Cell division protein kinase 8 is an enzyme that in humans is encoded by the CDK8 gene. [5] [6]
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. [7] [8] CDK8 phosphorylates the Notch intracellular domain, [9] SREBP, [10] and STAT1 S727. [11] CDK8 also inhibits transcriptional activation by influencing turnover of subunits in the mediator complex tail module. [12] [13] In addition, CDK8 influences binding of RNA polymerase II to the mediator complex. [14] [15]
CDK8 is a colorectal cancer oncogene: the CDK8 gene is amplified in human colorectal tumors, activating β-catenin-mediated transcription that drives colon tumorigenesis. [16] 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, [9] and inhibits EGFR signaling-driven cell fates in C. elegans . [13] 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 [17] 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.
An autosomal dominant syndrome has been described that is associated with mutations in the ATP binding pocket of the kinase domain. [18] The clinical features include agenesis of the corpus callosum, mild to moderate intellectual disability, hypotonia, seizures, hearing or visual impairments, behavioral disorders, variable facial dysmorphism, congenital heart disease and ano-rectal malformations.
The natural product cortistatin A is a potent and selective inhibitor of CDK8 and CDK19. [19] 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.
Cyclin-dependent kinase 8 has been shown to interact with:
Transcription factor II Human is an important protein complex, having roles in transcription of various protein-coding genes and DNA nucleotide excision repair (NER) pathways. TFIIH first came to light in 1989 when general transcription factor-δ or basic transcription factor 2 was characterized as an indispensable transcription factor in vitro. This factor was also isolated from yeast and finally named as TFIIH in 1992.
Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes. It was discovered in 1990 in the lab of Roger D. Kornberg, recipient of the 2006 Nobel Prize in Chemistry. Mediator complexes interact with transcription factors and RNA polymerase II. The main function of mediator complexes is to transmit signals from the transcription factors to the polymerase.
Cyclin-dependent kinase 9 or CDK9 is a cyclin-dependent kinase associated with P-TEFb.
DNA-directed RNA polymerase II subunit RPB1, also known as RPB1, is an enzyme that in humans is encoded by the POLR2A gene.
Cyclin-T1 is a protein that in humans is encoded by the CCNT1 gene.
Cyclin-dependent kinase 7, or cell division protein kinase 7, is an enzyme that in humans is encoded by the CDK7 gene.
DNA-directed RNA polymerase II subunit RPB11-a is an enzyme that in humans is encoded by the POLR2J gene.
DNA-directed RNA polymerase II subunit RPB4 is an enzyme that in humans is encoded by the POLR2D gene.
CDK-activating kinase assembly factor MAT1 is an enzyme that in humans is encoded by the MNAT1 gene.
Cyclin-H is a protein that in humans is encoded by the CCNH gene.
General transcription factor IIH subunit 4 is a protein that in humans is encoded by the GTF2H4 gene.
Cyclin-C is a protein that in humans is encoded by the CCNC gene.
Mediator of RNA polymerase II transcription subunit 21 is an enzyme that in humans is encoded by the MED21 gene.
Mediator of RNA polymerase II transcription subunit 6 is one of the subunits of the Mediator complex. It is an enzyme that in humans is encoded by the MED6 gene.
Cyclin-T2 is a protein that in humans is encoded by the CCNT2 gene.
General transcription factor IIH subunit 2 is a protein that in humans is encoded by the GTF2H2 gene.
General transcription factor IIH subunit 1 is a protein that in humans is encoded by the GTF2H1 gene.
Cyclin-K is a protein that in humans is encoded by the CCNK gene.
RNA polymerase II holoenzyme is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells. It consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as SRB proteins.
Mediator complex subunit 13 is a protein that in humans is encoded by the MED13 gene.