Tumour initiation and progression result from inappropriate activation of intracellular signalling cascades.  Rho-like GTPases are molecular switches in signalling pathways that regulate cytoskeletal and junctional organisation, as well as gene transcription.  In this way, Rho proteins influence cell morphology, adhesion, motility, as well as cell cycle progression and cell survival.  Rho proteins are transforming in vitro and are essential for Ras-mediated in vitro transformation.  Moreover, data has emerged to directly implicate Rho proteins in tumour initiation and progression in vivo.  Our group investigates how the activities of certain regulators of the Rho protein Rac are controlled.  We are also identifying signalling events downstream of Rac that modulate tumour susceptibility and disease progression.