DOCK 4 is a cytoplasmic peripheral membrane protein that belongs to the DOCK family of cytokinesis-regulating proteins. Expressed ubiquitously with highest expression in prostate, ovary and skeletal muscle, DOCK 4 functions as a guanine nucleotide exchange factor (GEF) that activates the small GTPase Rap 1 and, via this activation, plays a role in the regulation of adherens junctions between cells. Similar to other DOCK family members, DOCK 4 contains an N-terminal SH3 domain, a C-terminal proline-rich region and two internal DOCK homology regions designated DHR1 and DHR2. Defects in the gene encoding DOCK 4 result in the inactivation of Rap 1 and are, thus, implicated in the pathogenesis of various cancers such as ovarian, prostate, glioma and colorectal carcinomas. Four isoforms of DOCK 4 are expressed due to alternative splicing events.