RESUMO
Ataxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by cerebellar ataxia and oculocutaneous telangiectasias. Patients with A-T also have high incidences of type 2 diabetes mellitus. The gene mutated in this disease, ATM (A-T, mutated), encodes a protein kinase. Previous studies have demonstrated that cytoplasmic ATM is an insulin-responsive protein and a major upstream activator of Akt following insulin treatment. To further investigate the function of ATM in insulin signal transduction, insulin resistance was induced in rats by feeding them a high-fat diet. Muscle tissue of rats with insulin resistance had both dramatically reduced ATM levels and substantially decreased Akt phosphorylation at Ser473 in comparison to that of regular chow-fed controls. The decreased ATM expression suggests that ATM is involved in the development of insulin resistance through down-regulation of Akt activity. The role of ATM in activation of Akt was further confirmed in mouse embryonic fibroblast (MEF) A29 (ATM+/+) and A38 (ATM-/-) cells. In addition, insulin-mediated Akt phosphorylation in mouse L6 muscle cells was greatly reduced by KU-55933, a specific inhibitor of ATM. A 2-deoxyglucose incorporation assay showed that this inhibitor also caused a significant reduction in insulin-mediated glucose uptake in L6 cells. An immunofluorescence experiment demonstrated that in L6 cells transfected with wild-type (WT) ATM, insulin caused a dramatic increase of the cell surface glucose transporter 4 (GLUT4), while in cells transfected with kinase-dead (KD) ATM, translocation of GLUT4 to the cell surface in response to insulin was markedly inhibited.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Transportador de Glucose Tipo 4/metabolismo , Resistência à Insulina , Insulina/farmacologia , Músculo Esquelético/enzimologia , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Animais , Proteínas Mutadas de Ataxia Telangiectasia , Proteínas de Ciclo Celular/genética , Linhagem Celular , Proteínas de Ligação a DNA/genética , Ativação Enzimática , Masculino , Camundongos , Proteínas Serina-Treonina Quinases/genética , Transporte Proteico , Ratos , Ratos Wistar , Proteínas Supressoras de Tumor/genéticaRESUMO
Ataxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by cerebellar ataxia and oculocutaneous telangiectasias. The gene mutated in this disease, Atm (A-T mutated), encodes a serine/threonine protein kinase that has been traditionally considered to be a nuclear protein controlling cell-cycle progression. However, many of the growth abnormalities observed in patients with A-T, including neuronal degeneration and insulin resistance, remain difficult to explain with nuclear localization of ATM. Here, recent advances in elucidating the cytoplasmic localization and function of ATM are reviewed. Particular attention is given to the role of ATM in insulin signaling and Akt activation. The potential for cytoplasmic ATM protein kinase to be an emerging therapeutic target for treating diabetes, cancer and neuronal degeneration is discussed.
Assuntos
Ataxia Telangiectasia/fisiopatologia , Proteínas de Ciclo Celular/metabolismo , Citoplasma/enzimologia , Proteínas de Ligação a DNA/metabolismo , Diabetes Mellitus/tratamento farmacológico , Neoplasias/tratamento farmacológico , Degeneração Neural/tratamento farmacológico , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Ataxia Telangiectasia/genética , Proteínas Mutadas de Ataxia Telangiectasia , Proteínas de Ciclo Celular/genética , Proteínas de Ligação a DNA/genética , Diabetes Mellitus/genética , Diabetes Mellitus/metabolismo , Humanos , Terapia de Alvo Molecular , Neoplasias/genética , Neoplasias/metabolismo , Degeneração Neural/genética , Degeneração Neural/metabolismo , Proteínas Serina-Treonina Quinases/genética , Proteínas Supressoras de Tumor/genéticaRESUMO
Ataxia-telangiectasia (A-T) is a human autosomal recessive disorder characterized by neuronal degeneration as well as many other physiological and somatic defects. ATM (A-T, mutated), the gene mutated in A-T, encodes a 370 kDa protein kinase. ATM knockout mouse models (ATM(-/-)) show growth retardation, infertility, neurological dysfunction, defects in T-lymphocytes, and extreme sensitivity to ionizing radiation. We have recently established multiple ATM(+/-) breeding pairs and discovered that all ATM(-/-) offspring exhibit a nonpigmented section of tail, usually at or near the tip. To our knowledge, this is the first time that a phenotype of nonpigmented tail has been reported in ATM(-/-) knockout mice. We believe that the sections of nonpigmented tail of 129S6/SvEvTac-ATM(tm1Awb)/J mice provide a novel phenotypic marker for research using this ATM knockout mouse model. Results from histochemistry and immunoblotting analysis further demonstrate that while melanocyte precursors or melanoblasts are present in the nonpigmented tail tissue of ATM(-/-) mice, they fail to differentiate fully into mature melanocytes. The potential connection between this phenotype and other clinical symptoms caused by ATM deficiency, such as progressive neuronal degeneration, is discussed in this article.