title: Proprotein convertases generate a highly functional heterodimeric form of thymic stromal lymphopoietin in humans.
abstract: BACKGROUND
  Thymic stromal lymphopoietin (TSLP) is known to be elevated and truncated in nasal polyps (NPs) of patients with chronic rhinosinusitis and might play a significant role in type 2 inflammation in this disease. However, neither the structure nor the role of the truncated products of TSLP has been studied.
  
  
  OBJECTIVE
  We sought to investigate the mechanisms of truncation of TSLP in NPs and the function of the truncated products.
  
  
  METHODS
  We incubated recombinant human TSLP with NP extracts, and determined the protein sequence of the truncated forms of TSLP using Edman protein sequencing and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. We investigated the functional activity of truncated TSLP using a PBMC-based bioassay.
  
  
  RESULTS
  Edman sequencing and mass spectrometry results indicated that NP extracts generated 2 major truncated products, TSLP (residues 29-124) and TSLP (131-159). Interestingly, these 2 products remained linked with disulfide bonds and presented as a dimerized form, TSLP (29-124 + 131-159). We identified that members of the proprotein convertase were rate-limiting enzymes in the truncation of TSLP between residues 130 and 131 and generated a heterodimeric unstable metabolite TSLP (29-130 + 131-159). Carboxypeptidase N immediately digested 6 amino acids from the C terminus of the longer subunit of TSLP to generate a stable dimerized form, TSLP (29-124 + 131-159), in NPs. These truncations were homeostatic but primate-specific events. A metabolite TSLP (29-130 + 131-159) strongly activated myeloid dendritic cells and group 2 innate lymphoid cells compared with mature TSLP.
  
  
  CONCLUSIONS
  Posttranslational modifications control the functional activity of TSLP in humans and overproduction of TSLP may be a key trigger for the amplification of type 2 inflammation in diseases.
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Poposki
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Aiko I
authors.initials: AI
authors.lastname: Klingler
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Whitney W
authors.initials: WW
authors.lastname: Stevens
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Anju T
authors.initials: AT
authors.lastname: Peters
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Hulse
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Leslie C
authors.initials: LC
authors.lastname: Grammer
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill; Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Schleimer
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Welch
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Stephanie S
authors.initials: SS
authors.lastname: Smith
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Sidle
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: David B
authors.initials: DB
authors.lastname: Conley
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Tan
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill; Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Kern
authors.affiliation: Division of Allergy-Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Ill; Department of Otolaryngology - Head and Neck Surgery, Northwestern University Feinberg School of Medicine, Chicago, Ill. Electronic address: a-kato@northwestern.edu.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kato
mesh_terms: D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology; D009298:Nasal Polyps / Q000276:immunology*; D045664:Proprotein Convertase 1 / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000494:pharmacology; D000094632:Thymic Stromal Lymphopoietin
chemical_list: D016207:Cytokines; D011994:Recombinant Proteins; C587576:PCSK1 protein, human; D045664:Proprotein Convertase 1; D000094632:Thymic Stromal Lymphopoietin
keywords: Carboxypeptidase; chronic rhinosinusitis; dendritic cells; group 2 innate lymphoid cells; nasal polyps; posttranslational modification; proprotein convertases; thymic stromal lymphopoietin