ABSTRACT
The passage from proliferation to terminal differentiation is critical for normal development and is often perturbed in malignancies. To define the molecular mechanisms that govern this process during erythropoiesis, we have used tagging/proteomics approaches and characterized protein complexes nucleated by TAL-1/SCL, a basic helix-loop-helix transcription factor that specifies the erythrocytic lineage. In addition to known TAL-1 partners, GATA-1, E2A, HEB, LMO2 and Ldb1, we identify the ETO2 repressor as a novel component recruited to TAL-1 complexes through interaction with E2A/HEB. Ectopic expression and siRNA knockdown experiments in hematopoietic progenitor cells show that ETO2 actively represses erythroid TAL-1 target genes and governs the expansion of erythroid progenitors. At the onset of erythroid differentiation, a change in the stoichiometry of ETO2 within the TAL-1 complex activates the expression of known erythroid-specific TAL-1 target genes and of Gfi-1b and p21(Cip), encoding two essential regulators of erythroid cell proliferation. These results suggest that the dynamics of ETO2 recruitment within nuclear complexes couple cell proliferation to cell differentiation and determine the onset of terminal erythroid maturation.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Differentiation/physiology , Cell Proliferation , Erythropoiesis/physiology , Gene Expression Regulation, Developmental , Nuclear Proteins/physiology , Proto-Oncogene Proteins/metabolism , Transcription Factors/physiology , Animals , Cell Line , Chromatin Immunoprecipitation , Flow Cytometry , Green Fluorescent Proteins , Hematopoietic Stem Cells/metabolism , Immunoblotting , Immunoprecipitation , Mice , Nuclear Proteins/metabolism , RNA, Small Interfering/metabolism , Repressor Proteins , T-Cell Acute Lymphocytic Leukemia Protein 1 , Transcription Factors/metabolismABSTRACT
Mulibrey nanism is an autosomal recessive prenatal-onset growth disorder of unknown pathogenesis. The main clinical features are pre- and postnatal growth failure, characteristic dysmorphic craniofacial features, heart disease, and hepatomegaly. Five truncating mutations in the TRIM37 gene have previously been reported in Mulibrey nanism patients. The TRIM37 protein encodes a novel protein of unknown function. It contains a tripartite motif (TRIM, also denoted the RING-B-box-Coiled-coil or RBCC domain) and a TRAF (tumor necrosis factor-receptor associated factor) domain. TRIM37 localizes to peroxisomes classifying Mulibrey nanism as a peroxisomal disorder. Here we have characterized the genomic structure of the TRIM37 gene, which has 24 exons spanning approximately 109 kb of genomic DNA. Further, we report six novel disease-associated mutations, five of which predict a truncated protein: c.745C>T (p.Gln249X), c.1411C>T (p.Arg471X), c.2056C>T (p.Arg686X), and an 8.6 kb genomic deletion (c.1314+507_1668-207del resulting in p.Arg439fsX4). The sixth mutation (c.965G>T) is the first missense mutation (p.Gly322Val) associated with Mulibrey nanism. It affects the TRAF domain of TRIM37 and results in altered subcellular localization of the mutant TRIM37 protein, further suggesting that it is pathogenic.
