Lysosomal membrane glycoprotein which plays an important role in lysosome biogenesis, autophagy, and cholesterol homeostasis (By similarity). Also plays an important role in NK-cells cytotoxicity (PubMed:23632890, PubMed:2022921). Mechanistically, participates in cytotoxic granule movement to the cell surface and perforin trafficking to the lytic granule (PubMed:23632890). In addition, protects NK-cells from degranulation-associated damage induced by their own cytotoxic granule content (PubMed:23847195). Presents carbohydrate ligands to selectins. Also implicated in tumor cell metastasis. (Microbial infection) Acts as a receptor for Lassa virus glycoprotein (PubMed:24970085). Promotes also fusion of the virus with host membrane in less acidic endosomes (PubMed:29295909). (Microbial infection) Supports the FURIN-mediated cleavage of mumps virus fusion protein F by interacting with both FURIN and the unprocessed form but not the processed form of the viral protein F. (Microbial infection) Interacts with Lassa virus protein glycoprotein. (Microbial infection) Interacts with mumps virus protein F; this interaction promotes protein F cleavage by FURIN. Interacts with ABCB9; this interaction strongly stabilizes ABCB9 and protects ABCB9 against lysosomal degradation (PubMed:22641697). Interacts with FURIN (PubMed:32295904). This protein shuttles between lysosomes, endosomes, and the plasma membrane (By similarity). Colocalizes with OSBPL1A at the late endosome (PubMed:16176980). O- and N-glycosylated; some of the 18 N-linked glycans are polylactosaminoglycans. The glycosylation of N-76 is essential for Lassa virus entry into cells. Belongs to the LAMP family.