Signaling through the tetraspanin CD82 triggers its association with the cytoskeleton leading to sustained morphological changes and T cell activation.

In this report, we provide new evidence of a crosstalk between T cell activation and adhesion processes through a functional cytokeleton. We show that CD82 signaling induces long-lasting adhesion, spreading and development of membrane extensions, involving actin polymerization. Addition of various co-stimuli (phorbol 12-myristate 13-acetate or monoclonal antibodies to CD3 or CD2) increases the CD82-induced morphological alterations and, reciprocally, CD82 engagement synergizes with these stimuli to induce T cell activation as indicated by both primary tyrosine phosphorylation and IL-2 production. Different kinases are involved in both processes. CD82 co-signaling involves src kinases including p56 Ick. On the other hand, the CD82-induced alterations of cell morphology are negatively regulated by cAMP-dependent kinases independently of activation of src kinases. Simultaneously with cytoskeletal rearrangements, we observed an inducible association of CD82 with the cytoskeletal matrix. In addition, the potentiating and stabilizing effects induced by CD82 cross-linking on tyrosine phosphorylation were abolished by cytoskeleton-disrupting agents. These results suggest that the actin polymerization triggered by CD82, through its ability to associate with the cytoskeletal matrix, is the primary step involved in the CD82 induced co-stimulatory activity. Our data provide further evidence for a direct role of the actin cytoskeleton as a major component for sustained signal transduction in T cells and suggest that tetraspanins could be "membrane organizers" connecting both surface and intracellular molecules.