Association of Grb2 with Sos and Ras with Raf-1 upon gamma irradiation of breast cancer cells.
Raf-1 protein serine/threonine kinase has been implicated in growth and damage-responsive signal transduction pathways. Several reports indicate an important role of Ras protein in the growth factor-induced activation of Raf-1. Here we investigated the possible involvement of Ras in ionizing radiation-induced activation of Raf-1. Irradiation of MDA-MB 231 human breast cancer cells caused an increase in GTP-binding and hydrolysis on Ras, and co-immunoprecipitations of endogenous Grb2 with Sos and Raf-1 with Ras. An increase in the level of membrane-bound Raf-1, and tyrosine-phosphorylation of Raf-1 were observed after irradiation. Consistent with these changes, irradiation of cells stimulated the catalytic activity of Raf-1. Finally, radiation treatment of breast cancer cells led to an increase in the phosphorylation and activity of the mitogen-activated protein kinase. Based on these biochemical modifications in vivo, we conclude that Raf-1 functions as an effector of Ras in the radiation-responsive signal transduction pathway leading to the activities of Raf-1 and mitogen-activated protein kinase.
Suy
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Department of Radiation Medicine, Lombardi Cancer Center, Georgetown University, Washington, DC 20007, USA.
Anderson
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WB
Dent
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P
Chang
E
E
Kasid
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D048868:Adaptor Proteins, Signal Transducing; D001943:Breast Neoplasms / Q000378:metabolism*; D066246:ErbB Receptors / Q000528:radiation effects; D051380:GRB2 Adaptor Protein; D006801:Humans; D008565:Membrane Proteins / Q000528:radiation effects*; D008954:Models, Biological; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000528:radiation effects*; D011506:Proteins / Q000528:radiation effects*; D011518:Proto-Oncogene Proteins / Q000528:radiation effects*; D019908:Proto-Oncogene Proteins c-raf; D011839:Radiation, Ionizing; D015398:Signal Transduction; D020664:Son of Sevenless Proteins; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism / Q000528:radiation effects*
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D008565:Membrane Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D020664:Son of Sevenless Proteins; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins