title: R-Ras signals through specific integrin alpha cytoplasmic domains to promote migration and invasion of breast epithelial cells.
abstract: Specificity and modulation of integrin function have important consequences for cellular responses to the extracellular matrix, including differentiation and transformation. The Ras-related GTPase, R-Ras, modulates integrin affinity, but little is known of the signaling pathways and biological functions downstream of R-Ras. Here we show that stable expression of activated R-Ras or the closely related TC21 (R-Ras 2) induced integrin-mediated migration and invasion of breast epithelial cells through collagen and disrupted differentiation into tubule structures, whereas dominant negative R-Ras had opposite effects. These results imply novel roles for R-Ras and TC21 in promoting a transformed phenotype and in the basal migration and polarization of these cells. Importantly, R-Ras induced an increase in cellular adhesion and migration on collagen but not fibronectin, suggesting that R-Ras signals to specific integrins. This was further supported by experiments in which R-Ras enhanced the migration of cells expressing integrin chimeras containing the alpha2, but not the alpha5, cytoplasmic domain. In addition, a transdominant inhibition previously noted only between integrin beta cytoplasmic domains was observed for the alpha2 cytoplasmic domain; alpha2beta1-mediated migration was inhibited by the expression of excess alpha2 but not alpha5 cytoplasmic domain-containing chimeras, suggesting the existence of limiting factors that bind the integrin alpha subunit. Using pharmacological inhibitors, we found that R-Ras induced migration on collagen through a combination of phosphatidylinositol 3-kinase and protein kinase C, but not MAPK, which is distinct from the other Ras family members, Rac, Cdc42, and N- and K-Ras. Thus, R-Ras communicates with specific integrin alpha cytoplasmic domains through a unique combination of signaling pathways to promote cell migration and invasion.
authors.affiliation: Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina 27599, USA. pkeely@med.unc.edu
authors.forename: P J
authors.initials: PJ
authors.lastname: Keely
authors.forename: E V
authors.initials: EV
authors.lastname: Rusyn
authors.forename: A D
authors.initials: AD
authors.lastname: Cox
authors.forename: L V
authors.initials: LV
authors.lastname: Parise
mesh_terms: D001940:Breast / Q000473:pathology* / Q000502:physiology; D002461:Cell Line, Transformed; D002465:Cell Movement / Q000502:physiology*; D004847:Epithelial Cells / Q000473:pathology*; D005260:Female; D020558:GTP Phosphohydrolases / Q000502:physiology*; D006801:Humans; D016023:Integrins / Q000502:physiology*; D015398:Signal Transduction; D018631:ras Proteins / Q000502:physiology*
chemical_list: D016023:Integrins; D020558:GTP Phosphohydrolases; C085929:RRAS protein, human; D018631:ras Proteins