Comprehensive identification of the genes involved in the expression of Siglec-15 ligands on osteoclast precursors.

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.