Vav1/Rac-dependent actin cytoskeleton reorganization is required for lipidraft clustering in T cells

Formation of the immunological synapse (IS) in T cells involves large scale molecular movements that are mediated, at least in part, by reorganization of the actin cytoskeleton. Various signaling proteins accumulate at the IS and are localized in specialized membrane microdomains, known as lipid raf ts. We have shown previously that lipid rafts cluster and localize at the I S in antigen-stimulated T cells. Here, we provide evidence that lipid raft polarization to the IS depends on an intracellular pathway that involves Va v1, Rac, and actin cytoskeleton reorganization. hus, lipid rafts did not tr anslocate to the IS in Vav1-deficient (Vav1(-/-)) T cells upon antigen stim ulation. Similarly, T cell receptor transgenic Jurkat T cells also failed t o translocate lipid rafts to the IS when transfected with dominant negative Vav1 mutants. Raft polarization induced by membrane-bound cholera toxin cr oss-linking was also abolished in Jurkat T cells expressing dominant negati ve Vav1 or Rac mutants and in cells treated with inhibitors of actin polyme rization. However, Vav overexpression that induced F-actin polymerization f ailed to induce lipid rafts clustering. Therefore, Vav is necessary, but no t sufficient, to regulate lipid rafts clustering and polarization at the IS , suggesting that additional signals are required.