Paxillin localizes to the lymphocyte microtubule organizing center and associates with the microtubule cytoskeleton

Paxillin is a focal adhesion-associated protein that functions as a multi-d omain adapter protein, binding several structural and signaling molecules. alpha-Tubulin was identified as an interacting protein in a two-hybrid scre en using the paxillin C-terminal LIM domain as a bait. In vitro binding ass ays with glutathione S-transferase-paxillin demonstrated an interaction of cy-tubulin with the C terminus of paxillin. Another member of the tubulin f amily, gamma-tubulin, bound to both the N and the C terminus of paxillin. T he interaction between paxillin and both alpha- and gamma-tubulin in vivo w as confirmed by immunoprecipitation from human T lymphoblasts. Immunofluore scence studies revealed that, in adherent T cells, paxillin localized to si tes of cell-matrix interaction as well as to a large perinuclear region. Co nfocal microscopy revealed that this region corresponds to the lymphocyte m icrotubule organizing center, where paxillin colocalizes with alpha- and ga mma-tubulin. The localization of paxillin to this area was observed in cell s in suspension as well as during adhesion to integrin ligands. These data constitute the first characterization of the interaction of paxillin with t he microtubule cytoskeleton, and suggest that paxillin, in addition to its well established role at focal adhesions, could also be associated with the lymphocyte microtubule network.