title: E2F-3 accumulation is regulated by polypeptide stability.
abstract: E2F is a complex family of transcription factors which appears to regulate the transcription of genes required for the S phase of the mammalian cell cycle. In the present work, we have examined the mechanisms regulating E2F-3 accumulation in mouse fibroblasts. We have determined that E2F-3 DNA binding activity is restricted to the G1/S transition and S phase in both normal BALB/c-3T3 fibroblasts and in an SV40 virus-transformed BALB/c-3T3 derivative. Immunoblot analysis indicates that G0 and G1 cells have little or no E2F-3 polypeptide and that the increase in the DNA binding activity of E2F-3 at the G1/S boundary is reflected by an increase in total E2F-3 protein. In contrast to the E2F-3 polypeptide, RNAse protection assays demonstrate that the E2F-3 mRNA is clearly present in G0 and G1 cells. Finally, pulse/chase experiments indicate that the half-life of E2F-3 is approximately 40-fold greater in cells blocked in S phase relative to asynchronously growing cells. Together, these results indicate that the accumulation E2F-3 at S phase may be regulated, at least in part, at the level of protein stability.
authors.affiliation: H Lee Moffitt Cancer Center and Research Institute, Department of Biochemistry and Molecular Biology, University of South Florida, College of Medicine, Tampa 33612, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Flores
authors.forename: R F
authors.initials: RF
authors.lastname: Kassatly
authors.forename: W D
authors.initials: WD
authors.lastname: Cress
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division; D002472:Cell Transformation, Viral; D004261:DNA Replication; D050699:E2F3 Transcription Factor; D016193:G1 Phase; D005786:Gene Expression Regulation; D007700:Kinetics; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis; D016192:Resting Phase, Cell Cycle; D012260:Ribonucleases; D016196:S Phase; D013539:Simian virus 40 / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis*; D014158:Transcription, Genetic
chemical_list: D050699:E2F3 Transcription Factor; C490840:E2f3 protein, mouse; D012333:RNA, Messenger; D014157:Transcription Factors; D012260:Ribonucleases