Lysosyme-associated membrane proteins (LAMP) are transmembrane lysosomal glycoproteins, which share a common Gly-Tyr motif as a lysosomal targeting signal. While LAMP-1 and LAMP-2 contain type 1 transmembrane domains, LAMP-3 contains a transmembrane 4 superfamily domain, tetraspanin. FceRI-mediated stimulation of basophils causes LAMP-3 to be translocated from its intracellular localization to the plasma membrane. LAMP-3 thereby serves as a reliable marker for basophil activation. LAMP-3 expression is known to be reported in human bone marrow mast cells and in leukemic human mast cell line (HMC-1), among other cell lines. LAMP3 is shown to be regulated by hypoxia in a panel of tumor cells, via the unfolded protein response (UPR). UPR is a mechanism of adaptation to endoplasmic reticulum stress and is demonstrated to contribute to hypoxic adaptation in tumors through multiple mechanisms.