Proteolytic Origin of the Soluble Human IL-6R In Vivo and a Decisive Role of N-Glycosylation.

Steffen Riethmueller, Prasath Somasundaram, Johanna C Ehlers, Chien-Wen Hung, Charlotte M Flynn, Juliane Lokau, Maria Agthe, Stefan Düsterhöft, Yijue Zhu, Joachim Grötzinger, Inken Lorenzen, Tomas Koudelka, Kosuke Yamamoto, Ute Pickhinke, Rielana Wichert, Christoph Becker-Pauly, Marisa Rädisch, Alexander Albrecht, Markus Hessefort, Dominik Stahnke, Carlo Unverzagt, Stefan Rose-John, Andreas Tholey, Christoph Garbers

Journal: PLoS biology 2017;15(1):e2000080

PMID: 28060820

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Abstract

Signaling of the cytokine interleukin-6 (IL-6) via its soluble IL-6 receptor (sIL-6R) is responsible for the proinflammatory properties of IL-6 and constitutes an attractive therapeutic target, but how the sIL-6R is generated in vivo remains largely unclear. Here, we use liquid chromatography-mass spectrometry to identify an sIL-6R form in human serum that originates from proteolytic cleavage, map its cleavage site between Pro-355 and Val-356, and determine the occupancy of all O- and N-glycosylation sites of the human sIL-6R. The metalloprotease a disintegrin and metalloproteinase 17 (ADAM17) uses this cleavage site in vitro, and mutation of Val-356 is sufficient to completely abrogate IL-6R proteolysis. N- and O-glycosylation were dispensable for signaling of the IL-6R, but proteolysis was orchestrated by an N- and O-glycosylated sequon near the cleavage site and an N-glycan exosite in domain D1. Proteolysis of an IL-6R completely devoid of glycans is significantly impaired. Thus, glycosylation is an important regulator for sIL-6R generation.

Address: Institute of Biochemistry, Kiel University, Kiel, Germany.; Systematic Proteomics & Bioanalytics, Institute for Experimental Medicine, Kiel University, Kiel, Germany.; Institute of Biochemistry, Unit for Degradomics of the Protease Web, Kiel University, Kiel, Germany.; Bioorganic Chemistry, Gebaeude NWI, University of Bayreuth, Bayreuth, Germany.

DOI: 10.1371/journal.pbio.2000080

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MeSH Terms: ADAM10 Protein, ADAM17 Protein, Alternative Splicing, Amino Acid Sequence, Amyloid Precursor Protein Secretases, Cell Line, Cell Membrane, Glycosylation, Humans, Intracellular Space, Mass Spectrometry, Membrane Proteins, Mutation, Polysaccharides, Proline, Protein Domains, Protein Transport, Proteolysis, RNA, Messenger, Receptors, Interleukin-6, Signal Transduction, Solubility, Valine