EWI-2 Association with α-Actinin Regulates T Cell Immune Synapses and HIV Viral Infection

EWI motif-containing protein 2 (EWI-2) is a member of the Ig superfamily that links tetraspanin-enriched microdomains to the actin cytoskeleton. We found that EWI-2 colocalizes with CD3 and CD81 at the central supramolecular activation cluster of the T cell immune synapse. Silencing of the endogenous expression or overexpression of a cytoplasmic truncated mutant of EWI-2 in T cells increases IL-2 secretion upon Ag stimulation. Mass spectrometry experiments of pull-downs with the C-term intracellular domain of EWI-2 revealed the specific association of EWI-2 with the actin-binding protein alpha-actinin; this association was regulated by PIP2. alpha-Actinin regulates the immune synapse formation and is required for efficient T cell activation. We extended these observations to virological synapses induced by HIV and found that silencing of either EWI-2 or alpha-actinin-4 increased cell infectivity. Our data suggest that the EWI-2-alpha-actinin complex is involved in the regulation of the actin cytoskeleton at T cell immune and virological synapses, providing a link between membrane microdomains and the formation of polarized membrane structures involved in T cell recognition. The Journal of Immunology, 2012, 189: 689-700.