RESUMO
Transcription factor Growth factor independence 1 (Gfi1) is required for multilineage blood cell development, from stem and progenitor cells to differentiated lymphoid and myeloid cells. Gfi1 expression is rapidly induced by cytokines that control both the adaptive and innate immune systems. Gfi1 itself represses the expression of genes implicated in cell survival, proliferation and differentiation. Changes in Gfi1 expression and function have not only been implicated in neutropenia, allergy, autoimmunity and hyperinflammatory responses, but also in lymphoma and more recently in the development of leukemia. In this study, we review how Gfi1 and its paralogue Gfi1b control the development of blood cells, discuss how changes in Gfi1 and Gfi1b function contribute to hematological disease and report on the molecular function of these proteins.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Hematopoese/fisiologia , Células-Tronco Hematopoéticas/fisiologia , Proteínas Proto-Oncogênicas/fisiologia , Proteínas Repressoras/fisiologia , Fatores de Transcrição/fisiologia , Diferenciação Celular , Citocinas/fisiologia , Proteínas de Ligação a DNA/genética , Regulação da Expressão Gênica , Células-Tronco Hematopoéticas/citologia , Humanos , Proteínas Proto-Oncogênicas/genética , Proteínas Repressoras/genética , Fatores de Transcrição/genética , Transcrição Gênica , Ativação Transcricional , Dedos de Zinco/fisiologiaRESUMO
Ubiquitination plays a major role in many aspects of hematopoiesis. Alterations in ubiquitination have been implicated in hematological cancer. The ubiquitin ligase Triad1 controls the proliferation of myeloid cells. Here, we show that two RING (really interesting new gene) domains in Triad1 differentially bind ubiquitin-conjugating enzymes, UbcH7 and Ubc13. UbcH7 and Ubc13 are known to catalyze the formation of different poly-ubiquitin chains. These chains mark proteins for proteasomal degradation or serve crucial non-proteolytic functions, respectively. In line with the dual Ubc interactions, we observed that Triad1 catalyzes the formation of both types of ubiquitin chains. The biological relevance of this finding was studied by testing Triad1 mutants in myeloid clonogenic assays. Full-length Triad1 and three mutants lacking conserved domains inhibited myeloid colony formation by over 50%. Strikingly, deletion of either RING finger completely abrogated the inhibitory effect of Triad1 in clonogenic growth. We conclude that Triad1 exhibits dual ubiquitin ligase activity and that both of its RING domains are crucial to inhibit myeloid cell proliferation. The differential interaction of the RINGs with Ubcs strongly suggests that the ubiquitination mediated through UbcH7 as well as Ubc13 plays a major role in myelopoiesis.