New Material DNA Replica on Cell Cycle Cancer Cell Cycle II Overview mul ple CDKs cyclins S phase entry SCF ubiqui n ligase controls S phase entry sort of like S phase equivalent of APC which is used in M phase entry cannot enter S phase if CKI is bound to SCF CKIs inhibitors pRB E2F RB inhibitor of E2F RTKs Ras Myc G1 S CDKs checkpoints unreplicated DNA G2 DNA damage G1 S phase G2 p21 blocks CDKs CDC25 pathway blocks G1 S S phase G2 mito c spindle M phase MAD2 blocks APC sequesters CDC20 ATR Chk1 inhibi on of CDC25 phosphatase takes inhibitory phosphate o CDK p53 tumor suppressor protein promotes transcrip on of a CKI stops transcrip on can also signal programmed cell death if unsuccessful in stopping transcrip on Cyclins CDKs YEAST only 1 CDK responsible for cell cycle progression ssion yeast CDC2 budding yeast CDC28 CDK1 HIGHER EUKS mul ple CDKs YEAST METAZOA di erent cyclins synthesized di erent mes in cell cycle availability of di erent cyclins determines which CDK cyclin complexes form during each phase of cell cycle addi onal mechanisms control cyclin CDK ac va on In yeast only one CDK is responsible for cell cycle progression budding yeast CDC28 and fission yeast cdc2 Cdk1 In higher eukaryotes there are multiple CDKs In both yeast metazoa different cyclins are synthesized at different times in the cell cycle Availability of different cyclins determines which CDK cyclin complexes form during each phase of the cell cycle Additional mechanisms control activation of Cyclin CDKs Figure Cyclins CDKs CDKs and Cyclins Activate in Succession Cyclins CDKs Ac0vate in Succession CyclinHDependent Kinase Inhibitors CKIs Cyclin Dependent Kinase Inhibitors CKIs 2 mammalian p16 p21 p27 Mammalian p16 p21 p27 mechanism of ac on Mechanism of action 1 Inhibit assembly of CDK inhibit assembly of CDK and cyclin G1 CDKs Cyclin G1 CDKs Inhibit phosphoryla on of inhibit phosphorylation of CDK CDK by CAK G1 G1 S by CAK G1 and G1 S CDKs CDKs Inhibit phosphoryla on of inhibit phosphorylation of substrates like RB G1 substrates like RB G1 and G1 G1 S CDKs S CDKs destruc on of CKI Destruction of CKI contributes to S contributes to S phase entry phase entry CKIs degraded by CKIs are degraded by the proteasome aver proteasome after ubiquitination by ubiqui na on by SCF SCF complexes Skip Cullin F Box Skip Cullin F Box complexes 3 Active CDK S phase Rb CKI Inhibitor Sic Controls S Phase Entry CKI Sic Controls S Phase Entry only 1 PO4 on Sic in top graph CKI Inhibitor Sic Controls S Phase Entry G1 S cyclin CDK phosphorylates Sic mul ple mes DNA rep occurs destruc on of Sic allows Destruction of Sic allows S phase entry S phase entry Multiple sites in Sic rapid transition mul ple sites in Sic rapid Destruction of Sic allows S phase entry transi on Multiple sites in Sic rapid transition mul ple PO4 s on Sic makes mul ple weak sites creates sharp entry into S phase S Phase Entry Controlled by E ects of Cyclin DHCDK4 on E2F pRB in Higher Euks slide 1 of 2 S phase Entry Is Controlled by Effects of Cyclin D Cdk4 on E2F and pRB In Higher Eukaryotes 1 2 3 4 SCF degrades p16 CKI CDK inhibitor Cyclin DHCDK4 is ac ve pRB is phosphorylated releasing E2F E2F transcrip on factor for S phase genes ac vates S phase Entry Is Controlled by Effects of Cyclin D Cdk4 on E2F and pRB In Higher Eukaryotes w o RB lose S phase replica on P16 CKI CDK Inhibitor Is Degraded by SCF Cyclin D Cdk4 is active pRB is phosphorylated and releases E2F E2F Transcription Factor For S phase genes is activated S phase entry pRB and E2F P16 CKI CDK Inhibitor Is Degraded by SCF Cyclin D Cdk4 is active pRB is phosphorylated and releases E2F E2F Transcription Factor For S phase genes is activated S phase entry pRB and E2F S Phase Entry slide 2 of 2 E2F Transcription Factor S Phase Entry ribonucleotide reductase DNA polymerase primase RB protein binds E2F Cyclin D Cdk4 phosphorylates Rb Control effect of E2F on S phase entry Two Positive Feedback Loops G1 S and S cyclin CDKs also phosphorylate pRB E2F transcription factor promotes production of its own mRNA E2F transcrip on factor ribonucleo de reductase DNA polymerase primase 1 pRB binds E2F 2 Cyclin DHCDK4 phosphorylates RB control e ect of E2F on S phase entry 3 2 posi ve feedback loops G1 S S cyclin CDKs also phosphorylate pRB E2F transcrip on factor promotes produc on of its own mRNA RB E2F and Chromatin RB E2F Chroma0n RB brings histone deacetylase HDAC and repressive chromatin remodeling complexes to E2F promoters to inhibit transcription RB brings HDAC Histone Deacetylase repressive chroma n remodeling complexes to E2F promoters to inhibit transcrip on 1 RB E2F complex bound E2F 2 upstream of S phase genes Phosphoryla on of RB releases RB HDAC from chroma n 3 Acetyla on of histones following HDAC release promotes open conforma on Transcrip on of S phase genes ac vates 4 RB E2F complex is bound at E2F upstream of S phase genes Phosphorylation of Rb releases Rb and HDAC from chromatin Acetylation of histones following HDAC release promotes open conformation Transcription of S phase genes is activated S phase entry Myc RTKs and S phase Entry RTK Myc G1 CDK Rb E2F S Phase Entry Myc Cell resting in Go or stopped at restriction point Growth factor signal initiates RTK signaling Map K pathway promotes synthesis of myc Myc Drives entry into S phase Increase CycD Cdk4 RTKs and S phase Entry RTK Myc G1 CDK Rb E2F RTKs and S phase Entry RTK Myc G1 CDK Rb E2F all factors listed below turn on CDKs to regulate transcrip on Cell resting in Go or stopped at restriction point Growth factor signal initiates RTK signaling Map K pathway promotes synthesis of myc Cell resting in Go or stopped at restriction point Myc Drives entry into S phase Increase CycD Cdk4 Growth factor signal initiates RTK signaling Map K pathway promotes synthesis of myc Myc Drives entry into S phase Increase CycD Cdk4 RTKs S phase entry RTK Myc G1 CDK RB E2F 1 Cell res ng in G0 or early genes include CHFos CHJun Myc Early genes include c fos c jun 2 Review Slides CDKs in S phase stopped restric on point 2 Growth factor signal ini ates RTK signaling 3 MAP K pathway promotes synthesis of Myc 4 Myc drives S phase entry increase Cyclin DHCDK4 Early genes include c fos c jun 2 Review Slides CDKs in S phase Early genes include c fos c jun 2 Review Slides CDKs in S phase RTKs ac vate Ras CDKs Roles in S Phase Review Roles of CDKs in S Phase produces Myc leads to ac va on of G1 S CDK RTKs activate ras myc is produced and cyclins this leads to