title: Transforming growth factor-beta differentially inhibits MyD88-dependent, but not TRAM- and TRIF-dependent, lipopolysaccharide-induced TLR4 signaling.
abstract: Transforming growth factor-beta1 (TGF-beta1) is a multifunctional, potent anti-inflammatory cytokine produced by many cell types that regulates cell proliferation, apoptosis, and immune responses. Toll-like receptors (TLRs) recognize various pathogen-associated molecular patterns and are therefore a pivotal component of the innate immune system. In this study we show that TGF-beta1 blocks the NF-kappaB activation and cytokine release that is stimulated by ligands for TLRs 2, 4, and 5. We further show that TGF-beta1 can specifically interfere with TLR2, -4, or -5 ligand-induced responses involving the adaptor molecule MyD88 (myeloid differentiation factor 88) but not the TRAM/TRIF signaling pathway by decreasing MyD88 protein levels in a dose- and time-dependent manner without altering its mRNA expression. The proteasome inhibitor epoxomicin abolished the MyD88 degradation induced by TGF-beta1. Furthermore, TGF-beta1 resulted in ubiquitination of MyD88 protein, suggesting that TGF-beta1 facilitates ubiquitination and proteasomal degradation of MyD88 and thereby attenuates MyD88-dependent signaling by decreasing cellular levels of MyD88 protein. These findings importantly contribute to our understanding of molecular mechanisms mediating anti-inflammatory modulation of immune responses by TGF-beta1.
authors.affiliation: Department of Pediatric Infectious Diseases, Cedars-Sinai Medical Center, University of California Los Angeles, 8700 Beverly Blvd., Los Angeles, CA 90048, USA.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Naiki
authors.forename: Kathrin S
authors.initials: KS
authors.lastname: Michelsen
authors.forename: Wenxuang
authors.initials: W
authors.lastname: Zhang
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.forename: Terence M
authors.initials: TM
authors.lastname: Doherty
authors.forename: Moshe
authors.initials: M
authors.lastname: Arditi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000096:biosynthesis / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D018946:Chemokine CCL5 / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000943:Antigens, Differentiation; D018946:Chemokine CCL5; D008024:Ligands; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D008562:Membrane Glycoproteins; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; C508960:TGFB1 protein, human; C470409:TICAM1 protein, human; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; C074282:translocating chain-associating membrane protein (TRAM); D007371:Interferon-gamma; D046988:Proteasome Endopeptidase Complex