CRKL links p210(BCR/ABL) with paxillin in chronic myelogenous leukemia cells

The Philadelphia chromosome translocation generates a chimeric oncogene, BCR/ABL, which causes chronic myelogenous leukemia (CML). In primary neutrophils from patients with CML, the major novel tyrosine-phosphorylated protein is CRKL, an SH2-SH3-SH3 linker protein which has an overall homology of 60% to CRK, the human homologue of the v-crk oncogene product. Anti-CRKL immunoprecipitates from CML cells, but not normal cells, were found to contain p210(BCR/ABL) and c-ABL. Several other phosphoproteins were also detected in anti-CRKL immunoprecipitates, one of which has been identified as paxillin, a 68-kDa focal adhesion protein which we have previously shown to be phosphorylated by p210(BCR/ABL). Using GST-CRKL fusion proteins, the SH3 domains of CRKL were found to bind c-ABL and p210(BCR/ABL), while the SH2 domain of CRKL bound to paxillin, suggesting that CRKL could physically link p210(BCR/ABL) to paxillin. Paxillin contains three tyrosines in Tyr-X-X-Pro (Y-X-X-P) motifs consistent with amino acid sequences predicted to be optimal for binding to the CRKL-SH2 domain (at positions Tyr-31, Tyr-118, and Tyr- 181). Each of these tyrosine residues was mutated to a phenylalanine residue, and in vitro binding assays indicated that paxillin tyrosines at positions 31 and 118, but not 181, are likely to be involved in CRKL-SH2 binding. These results suggest that the p210(BCR/ABL) oncogene may be physically linked to the focal adhesion-associated protein paxillin in hematopoietic cells by CRKL. This interaction could contribute to the known adhesive defects of CML cells.