title: Effects of cell tension on the small GTPase Rac.
abstract: Cells in the body are subjected to mechanical stresses such as tension, compression, and shear stress. These mechanical stresses play important roles in both physiological and pathological processes; however, mechanisms transducing mechanical stresses into biochemical signals remain elusive. Here, we demonstrated that equibiaxial stretch inhibited lamellipodia formation through deactivation of Rac. Nearly maximal effects on Rac activity were obtained with 10% strain. GAP-resistant, constitutively active V12Rac reversed this inhibition, supporting a critical role for Rac inhibition in the response to stretch. In contrast, activation of endogenous Rac with a constitutively active nucleotide exchange factor did not, suggesting that regulation of GAP activity most likely mediates the inhibition. Uniaxial stretch suppressed lamellipodia along the sides lengthened by stretch and increased it at the adjacent ends. A fluorescence assay for localized Rac showed comparable changes in activity along the sides versus the ends after uniaxial stretch. Blocking polarization of Rac activity by expressing V12Rac prevented subsequent alignment of actin stress fibers. Treatment with Y-27632 or ML-7 that inhibits myosin phosphorylation and contractility increased lamellipodia through Rac activation and decreased cell polarization. We hypothesize that regulation of Rac activity by tension may be important for motility, polarization, and directionality of cell movement.
authors.affiliation: Division of Vascular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Akira
authors.initials: A
authors.lastname: Katsumi
authors.forename: Julie
authors.initials: J
authors.lastname: Milanini
authors.forename: William B
authors.initials: WB
authors.lastname: Kiosses
authors.forename: Miguel A
authors.initials: MA
authors.lastname: del Pozo
authors.forename: Roland
authors.initials: R
authors.lastname: Kaunas
authors.forename: Shu
authors.initials: S
authors.lastname: Chien
authors.forename: Klaus M
authors.initials: KM
authors.lastname: Hahn
authors.forename: Martin Alexander
authors.initials: MA
authors.lastname: Schwartz
mesh_terms: D000577:Amides / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D003094:Collagen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004735:Energy Transfer; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D018715:Microscopy, Video; D009281:Naphthalenes / Q000494:pharmacology; D009363:Neoplasm Proteins; D011506:Proteins / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D013314:Stress, Mechanical; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D013997:Time Factors; D014162:Transfection; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000577:Amides; D001381:Azepines; D020662:Guanine Nucleotide Exchange Factors; D009281:Naphthalenes; D009363:Neoplasm Proteins; D011506:Proteins; D011725:Pyridines; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513259:Tiam1 protein, rat; C070571:ML 7; C108830:Y 27632; D003094:Collagen; D020558:GTP Phosphohydrolases; D020744:rac GTP-Binding Proteins