RESUMO
The LIM-only protein LMO2 is expressed aberrantly in acute T-cell leukaemias as a result of the chromosomal translocations t(11;14) (p13;q11) or t(7;11) (q35;p13). In a transgenic model of tumorigenesis by Lmo2, T-cell acute leukaemias arise after an asymptomatic phase in which an accumulation of immature CD4(-) CD8(-) double negative thymocytes occurs. Possible molecular mechanisms underlying these effects have been investigated in T cells from Lmo2 transgenic mice. Isolation of DNA-binding sites by CASTing and band shift assays demonstrates the presence of an oligomeric complex involving Lmo2 which can bind to a bipartite DNA motif comprising two E-box sequences approximately 10 bp apart, which is distinct from that found in erythroid cells. This complex occurs in T-cell tumours and it is restricted to the immature CD4(- )CD8(-) thymocyte subset in asymptomatic transgenic mice. Thus, ectopic expression of Lmo2 by transgenesis, or by chromosomal translocations in humans, may result in the aberrant protein interactions causing abnormal regulation of gene expression, resulting in a blockage of T-cell differentiation and providing precursor cells for overt tumour formation.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Metaloproteínas/metabolismo , Linfócitos T/metabolismo , Proteínas Adaptadoras de Transdução de Sinal , Animais , Sequência de Bases , Linhagem Celular , Proteínas de Ligação a DNA/imunologia , Soros Imunes , Proteínas com Domínio LIM , Linfoma de Células T/metabolismo , Linfoma de Células T/patologia , Metaloproteínas/imunologia , Camundongos , Camundongos Transgênicos , Oligodesoxirribonucleotídeos , Homologia de Sequência do Ácido Nucleico , Células Tumorais CultivadasRESUMO
The LIM-only protein Lmo2, activated by chromosomal translocations in T-cell leukaemias, is normally expressed in haematopoiesis. It interacts with TAL1 and GATA-1 proteins, but the function of the interaction is unexplained. We now show that in erythroid cells Lmo2 forms a novel DNA-binding complex, with GATA-1, TAL1 and E2A, and the recently identified LIM-binding protein Ldb1/NLI. This oligomeric complex binds to a unique, bipartite DNA motif comprising an E-box, CAGGTG, followed approximately 9 bp downstream by a GATA site. In vivo assembly of the DNA-binding complex requires interaction of all five proteins and establishes a transcriptional transactivating complex. These data demonstrate one function for the LIM-binding protein Ldb1 and establish a function for the LIM-only protein Lmo2 as an obligatory component of an oligomeric, DNA-binding complex which may play a role in haematopoiesis.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Hematopoese/genética , Proteínas Proto-Oncogênicas , Fatores de Transcrição/metabolismo , Transcrição Gênica , Ativação Transcricional , Proteínas Adaptadoras de Transdução de Sinal , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos , Sítios de Ligação , Células COS , Sequência Consenso , Fatores de Ligação de DNA Eritroide Específicos , Genes Reporter , Proteínas com Domínio LIM , Metaloproteínas/metabolismo , Modelos Genéticos , Proteínas Nucleares/metabolismo , Ligação Proteica , Sequências Reguladoras de Ácido Nucleico , Proteína 1 de Leucemia Linfocítica Aguda de Células T , Fatores de Transcrição TCF , Proteína 1 Semelhante ao Fator 7 de Transcrição , TransfecçãoRESUMO
The LIM-only protein Lmo2, originally identified as an oncogenic protein in human T cell leukemia, is essential for erythropoiesis. A possible role for Lmo2 in transcription during erythropoiesis has been investigated. Direct interaction of Lmo2 was observed in vitro and in vivo with the zinc finger transcription factor GATA-1, as well as with the basic helix-loop-helix (bHLH) transcription factor Tall. By using mammalian two-hybrid analysis, E47/Tall/Lmo2/GATA-1 protein complex could be demonstrated. Thus, a molecular link exists between three proteins crucial for erythropoiesis. This data suggest that variations in amounts of complexes involving Lmo2, Tall, and GATA-1 could be important for erythroid differentiation.
