Signalling by Ras and Rho GTPases

Abstract RAS and RHO proteins constitute two branches of the RAS superfamily of small guanosine triphosphatases (GTPases) (Figure 1). Like all GTPases, these proteins cycle between an active, guanosine triphosphate (GTP)‐bound form, and an inactive, guanosine diphosphate (GDP)‐bound form. Two families of proteins, guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs), activate and inactivate the GTPases, respectively, and the activity of GEFs and GAPs are controlled by a large number of cellular cues. Active GTPases interact with a diverse group of proteins, termed effectors , which transduce the signal from the GTPase, resulting in a range of cellular responses. RAS GTPases and components of the signalling pathways controlled by them are frequently mutated in human cancers. RHO GTPases are key regulators of many normal cellular processes which go awry during tumour progression.