Human IL-34 and CSF-1 Establish Structurally Similar Extracellular Assemblies with Their Common Hematopoietic Receptor

J. Felix, J. Elegheert, I. Gutsche, A. Shkumatov, Y. Wen, N. Bracke, E. Pannecoucke, I. Vandenberghe, B. Devreese, D.I. Svergun, E. Pauwels, B. Vergauwen, S.N. Savvides
21 (4), 528-539


The discovery that hematopoietic human colony stimulating factor-1 receptor (CSF-1R) can be activated by two distinct cognate cytokines, colony stimulating factor-1 (CSF-1) and interleukin-34 (IL-34), created puzzling scenarios for the two possible signaling complexes. We here employ a hybrid structural approach based on small-angle X-ray scattering (SAXS) and negative-stain EM to reveal that bivalent binding of human IL-34 to CSF-1R leads to an extracellular assembly hallmarked by striking similarities to the CSF-1:CSF-1R complex, including homotypic receptor-receptor interactions. Thus, IL-34 and CSF-1 have evolved to exploit the geometric requirements of CSF-1R activation. Our models include N-linked oligomannose glycans derived from a systematic approach resulting in the accurate fitting of glycosylated models to the SAXS data. We further show that the C-terminal region of IL-34 is heavily glycosylated and that it can be proteolytically cleaved from the IL-34:hCSF-1R complex, providing insights into its role in the functional nonredundancy of IL-34 and CSF-1.