Bcr-Abl oncoproteins bind directly to activators of the Ras signalling pathway.

Abstract

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)

Effect of Bcr sequences on the cellular function of the Bcr-Abl oncoprotein

“…The Bcr domains are: Region 1, OLIGO: oligomerization domain, which is the coiled-coil in Bcr aa 1 ± 63 . Region 2, Y177: tyrosine 177 which when phosphorylated binds to the GRB-2 SH2 domain (Pendergast et al, 1993;Puil et al, 1994). Region 3 SH2-B: SH2 binding domain, in Bcr aa 192 ± 413.…”

“…However, the contribution of these domains is dependent on the transforming assays. For example, tyrosine 177 of Bcr, a binding site for SH2 domains such as the one in the adaptor GRB2, is required for the transformation of Rat-1/myc cells (Pendergast et al, 1993;Puil et al, 1994), but dispensable for transformation of bone marrow cells (Goga et al, 1995). The SH2 domain of Abl is required for the transformation of Rat-1/myc cells and bone marrow cells, but is not required for the abrogation of IL-3 dependence .…”

“…The Bcr sequence between aa 175 ± 191 is critical for transformation of Rat-1/myc cells (Table 1) most likely because this region contains tyrosine 177 which when phosphorylated binds to GRB2 (Pendergast et al, 1993;Puil et al, 1994). There is strong evidence that Bcr-Abl must form a complex with GRB2 in order to transform ®broblastic cells (Pendergast et al, 993;Puil et al, 1994).…”

“…There is strong evidence that Bcr-Abl must form a complex with GRB2 in order to transform ®broblastic cells (Pendergast et al, 993;Puil et al, 1994). The association of Bcr-Abl with GRB2 is thought to induce the constitutive activation of the mitogenic RasRaf-MAP-kinase signaling pathway.…”

The SH2-containing adapter protein GRB10 interacts with BCR-ABL

“…SH2-containing molecules known to interact with Bcr-Abl include the adapter molecule Grb2 and SHC (Pendergast et al, 1993b;Puil et al, 1994;Tauchi et al, 1994a), the phosphotyrosine phosphatase Syp (Tauchi et al, 1994b) and the regulatory subunit (p85) of phosphatidylinositol 3'-kinase (p85PI3K) (Skorski et al, 1995).…”