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)
Mesh Terms:
Adaptor Proteins, Signal Transducing, Amino Acid Sequence, Animals, Binding Sites, Cell Line, Transformed, Cell Transformation, Neoplastic, Fusion Proteins, bcr-abl, GRB2 Adaptor Protein, Mice, Molecular Sequence Data, Oncogene Protein p21(ras), Phosphorylation, Proteins, Signal Transduction, Tyrosine
EMBO J.
Date: Feb. 15, 1994
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