Cell membrane-cytoskeleton-associated protein that plays a role in the regulation of actin polymerization at the barbed end of actin filaments. Prevents F-actin heterodimeric capping protein (CP) activity at the leading edges of migrating cells, and hence generates uncapped barbed ends and enhances actin polymerization. Plays a role in cell protrusion formations; involved in cell polarity, lamellipodial assembly, membrane ruffling and macropinosome formations. Involved as well in cell migration and invadopodia formation during wound healing (By similarity). Required for CD28-mediated stimulation of NF-kappa-B signaling, involved in naive T cells activation, maturation into T memory cells, and differentiation into T helper cells (PubMed:27647348). Required for CD28-mediated differentiation of T regulatory cells (By similarity). Forms homodimers. Interacts (via C-terminus) with heterodimeric capping protein (CP); the interaction inhibits CP activity and hence promotes actin polymerization at the barbed end of actin filaments. Colocalizes to dynamic vimentin filaments both in the central cytoplasm and at leading edges of migrating cells. Colocalizes with F-actin, Arp2/3 complex and cortactin to leading edge lamellipodia, ruffles and macropinosomes of migrating cells. The N-terminal leucine-rich repeat (LRR) domain is necessary for localization to vimentin filaments. The C-terminus is necessary for localization to the cell membrane. Belongs to the CARMIL family.