Actin-binding protein (PubMed:16636079, PubMed:17294403, PubMed:28493397). Plays a role in the activation of T-cells in response to costimulation through TCR/CD3 and CD2 or CD28 (PubMed:17294403). Modulates the cell surface expression of IL2RA/CD25 and CD69 (PubMed:17294403). Monomer. Interacts with AIF1 (By similarity). Interacts with actin (PubMed:28493397). 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 (PubMed:17294403). Associated with the actin cytoskeleton at membrane ruffles. Relocalizes to actin-rich cell projections upon serine phosphorylation (PubMed:16636079). Detected in intestinal microvilli, hair cell stereocilia, and fibroblast filopodia, in spleen and other lymph node-containing organs. Expressed in peripheral blood T-lymphocytes, neutrophils, monocytes, B-lymphocytes, and myeloid cells. 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. Chromosomal aberrations involving LCP1 is a cause of B-cell non-Hodgkin lymphomas (B-cell NHL). Translocation t(3;13)(q27;q14), with BCL6. Defects in LCP1 has been found in a patient with isolated coloboma, a defect of the eye characterized by the absence of ocular structures due to abnormal morphogenesis of the optic cup and stalk, and the fusion of the fetal fissure (optic fissure). Isolated colobomas may be associated with an abnormally small eye (microphthalmia) or small cornea.