Receptor-type Protein-tyrosine Phosphatase ζ Is a Functional Receptor for Interleukin-34

Interleukin-34 (IL-34) is highly expressed in brain. IL-34 signaling via its cognate receptor, colony-stimulating factor-1 receptor (CSF-1R), is required for the development of microglia. However, the differential expression of IL-34 and the CSF-1R in brain suggests that IL-34 may signal via an alternate receptor. By IL-34 affinity chromatography of solubilized mouse brain membrane followed by mass spectrometric analysis, we identified receptor-type protein-tyrosine phosphatase (PTP-), a cell surface chondroitin sulfate (CS) proteoglycan, as a novel IL-34 receptor. PTP- is primarily expressed on neural progenitors and glial cells and is highly expressed in human glioblastomas. IL-34 selectively bound PTP- in CSF-1R-deficient U251 human glioblastoma cell lysates and inhibited the proliferation, clonogenicity, and motility of U251 cells in a PTP--dependent manner. These effects were correlated with an increase in tyrosine phosphorylation of the previously identified PTP- downstream effectors focal adhesion kinase and paxillin. IL-34 binding to U251 cells was abrogated by chondroitinase ABC treatment, and CS competed with IL-34 for binding to the extracellular domain of PTP- and to the cells, indicating a dependence of binding on PTP- CS moieties. This study identifies an alternate receptor for IL-34 that may mediate its action on novel cellular targets.