RESUMO
The growth factor independence-1 (Gfi1) transcription factor is required for proper development of neuroendocrine cells, sensory neurons, and blood. Patients with mutations in Gfi1 exhibit severe congenital neutropenia (SCN) or non-immune chronic idiopathic neutropenia of adults. Gfi1 was initially described as an oncoprotein that mediates tumor progression in a mouse model of leukemia; however, recent data suggest that Gfi1 may act as either an oncogene or an anti-proliferative tumor suppressor gene depending on the cell type. Here we review the latest literature on Gfi1, and emphasize its role in the hematopoietic, sensory and neuroendocrine systems.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Proteínas Oncogênicas/metabolismo , Fatores de Transcrição/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Animais , Proteínas de Ligação a DNA/genética , Hematopoese/genética , Humanos , Camundongos , Neurônios Aferentes/metabolismo , Sistemas Neurossecretores/metabolismo , Neutropenia/genética , Neutropenia/metabolismo , Proteínas Oncogênicas/genética , Especificidade de Órgãos , Fatores de Transcrição/genética , Proteínas Supressoras de Tumor/genéticaRESUMO
DNA damage induced by ionizing radiation (IR) activates a complex cellular response that includes checkpoints leading to cell cycle arrest. The stress-activated mitogen-activated protein kinase (MAPK) p38gamma has been implicated in the G(2) phase checkpoint induced by IR. We recently discovered MRK as a member of the MAPK kinase kinase family that activates p38gamma. Here we investigated the role of MRK in the checkpoint response to IR. We identified autophosphorylation sites on MRK that are important for its kinase activity. A phosphospecific antibody that recognizes these sites showed that MRK is activated upon IR in a rapid and sustained manner. MRK depletion by RNA interference resulted in defective S and G(2) checkpoints induced by IR that were accompanied by reduced Chk2 phosphorylation and delayed Cdc25A degradation. We also showed that Chk2 is a substrate for MRK in vitro and is phosphorylated at Thr(68) by active MRK in cells. MRK depletion also increased sensitivity to the killing effects of IR. In addition, MRK depletion reduced IR-induced activation of p38gamma but had no effect on p38alpha activation, indicating that MRK is a specific activator of p38gamma after IR. Inhibition of p38gamma by RNA interference, however, did not impair IR-induced checkpoints. Thus, in response to IR MRK controls two independent pathways: the Chk2-Cdc25A pathway leading to cell cycle arrest and the p38gamma MAPK pathway.
Assuntos
Ciclo Celular/fisiologia , Dano ao DNA , Proteína Quinase 12 Ativada por Mitógeno/metabolismo , Proteínas Quinases/metabolismo , Sequência de Aminoácidos , Animais , Proteínas Mutadas de Ataxia Telangiectasia , Proteínas de Ciclo Celular , Linhagem Celular , Quinase do Ponto de Checagem 2 , Proteínas de Ligação a DNA , Ativação Enzimática , Humanos , MAP Quinase Quinase Quinases , Dados de Sequência Molecular , Fosforilação , Proteínas Quinases/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Radiação Ionizante , Alinhamento de Sequência , Proteínas Supressoras de Tumor , Fosfatases cdc25/metabolismoRESUMO
Mitogen-activated protein (MAP) kinase pathways are three-kinase modules that mediate diverse cellular processes and have been highly conserved among eukaryotes. By using a functional complementation screen in yeast, we have identified a human MAP kinase kinase kinase (MAPKKK) that shares homology with members of the mixed lineage kinase (MLK) family and therefore was called MRK (MLK-related kinase). We report the structure of the MRK gene, from which are generated two splice forms of MRK, MRK-alpha and MRK-beta, encoding for proteins of 800 and 456 amino acids, respectively. By using a combination of solid phase protein kinase assays, transient transfections in cells, and analysis of endogenous proteins in stably transfected Madin-Darby canine kidney cells, we found that MRK-beta preferentially activates ERK6/p38gamma via MKK3/MKK6 and JNK through MKK4/MKK7. We also show that expression of wild type MRK increases the cell population in the G(2)/M phase of the cell cycle, whereas dominant negative MRK attenuates the G(2) arrest caused by gamma-radiation. In addition, exposure of cells to gamma-radiation induces MRK activity. These data suggest that MRK may mediate gamma-radiation signaling leading to cell cycle arrest and that MRK activity is necessary for the cell cycle checkpoint regulation in cells.