Interleukin 34 (IL-34) cell-surface localization regulated by the molecular chaperone 78-kDa glucose-regulated protein facilitates the differentiation of monocytic cells

Abstract

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, FLY. 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 FLY cells to induce FDMCs completely depends on the IL-34 expressed by FLY cells. Transwell culture experiments revealed that FDMC differentiation requires a signal from a membrane-anchored form of IL-34 on the FLY cell surface, but not from a secreted form, in a direct interaction between FDMC precursor cells and FLY cells. Furthermore, flow cytometric analysis using an anti-IL-34 antibody indicated that IL-34 was also expressed on the FLY cell surface. Thus, we explored proteins interacting with IL-34 in FLY cells. Mass spectrometry analysis and pulldown assay identified that IL-34 was associated with the molecular chaperone 78-kDa glucoseregulated protein (GRP78) in the plasma membrane fraction of FLY cells. Consistent with this finding, GRP78-heterozygous FLY 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 FLY cells. These results indicated a novel GRP78-dependent localization and specific function of IL-34 in FLY cells related to monocytic cell differentiation. Colony-stimulating factor-1 receptor (CSF-1R) 2 activation promotes the proliferation, survival, and differentiation of mononuclear phagocytes, such as macrophages, Langerhans cells, and osteoclasts (1-4). Specifically, binding of CSF-1 to CSF-1R can induce the activation of the tyrosine kinase activity of CSF-1R through the phosphorylation of seven tyrosine residues (Tyr 559 , Tyr 697 , Tyr 706 , Tyr 721 , Tyr 807 , Tyr 921 , and Tyr 974) of the cytoplasmic domain, followed by activation of signal transduction cascades including Src/Pyk2 and PI3K pathways (5, 6). Accordingly, CSF1 op/op mice bearing a null mutation in the Csf1 gene exhibit osteoperitrotic phenotypes including toothlessness, skeletal defects, and impaired development of macrophages and osteoclasts (7). However, the phenotype of CSF-1Rdeficient mice is more severe than that of the CSF1 op/op mice; for example, Langerhans cells and microglia are completely absent in CSF-1R-deficient mice (8, 9). Interleukin 34 (IL-34) has been identified as an alternative ligand for CSF-1R (10). IL-34 exhibits a similar stimulating activity for CSF-1R as the primary identified ligand, CSF-1 (11), although these two proteins share no sequence homology. Moreover, Il34 gene expression driven by the Csf1 promoter was shown to rescue the bone, osteoclast, tissue macrophage, and fertility defects of CSF1 op/op mice; thus, IL-34 is consider...

The twin cytokines interleukin-34 and CSF-1: masterful conductors of macrophage homeostasis

“…These differences in CSF-1R activation generated a variety of downstream signaling pathway activations and, as a consequence, a wide range of biological functions in macrophages and other cell types. Adding another layer of complexity, CSF-1 and IL-34 were able to generate a functional heterodimer 48 , and both cytokines could be present in several isoforms 57 , 58 . Moreover, IL-34 bound to RPTP-ζ and syndecan-1 receptors with particular bioactivities 52 , 53 .…”

“…Three isoforms of CSF-1 are described: a secreted glycoprotein, a secreted proteoglycan and a membrane-spanning cell surface glycoprotein 57 . Two isoforms of IL-34 generated by mRNA alternative splicing are described and recently, Ogawa et al 58 showed the existence of a third isoform bound to the cell surface. In secondary lymphoid tissue, follicular dendritic cells (FDC) expressed IL-34 that induced, via CSF-1R, the differentiation of a novel class of monocytes, named FDC-induced monocytic cells.…”

“…In secondary lymphoid tissue, follicular dendritic cells (FDC) expressed IL-34 that induced, via CSF-1R, the differentiation of a novel class of monocytes, named FDC-induced monocytic cells. IL-34 needs the participation of the molecular chaperone 78-KDa glucose-regulated protein (GRP78) 58 . How the cell-surface IL-34 variant induces the differentiation of monocytes remains unclear.…”

The M-CSF receptor in osteoclasts and beyond

“…Brain-derived IL-34 is responsible for the migration of microglial precursors to the proximal brain region 142 . Finally, IL-34 secreted from the follicular dendritic cell line FL-Y was found to induce the differentiation of a new type of monocytic cell called follicular dendritic cell-induced monocytic cells by associating with the molecular chaperone 78-kDa glucose regulated protein 143 .…”

Loss of IL-34 Expression Indicates Poor Prognosis in Patients With Lung Adenocarcinoma

“…Interleukin 34 (IL-34) is a cytokine that shares a common receptor with colony-stimulating factor (CSF)-1, namely CSF-1R (5). Previous studies have shown that IL-34 helps the development and maintenance of Langerhans cells and microglia (6,7).…”