title: Differential regulation of gene expression by PITX2 isoforms.
abstract: Three major PITX2 isoforms are differentially expressed in human, mice, zebrafish, chick, and frog tissues. To demonstrate differential regulation of gene expression by these isoforms we used three different promoters and three cell lines. Transient transfection of Chinese hamster ovary, HeLa, and LS-8 cell lines revealed differences in PITX2A and PITX2C activation of the PLOD1 and Dlx2 promoters, however, PITX2B is inactive. In contrast, PITX2B actives the pituitary-specific Prolactin promoter at higher levels than either PITX2A or PITX2C. Interestingly, co-transfection of either PITX2A or PITX2C with PITX2B results in a synergistic activation of the PLOD1 and Dlx2 promoters. Furthermore, PITX2 isoforms have different transcriptional activity dependent upon the cells used for transfection analysis. We have isolated a fourth PITX2 isoform (PITX2D) expressed only in humans, which acts to suppress the transcriptional activity of the other PITX2 isoforms. Electrophoretic mobility shift assays and glutathione S-transferase pull-down experiments demonstrated that all isoforms interact with PITX2D and that PITX2B forms heterodimeric complexes with PITX2A and PITX2C. Our research provides a molecular basis for differential gene regulation through the expression of PITX2 isoforms. PITX2 isoform activities are both promoter- and cell-specific, and our data reveal new mechanisms for PITX2-regulated gene expression.
authors.affiliation: Department of Biological Science, The University of Tulsa, Oklahoma 74104-3189, USA.
authors.forename: Carol J
authors.initials: CJ
authors.lastname: Cox
authors.forename: Herbert M
authors.initials: HM
authors.lastname: Espinoza
authors.forename: Bryan
authors.initials: B
authors.lastname: McWilliams
authors.forename: Kimberly
authors.initials: K
authors.lastname: Chappell
authors.forename: Lisa
authors.initials: L
authors.lastname: Morton
authors.forename: Tord A
authors.initials: TA
authors.lastname: Hjalt
authors.forename: Elena V
authors.initials: EV
authors.lastname: Semina
authors.forename: Brad A
authors.initials: BA
authors.lastname: Amendt
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003598:Cytoskeletal Proteins; D004247:DNA; D004268:DNA-Binding Proteins / Q000235:genetics; D019281:Dimerization; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000502:physiology*; D006801:Humans; D009687:Nuclear Proteins; D011388:Prolactin / Q000235:genetics; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000502:physiology*; D016601:RNA-Binding Proteins; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D000097577:Homeobox Protein PITX2
chemical_list: D003598:Cytoskeletal Proteins; D004247:DNA; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D011388:Prolactin; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2; C088334:Distal-less homeobox proteins; C093661:Tes protein, mouse