RESUMO
The bZip transcription factor MafB is expressed specifically in the myeloid lineage of the hematopoietic system and is up-regulated successively during myeloid differentiation from multipotent progenitors to macrophages. Here we report that this induction reflects an essential role of MafB in early myeloid and monocytic differentiation. We observed that the expression of MafB in transformed chicken hematopoietic precursors dramatically increases the proportion of myeloid colony formation at the expense of multipotent progenitor-type colonies. In addition, the overexpression of MafB in transformed myeloblasts stimulates the rapid formation of macrophages, as judged by morphology, surface marker expression and functional criteria. MafB-induced macrophages exhibit typical levels of phagocytic activity and nitric oxide release after activation by lipopolysaccharide. By contrast, overexpression of the myeloid transcription factor PU.1 in these cells does not induce macrophage differentiation. Furthermore, a dominant-negative allele of MafB inhibits both myeloid colony formation and the differentiation of myeloblasts into macrophages. Taken together, our results indicate that MafB induction is a specific and essential determinant of the monocytic program in hematopoietic cells.
Assuntos
Proteínas Aviárias , Diferenciação Celular , Proteínas de Ligação a DNA , Macrófagos/citologia , Monócitos/citologia , Proteínas Oncogênicas/metabolismo , Transativadores/metabolismo , Fatores de Transcrição , Sequência de Aminoácidos , Animais , Biomarcadores/análise , Linhagem Celular Transformada , Tamanho Celular , Embrião de Galinha , Ensaio de Unidades Formadoras de Colônias , Genes Dominantes/genética , Células-Tronco Hematopoéticas/citologia , Células-Tronco Hematopoéticas/metabolismo , Lipopolissacarídeos/farmacologia , Ativação de Macrófagos/efeitos dos fármacos , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Fator de Transcrição MafB , Monócitos/metabolismo , Mutação/genética , Óxido Nítrico/metabolismo , Proteínas Oncogênicas/genética , Proteínas Oncogênicas v-myb/genética , Proteínas Oncogênicas v-myb/fisiologia , Fagocitose , Ligação Proteica , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Codorniz , Temperatura , Transativadores/genética , Ativação Transcricional , TransfecçãoRESUMO
The transcription factors Ets-1 and AML1 (the alphaBl subunit of PEBP2/CBF) play critical roles in hematopoiesis and leukemogenesis, and cooperate in the transactivation of the T cell receptor (TCR) beta chain enhancer. The DNA binding capacity of both factors is blocked intramolecularly but can be activated by the removal of negative regulatory domains. These include the exon VII domain for Ets-1 and the negative regulatory domain for DNA binding (NRDB) for alphaB1. Here we report that the direct interaction between the two factors leads to a reciprocal stimulation of their DNA binding activity and activation of their transactivation function. Detailed mapping revealed two independent contact points involving the exon VII and NRDB regions as well as the two DNA binding domains. Using deletion variants and dominant interfering mutants, we demonstrate that the interaction between exon VII and NRDB is necessary and sufficient for cooperative DNA binding. The exon VII and NRDB motifs are highly conserved in evolution yet deleted in natural variants, suggesting that the mechanism described is of biological relevance. The mutual activation of DNA binding of Ets and AML1 through the intermolecular interaction of autoinhibitory domains may represent a novel principle for the regulation of transcription factor function.