Bcr-Abl oncoproteins bind directly to activators of the Ras signalling pathway.
The cytosolic 185 and 210 kDa Bcr-Abl protein tyrosine kinases play important roles in the development of Philadelphia chromosome positive (Ph+) chronic myelogenous leukemia (CML) and acute lymphoblastic leukemia (Ph+ ALL). p185 and p210 Bcr-Abl contain identical abl-encoded sequences juxtaposed to a variable number of bcr-derived amino acids. As the mitogenic and transforming activities of tyrosine kinases involve stimulation of the Ras pathway, we analyzed Bcr-Abl oncoproteins for interactions with cytoplasmic proteins that mediate Ras activation. Such polypeptides include Grb2, which comprises a single Src homology 2 (SH2) domain flanked by two SH3 domains, and the 66, 52 and 46 kDa Shc proteins which possess an SH2 domain in their carboxy-terminus. Grb2 associates with tyrosine phosphorylated proteins through its SH2 domain, and with the Ras guanine nucleotide releasing protein mSos1 through its SH3 domains. mSos1 stimulates conversion of the inactive GDP-bound form of Ras to the active GTP-bound state. In bcr-abl-transformed cells, Grb2 and mSos1 formed a physical complex with Bcr-Abl. In vitro, the Grb2 SH2 domain bound Bcr-Abl through recognition of a tyrosine phosphorylation site within the amino-terminal bcr-encoded sequence (p.Tyr177-Val-Asn-Val), that is common to both Bcr-Abl proteins. These results suggest that autophosphorylation within the Bcr element of Bcr-Abl creates a direct physical link to Grb2-mSos1, and potentially to the Ras pathway, and thereby modifies the target specificity of the Abl tyrosine kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
Puil
L
L
Division of Molecular and Developmental Biology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
Liu
J
J
Gish
G
G
Mbamalu
G
G
Bowtell
D
D
Pelicci
P G
PG
Arlinghaus
R
R
Pawson
T
T
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D051380:GRB2 Adaptor Protein; D051379:Mice; D008969:Molecular Sequence Data; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D011506:Proteins; D014443:Tyrosine; D016044:Fusion Proteins, bcr-abl; D015689:Oncogene Protein p21(ras)