title: Structural and functional analysis of the human KB cell folate receptor gene P4 promoter: cooperation of three clustered Sp1-binding sites with initiator region for basal promoter activity.
abstract: The human folate receptors (hFRs) are important in the cellular accumulation of folates and antifolates. We described the structure of the human KB cell FR (hFR-KB) gene and identified two discrete promoter regions (P1 and P4) upstream from exons 1 and 4, respectively (Elwood et al., 1993). To further understand the molecular basis of hFR expression, we have now analyzed the basal transcription of the P4 promoter localized upstream of a major transcription start site. The sequence upstream from exon 4 contains several potential transcriptional factor-binding sites and a consensus initiator region sequence at the transcription start site but does not contain canonical TATA or CAAT boxes. While deletion of a 5' flanking sequence from nt -1023 to nt -605 of P4 promoter region decreases the luciferase reporter gene expression in KB cells to 54-70% of control construct, the removal of the sequence between nt -292 and nt -46 markedly decreases the activity to 3%. DNase I footprints and competitive mobility shift and supershift mobility assays indicate that Sp1 or Sp1-related nuclear protein(s) bind to three clustered GC-rich regions within the sequence between nt -292 and nt -46 of the hFR-KB P4 promoter. Both in vitro and in vivo analyses of the expression of promoter constructs containing site-specific mutation(s) of these three Sp1-binding sites and initiator sequence demonstrate that each of three Sp1 sites and the initiator sequence are required for optimum promoter activity and that they interact cooperatively in this P4 promoter of the hFR-KB gene.
authors.affiliation: Medicine Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Saikawa
authors.forename: K
authors.initials: K
authors.lastname: Price
authors.forename: K W
authors.initials: KW
authors.lastname: Hance
authors.forename: T Y
authors.initials: TY
authors.lastname: Chen
authors.forename: P C
authors.initials: PC
authors.lastname: Elwood
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000235:genetics*; D002474:Cell-Free System; D004252:DNA Mutational Analysis; D058973:Folate Receptors, GPI-Anchored; D017930:Genes, Reporter; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000235:genetics*; D017384:Sequence Deletion; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D009687:Nuclear Proteins; D011956:Receptors, Cell Surface; D016329:Sp1 Transcription Factor