GTP-dependent association of Raf-1 with Ha-Ras: identification of Raf as a target downstream of Ras in mammalian cells.
Ras is involved in signal transduction of various factors for growth, differentiation, and oncogenesis. Recent studies have revealed several proteins that function upstream and downstream of the Ras signaling pathway. However, its immediate downstream target molecular has not yet been identified. In an effort to identify the Ras-associated downstream proteins, we added recombinant Ha-Ras in a GTP-bound form to cell-free lysates and used several antibodies against Ras to immunoprecipitate Ras complexes. We found that a serine/threonine kinase, Raf-1, was coimmunoprecipitated with Ha-Ras by two anti-Ras antibodies (LA069 and Y13-238), whereas a neutralizing antibody against Ras (Y13-259) could not precipitate Raf-1. The coimmunoprecipitation was observed with a complex of Ras and guanosine 5'-[gamma- thio]triphosphate but not with a complex of Ras and guanosine 5'-[beta-thio]diphosphate. The GTP-dependent association of Ha-Ras with Raf-1 was observed with lysates of various types of cultured cells, including NIH 3T3, pheochromocytoma (PC) 12, Ba/F3, and Jurkat T cells, and also with crude extracts from rat brain. Furthermore, Raf-1 was precipitated with a transforming Ha-Ras mutant ([Val12]Ras) and wild-type Ha-Ras but not with an effector-region mutant ([Leu35,ARg37]Ras) that lacks transforming activity. These results indicate that Ras.GTP physically associates with Raf either directly or through other component(s) and strongly suggest that Raf functions in close downstream proximity to Ras in mammalian cells.
Koide
H
H
DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304-1104.
Satoh
T
T
Nakafuku
M
M
Kaziro
Y
Y
D016475:3T3 Cells; D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008214:Lymphocytes; D051379:Mice; D016716:PC12 Cells; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000302:isolation & purification / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013873:Thionucleotides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)