title: Distinct roles for Sp1 and E2F sites in the growth/cell cycle regulation of the DHFR promoter.
abstract: Dihydrofolate reductase activity is required for many biosynthetic pathways including nucleotide synthesis. Its expression is therefore central to cellular growth, and it has become a key target for cancer chemotherapy. Transcription of the dihydrofolate reductase gene is regulated with growth, being expressed maximally in late G1/early S phase following serum stimulation of quiescent cells. This regulation is directed by a promoter which contains binding sites for only the transcription factors Sp1 and E2F. In this study, the role of these promoter elements in growth/cell cycle regulation of dihydrofolate transcription was addressed directly by transient transfection of Balb/c 3T3 cells with mutant promoter-reporter gene constructs. The E2F sites were found to repress transcription in G0 and early G1 but did not contribute to the level of transcription in late G1/S phase. In contrast, Sp1 sites were able to mediate induction of transcription from the dihydrofolate reductase promoter, as well as a heterologous promoter, following serum stimulation of quiescent cells. These findings add dihydrofolate reductase to a growing list of genes at which E2F sites are primarily repressive elements and delineate a role for Sp1 sites in the growth/cell cycle regulation of transcription.
authors.affiliation: Department of Experimental Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Jensen
authors.forename: A R
authors.initials: AR
authors.lastname: Black
authors.forename: A G
authors.initials: AG
authors.lastname: Swick
authors.forename: J C
authors.initials: JC
authors.lastname: Azizkhan
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D001769:Blood; D002352:Carrier Proteins; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins; D002455:Cell Division; D006224:Cricetinae; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011993:Recombinant Fusion Proteins; D056465:Retinoblastoma-Binding Protein 1; D016329:Sp1 Transcription Factor / Q000502:physiology*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D011993:Recombinant Fusion Proteins; D056465:Retinoblastoma-Binding Protein 1; D016329:Sp1 Transcription Factor; D050680:Transcription Factor DP1; D014157:Transcription Factors; D013762:Tetrahydrofolate Dehydrogenase