DIFFERENTIAL SIGNALING AFTER BETA-1 INTEGRIN LIGATION IS MEDIATED THROUGH BINDING OF CRKL TO P120(CBL) AND P110(HEF1)

CRKL is an SH2-SH3-SH3 adapter protein that is a major substrate of th e BCR/ABL oncogene, The function of CRKL in normal cells is unknown, I n cells transformed by BCR/ABL we have previously shown that CRKL is a ssociated with two focal adhesion proteins, tensin and paxillin, sugge sting that CRKL, could be involved in integrin signaling, In two hemat opoietic cell lines, MO7e and H9, we found that CRKL rapidly associate s with tyrosine-phosphorylated proteins after cross-linking of beta 1 integrins with fibronectin or anti-beta 1 integrin monoclonal antibodi es, The major tyrosine-phosphorylated CRKL-binding protein in the mega karyocytic MO7e cells was identified as p120(CBL), the cellular homolo g of the v-Cbl oncoprotein, However in the lymphoid He cell line, the major tyrosine-phosphorylated CRKL-binding protein was p110(HEF1), In both cases, this binding was mediated by the CRKL SH2 domain, Interest ingly, although both MO7e and H9 cells express p120(CBL) and p110(HEF1 ), beta 1 integrin cross-linking induces tyrosine phosphorylation of p 120(CBL) (but not p110(HEF1)) in MO7e cells and of p110(HEF1) (but not p120(CBL)) in H9 cells, In both cell types, CRKL is constitutively co mplexed to C3G, SOS, and c-ABL through its SH3 domains, and the stoich iometry of these complexes does not change upon integrin ligation, Thu s, in different cell types CRKL and its SH3-associated proteins may fo rm different multimeric complexes depending on whether p120(CBL) or p1 10(HEF1) is tyrosine-phosphorylated after integrin ligation, The shift in association of CRKL and its SH3-associated proteins from p120(CBL) to p110(HEF1) could contribute to different functional outcomes of '' outside-in'' integrin signaling in different cells.