Expression of the Rac-guanine nucleotide exchange factor (RacGEF), P-Rex1 is a 
key determinant of progression to metastasis in a number of human cancers. In 
accordance with this proposed role in cancer cell invasion and metastasis, we 
find that ectopic expression of P-Rex1 in an immortalised human fibroblast cell 
line is sufficient to drive multiple migratory and invasive phenotypes. The 
invasive phenotype is greatly enhanced by the presence of a gradient of serum or 
platelet-derived growth factor, and is dependent upon the expression of 
functional PDGF receptor β. Consistently, the invasiveness of WM852 melanoma 
cells, which endogenously express P-Rex1 and PDGFRβ, is opposed by siRNA of 
either of these proteins. Furthermore, the current model of P-Rex1 activation is 
advanced through demonstration of P-Rex1 and PDGFRβ as components of the same 
macromolecular complex. These data suggest that P-Rex1 has an influence on 
physiological migratory processes, such as invasion of cancer cells, both 
through effects upon classical Rac1-driven motility and a novel association with 
RTK signalling complexes.