Lysosomal-associated membrane protein 1 is a glycoprotein from a family of Lysosome-associated membrane glycoproteins. The LAMP-1 glycoprotein is a type I transmembrane protein which is expressed at high or medium levels in at least 76 different normal tissue cell types. It resides primarily across lysosomal membranes, and functions to provide selectins with carbohydrate ligands. CD107a has also been shown to be a marker of degranulation on lymphocytes such as CD8+ and NK cells, and may also play a role in tumor cell differentiation and metastasis. Although the LAMP1 glycoproteins primarily reside across lysosomal membranes, in certain cases they can be expressed across the plasma membrane of the cell. Expression of LAMP1 at the cell surface can occur due to lysosomal fusion with the cell membrane. Cell surface expression of LAMP1 can serve as a ligand for selectins and help mediate cell-cell adhesion. Accordingly, cell surface expression of LAMP1 is seen in cells with migratory or invasive functions, such as cytotoxic T cells, platelets and macrophages. Cell surface expression of LAMP1 and LAMP2 is also often seen in cancer cells, particularly cancers with high metastatic potential, such as colon carcinoma and melanoma, and has been shown to correlate with their metastatic potential.
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