title: TLR9 stability and signaling are regulated by phosphorylation and cell stress.
abstract: Innate sensing of pathogens elicits protective immune responses through pattern recognition receptors, including Toll-like receptors. Although signaling by Toll-like receptors is regulated at multiple steps, including localization, trafficking, proteolytic cleavage, and phosphorylation, the significance of post-translational modifications and cellular stress response on Toll-like receptor stability and signaling is still largely unknown. In the present study, we investigated the role of cytoplasmic tyrosine motifs in Toll-like receptor-9 stability, proteolytic cleavage, and signaling. We demonstrated that tyrosine phosphorylation is essential for mouse Toll-like receptor-9 protein stability and signaling. Upon inhibition of tyrosine kinases with piceatannol, Toll-like receptor-9 tyrosine phosphorylation induced by CpG deoxyribonucleic acid was inhibited, which correlated with decreased signaling. Furthermore, inhibition of Src kinases with 1-tert-Butyl-3-(4-chlorophenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine also inhibited response to CpG deoxyribonucleic acid. Toll-like receptor-9 protein stability was also sensitive to autophagy, the cellular stress response pathway, and infection by a deoxyribonucleic acid virus. Whereas autophagy induced by rapamycin or low serum levels caused a preferential loss of the mature p80 proteolytic cleavage product, infection with herpes simplex virus-1 and induction of cell stress with tunicamycin caused preferential loss of full-length Toll-like receptor-9, which is localized to the endoplasmic reticulum. Our data reveal new information about the stability and signaling of Toll-like receptor-9 and suggest that immune evasion mechanisms may involve targeted loss of innate sensing receptors.
authors.affiliation: Department of Microbiology and Immunology, Cornell University, Ithaca, New York, USA.
authors.forename: Maroof
authors.initials: M
authors.lastname: Hasan
authors.affiliation: Department of Microbiology and Immunology, Cornell University, Ithaca, New York, USA.
authors.forename: Erika
authors.initials: E
authors.lastname: Gruber
authors.affiliation: Department of Microbiology and Immunology, Cornell University, Ithaca, New York, USA.
authors.forename: Jody
authors.initials: J
authors.lastname: Cameron
authors.affiliation: Department of Microbiology and Immunology, Cornell University, Ithaca, New York, USA cal59@cornell.edu.
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Leifer
mesh_terms: D000818:Animals; D059865:Endoplasmic Reticulum Stress; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D059748:Proteolysis; D015398:Signal Transduction; D051217:Toll-Like Receptor 9 / Q000737:chemistry* / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D014443:Tyrosine
keywords: CpG DNA; autophagy; inflammation; innate immunity