title: Critical role of IRF-8 in negative regulation of TLR3 expression by Src homology 2 domain-containing protein tyrosine phosphatase-2 activity in human myeloid dendritic cells.
abstract: Despite extensive studies that unraveled ligands and signal transduction pathways triggered by TLRs, little is known about the regulation of TLR gene expression. TLR3 plays a crucial role in the recognition of viral pathogens and induction of immune responses by myeloid DCs. IFN regulatory factor (IRF)-8, a member of the IRF family, is a transcriptional regulator that plays essential roles in the development and function of myeloid lineage, affecting different subsets of myeloid DCs. In this study, we show that IRF-8 negatively controls TLR3 gene expression by suppressing IRF-1- and/or polyinosinic-polycytidylic acid-stimulated TLR3 expression in primary human monocyte-derived DCs (MDDCs). MDDCs expressed TLR3 increasingly during their differentiation from monocytes to DCs with a peak at day 5, when TLR3 expression was further enhanced upon stimulation with polyinosinic-polycytidylic acid and then was promptly downregulated. We found that both IRF-1 and IRF-8 bind the human TLR3 promoter during MDDC differentiation in vitro and in vivo but with different kinetic and functional effects. We demonstrate that IRF-8-induced repression of TLR3 is specifically mediated by ligand-activated Src homology 2 domain-containing protein tyrosine phosphatase association. Indeed, Src homology 2 domain-containing protein tyrosine phosphatase-dephosphorylated IRF-8 bound to the human TLR3 promoter competing with IRF-1 and quashing its activity by recruitment of histone deacetylase 3. Our findings identify IRF-8 as a key player in the control of intracellular viral dsRNA-induced responses and highlight a new mechanism for negative regulation of TLR3 expression that can be exploited to block excessive TLR activation.
authors.affiliation: Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Fragale
authors.forename: Emilia
authors.initials: E
authors.lastname: Stellacci
authors.forename: Ramona
authors.initials: R
authors.lastname: Ilari
authors.forename: Anna Lisa
authors.initials: AL
authors.lastname: Remoli
authors.forename: Angela
authors.initials: A
authors.lastname: Lanciotti
authors.forename: Edvige
authors.initials: E
authors.lastname: Perrotti
authors.forename: Iart
authors.initials: I
authors.lastname: Shytaj
authors.forename: Roberto
authors.initials: R
authors.lastname: Orsatti
authors.forename: Harshani R
authors.initials: HR
authors.lastname: Lawrence
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Lawrence
authors.forename: Jerry
authors.initials: J
authors.lastname: Wu
authors.forename: Michael
authors.initials: M
authors.lastname: Rehli
authors.forename: Keiko
authors.initials: K
authors.lastname: Ozato
authors.forename: Angela
authors.initials: A
authors.lastname: Battistini
mesh_terms: D003713:Dendritic Cells / Q000201:enzymology / Q000276:immunology* / Q000821:virology; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology*; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007424:Intracellular Fluid / Q000276:immunology / Q000378:metabolism / Q000821:virology; D008024:Ligands; D022423:Myeloid Cells / Q000201:enzymology / Q000276:immunology* / Q000821:virology; D011070:Poly I-C / Q000494:pharmacology; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2 / Q000378:metabolism* / Q000502:physiology; D012367:RNA, Viral / Q000494:pharmacology; D051196:Toll-Like Receptor 3 / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D018909:src Homology Domains / Q000235:genetics / Q000276:immunology*; D000099185:Interferon Regulatory Factor-8
chemical_list: D050835:Interferon Regulatory Factors; D008024:Ligands; D011070:Poly I-C; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D012367:RNA, Viral; D051196:Toll-Like Receptor 3; D000099185:Interferon Regulatory Factor-8; C495344:TLR3 protein, human; C516649:PTPN2 protein, human