title: Apoptosis regulation by interaction of Bcl-2 protein and Raf-1 kinase.
abstract: The Bcl-2 protein is over-produced in many types of human tumors and suppresses apoptosis induced by a wide-variety of stimuli, including chemotherapeutic drugs and gamma-irradiation. The biochemical mechanism of action of the Bcl-2 protein however remains enigmatic. Here we show that Bcl-2 can be co-immunoprecipitated with the serine/threonine-specific Raf-1 kinase both in a mammalian hemopoietic cell 32D.3 and when the two proteins are produced in Sf9 insect cells using recombinant baculoviruses. Though analysis of Raf-1 deletion mutants suggested that the C-terminal half of the protein which contains the catalytic domain is sufficient for co-immunoprecipitation with Bcl-2, Raf-1 does not appear to induce phosphorylation of Bcl-2 protein in 32D.3 and Sf9 cells. Furthermore, a mutant form of Raf-1 that lacks kinase activity could still be co-immunoprecipitated with Bcl-2 in Sf9 cells, suggesting that the interaction of these proteins does not reflect a kinase-substrate relation. Gene transfer experiments using 32D.3 hemopoietic cells demonstrated functional synergy between Bcl-2 and Raf-1 with regards to suppression of apoptosis induced by growth factor withdrawal. Taken together, these observations for the first time functionally link Bcl-2 to a signal transducing protein and suggest that the interaction of the Bcl-2 and Raf-1 proteins may be responsible for their ability to cooperate in the suppression of apoptosis.
authors.affiliation: La Jolla Cancer Research Foundation, Cancer Research Center, CA 92037.
authors.forename: H G
authors.initials: HG
authors.lastname: Wang
authors.forename: T
authors.initials: T
authors.lastname: Miyashita
authors.forename: S
authors.initials: S
authors.lastname: Takayama
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Torigoe
authors.forename: S
authors.initials: S
authors.lastname: Krajewski
authors.forename: S
authors.initials: S
authors.lastname: Tanaka
authors.forename: L
authors.initials: L
authors.lastname: Hovey
authors.forename: J
authors.initials: J
authors.lastname: Troppmair
authors.forename: U R
authors.initials: UR
authors.lastname: Rapp
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2; D019908:Proto-Oncogene Proteins c-raf; D014162:Transfection
chemical_list: D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf