Actin-binding protein involved in motile and morphological processes. Inhibits actin polymerization, likely by sequestering G-actin. By capping the barbed ends of filaments, it also regulates motility. Seems to play an important role in clathrin-mediated endocytosis and distribution of endocytic organelles. Interacts with G-actin; ADP-actin form and capping protein (CP). May also be able to interact with TWF2 and phosphoinositides, PI(4,5)P2. When bound to PI(4,5)P2, it is down- regulated. Expressed at high levels in the colon, testis, ovary, prostate and lung. Expressed at lower levels in the brain, bladder and heart. Not detected in liver. Belongs to the actin-binding proteins ADF family. Twinfilin subfamily. 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.