Siglec-15 regulates osteoclast differentiation. The cellular pathways contributing to the expression of Siglec-15 ligand on osteoclast precursors are incompletely understood. We used genome-wide knockout screening to identify genes contributing to the expression of Siglec-15 ligands in the RAW264.7 cell line based on Siglec-15 binding. These genes include sialyltransferase St3gal4 and other enzymes involved in sialic acid biosynthesis and N-glycan processing, indicating that α2-3-linked sialic acid on N-glycans is the glycan epitope (glycotope) recognized by Siglec-15. LRP1 is identified as a Siglec-15 counterreceptor. In addition, the retriever complex that mediates endosome-to-plasma membrane protein recycling is found to contribute to Siglec-15 ligand expression. The LRP1 expression is impaired in retriever-deficient cells, underscoring the relevance of glycoprotein recycling in the maintenance of Siglec-15 ligands. RAW264.7 cells deficient in St3gal4, Lrp1, or Vps35l exhibit impaired osteoclast differentiation, verifying their functional relevance. Taken together, our study reveals pathways contributing to osteoclast differentiation.
Jiang et al. (Wed,) studied this question.