Molecular cloning of human paxillin, a focal adhesion protein phosphorylated by P210BCR/ABL

Abstract

Paxillin is a 68-kDa focal adhesion protein that is phosphorylated on tyrosine residues in fibroblasts in response to transformation by v-src, treatment with platelet-derived growth factor, or cross-linking of integrins. Paxillin has been shown to have binding sites for the SH3 domain of Src and the SH2 domain of Crk in vitro and to coprecipitate with two other focal adhesion proteins, vinculin and focal adhesion kinase (p125fak). After preliminary studies showed that paxillin was a substrate for the hematopoietic oncogene p210 BCR/ABL, we investigated the role of this protein in hematopoietic cell transformation and signal transduction. A full-length cDNA encoding human paxillin was cloned, revealing multiple protein domains, including four tandem LIM domains, a proline-rich domain containing a consensus SH3 binding site, and three potential Crk-SH2 binding sites. The paxillin gene was localized 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 coprecipitated with p210BCR/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 phosphorylation of paxillin and co-precipitation with other cellular proteins was rapidly and transiently induced by interleukin-3 and several other hematopoietic growth factors. The predicted structure of paxillin implicates this molecule in protein-protein interactions involved in signal transduction from growth factor receptors and the BCR/ABL oncogene fusion protein to the cytoskeleton.