MOLECULAR-CLONING OF HUMAN PAXILLIN, A FOCAL ADHESION PROTEIN PHOSPHORYLATED BY P210(BCR ABL)/

Paxillin is a 68-kDa focal adhesion protein that is phosphorylated on tyrosine residues in fibroblasts in response to transformation by v-sr c, treatment with platelet-derived growth factor, or cross-linking of integrins. Paxillin has been shown to have binding sites for the SH3 d omain of Src and the SH2 domain of Crk in vitro and to coprecipitate w ith two other focal adhesion proteins, vinculin and focal adhesion kin ase (p125(fak)). After preliminary studies showed that paxillin was a substrate for the hematopoietic oncogene p210(BCR/ABL), we investigate d the role of this protein in hematopoietic cell transformation and si gnal transduction. A full-length cDNA encoding human paxillin was clon ed, revealing multiple protein domains, including four tandem LIM doma ins, a proline-rich domain containing a consensus SH3 binding site, an d three potential Crk-SH2 binding sites. The paxillin gene was localiz ed to chromosome 12q24 by fluorescence in situ hybridization analysis. A chicken paxillin cDNA was also cloned and is predicted to encode a protein approximately 90% identical to human paxil-lin. Paxillin copre cipitated with p210(BCR/ABL) and mul-tiple other cellular proteins in myeloid cell lines, suggesting the formation of multimeric complexes. In normal hematopoietic cells and myeloid cell lines, tyrosine phospho rylation of paxillin and co-precipitation with other cellular proteins was rapidly and transiently induced by interleukin-3 and several othe r hematopoietic growth factors. The predicted structure of paxillin im plicates this molecule in protein protein interactions involved in sig nal transduction from growth factor receptors and the BCR/ABL oncogene fusion protein to the cytoskeleton.