PSTPIP1 CONTROLS IMMUNE SYNAPSE FORMATION IN HUMAN T-CELLS

PSTPIP1 is an adaptor protein that upon T-cell receptor triggering is recruited to the cytosolic domain of the adhesion molecule CD2, and mediates remodeling of the f-actin-based cytoskeleton. The function of CD2 and PSTPIP1 in activation of human T-cells is not fully understood. PSTPIP1 mutations are found in autoinflammatory disease patients suffering from PAPA syndrome (Pyogenic Arthritis, Pyoderma gangrenosum, and Acne). From genetic screening of immunodeficiency patients we identified mutations in the PSTPIP1 coiled coil domain, R228C and T274M. Using these 2 mutant and the common PSTPIP1 versions, we investigated the role of PSTPIP1 and CD2 signaling in early human T-cell activation.
We show in both primary T-cells and transfected Jurkat cells that CD2 crosslinking on R228C cells impairs f-actin polymerization while CD2 crosslinking on T274M cells enhances f-actin polymerization, compared to the common PSTPIP1 variant. We next investigated the ability of T-cells to form immune synapses, using anti-CD3/CD28 beads and confocal imaging-based techniques. Both R228C and T274M PSTPIP1 mutations affected the ability of T-cells to make stable immune synapses with interacting beads. Co-immunoprecipitation experiments suggest that CD2 crosslinking triggers stronger binding of T274M PSTPIP1 to CD2, for enhanced f-actin polymerization. Similar tests are still ongoing for R228C PSTPIP1.
T-cell activation requires the formation of an immune synapse and recruitment of signaling molecules. Both depend on dynamic remodeling of the f-actin cytoskeleton, as triggered by CD2 ligation and propagated by the downstream mediator PSTPIP1. Our data supports a critical role for PSTPIP1 in the formation of a productive T-cell immune synapse. The R228C PSTPIP1 patient phenotype of naive T-cells overall likely involves defective T-cell activation due to poor synapse formation. The T274M patient phenotype of decreased T-cell numbers may reflect a more severe phenotype of T-cell depletion, supporting a role for CD2 signaling in the maintenance of a naive T-cell repertoire. Current experiments are aimed at clarifying a role for CD2 signaling and PSTPIP1 in naive and memory T-cells.