Actin-organizing protein that may cause stress fiber formation together with cell elongation (By similarity). Isoform 4 may play a role in actin filament polymerization in cardiomyocytes. Interacts with nestin/NES-based interfilament (IF) (By similarity). Interacts with SQSTM1; isoform 4 threonine phosphorylation disrupts SQSTM1-binding. Main part of the protein localizes to actin fibers and the remaining part displays filamentous staining. Threonine phosphorylation in isoform 4-specific sequence TDTDEEEEVE is required for targeting to myofibrils in cardiomyocytes. Expressed in the heart, kidney and brain. May be down-regulated in various types of heart diseases, including idiopathic dilated, ventricular dilated, familial dilated and perinatal dilated cardiomyopathies, as well as ischemic heart disease (at protein level). The DAD domain regulates activation via by an autoinhibitory interaction with the GBD/FH3 domain. This autoinhibition is released upon competitive binding of an activated GTPase. The release of DAD allows the FH2 domain to then nucleate and elongate nonbranched actin filaments (By similarity). Phosphorylated on Thr-1474 and Thr-1476 by CK2. The disease is caused by variants affecting the gene represented in this entry. Belongs to the formin homology family. Truncated N-terminus. Truncated N-terminus.