Rho GTPase activating protein 21 is a protein that in humans is encoded by the ARHGAP21 gene.
ARHGAP21 functions preferentially as a GTPase-activating protein (GAP) for CDC42 (MIM 116952) and regulates the ARP2/3 complex (MIM 604221) and F-actin dynamics at the Golgi through control of CDC42 activity (Dubois et al., 2005 [PubMed 15793564]). There is little scientific literature on ARHGAP21, but recent reviews highlighted that it plays an important role in cytoskeletal processes in cancer, substance transport within the cell, and insulin secretion