complexes indicates novel pathways for the function of nuclear receptors and diverse mammalian activators". Molecular Cell. 3 (3): 361–70. doi:10.1016/s1097-2765(00)80463-3. PMID10198638.
Schultz SJ, Nigg EA (Oct 1993). "Identification of 21 novel human protein kinases, including 3 members of a family related to the cell cycle regulator nimA of Aspergillus nidulans". Cell Growth & Differentiation. 4 (10): 821–30. PMID8274451.
Rickert P, Seghezzi W, Shanahan F, Cho H, Lees E (Jun 1996). "Cyclin C/CDK8 is a novel CTD kinase associated with RNA polymerase II". Oncogene. 12 (12): 2631–40. PMID8700522.
Sun X, Zhang Y, Cho H, Rickert P, Lees E, Lane W, Reinberg D (Aug 1998). "NAT, a human complex containing Srb polypeptides that functions as a negative regulator of activated transcription". Molecular Cell. 2 (2): 213–22. doi:10.1016/S1097-2765(00)80131-8. PMID9734358.
Rickert P, Corden JL, Lees E (Jan 1999). "Cyclin C/CDK8 and cyclin H/CDK7/p36 are biochemically distinct CTD kinases". Oncogene. 18 (4): 1093–102. doi:10.1038/sj.onc.1202399. PMID10023686.
Gu W, Malik S, Ito M, Yuan CX, Fondell JD, Zhang X, Martinez E, Qin J, Roeder RG (Jan 1999). "A novel human SRB/MED-containing cofactor complex, SMCC, involved in transcription regulation". Molecular Cell. 3 (1): 97–108. doi:10.1016/S1097-2765(00)80178-1. PMID10024883.
Ito M, Yuan CX, Malik S, Gu W, Fondell JD, Yamamura S, Fu ZY, Zhang X, Qin J, Roeder RG (Mar 1999). "Identity between TRAP and SMCC complexes indicates novel pathways for the function of nuclear receptors and diverse mammalian activators". Molecular Cell. 3 (3): 361–70. doi:10.1016/S1097-2765(00)80463-3. PMID10198638.
Di Pietro C, Rapisarda A, Bonaiuto C, Lizzio MN, Engel H, Amico V, Scalia M, Amato A, Grzeschik KH, Sichel G, Purrello M (May 1999). "Genomics of the human genes encoding four TAFII subunits of TFIID, the three subunits of TFIIA, as well as CDK8 and SURB7". Somatic Cell and Molecular Genetics. 25 (3): 185–9. doi:10.1023/A:1018897624615. PMID11441538.
Vogel L, Baratte B, Détivaud L, Azzi L, Leopold P, Meijer L (Apr 2002). "Molecular cloning and characterisation of p15(CDK-BP), a novel CDK-binding protein". Biochimica et Biophysica Acta. 1589 (2): 219–31. doi:10.1016/S0167-4889(02)00175-1. PMID12007796.
Crowley TE, Kaine EM, Yoshida M, Nandi A, Wolgemuth DJ (Aug 2002). "Reproductive cycle regulation of nuclear import, euchromatic localization, and association with components of Pol II mediator of a mammalian double-bromodomain protein". Molecular Endocrinology. 16 (8): 1727–37. doi:10.1210/me.2001-0353. PMID12145330.
Sato S, Tomomori-Sato C, Banks CA, Sorokina I, Parmely TJ, Kong SE, Jin J, Cai Y, Lane WS, Brower CS, Conaway RC, Conaway JW (Apr 2003). "Identification of mammalian Mediator subunits with similarities to yeast Mediator subunits Srb5, Srb6, Med11, and Rox3". The Journal of Biological Chemistry. 278 (17): 15123–7. doi:10.1074/jbc.C300054200. PMID12584197.