1、分子细胞生物学专题分子细胞生物学专题-转录延伸因子转录延伸因子P-TEFb及其活性调控及其活性调控生命科学学院生命科学学院陈瑞川细胞生物学博士研究生课程细胞生物学博士研究生课程 Main PointsTranscription process of eukaryotic gene.P-TEFb:functions and its Activity regulationI.Transcription processSteps of class II gene transcriptionPromotor clearenceInitiationPIC assemblyTerminationElong
2、ation TFIIA,TFIIB,TFIID,TFIIE,TFIIF,and TFIIH RNA polymerase II(Pol II)The class II pre-initiation complex(PIC)RNA polymerase II(Pol II)12 subunites:Rpb1-Rpb12About 500Kda of MW Rpb1:largest subunit,CTD:Y1S2P3T4S5P6S7 Yest:26 repeats C.elegans:32 repeats Drosophila 42 repeats Mammals:52 repeatsPre-i
3、nitiationPol IICTDPIC assemblyIIFIIHIIEPICPol IICTDIIFPol IICTDIIFII DII AIIBIIHIIE+1DNA tempTATAPICPol IICTDII DII AIIBIIFIIHIIEInitiation55555Pol II55555+1DNA tempTATAPromoter clearance20-30 ntPol IICTD55555DNA tempTATAIISDSIFNELFMTPausingCappingPol IICTD55555DNA tempTATAIISRNADSIFNELFEarly elonga
4、tion5-triphosphataseguanyltransferaseNCNCmethyltransferaseMTMTNCNCCappingEarly elongationDNA tempProductiveElongationCycT1CDK9P-TEFbRNACycT1CDK9P-TEFbPol IICTD55555IISDSIF2222CycT1CDK9P-TEFbNELFPol IICTD55555IISDSIFCapped short mRNA2222PPCycT1CDK9P-TEFbSplicing55555Pol II22222RNADNA tempRNAU snRNPPr
5、oductive ElongationSplicingCycT1CDK9P-TEFbFCP1Pol IIPol IICTD25555222Pol II25555222+15555Pol II5 capRNA55552222Pol IICTDTFIIHNFk kBSp1NFATPol II Steps:Pre-initiation Initiation Promoter clearance Elongation Termination InitiationEarly elongationPromoter clearanceElongationTerminationPre-initiationTr
6、anscription cycleTranscription ProcessP-TEFb,its functions and activity regulationP-TEFb:composition and property Discovered in 1995.(positive transcription elongation factor b)A heterodimer of Cdk9 and cyclin T,including T1,T2a,T2b and Cyclin K.But 80%P-TEFb is CDK9/Cyclin T1.kinase,phosphorylates
7、CTD of Pol II,DSIF and NELF.CycT1Cdk9Physiological functionsA global transcriptional elongation factorEssential for more than 80%mRNA transcription Essential for embryo developmentCTDPol IIRNANELFNuc失败转录失败转录CycT1Cdk9P-TEFb成功转录成功转录RNAPPPPPPPPCycT1Cdk9Adapted after Price,MCB 20:2629(2000)P-TEFb在基因转录过程
8、中的作用机制在基因转录过程中的作用机制模式图模式图B.Pathological functionsExquisitely required for HIV-1 gene expression Abnormally high P-TEFb activity direct link to cardiac hypertrophy May also relate to tumor progressionTAR RNACTDPol II5555CTDPol II5555Abortive TranscriptionCTDPol II5555Short RNACycT1CDK9TatCycT1CDK9Tat
9、HIV LTR+1TatTatCycT1CDK9TatCycT1CDK9TatCycT1CDK9Tat2222HIVP-TEFb is essential for HIV-1 replication and gene expressionTat,a HIV-1 encoded protein.Trans-cyclin T1 gene causes cardiac hypertrophyTrans-vectorTrans-cyclin T1CycT1Cdk97SK snRNAInactive P-TEFb-7SK snRNPHEXIM1HEXIM2LARP7MePCEHEXIM1LARP7Met
10、hyl donorCycT1CDK9HEXIM1CycT1CDK9HEXIM1MePCEMePCELARP7CycT1CDK9HEXIM1MePCE7SKLARP75-Cap3-tailMePCE3-tailcapped 7SK7SK5-Cap3-tailTrinity compled7SK snRNP3-tailNascent 7SK5-termini5-CapCycT1CDK9HEXIM17SK snRNP assembleActive P-TEFb for general transcriptionCycT1Cdk9Brd4PPPPPPPPCycT1Cdk9Brd4CTDPol IImR
11、NAmRNAPol IICycT1Cdk9HEXIM17SK RNACycT1Cdk9Brd4Stress/hypertrophic signals/estrogen/HIV infectioninactiveP-TEFbCycT1Cdk9Brd4activeP-TEFbRecruitment of P-TEFb for stimulation of transcriptional elongation by bromodomain protein Brd4(Submitted to:Mol Cell)CycT1Cdk9Brd4CycT1Cdk9HEXIM17SK snRNAInactive
12、P-TEFbActive P-TEFbCycT1Cdk9PPP3/41/4?How is 7SK snRNP disrupted?CycT1Cdk9HEXIM17SK snRNAInactive P-TEFbPPPPPPPPPPPPPPPPPhosphorylated P-TEFb is tagged for inhibition through association with 7SK snRNAPP1 treatmentOrStress:Act D,DRB,UVDephosphorylationActive P-TEFbCycT1Cdk9HEXIM1+PPPPPPPPhosphorylat
13、ionATPHow does cell signaling control the disruption of the inactive complex?Control P-TEFb activity by calcium signaling pathwayUV and HMBA can trigger Ca+2 influxF1C2 cellSignal pathway inhibitorsCycT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPStress treatmentCycT1Cdk9Active P-TEFbPPPPPPPHE
14、XIM1+A calcium-dependent signaling pathway controls P-TEFb transcriptional activity(in writing)Inhibitor:UV:HEXIM1CDK9-f1 2 3 4 5Calcium signaling pathwaysCa+InfluxCycT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPCycT1Cdk9Active P-TEFbPPPPPPPHEXIM1+Cell membraneL-type channelF1C2 cellCalciumCy
15、cT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPStress treatmentCycT1Cdk9Active P-TEFbPPPPPPPHEXIM1+F1C2 cellCa+InfluxCalcium signaling pathwaysF1C2 cellCa+InfluxCaM-dependent protein kinasesCaMCaM-dependent protein phosphatasesCaMKK,CaMKI,CaMKII,CaMKIVCalcineurin(CaN,PP2B)W7CsA,FK506F1C2 cellW
16、7,CsA,FK506CycT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPStress treatmentCycT1Cdk9Active P-TEFbPPPPPPPHEXIM1+A calcium-dependent signaling pathway controls P-TEFb transcriptional activity(in writing)F1C2 cellCa+InfluxCaMPP2BHiding and seeking.Who is the second one?isoform of PP1 catalytic s
17、ubunit involves in mediating the disruption of 7SK snRNPF1C2 cellCycT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPCycT1Cdk9Active P-TEFbPPPPPPPHEXIM1+A calcium-dependent signaling pathway controls P-TEFb transcriptional activity(in writing)F1C2 cellCa+InfluxCaMPP2BPP1PP2B+PP1?In vivo:PP2B and
18、PP1 work cooperatively to disrupt the inactive complexIn vitro:PP2B and PP1 directly disrupt inactive complex PP2B:let me work first.F1C2 cellCalciumCycT1Cdk9HEXIM17SK snRNPInactive P-TEFbPPPPPPPPPPPPPPPPStress treatmentCycT1Cdk9Active P-TEFbPPPPPPPHEXIM1+F1C2 cellCa+InfluxCaMPP2BPP1Ca+2/PP2B and PP
19、1 pathways cooperatively mediate UV and HMBA induced disruption of inactive complexHow do PP2B and PP1 cooperatively disrupt inactive P-TFb complex?In vitro.Only PP1 can dephosphorylate pT186 of CDK9In vitro.PP2B and PP1 work cooperatively to dephosphorylate pT186 of CDK9CycT1Cdk9Inactive P-TEFbPPHE
20、XIM17SK snRNAPP2BPP1Two steps dephosphorylation fro dissociating 7SK snRNPCycT1Cdk9plasma membraneLTCCCa2+PP2BnucleusPP1 CaMPP2BPP1 inactiveP-TEFbCycT1Cdk9UV or HMBAPPHEXIM1A calcium signaling pathway dependent two-step dephosphorylation to release P-TEFbCycT1Cdk9?PHEXIM1pT186Brd4How is liberated P-
21、TFFb Recruited to chromatinActive P-TEFb for general transcriptionCycT1Cdk9Brd4PPPPPPPPCycT1Cdk9Brd4CTDPol IImRNAmRNAPol IICycT1Cdk9HEXIM17SK RNACycT1Cdk9Brd4Stress/hypertrophic signals/estrogen/HIV infectioninactiveP-TEFbBrd4CycT1Cdk9Brd4?Dynamic shift between different complex.CycT1Cdk9activeP-TEF
22、bHEXIM1CycT1Cdk9activeP-TEFb1/4Modified Nuclear FractionationChromatin-freefraction(LSF)NucleusLow-salt bufferextractionHigh-salt bufferextractionChromatin-boundfraction(HSF)Nuclear lysisfraction(NLF)NucleusNucleusAlmost all of Brd4 associate with chromatin at basal stateStimuation induces Brd4 rele
23、ase from chromatinThe release of Brd4 from chromatin is essential from P-TEFb recruitmentThe release of Brd4 from chromatin is HDAC-dependentThe release of Brd4 from chromatin is essential from elongationCycT1Cdk9ProductiveelongationHEXIM1+222 2PP2B+PP1Kinase?T186CycT1Cdk9PBrd4mRNAPol II555 5AcAcHDACRecruitP-TEFb topromotermRNAPol IIH4 tail555 5H4K5/8deacetylatedSignalDeacetylateH4K5/8AcmRNAPol IIAcAcBrd4Acetyl-nucleosome555 5CTDReleaseBrd4 fromchromatin7SKT1867SKCycT1Cdk9PHEXIM17SK snRNPAi_Fig7CycT1Cdk9PAdaptorBrd4Brd4HDACSignal?CycT1Cdk9KinaseT186CycT1Cdk9P?Thank you!
