Distinct structural and catalytic roles for Zap70 in formation of the immunological synapse in CTL

Abstract

T cell receptor (TCR) activation leads to a dramatic reorganisation of both membranes and receptors as the immunological synapse forms. Using a genetic model to rapidly inhibit Zap70 catalytic activity we examined synapse formation between cytotoxic T lymphocytes and their targets. In the absence of Zap70 catalytic activity Vav-1 activation occurs and synapse formation is arrested at a stage with actin and integrin rich interdigitations forming the interface between the two cells. The membranes at the synapse are unable to flatten to provide extended contact, and Lck does not cluster to form the central supramolecular activation cluster (cSMAC). Centrosome polarisation is initiated but aborts before reaching the synapse and the granules do not polarise. Our findings reveal distinct roles for Zap70 as a structural protein regulating integrin-mediated control of actin vs its catalytic activity that regulates TCR-mediated control of actin and membrane remodelling during formation of the immunological synapse.

DOI: http://dx.doi.org/10.7554/eLife.01310.001

eLife digest

White blood cells are responsible for defending the body against infection and disease. Cytotoxic T-lymphocytes, or cytotoxic T cells, are white blood cells that recognise and kill cells that are infected, cancerous or otherwise damaged. Receptors on the surface of these T cells recognise ‘foreign’ molecules on the surface of diseased or damaged cells: this activates the T cells, which then release cytotoxic proteins that destroy the target cells.

During this process the T cell and the target cell are brought into close contact with each other, and their membranes undergo a dramatic rearrangement to form an ‘immunological synapse’. Although the structure of the immunological synapse is understood in detail, the mechanisms controlling the membrane reorganisation are not well understood. Previous studies have shown that an enzyme called Zap70 needs to be present to activate receptors involved in cell adhesion, termed integrins. Now, Jenkins, Stinchcombe et al. have shown a dual role for Zap70 in the formation of the immunological synapse.

Jenkins, Stinchcombe et al. used mice that had been engineered to produce a modified version of Zap70 that worked as normal until its activity was ‘switched off’ by the addition of a specific drug. When Zap70 was switched off, integrins were still activated but the formation of the immunological synapse was halted with only finger-tip-like contacts between the T cell and the target cell. These contacts were formed by projections from the T cell made of a protein called actin, which forms a kind of scaffolding within cells. Without active Zap70, the T cell receptors could not trigger the dynamic rearrangement of the actin proteins and the membrane remodelling required to form a tight contact between the two cells. This disrupted the delivery of the cytotoxic proteins to their target. These results clearly show that Zap70 has at least two distinct roles that it must carry out for an immunological synapse to form.

DOI: http://dx.doi.org/10.7554/eLife.01310.002