Journal of Biological Chemistry
Volume 294, Issue 7, 15 February 2019, Pages 2386-2396
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Immunology
Interleukin 34 (IL-34) cell-surface localization regulated by the molecular chaperone 78-kDa glucose-regulated protein facilitates the differentiation of monocytic cells

https://doi.org/10.1074/jbc.RA118.006226Get rights and content
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Interleukin 34 (IL-34) constitutes a cytokine that shares a common receptor, colony-stimulating factor-1 receptor (CSF-1R), with CSF-1. We recently identified a novel type of monocytic cell termed follicular dendritic cell-induced monocytic cells (FDMCs), whose differentiation depended on CSF-1R signaling through the IL-34 produced from a follicular dendritic cell line, FL-Y. Here, we report the functional mechanisms of the IL-34–mediated CSF-1R signaling underlying FDMC differentiation. CRIPSR/Cas9-mediated knockout of the Il34 gene confirmed that the ability of FL-Y cells to induce FDMCs completely depends on the IL-34 expressed by FL-Y cells. Transwell culture experiments revealed that FDMC differentiation requires a signal from a membrane-anchored form of IL-34 on the FL-Y cell surface, but not from a secreted form, in a direct interaction between FDMC precursor cells and FL-Y cells. Furthermore, flow cytometric analysis using an anti–IL-34 antibody indicated that IL-34 was also expressed on the FL-Y cell surface. Thus, we explored proteins interacting with IL-34 in FL-Y cells. Mass spectrometry analysis and pulldown assay identified that IL-34 was associated with the molecular chaperone 78-kDa glucose-regulated protein (GRP78) in the plasma membrane fraction of FL-Y cells. Consistent with this finding, GRP78-heterozygous FL-Y cells expressed a lower level of IL-34 protein on their cell surface and exhibited a reduced competency to induce FDMC differentiation compared with the original FL-Y cells. These results indicated a novel GRP78-dependent localization and specific function of IL-34 in FL-Y cells related to monocytic cell differentiation.

monocyte
cell differentiation
interleukin
cytokine
chaperone
GRP78
cell surface protein
plasma membrane
CRISPR/Cas
Western blot
colony-stimulating factor-1 receptor
follicular dendritic cell
interleukin 34

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This work was supported in part by Grant-in-aid for Scientific Research (C) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan 25460590 and funds from the Ryobi Teien Foundation and the Takeda Science Foundation (to M. M.). The authors declare that they have no conflicts of interest with the contents of this article.

This article contains Table S1 and Figs. S1–S6.