title: SCF E3 ligase F-box protein complex SCF(FBXL19) regulates cell migration by mediating Rac1 ubiquitination and degradation.
abstract: Rac1, a member of the Rho family of GTPases, regulates diverse cellular functions, including cytoskeleton reorganization and cell migration. F-box proteins are major subunits within the Skp1-Cul1-F-box (SCF) E3 ubiquitin ligases that recognize specific substrates for ubiquitination. The role of F-box proteins in regulating Rac1 stability has not been studied. Mouse lung epithelial (MLE12) cells were used to investigate Rac1 stability and cell migration. Screening of an F-box protein library and in vitro ubiquitination assays identified FBXL19, a relatively new member of the F-box protein family that targets Rac1 for its polyubiquitination and proteasomal degradation. Overexpression of FBXL19 decreased both Rac1 active and inactive forms and significantly reduced cellular migration. Protein kinase AKT-mediated phosphorylation of Rac1 at serine(71) was essential for FBXL19-mediated Rac1 ubiquitination and depletion. Lysine(166) within Rac1 was identified as a polyubiquitination acceptor site. Rac1(S71A) and Rac1(K166R) mutant proteins were resistant to FBXL19-mediated ubiquitination and degradation. Further, ectopically expressed FBXL19 reduced cell migration in Rac1-overexpressing cells (P<0.01, Rac1 cells vs. FBXL19+Rac1 cells), but not in Rac1 lysine(166) mutant-overexpressing cells. FBXL19 diminished formation of the migratory leading edge. Thus, SCF(FBXL19) targets Rac1 for its disposal, a process regulated by AKT. These findings provide the first evidence of an F-box protein targeting a small G protein for ubiquitination and degradation to modulate cell migration.
authors.affiliation: Department of Medicine, University of Pittsburgh School of Medicine, 3459 Fifth Ave., Pittsburgh, PA 15213, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Mialki
authors.forename: Jianxin
authors.initials: J
authors.lastname: Wei
authors.forename: Tiffany A
authors.initials: TA
authors.lastname: Coon
authors.forename: Chunbin
authors.initials: C
authors.lastname: Zou
authors.forename: Bill B
authors.initials: BB
authors.lastname: Chen
authors.forename: Rama K
authors.initials: RK
authors.lastname: Mallampalli
authors.forename: Yutong
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D000818:Animals; D002460:Cell Line; D002465:Cell Movement; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D009154:Mutation; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D025821:Polyubiquitin / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D059748:Proteolysis; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012694:Serine / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein
chemical_list: D004268:DNA-Binding Proteins; D044783:F-Box Proteins; C574750:FBXL19 protein, mouse; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D025821:Polyubiquitin; D012694:Serine; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein
keywords: cell motility; phosphorylation; protein stability; small GTPase protein