The actin capping protein alpha-adducin is required for CD28 costimulation (IRM12P.658)

Abstract

Abstract Alpha-adducin (Add1) is a critical component of the actin-spectrin network, acting to cap the barbed ends of actin filaments, and recruiting spectrin to these junctions. Add1 is expressed at high levels in naïve T cells and is down-modulated upon TCR stimulation, but the role that Add1 plays in the cytoskeletal rearrangements that occur in motile T cells and during immunological synapse formation have not been investigated. Using CD4 T cells from knockout mice, we show that Add1 is necessary for complete activation of T cells in response to low levels of antigen, as measured by proliferation and cytokine production. Interestingly, the defective proliferation we observed in Add1-/- T cells was due to an inability to respond to respond to CD28 costimulatory signals. Additionally, we demonstrate that naïve and recently activated T cells lacking Add1 have a defect in motility. Using CD4 T cells transduced with GFP-tagged Add1, we found that Add1 is located cortically in non-motile cells, but rapidly moves to the nascent uropod in T cells initiating a crawling phenotype. While the bulk of GFP-Add1 is located in the uropod of crawling cells, brief accumulations are seen at the leading edge. Real-time imaging of interactions between transduced T cells and peptide-loaded antigen presenting cells revealed that Add1 becomes concentrated at the distal pole complex. Together, these results demonstrate that Add1 plays an unexpected and central role in T cell activation and migration.