The SCL complex regulates c-kit expression in hematopoietic cells through functional interaction with Sp1

• Published in: Blood Vol. 100; no. 7; pp. 2430 - 2440
• Main Authors: LECUYER, Eric, HERBLOT, Sabine, SAINT-DENIS, Marianne, MARTIN, Richard, BEGLEY, C. Glenn, PORCHER, Catherine, ORKIN, Stuart H, HOANG, Trang
• Format: Journal Article
• Language: English
• Published: Washington, DC The Americain Society of Hematology 01.10.2002
• Subjects: 3T3 Cells; Animals; Base Sequence; Basic Helix-Loop-Helix Transcription Factors; Biological and medical sciences; Bone Marrow Cells - cytology; Bone Marrow Cells - physiology; Cell differentiation, maturation, development, hematopoiesis; Cell Line; Cell physiology; DNA Primers; DNA-Binding Proteins - deficiency; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Helix-Loop-Helix Motifs; Hematologic and hematopoietic diseases; Hematopoietic Stem Cells - physiology; Leukemias. Malignant lymphomas. Malignant reticulosis. Myelofibrosis; Medical sciences; Mice; Mice, Knockout; Molecular and cellular biology; Molecular Sequence Data; Polymerase Chain Reaction; Proto-Oncogene Proteins - deficiency; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-kit - genetics; Proto-Oncogenes; Recombinant Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Sp1 Transcription Factor - metabolism; T-Cell Acute Lymphocytic Leukemia Protein 1; Transcription Factors - deficiency; Transcription Factors - genetics; Transcription Factors - metabolism; Transfection; Gene interaction; Rodentia; Hematopoietic cell; Molecular interaction; Gene expression; Vertebrata; Regulation(control); Mammalia; Transcription factor SCL/TAL1; Mouse; Hematopoiesis; Animal; C-Onc gene; Established cell line; Genetics; Transcription factor
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2002-02-0568

The combinatorial interaction among transcription factors is believed to determine hematopoietic cell fate. Stem cell leukemia (SCL, also known as TAL1 [T-cell acute lymphoblastic leukemia 1]) is a tissue-specific basic helix-loop-helix (bHLH) factor that plays a central function in hematopoietic development; however, its target genes and molecular mode of action remain to be elucidated. Here we show that SCL and the c-Kit receptor are coexpressed in hematopoietic progenitors at the single-cell level and that SCL induces c-kit in chromatin, as ectopic SCL expression in transgenic mice sustains c-kit transcription in developing B lymphocytes, in which both genes are normally down-regulated. Through transient transfection assays and coimmunoprecipitation of endogenous proteins, we define the role of SCL as a nucleation factor for a multifactorial complex (SCL complex) that specifically enhances c-kit promoter activity without affecting the activity of myelomonocytic promoters. This complex, containing hematopoietic-specific (SCL, Lim-only 2 (LMO2), GATA-1/GATA-2) and ubiquitous (E2A, LIM- domain binding protein 1 [Ldb-1]) factors, is tethered to DNA via a specificity protein 1 (Sp1) motif, through direct interactions between elements of the SCL complex and the Sp1 zinc finger protein. Furthermore, we demonstrate by chromatin immunoprecipitation that SCL, E2A, and Sp1 specifically co-occupy the c-kit promoter in vivo. We therefore conclude that c-kit is a direct target of the SCL complex. Proper activation of the c-kit promoter depends on the combinatorial interaction of all members of the complex. Since SCL is down-regulated in maturing cells while its partners remain expressed, our observations suggest that loss of SCL inactivates the SCL complex, which may be an important event in the differentiation of pluripotent hematopoietic cells.