Actin-binding protein. Plays a role in the activation of T-cells in response to costimulation through TCR/CD3 and CD2 or CD28. Modulates the cell surface expression of IL2RA/CD25 and CD69. Monomer (By similarity). Interacts with AIF1 (PubMed:14756805). Interacts with actin (By similarity). Relocalizes to the immunological synapse between peripheral blood T-lymphocytes and antibody-presenting cells in response to costimulation through TCR/CD3 and CD2 or CD28. Relocalizes to actin-rich cell projections upon serine phosphorylation (By similarity). Associated with the actin cytoskeleton at membrane ruffles. Phosphorylated on a serine residue in response to costimulation through TCR/CD3 and CD2 or CD28. Serine phosphorylation promotes association with the actin cytoskeleton and targeting to peripheral cell projections (By similarity).