Diverse functions of reactive cysteines facilitate unique biosynthetic processes of aggregate-prone interleukin-31

作者：Shen Min; Siu Sophia; Byrd Samantha; Edelmann Kurt H; Patel Neha; Ketchem Randal R; Mehlin Christopher; Arnett Heather A; Hasegawa Haruki^*

来源：Experimental Cell Research, 2011, 317(7): 976-993.

DOI：10.1016/j.yexcr.2010.12.012

• Interleukin-31
• Protein biosynthesis
• Disulfide bond
• ER quality control
• Protein aggregation
• Secretory pathway

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.

• 出版日期2011-4-15