title: Identification of a pH-responsive DNA region upstream of the transcription start site of human NBCe1-B.
abstract: In rodent incisors two distinct stages of enamel formation can be identified visually based on cell morphology: the secretory stage and the maturation stage. The expression profiles of many genes characterize both stages, including the bicarbonate transport protein NBCe1. Bicarbonate is a requirement for the mineralizing enamel matrix to buffer excessive protons that form as a consequence of hydroxyapatite formation. NBCe1-B mRNA is up-regulated during the maturation stage of amelogenesis, where hydroxyapatite formation predominates. In this study, a presumed 572-bp NBCe1-B promoter region was subcloned into a reporter construct, and within this 572-bp region of DNA we characterized a 285-bp segment that shows an increase of ≈ 2.3-fold in gene-transcription activity when transfected into ameloblast-like cells and cultured in medium maintained at pH 6.8 (vs. pH 7.4). A presumed pH-responsive transcriptional factor-binding domain(s) thus resides in the 285-bp NBCe1-B promoter region where candidate domains include the nuclear factor of kappa light polypeptide gene enhancer in B-cells1(NFKB1), jun proto-oncogene (JUN), and tumor protein p53(TP53)-binding sites. Mutagenesis studies identify that both the NFKB1- and TP53-binding sites are responsive to changes in the extracellular pH. These data help to explain how ameloblasts respond to the altered extracellular milieu of protons by changing their gene-expression profile throughout the stages of amelogenesis.
authors.affiliation: Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Christian M
authors.initials: CM
authors.lastname: Snead
authors.forename: Susan M
authors.initials: SM
authors.lastname: Smith
authors.forename: Negar
authors.initials: N
authors.lastname: Sadeghein
authors.forename: Rodrigo S
authors.initials: RS
authors.lastname: Lacruz
authors.forename: Ping
authors.initials: P
authors.lastname: Hu
authors.forename: Ira
authors.initials: I
authors.lastname: Kurtz
authors.forename: Michael L
authors.initials: ML
authors.lastname: Paine
mesh_terms: D000565:Ameloblasts / Q000378:metabolism*; D000566:Amelogenesis / Q000235:genetics*; D001665:Binding Sites; D002478:Cells, Cultured; D003001:Cloning, Molecular; D017886:Durapatite / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D017930:Genes, Reporter; D006801:Humans; D006863:Hydrogen-Ion Concentration; D052002:NF-kappa B p50 Subunit / Q000235:genetics; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D017422:Sequence Analysis, DNA; D027982:Sodium-Bicarbonate Symporters / Q000096:biosynthesis / Q000235:genetics*; D024363:Transcription Initiation Site; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D015854:Up-Regulation
chemical_list: C000715470:MAS1 protein, human; D052002:NF-kappa B p50 Subunit; C489548:NFKB1 protein, human; D000090063:Proto-Oncogene Mas; D016755:Proto-Oncogene Proteins c-jun; C498898:SLC4A4 protein, human; D027982:Sodium-Bicarbonate Symporters; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D017886:Durapatite