The CRKL adaptor protein transforms fibroblasts and functions in transformation by the BCR-ABL oncogene

The CRKL adaptor protein was recently identified as a substrate for the BCR-ABL tyrosine kinase in patients with chronic myelogenous leukemia, but its function is unknown. Here we report that CRKL is phosphorylated when overexpressed, activates RAS and JUN kinase signaling pathways, and transforms fibroblasts in a RAS-dependent fashion. We examined the potential role of CRKL in BCR-ABL function by deleting the CRKL binding site in BCR-ABL. This mutant BCR-ABL protein shows a 50% reduction in fibroblast transforming activity. The GRB2 adaptor protein has previously been implicated in this pathway, presumably linking BCR-ABL to RAS. To address the relative roles of CRKL and GRB2 in this system, we compared BCR-ABL mutants with defects in binding to one or both adaptors. Whereas each single mutant showed a 2-3-fold loss in transforming activity, the double mutant showed a 15-fold reduction, suggesting that GRB2 and CRKL both contribute to BCR-ABL transformation. These results demonstrate the oncogenic potential of CRKL and provide functional evidence that CRKL plays a role in fibroblast transformation by BCR-ABL in conjunction with other adaptor proteins.