title: A new mechanism of RhoA ubiquitination and degradation: roles of SCF(FBXL19) E3 ligase and Erk2.
abstract: RhoA is a small GTPase multifunctional protein that regulates cell proliferation and cytoskeletal reorganization. Regulation of its protein stability plays an important role in its biological functions. We have shown that a Skp1-Cul1-F-box (SCF) FBXL19 E3 ubiquitin ligase targets Rac1, a related member of the Rho family for ubiquitination and degradation. Here, SCF(FBXL19) mediates RhoA ubiquitination and proteasomal degradation in lung epithelial cells. Ectopically expressed FBXL19 decreased RhoA wild type, active, and inactive forms. Cellular depletion of FBXL19 increased RhoA protein levels and extended its half-life. FBXL19 bound the small GTPase in the cytoplasm leading to RhoA ubiquitination at Lys(135). A RhoA(K135R) mutant protein was resistant to SCF(FBXL19)-mediated ubiquitination and degradation and exhibited a longer lifespan. Protein kinase Erk2-mediated phosphorylation of RhoA was both sufficient and required for SCF(FBXL19)-mediated RhoA ubiquitination and degradation. Thus, SCF(FBXL19) targets RhoA for its disposal, a process regulated by Erk2. Ectopically expressed FBXL19 reduced phosphorylation of p27 and cell proliferation, a process mediated by RhoA. Further, FBXL19 cellular expression diminished lysophosphatidic acid (LPA)-induced phosphorylation of myosin light chain (MLC) and stress fiber formation. Hence, SCF(FBXL19) functions as a RhoA antagonist during cell proliferation and cytoskeleton rearrangement. These results provide the first evidence of an F-box protein targeting RhoA thereby modulating its cellular lifespan that impacts cell proliferation and cytoskeleton rearrangement.
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Jianxin
authors.initials: J
authors.lastname: Wei
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Mialki
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; Department of Anesthesia, First Hospital of Jilin University, Changchun, Jilin, China.
authors.forename: Su
authors.initials: S
authors.lastname: Dong
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Khoo
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA; Medical Specialty Service Line, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, PA, USA.
authors.forename: Rama K
authors.initials: RK
authors.lastname: Mallampalli
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Yutong
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA. Electronic address: zhaoj@upmc.edu.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004795:Enzyme Stability; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology; D044783:F-Box Proteins / Q000378:metabolism*; D008168:Lung / Q000166:cytology; D008239:Lysine / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D059748:Proteolysis; D022502:Stress Fibers / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D044783:F-Box Proteins; C574750:FBXL19 protein, mouse; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D019950:Mitogen-Activated Protein Kinase 1; D046988:Proteasome Endopeptidase Complex; D020742:rhoA GTP-Binding Protein; D008239:Lysine
keywords: Cell proliferation; Phosphorylation; Protein stability; Small GTPase protein; Stress fiber; Ubiquitin-proteasome system