Molecular characterization of the craniosynostosis‐associated interleukin‐11 receptor variants p.T306_S308dup and p.E364_V368del

Abstract

Interleukin‐11 (IL‐11) is a member of the IL‐6 family of cytokines and is an important factor for bone homeostasis. IL‐11 binds to and signals via the membrane‐bound IL‐11 receptor (IL‐11R, classic signaling) or soluble forms of the IL‐11R (sIL‐11R, trans‐signaling). Mutations in the IL11RA gene, which encodes the IL‐11R, are associated with craniosynostosis, a human condition in which one or several of the sutures close prematurely, resulting in malformation of the skull. The biological mechanisms of how mutations within the IL‐11R are linked to craniosynostosis are mostly unexplored. In this study, we analyze two variants of the IL‐11R described in craniosynostosis patients: p.T306_S308dup, which results in a duplication of three amino‐acid residues within the membrane‐proximal fibronectin type III domain, and p.E364_V368del, which results in a deletion of five amino‐acid residues in the so‐called stalk region adjacent to the plasma membrane. The stalk region connects the three extracellular domains to the transmembrane and intracellular region of the IL‐11R and contains cleavage sites for different proteases that generate sIL‐11R variants. Using a combination of bioinformatics and different biochemical, molecular, and cell biology methods, we show that the IL‐11R‐T306_S308dup variant does not mature correctly, is intracellularly retained, and does not reach the cell surface. In contrast, the IL‐11R‐E364_V368del variant is fully biologically active and processed normally by proteases, thus allowing classic and trans‐signaling of IL‐11. Our results provide evidence that mutations within the IL11RA gene may not be causative for craniosynostosis and suggest that other regulatory mechanism(s) are involved but remain to be identified.