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-domain adapter protein, binding several structural and signaling molecules. α-Tubulin was identified as an interacting protein in a two-hybrid screen using the paxillin C-terminal LIM domain as a bait. In vitro binding assays with glutathione S-transferase-paxillin demonstrated an interaction of α-tubulin with the C terminus of paxillin. Another member of the tubulin family, γ-tubulin, bound to both the N and the C terminus of paxillin. The interaction between paxillin and both α- and γ-tubulin in vivo was confirmed by co-immunoprecipitation from human T lymphoblasts. Immunofluorescence studies revealed that, in adherent T cells, paxillin localized to sites of cell-matrix interaction as well as to a large perinuclear region. Confocal microscopy revealed that this region corresponds to the lymphocyte microtubule organizing center, where paxillin colocalizes with α- and γ-tubulin. The localization of paxillin to this area was observed in cells in suspension as well as during adhesion to integrin ligands. These data constitute the first characterization of the interaction of paxillin with the 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.