title: Tyrosine phosphorylation of p120cbl in BCR/abl transformed hematopoietic cells mediates enhanced association with phosphatidylinositol 3-kinase.
abstract: Increased tyrosine kinase activity of abl oncogene in Philadelphia chromosome positive-leukemic cells leads to activation of p21ras and phosphatidylinositol 3'-kinase (PI 3-Kinase). The mechanism of activation of these signaling pathways is not understood, but numerous studies have focused on the identification and characterization of downstream substrates of BCR/abl tyrosine kinase as potential mediators of oncogenic signaling. It was recently found that the 120 kDa protein product of the c-cbl proto-oncogene is highly tyrosine phosphorylated and associates with BCR/abl in transformed hematopoietic cells. We have characterized further cbl's involvement in BCR/abl mediated tumorigenesis using growth factor independent BCR/abl transformed BaF3 cells. Our experiments show that, in contrast to other cell types, the in vivo interaction of cbl with GRB2 and p85 is significantly enhanced in BCR/abl transformed BaF3 cells and that tyrosine phosphorylation of cbl leads to a direct interaction with GRB2, p85 and abl SH2 domains. A 14-fold increase in cbl associated PI 3-kinase activity in BCR/abl transformed cells suggests that the binding of p85 SH2 domains to tyrosine phosphorylated cbl may contribute to PI 3-kinase activation. Domain analysis studies indicate that both SH3 domains of GRB2 bind to the proline rich region of cbl in quiescent BaF3 cells, whereas GRB2 SH2 domain interacts with a non-contiguous sequence of cbl in transformed cells. Although the interaction of cbl with GRB2 in transformed cells was facilitated by binding of GRB2 to BCR/abl, phosphorylation of cbl and its interaction with p190 BCR/abl remained unaltered in BaF3 cells transformed by p190Y177F BCR/abl mutant which is unable to bind GRB2. The current information and the data presented here suggest that, although cbl lacks src homology domains, it represents a novel intermediate protein which, by interaction with key SH-containing adaptor proteins, may participate in regulation of the Ras and PI 3-kinase pathways in BCR/abl transformed hematopoietic cells.
authors.affiliation: Tufts University School of Medicine, St. Elizabeth's Medical Center, Boston, Massachusetts 02135, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Jain
authors.forename: W Y
authors.initials: WY
authors.lastname: Langdon
authors.forename: L
authors.initials: L
authors.lastname: Varticovski
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001665:Binding Sites; D001854:Bone Marrow Cells; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D016044:Fusion Proteins, bcr-abl / Q000235:genetics* / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011233:Precipitin Tests; D011506:Proteins / Q000276:immunology / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000276:immunology / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D011817:Rabbits; D014443:Tyrosine / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D018909:src Homology Domains / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D011506:Proteins; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D016044:Fusion Proteins, bcr-abl; C493849:Cbl protein, mouse