title: Identification of a TAL1 target gene reveals a positive role for the LIM domain-binding protein Ldb1 in erythroid gene expression and differentiation.
abstract: The TAL1 (or SCL) gene, originally identified from its involvement by a recurrent chromosomal translocation, encodes a basic helix-loop-helix transcription factor essential for erythropoiesis. Although presumed to regulate transcription, its target genes are largely unknown. We show here that a nuclear complex containing TAL1, its DNA-binding partner E47, zinc finger transcription factor GATA-1, LIM domain protein LMO2, and LIM domain-binding protein Ldb1 transactivates the protein 4.2 (P4.2) gene through two E box GATA elements in its proximal promoter. Binding of this complex to DNA was dependent on the integrity of both E box and GATA sites and was demonstrated to occur on the P4.2 promoter in cells. Maximal transcription in transiently transfected cells required both E box GATA elements and expression of all five components of the complex. This complex was shown, in addition, to be capable of linking in solution double-stranded oligonucleotides corresponding to the two P4.2 E box GATA elements. This DNA-linking activity required Ldb1 and increased with dimethyl sulfoxide-induced differentiation of murine erythroleukemia (MEL) cells. In contrast, enforced expression in MEL cells of dimerization-defective mutant Ldb1, as well as wild-type Ldb1, significantly decreased E box GATA DNA-binding activities, P4.2 promoter activity, and accumulation of P4.2 and beta-globin mRNAs. These studies define a physiologic target for a TAL1- and GATA-1-containing ternary complex and reveal a positive role for Ldb1 in erythroid gene expression and differentiation.
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
authors.forename: Zhixiong
authors.initials: Z
authors.lastname: Xu
authors.forename: Suming
authors.initials: S
authors.lastname: Huang
authors.forename: Long-Sheng
authors.initials: LS
authors.lastname: Chang
authors.forename: Alan D
authors.initials: AD
authors.lastname: Agulnick
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Brandt
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001798:Blood Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D050981:Erythroid-Specific DNA-Binding Factors; D050982:GATA1 Transcription Factor; D005786:Gene Expression Regulation; D005809:Genes, Regulator; D018257:Helix-Loop-Helix Motifs; D060588:LIM Domain Proteins; D004915:Leukemia, Erythroblastic, Acute; D008565:Membrane Proteins; D051379:Mice; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D001798:Blood Proteins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D050982:GATA1 Transcription Factor; D060588:LIM Domain Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors; C494689:Gata1 protein, mouse; C486312:LDB1 protein, human; C102084:Ldb1 protein, mouse; C489366:Tal1 protein, mouse; C044791:erythrocyte membrane band 4.2 protein