title: p27Kip1 induces an accumulation of the repressor complexes of E2F and inhibits expression of the E2F-regulated genes.
abstract: p27Kip1 is an inhibitor of the cyclin-dependent kinases and it plays an inhibitory role in the progression of cell cycle through G1 phase. To investigate the mechanism of cell cycle inhibition by p27Kip1, we constructed a cell line that inducibly expresses p27Kip1 upon addition of isopropyl-1-thio-beta-D-galactopyranoside in the culture medium. Isopropyl-1-thio-beta-D-galactopyranoside-induced expression of p27Kip1 in these cells causes a specific reduction in the expression of the E2F-regulated genes such as cyclin E, cyclin A, and dihydrofolate reductase. The reduction in the expression of these genes correlates with the p27Kip1-induced accumulation of the repressor complexes of the E2F family of factors (E2Fs). Our previous studies indicated that p21WAF1 could disrupt the interaction between cyclin/cyclin-dependent kinase 2 (cdk2) and the E2F repressor complexes E2F-p130 and E2F-p107. We show that p27Kip1, like p21WAF1, disrupts cyclin/cdk2-containing complexes of E2F-p130 leading to the accumulation of the E2F-p130 complexes, which is found in growth-arrested cells. In transient transfection assays, expression of p27Kip1 specifically inhibits transcription of a promoter containing E2F-binding sites. Mutants of p27Kip1 harboring changes in the cyclin- and cdk2-binding motifs are deficient in inhibiting transcription from the E2F sites containing reporter gene. Moreover, these mutants of p27Kip1 are also impaired in disrupting the interaction between cyclin/cdk2 and the repressor complexes of E2Fs. Taken together, these observations suggest that p27Kip1 reduces expression of the E2F-regulated genes by generating repressor complexes of E2Fs. Furthermore, the results also demonstrate that p27Kip1 inhibits expression of cyclin A and cyclin E, which are critical for progression through the G1-S phases.
authors.affiliation: Department of Biochemistry, University of Illinois at Chicago 60612, USA.
authors.forename: P
authors.initials: P
authors.lastname: Shiyanov
authors.forename: S
authors.initials: S
authors.lastname: Hayes
authors.forename: N
authors.initials: N
authors.lastname: Chen
authors.forename: D G
authors.initials: DG
authors.lastname: Pestov
authors.forename: L F
authors.initials: LF
authors.lastname: Lau
authors.forename: P
authors.initials: P
authors.lastname: Raychaudhuri
mesh_terms: D000818:Animals; D002352:Carrier Proteins; D018929:Cell Culture Techniques / Q000379:methods; D018797:Cell Cycle Proteins; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D005786:Gene Expression Regulation / Q000187:drug effects; D016147:Genes, Tumor Suppressor; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis / Q000502:physiology*; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: C533431:Arid4a protein, mouse; D002352:Carrier Proteins; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D008869:Microtubule-Associated Proteins; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases