Discovery of a Cytokine and Its Receptor by Functional Screening of the Extracellular Proteome

Abstract

To understand the system of secreted proteins and receptors involved in cell-cell signaling, we produced a comprehensive set of recombinant secreted proteins and the extracellular domains of transmembrane proteins, which constitute most of the protein components of the extracellular space. Each protein was tested in a suite of assays that measured metabolic, growth, or transcriptional responses in diverse cell types. The pattern of responses across assays was analyzed for the degree of functional selectivity of each protein. One of the highly selective proteins was a previously undescribed ligand, designated interleukin-34 (IL-34), which stimulates monocyte viability but does not affect responses in a wide spectrum of other assays. In a separate functional screen, we used a collection of extracellular domains of transmembrane proteins to discover the receptor for IL-34, which was a known cytokine receptor, colony-stimulating factor 1 (also called macrophage colony-stimulating factor) receptor. This systematic approach is thus useful for discovering new ligands and receptors and assessing the functional selectivity of extracellular regulatory proteins.

Bone Morphogenetic Protein 2 and Transforming Growth Factor β1 Inhibit the Expression of the Proinflammatory Cytokine IL-34 in Rheumatoid Arthritis Synovial Fibroblasts

“…1 Among the cells located in the inflamed joint, synovial fibroblasts are crucial players driving inflammation and bone erosion. 2 IL-34, 3 basically described as promoting monocyte proliferation and survival, and osteoclast differentiation, 4 is expressed by synovial fibroblasts of RA patients. Its expression, correlated with inflammation, the number of leucocytes and the severity of the synovitis, is upregulated by TNFα and IL-1β.…”

Glial and Neuroimmune Mechanisms as Critical Modulators of Drug Use and Abuse

“…The maintenance and survival of microglia also depends on signaling at colony stimulating factor 1 receptor (CSF1R). The cytokine IL-34, which is primarily produced by neurons in the CNS, was identified as a separate ligand for CSF1R with a unique spatial distribution in the CNS; mice deficient in IL-34 have reduced numbers of microglia compared with wild-type mice, but only localized to brain regions where IL-34 would normally be expressed, including the cerebral cortex, basal ganglia, and hippocampus (Greter et al, 2012;Lin et al, 2008;Wang et al, 2012b). Moreover, microglia are curiously found in higher densities in regions that either produce or receive dopamine (Lawson et al, 1990), suggesting some unknown chemotactic or proliferation signal.…”

Induction of Functional Human Macrophages from Bone Marrow Promonocytes by M-CSF in Humanized Mice

“…Unlike M-CSF, deficiency in GM-CSF does not compromise the steady state of myelopoiesis and production of tissue macrophages, except the maturation of alveolar macrophages in the lungs (11). Recently, IL-34 was found to bind to M-CSF receptor and exhibited similar functions as M-CSF in promoting the formation of CFU-macrophage (CFU-M) and proliferation of monocytes in vitro (12). In IL-34-deficient mice, development of Langerhans cells in the skin epidermis and microglia in the CNS is selectively impaired (13).…”