title: Negative regulation of p120GAP GTPase promoting activity by p210bcr/abl: implication for RAS-dependent Philadelphia chromosome positive cell growth.
abstract: The p210bcr/abl tyrosine kinase appears to be responsible for initiating and maintaining the leukemic phenotype in chronic myelogenous leukemia (CML) patients. p21ras-p120GAP interactions play a central role in transducing mitogenic signals. Therefore, we investigated whether p21ras and p120GAP are regulated by p210bcr/abl, and whether this activation is functionally significant for CML cell proliferation. We report that transient expression of p210bcr/abl in fibroblast-like cells induces simultaneous activation of p21ras and inhibition of GTPase-promoting activity of p120GAP, and confirm these data showing that downregulation of p210bcr/abl expression in CML cells with bcr/abl antisense oligodeoxynucleotides induces both inhibition of p21ras activation and stimulation of GTPase-promoting activity of p120GAP. Tyrosine phosphorylation of two p120GAP-associated proteins, p190 and p62, which may affect p120GAP activity, also depends on p210bcr/abl tyrosine kinase expression. Direct dependence of these effects on the kinase activity is proven in experiments in which expression of c-MYB protein in fibroblast-like cells or downregulation of c-MYB expression resulting in analogous inhibition of CML cell proliferation does not result in the same changes. Use of specific antisense oligodeoxynucleotides to downregulate p21ras expression revealed a requirement for functional p21ras in the proliferation of Philadelphia chromosome-positive CML primary cells. Thus, the p210bcr/abl-dependent regulation of p120GAP activity is responsible, in part, for the maintenance of p21ras in the active GTP-bound form, a crucial requirement for CML cell proliferation.
authors.affiliation: Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: T
authors.initials: T
authors.lastname: Skorski
authors.forename: P
authors.initials: P
authors.lastname: Kanakaraj
authors.forename: D H
authors.initials: DH
authors.lastname: Ku
authors.forename: M
authors.initials: M
authors.lastname: Nieborowska-Skorska
authors.forename: E
authors.initials: E
authors.lastname: Canaani
authors.forename: G
authors.initials: G
authors.lastname: Zon
authors.forename: B
authors.initials: B
authors.lastname: Perussia
authors.forename: B
authors.initials: B
authors.lastname: Calabretta
mesh_terms: D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002884:Chromosomes, Human, Pair 15; D002886:Chromosomes, Human, Pair 17; D002892:Chromosomes, Human, Pair 22; D002899:Chromosomes, Human, Pair 9; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006706:Homeostasis; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics; D008969:Molecular Sequence Data; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D009857:Oncogenes / Q000187:drug effects; D010677:Philadelphia Chromosome; D011506:Proteins / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D011519:Proto-Oncogenes / Q000187:drug effects; D015398:Signal Transduction; D014178:Translocation, Genetic; D014407:Tumor Cells, Cultured; D020703:ras GTPase-Activating Proteins
chemical_list: D020690:GTPase-Activating Proteins; D016376:Oligonucleotides, Antisense; D011506:Proteins; D020703:ras GTPase-Activating Proteins; D016044:Fusion Proteins, bcr-abl; D020558:GTP Phosphohydrolases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)