Cyclin A is a functional target of retinoblastoma tumor suppressor protein-mediated cell cycle arrest.
Although RB inhibits the G(1)-S transition, the mechanism through which RB prevents cell cycle advancement remains unidentified. To delineate the mechanism(s) utilized by RB to exert its anti-proliferative activity, constitutively active RB proteins (which cannot be inactivated by phosphorylation) or p16ink4a (which prevents RB inactivation) were utilized. Both proteins inhibited the G(1)-S transition, whereas wild-type RB did not. We show that active RB acts to attenuate cyclin A promoter activity, and that overexpression of cyclin E reverses RB-mediated repression of the cyclin A promoter. Although cyclin A is an E2F-regulated gene, and it has been long hypothesized that RB mediates cell cycle advancement through binding to E2F and attenuating its transactivation potential, cyclin E does not reverse dominant negative E2F-mediated repression of the cyclin A promoter. Although active RB repressed both cyclin A and two other paradigm E2F-regulated promoters, only cyclin A transcription was restored upon co-expression of cyclin E. Additionally, we show that RB but not dominant negative E2F regulates the cyclin A promoter through the CCRE element. These data identify cyclin A as a downstream target of RB-mediated arrest. Consistent with this idea, ectopic expression of cyclin A reversed RB-mediated G(1) arrest. The findings presented suggest a pathway wherein cyclin A is a downstream target of RB, and cyclin E functions to antagonize this aspect of RB-mediated G(1)-S inhibition.
Knudsen
K E
KE
Department of Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, USA. Erik.Knudsen@UC.Edu
Fribourg
A F
AF
Strobeck
M W
MW
Blanchard
J M
JM
Knudsen
E S
ES
D000818:Animals; D002352:Carrier Proteins; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins; D002455:Cell Division; D002460:Cell Line; D019925:Cyclin A / Q000235:genetics* / Q000502:physiology; D019927:Cyclin E / Q000235:genetics / Q000502:physiology; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D016193:G1 Phase; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D008156:Luciferases / Q000235:genetics; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D016160:Retinoblastoma Protein / Q000502:physiology*; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019927:Cyclin E; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; D008156:Luciferases; D013762:Tetrahydrofolate Dehydrogenase