Lysosomal membrane glycoprotein which plays a role in the unfolded protein response (UPR) that contributes to protein degradation and cell survival during proteasomal dysfunction (PubMed:25681212). Plays a role in the process of fusion of the lysosome with the autophagosome, thereby modulating the autophagic process (PubMed:24434718). Promotes hepatocellular lipogenesis through activation of the PI3K/Akt pathway (PubMed:29056532). May also play a role in dendritic cell function and in adaptive immunity (PubMed:9768752). (Microbial infection) Plays a positive role in post-entry steps of influenza A virus replication, either virus uncoating, cytosolic transport, or nuclear import of viral components, and promotes nuclear accumulation of influenza nucleoprotein/NP at early stages of viral infection. (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) Promotes the intracellular proliferation of Salmonella typhimuium. Monomer (PubMed:22809326). Interacts with FURIN (PubMed:32295904). (Microbial infection) Interacts with mumps virus protein F; this interaction promotes protein F cleavage by FURIN. During dendritic cell maturation, detected on cytoplasmic vesicles (the MHC II compartment) that contain MHC II proteins, LAMP1, LAMP2 and LAMP3 (PubMed:9768752). Detected on lysosomes in mature dendritic cells (PubMed:9768752). Detected in tonsil interdigitating dendritic cells, in spleen, lymph node, Peyer's patches in the small instestine, in thymus medulla and in B-cells (at protein level). Expressed in lymphoid organs and dendritic cells. Expressed in lung. Up-regulated in carcinomas of the esophagus, colon, rectum, ureter, stomach, breast, fallopian tube, thyroid and parotid tissues. Up-regulated during dendritic cell maturation. By UPR transcription factor ATF4 signaling. (Microbial infection) Upon Salmonella typhimurium infection, at both transcriptional and translational levels. Belongs to the LAMP family.