title: Toll-like Receptor 4 Ligands Down-regulate Fcγ Receptor IIb (FcγRIIb) via MARCH3 Protein-mediated Ubiquitination.
abstract: Monocytes and macrophages are critical for the effectiveness of monoclonal antibody therapy. Responses to antibody-coated tumor cells are largely mediated by Fcγ receptors (FcγRs), which become activated upon binding to immune complexes. FcγRIIb is an inhibitory FcγR that negatively regulates these responses, and it is expressed on monocytes and macrophages. Therefore, deletion or down-regulation of this receptor may substantially enhance therapeutic outcomes. Here we screened a panel of Toll-like receptor (TLR) agonists and found that those selective for TLR4 and TLR8 could significantly down-regulate the expression of FcγRIIb. Upon further examination, we found that treatment of monocytes with TLR4 agonists could lead to the ubiquitination of FcγRIIb protein. A search of our earlier microarray database of monocytes activated with the TLR7/8 agonist R-848 (in which FcγRIIb was down-regulated) revealed an up-regulation of membrane-associated ring finger (C3HC4) 3 (MARCH3), an E3 ubiquitin ligase. Therefore, we tested whether LPS treatment could up-regulate MARCH3 in monocytes and whether this E3 ligase was involved with LPS-mediated FcγRIIb down-regulation. The results showed that LPS activation of TLR4 significantly increased MARCH3 expression and that siRNA against MARCH3 prevented the decrease in FcγRIIb following LPS treatment. These data suggest that activation of TLR4 on monocytes can induce a rapid down-regulation of FcγRIIb protein and that this involves ubiquitination.
authors.affiliation: From the Medical Scientist Training Program.
authors.forename: Kavin
authors.initials: K
authors.lastname: Fatehchand
authors.affiliation: the Key Laboratory for Molecular Enzymology and Engineering, Ministry of Education, Jilin University, Changchun, 130000 Jilin, China.
authors.forename: Li
authors.initials: L
authors.lastname: Ren
authors.affiliation: Department of Internal Medicine, and.
authors.forename: Saranya
authors.initials: S
authors.lastname: Elavazhagan
authors.affiliation: Department of Internal Medicine, and.
authors.forename: Huiqing
authors.initials: H
authors.lastname: Fang
authors.affiliation: Center for Biostatistics, Ohio State University, Columbus, Ohio 43210.
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Mo
authors.affiliation: the 3M Drug Delivery Systems Division, St. Paul, Minnesota 55144, and.
authors.forename: John P
authors.initials: JP
authors.lastname: Vasilakos
authors.affiliation: VentiRx Pharmaceuticals, Seattle, Washington 98101.
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Dietsch
authors.affiliation: VentiRx Pharmaceuticals, Seattle, Washington 98101.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Hershberg
authors.affiliation: Department of Internal Medicine, and tridandapani.2@osu.edu.
authors.forename: Susheela
authors.initials: S
authors.lastname: Tridandapani
authors.affiliation: Department of Internal Medicine, and butchar.2@osu.edu.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Butchar
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects* / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D017452:Receptors, IgG / Q000096:biosynthesis*; D051197:Toll-Like Receptor 4 / Q000819:agonists* / Q000378:metabolism; D051199:Toll-Like Receptor 7 / Q000378:metabolism; D051200:Toll-Like Receptor 8 / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination / Q000187:drug effects* / Q000502:physiology
chemical_list: D002352:Carrier Proteins; C499173:FCGR2B protein, human; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D017452:Receptors, IgG; C495345:TLR4 protein, human; C495348:TLR7 protein, human; C495349:TLR8 protein, human; D051197:Toll-Like Receptor 4; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; C502926:MARCHF2 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: Fc receptor; Toll-like receptor 4 (TLR4); cell biology; immunology; monocyte; signal transduction; ubiquitylation (ubiquitination)