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

• Main Authors: 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
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2017-01-01
• Series: PLoS Biology
• Online Access: http://europepmc.org/articles/PMC5218472?pdf=render
• ISSN: 1544-9173; 1545-7885

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.