CtIP activates its own and cyclin D1 promoters via the E2F/RB pathway during G1/S progression.
Cell cycle progression from G(1) to S phase is mainly controlled by E2F transcription factors and RB family proteins. Previously we showed that the presence of CtIP is essential for G(1)/S transition in primary mouse blastocysts, as well as in NIH 3T3 cells. However, how CtIP executes this function remains to be elucidated. Here we show that in NIH 3T3 cells the expression of CtIP is regulated by the E2F/RB pathway during late G(1) and S phases. The presence of wild-type CtIP, but not the E157K mutant form, which failed to interact with RB, enhanced its own promoter activity. Chromatin immunoprecipitation analysis indicated that the recruitment of CtIP to its promoter occurs concomitantly with TFIIB, a component of the RNA polymerase II complex, and with dissociation of RB from the promoter during late G(1) and G(1)/S transition. Similar positive regulation of cyclin D1 expression by CtIP was also observed. Consistently, cells expressing the CtIP(E157K) protein alone exhibited growth retardation, an increase in the G(1) population, and a decrease in the S-phase population. Taken together, these results suggest that, contrary to the postulated universal corepressor role, CtIP activates a subset of E2F-responsive promoters by releasing RB-imposed repression and therefore promotes G(1)/S progression.
Department of Biological Chemistry, 839 Medical Science Court, 124 Sprague Hall, University of California, Irvine, CA 92697, USA.
Feng
F
Liu
Wen-Hwa
WH
Lee
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors / Q000378:metabolism; D004706:Endodeoxyribonucleases; D016193:G1 Phase; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D056465:Retinoblastoma-Binding Protein 1; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019938:Cyclin D1; D050684:E2F Transcription Factors; D004706:Endodeoxyribonucleases; D008156:Luciferases; D009687:Nuclear Proteins; D056465:Retinoblastoma-Binding Protein 1; C533431:Arid4a protein, mouse; C501070:RBBP8 protein, mouse; C410741:RBBP8 protein, human