Proprotein convertases generate a highly functional heterodimeric form of thymic stromal lymphopoietin in humans

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Abstract

Rationale:

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.

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