Rho GTPase
The family of Rho GTPases ( R as ho mologue) belongs to the superfamily of small GTPases with a molar mass of 20 to 40 kDa. They are important regulators of signal transduction in that they transmit signals from the receptors to the effectors and thus influence a wide variety of cell functions. So far, over 20 genes , the proteins , have been identified in the human genomeof the Rho family. Rho GTPases can be divided into five subfamilies, each with several members: Rho, Rac, Cdc42, Rnd and RhoBTB. There are also individual Rho GTPases that cannot be assigned to any of this subfamily. Rho-GTPases regulate many cellular processes such as the organization and remodeling of the actin cytoskeleton , cell adhesion , migration , cell polarity , cell division , membrane transport , vesicle transport and oncogenesis .
Three well-studied subfamilies are Rho, Rac, and Cdc42:
- Rho is responsible for the formation and contraction of stress fibers as well as for the formation of focal adhesion contacts , places where stress fibers are coupled to the extracellular matrix by means of integrins . Stress fibers can run through the entire cell or through parts of a cell . They also serve to constrict the cells during cell division after mitosis is complete .
- If Rac is activated, it comes to the formation of lamellipodia , flat protuberances of the cell membrane , and the development of membrane ripples. Lamellipodia are found on the conducting edge of the membrane and consist of actin polymerized in a network. They are able to form new adhesive contacts and drive the cell forward during cell migration.
- Cdc42 regulates the formation of filopodia , which are thin elongated protuberances of the plasma membrane. They consist of bundles of actin filaments that are linked by actin-binding proteins.