Mutations in Craniosynostosis Patients Cause Defective Interleukin-11 Receptor Maturation and Drive Craniosynostosis-like Disease in Mice.

Premature closure of the sutures that connect the cranial bones during development of the mammalian skull results in a phenotype called craniosynostosis. Recently, several craniosynostosis patients with missense mutations within the gene encoding the interleukin-11 receptor (IL-11R) have been described, but the underlying molecular mechanisms have remained elusive. IL-11 is a cytokine that has a crucial role in bone remodeling and activates cells via binding to the IL-11R. Here, we show that patient mutations prevented maturation of the IL-11R, resulting in endoplasmic reticulum retention and diminished cell surface appearance. Disruption of a conserved tryptophan-arginine zipper within the third domain of the IL-11R was the underlying cause of the defective maturation. IL-11 classic signaling via the membrane-bound receptor, but not IL-11 trans-signaling via the soluble receptor, was the crucial pathway for normal skull development in mice in vivo. Thus, the specific therapeutic inhibition of IL-11 trans-signaling does not interfere with skull development.

Enhancing Interleukin-6 and Interleukin-11 receptor cleavage.

Proteolytic cleavage of the membrane-bound Interleukin-6 receptor (IL-6R) by the metalloprotease ADAM17 releases an agonistic soluble form of the IL-6R (sIL-6R), which is responsible for the pro-inflammatory trans-signaling branch of the cytokine's activities. This proteolytic step, which is also called ectodomain shedding, is critically regulated by the cleavage site within the IL-6R stalk, because mutations or small deletions within this region are known to render the IL-6R irresponsive towards proteolysis. In the present study, we employed cleavage site profiling data of ADAM17 to generate an IL-6R with increased cleavage susceptibility. Using site-directed mutagenesis, we showed that the non-prime sites P3 and P2 and the prime site P1' were critical for this increase in proteolysis, whereas other positions within the cleavage site were of minor importance. Insertion of this optimized cleavage site into the stalk of the Interleukin-11 receptor (IL-11R) was not sufficient to enable ADAM17-mediated proteolysis, but transfer of different parts of the IL-6R stalk enabled shedding by ADAM17. These findings shed light on the cleavage site specificities of ADAM17 using a native substrate and reveal further differences in the proteolysis of IL-6R and IL-11R.