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, however, seems unable to nucleate filaments (PubMed:16054028). Plays a role in lamellipodial protrusion formations and cell migration (PubMed:19846667). {ECO:0000269|PubMed:16054028, ECO:0000269|PubMed:19846667}. This is the function of CARMIL1 (capping protein regulator and myosin 1 linker 1, Ensembl gene identifier ENSG00000079691).