title: TLR regulation of SPSB1 controls inducible nitric oxide synthase induction.
abstract: The mammalian innate immune system has evolved to recognize foreign molecules derived from pathogens via the TLRs. TLR3 and TLR4 can signal via the TIR domain-containing adapter inducing IFN-β (TRIF), which results in the transcription of a small array of genes, including IFN-β. Inducible NO synthase (iNOS), which catalyzes the production of NO, is induced by a range of stimuli, including cytokines and microbes. NO is a potent source of reactive nitrogen species that play an important role in killing intracellular pathogens and forms a crucial component of host defense. We have recently identified iNOS as a target of the mammalian SPSB2 protein. The SOCS box is a peptide motif, which, in conjunction with elongins B and C, recruits cullin-5 and Rbx-2 to form an active E3 ubiquitin ligase complex. In this study, we show that SPSB1 is the only SPSB family member to be regulated by the same TLR pathways that induce iNOS expression and characterize the interaction between SPSB1 and iNOS. Through the use of SPSB1 transgenic mouse macrophages and short hairpin RNA knockdown of SPSB1, we show that SPSB1 controls both the induction of iNOS and the subsequent production of NO downstream of TLR3 and TLR4. Further, we demonstrate that regulation of iNOS by SPSB1 is dependent on the proteasome. These results suggest that SPSB1 acts through a negative-feedback loop that, together with SPSB2, controls the extent of iNOS induction and NO production.
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia.
authors.forename: Rowena S
authors.initials: RS
authors.lastname: Lewis
authors.forename: Tatiana B
authors.initials: TB
authors.lastname: Kolesnik
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Kuang
authors.forename: Akshay A
authors.initials: AA
authors.lastname: D'Cruz
authors.forename: Marnie E
authors.initials: ME
authors.lastname: Blewitt
authors.forename: Seth L
authors.initials: SL
authors.lastname: Masters
authors.forename: Andrew
authors.initials: A
authors.lastname: Low
authors.forename: Tracy
authors.initials: T
authors.lastname: Willson
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Norton
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Nicholson
mesh_terms: D000818:Animals; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000276:immunology*; D047468:Immunoprecipitation; D008264:Macrophages / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009569:Nitric Oxide / Q000096:biosynthesis / Q000276:immunology; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051193:Toll-Like Receptors / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; C515022:SSB-1 protein, mouse; C508499:SSB-2 protein, mouse; D050826:Suppressor of Cytokine Signaling Proteins; D051193:Toll-Like Receptors; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II