THE PROTOONCOGENE PRODUCT P120(CBL) AND THE ADAPTER PROTEINS CRKL ANDC-CRK LINK C-ABL, P190(BCR ABL) AND P210(BCR/ABL) TO THE PHOSPHATIDYLINOSITOL-3' KINASE PATHWAY/

Chronic myelogenous leukemia (CML) and some acute lymphoblastic leukem ias (ALL) are caused by the t(9;22) chromosome translocation, which pr oduces the constitutively activated BCR/ABL tyrosine kinase. When intr oduced into factor dependent hematopoietic cell lines, BCR/ABL induces the tyrosine phosphorylation of many cellular proteins. One prominent BCR/ABL substrate is p120(CBL), the cellular homolog of the v-Cbl onc oprotein. In an effort to understand the possible contribution of p120 (CBL) to transformation by BCR/ABL, we looked for cellular proteins wh ich associate with p120(CBL) in hematopoietic cell lines transformed b y BCR/ABL. In addition to p210(BCR/ABL) and c-ABL, p120(CBL) coprecipi tated with an 85 kDa phosphoprotein, which was identified as the p85 s ubunit of PI3K. Anti-p120(CBL) immunoprecipitates from BCR/ABL-transfo rmed, but not from untransformed, cell lines contained PI3K lipid kina se activity. Interestingly, the adaptor proteins CRKL and c-CRK were a lso found in these complexes. In vitro binding studies indicated that the SH2 domains of CRKL and c-CRK bound directly to p120(CBL), while t he SH3 domains of c-CRK and CRKL bound to BCR/ABL and c-ABL. The N-ter minal and the C-terminal SH2 and the SH3 domain of p85(P13K) bound dir ectly in vitro to p120(CBL). The ABL-SH2, but not ABL-SH3, could also bind to p120(CBL). These data suggest that BCR/ABL may induce the form ation of multimeric complexes of signaling proteins which include p120 (CBL), PI3K, c-CRK or CRKL, c-ABL and BCR/ABL itself.