Dendritic Cell-Specific Transmembrane Protein (DC-STAMP) Regulates Osteoclast Differentiation via the Ca ²⁺/NFATc1 axis

Abstract

DC-STAMP is a multi-pass transmembrane protein essential for cell-cell fusion of osteoclast precursors during osteoclast (OC) development. DC-STAMP−/− mice have mild osteopetrosis and form mononuclear cells with limited resorption capacity. The identification of an Immunoreceptor Tyrosine-based Inhibitory Motif (ITIM) on the cytoplasmic tail of DC-STAMP suggested a potential signaling function but the absence of known DC-STAMP ligand has hindered examination of downstream signaling pathways. To address this problem, we engineered a light-activatable DC-STAMP chimeric molecule in which light exposure mimics ligand engagement that can be traced by downstream Ca ²⁺ signaling. Deletion of the cytoplasmic ITIM resulted in a significant elevation in the amplitude and duration of intracellular Ca ²⁺ flux. We also found that decreased NFATc1 expression in DC-STAMP−/− cells was restored by DC-STAMP over-expression. Multiple biological phenotypes including cell-cell fusion, bone erosion, cell mobility, DC-STAMP cell surface distribution, and NFATc1 nuclear translocation were altered by deletion of the ITIM and adjacent amino acids. In contrast, mutations on each of tyrosine residues in the ITIM showed no effect on DC-STAMP function. Collectively, our results suggest that ITIM on DC-STAMP is a functional motif that regulates osteoclast differentiation through the NFATc1 / Ca ²⁺ axis.