title: Direct binding of SWAP-70 to non-muscle actin is required for membrane ruffling.
abstract: Membrane ruffling induced by growth factor stimulation is caused by actin remodeling, which is mediated by various signaling molecules including Rac. We have shown that SWAP-70, which binds phosphatidylinositol trisphosphate, is one such molecule required for membrane ruffling in mouse kidney cells. Here, we show that SWAP-70 directly binds to F-actin. The bacterially expressed C-terminal region of SWAP-70 co-sedimented with non-muscle F-actin, suggesting direct binding of SWAP-70 to F-actin. The binding was much weaker in muscle F-actin. A truncated mutant of SWAP-70 containing only the C-terminal region readily colocalizes with F-actin, supporting this idea. Full-length SWAP-70 does not colocalize with F-actin unless cells are stimulated with growth factors, suggesting the presence of a stimuli-dependent regulatory mechanism for actin-binding activity in vivo. Overexpression of the mutant SWAP-70 lacking this binding domain inhibits the membrane ruffling induced by epidermal growth factor stimulation in COS7 cells. This dominant-negative effect is also observed in membrane ruffling induced by a dominant-active Rac, suggesting that SWAP-70 cooperates with Rac. These results suggest that the binding activity of SWAP-70 to non-muscle F-actin is required for membrane ruffling.
authors.affiliation: Division of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Sayoko
authors.initials: S
authors.lastname: Ihara
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Oka
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Fukui
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006133:Growth Substances / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D051379:Mice; D015778:Minor Histocompatibility Antigens; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
chemical_list: D000199:Actins; D004268:DNA-Binding Proteins; D006133:Growth Substances; D020662:Guanine Nucleotide Exchange Factors; D015778:Minor Histocompatibility Antigens; D009687:Nuclear Proteins; C491873:SWAP70 protein, human; D051057:Proto-Oncogene Proteins c-akt