title: Diverse functions of reactive cysteines facilitate unique biosynthetic processes of aggregate-prone interleukin-31.
abstract: Interleukin-31 (IL-31) is a member of the four helical-bundle gp130/IL-6 cytokine family. Despite its implicated roles in inflammatory diseases, the biosynthetic processes of IL-31 have been poorly investigated. A detailed understanding of IL-31 biosynthesis and the nature of ligand-receptor interactions can provide insights into effective strategies for the design of therapeutic approaches. By using various heterologous protein expression systems, we demonstrated that murine IL-31 was secreted as inter-molecularly disulfide-bonded covalent aggregates. Covalently aggregated IL-31 appeared while trafficking in the secretory pathway, but was not actively retained in the ER. The aggregate formation was not caused by a dysfunctional ER quality control mechanism or an intrinsic limitation in protein folding capacity. Furthermore, secreted IL-31 aggregates were part of a large complex composed of various pleiotropic secretory factors and immune-stimulators. The extent and the heterogeneous nature of aggregates may imply that IL-31 was erroneously folded, but it was capable of signaling through cognate receptors. Mutagenesis revealed the promiscuity of all five cysteines in inter-molecular disulfide formation with components of the hetero-aggregates, but no cysteine was required for IL-31 secretion itself. Our present study not only illustrated various functions that cysteines perform during IL-31 biosynthesis and secretion, but also highlighted their potential roles in cytokine effector functions.
authors.affiliation: Department of Protein Science, Amgen Inc, Seattle, WA 98119, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Shen
authors.forename: Sophia
authors.initials: S
authors.lastname: Siu
authors.forename: Samantha
authors.initials: S
authors.lastname: Byrd
authors.forename: Kurt H
authors.initials: KH
authors.lastname: Edelmann
authors.forename: Neha
authors.initials: N
authors.lastname: Patel
authors.forename: Randal R
authors.initials: RR
authors.lastname: Ketchem
authors.forename: Christopher
authors.initials: C
authors.lastname: Mehlin
authors.forename: Heather A
authors.initials: HA
authors.lastname: Arnett
authors.forename: Haruki
authors.initials: H
authors.lastname: Hasegawa
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D003545:Cysteine / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D002479:Inclusion Bodies / Q000737:chemistry*; D007378:Interleukins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D011499:Protein Processing, Post-Translational; D015398:Signal Transduction / Q000502:physiology
chemical_list: C502187:IL31 protein, human; D007378:Interleukins; C502588:interleukin-31, mouse; D003545:Cysteine