Background
The Rho subfamily of small GTP-binding proteins mediates many fundamental cellular functions. The commonly studied members (Rho, Rac, and CDC42) regulate actin reorganization and affect diverse cellular responses, including adhesion, cytokinesis, and motility. RhoH, also known as TTF (Translocation Three Four), Rho-related GTP-binding protein and ras homolog gene family member H, is unlike most other small G proteins. Most small G proteins are expressed ubiquitously, however, Rho H is expressed only in hemopoietic cells and tissues. Translocations and a high frequency of Rho H mutation have been detected in primary lymphoma cells. Rho H expression has also been observed in activated neutrophils. RhoH is GTPase deficient, remaining in a GTP-bound activated state without cycling. Rho H may be involved in the functional differentiation of T cells and in cytoskeleton organization. The RhoH/TTF (ARHH) gene maps to chromosome 4p13 and encodes a 191 -amino acid polypeptide.