title: Interaction of cyclin-dependent kinase 12/CrkRS with cyclin K1 is required for the phosphorylation of the C-terminal domain of RNA polymerase II.
abstract: CrkRS (Cdc2-related kinase, Arg/Ser), or cyclin-dependent kinase 12 (CKD12), is a serine/threonine kinase believed to coordinate transcription and RNA splicing. While CDK12/CrkRS complexes were known to phosphorylate the C-terminal domain (CTD) of RNA polymerase II (RNA Pol II), the cyclin regulating this activity was not known. Using immunoprecipitation and mass spectrometry, we identified a 65-kDa isoform of cyclin K (cyclin K1) in endogenous CDK12/CrkRS protein complexes. We show that cyclin K1 complexes isolated from mammalian cells contain CDK12/CrkRS but do not contain CDK9, a presumed partner of cyclin K. Analysis of extensive RNA-Seq data shows that the 65-kDa cyclin K1 isoform is the predominantly expressed form across numerous tissue types. We also demonstrate that CDK12/CrkRS is dependent on cyclin K1 for its kinase activity and that small interfering RNA (siRNA) knockdown of CDK12/CrkRS or cyclin K1 has similar effects on the expression of a luciferase reporter gene. Our data suggest that cyclin K1 is the primary cyclin partner for CDK12/CrkRS and that cyclin K1 is required to activate CDK12/CrkRS to phosphorylate the CTD of RNA Pol II. These properties are consistent with a role of CDK12/CrkRS in regulating gene expression through phosphorylation of RNA Pol II.
authors.affiliation: Michael Smith Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: S-W Grace
authors.initials: SW
authors.lastname: Cheng
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kuzyk
authors.forename: Annie
authors.initials: A
authors.lastname: Moradian
authors.forename: Taka-Aki
authors.initials: TA
authors.lastname: Ichu
authors.forename: Vicky C-D
authors.initials: VC
authors.lastname: Chang
authors.forename: Jerry F
authors.initials: JF
authors.lastname: Tien
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Vollett
authors.forename: Malachi
authors.initials: M
authors.lastname: Griffith
authors.forename: Marco A
authors.initials: MA
authors.lastname: Marra
authors.forename: Gregg B
authors.initials: GB
authors.lastname: Morin
mesh_terms: D001665:Binding Sites; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D008156:Luciferases; D013058:Mass Spectrometry; D010766:Phosphorylation; D011485:Protein Binding; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics
chemical_list: C113028:CCNK protein, human; D016213:Cyclins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D008156:Luciferases; C447339:CDK12 protein, human; D018844:Cyclin-Dependent Kinases; D012319:RNA Polymerase II