title: Cell cycle-regulated association of E2F1 and Sp1 is related to their functional interaction.
abstract: Because of the large number of growth-regulated genes containing binding sites for the transcription factors Sp1 and E2F and the reported ability of E2F to mediate cell cycle (growth) regulation, we studied interactions between E2F1 and Sp1. In transient transfection assays using Drosophila melanogaster SL2 cells, transfection with both Sp1 and E2F1 expression vectors resulted in greater than 85-fold activation of transcription from a hamster dihydrofolate reductase reporter construct, whereas cotransfection with either the Sp1 or E2F1 expression vector resulted in 30- or <2-fold activation, respectively. Therefore, these transcription factors act synergistically in activation of dihydrofolate reductase transcription. Transient transfection studies demonstrated that E2F1 could superactivate Sp1-dependent transcription in a promoter containing only Sp1 sites and that Sp1 could superactivate transcription of promoters through E2F sites, further demonstrating that these physically associated in Drosophila cells transfected with Sp1 and E2F1 expression vectors and in human cells, with maximal interaction detected in mid- to late G1. Additionally, E2F1 and Sp1 interact in vitro through specific domains of each protein, and the physical interaction and functional synergism appear to require the same regions. Taken together, these data demonstrate that E2F1 and Sp1 both functionally and physically interact; therefore this interaction, Sp1 and E2F1 may regulate transcription of genes containing binding sites for either or both factors.
authors.affiliation: Department of Experimental Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors.forename: S Y
authors.initials: SY
authors.lastname: Lin
authors.forename: A R
authors.initials: AR
authors.lastname: Black
authors.forename: D
authors.initials: D
authors.lastname: Kostic
authors.forename: S
authors.initials: S
authors.lastname: Pajovic
authors.forename: C N
authors.initials: CN
authors.lastname: Hoover
authors.forename: J C
authors.initials: JC
authors.lastname: Azizkhan
mesh_terms: D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation; D011401:Promoter Regions, Genetic; D056465:Retinoblastoma-Binding Protein 1; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C088053:Dp transcription factor, Drosophila; D029721:Drosophila Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D056465:Retinoblastoma-Binding Protein 1; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D050680:Transcription Factor DP1; D014157:Transcription Factors