INCREASED TYROSINE PHOSPHORYLATION OF FOCAL ADHESION PROTEINS IN MYELOID CELL-LINES EXPRESSING P210(BCR ABL)/

The BCR/ABL oncogene causes chronic myelogenous leukemia (CML) in huma ns and induces growth factor independence of hematopoietic cell lines in tissue culture. p210(BCR/ABL) is localized at least in part to the cytoskeleton, and has been shown to interact directly with actin filam ents through an actin binding domain located in the C-terminus of ABL. CML cells have reduced adhesion to some extracellular matrix componen ts but the mechanism of this phenomenon is unknown. In this study we e xamined tyrosine phosphorylation of focal adhesion proteins in cells e xpressing p210(BCR/ABL) An interleukin-3 (IL-3)-dependent cell line, 3 2Dc13, was transformed with a BCR/ABL cDNA, and the patterns of locali zation, expression, and tyrosine phosphorylation of focal adhesion pro teins were compared among untransformed 32Dc13 cells with and without IL-3 stimulation and BCR/ABL-transformed 32Dc13 cells. Of the focal ad hesion proteins examined, only paxillin exhibited tyrosine phosphoryla tion in response to IL-3; while in cells transformed by p210(BCR/ABL), paxillin, vinculin, p125(FAK), talin and tensin were constitutively t yrosine phosphorylated. IL-3 induced a transient association between p axillin and vinculin, while in BCR/ABL-transformed cells, several prot eins coimmunoprecipitated with paxillin, including vinculin, p125(FAK) , talin and tensin. Pseudopodia enriched in focal adhesion proteins we re transiently detected in 32Dc13 cells in response to IL-3, but const itutively detected in cells expressing p210(BCR/ABL). P210(BCR/ABL) pr otein was also found concentrated in punctate structures adjacent to t he cell membrane in myeloid cell lines, which often contained vinculin and paxillin. Since the focal adhesion is where the interaction betwe en integrins and actin filaments is believed to occur, the observed ef fect of p210(BCR/ABL) on food adhesion protein interactions in myeloid cell lines could contribute to the adhesion defects in CML cells.