Lysosome-associated
membrane protein 2 (LAMP 2), also known as lgp2 or lgp110, is
a type 1 integral membrane protein that is transported from the
trans-Golgi network to endosomes and then lysosomes. LAMPs, also
known as lysosomal integral membrane proteins (LIMPs), are ubiquitous,
highly glycosylated and account for ~50% of lysosomal membrane
protein; their function is largely unknown. All LAMPs have a
short, 10-20 amino acid, cytosolic domain which contain single
tyrosine or di-leucine motifs, that interact with adaptor complexes
(APS) for sorting at the trans-Golgi network and targeting to
lysosomes. LAMP 2 has also been detected at the plasma membrane
of cells in a differentiation and activation dependant manner,
as well as in cells that secrete lysosomal hydrolases. A study
in the developmental expression patterns of membrane LAMP 2 transcripts
indicate a possible involvement of this protein in cell-cell
or cell-extracellular matrix interaction, and appear to reflect
tissue and cell type specific roles of lysosomes during morphogenesis.
Cell surface LAMP 1 and 2 have been shown to promote adhesion
of human peripheral blood mononuclear cells (PBMC) to vascular
endothelium, possibly involved in the adhesion of PBMC to the
site of inflammation. Studies with LAMP 2 deficient mice indicate
LAMP 2 is critical for autophagy, in conversion of early autophagic
vacuoles to vacuoles, which rapidly degrade their content. It
is also the primary defect in Danon disease. The trans-Golgi
network (TGN) is part of the secretory pathway of eukaryotic
cells which is distinct from the Golgi stack. The TGN is important
in the later stages of protein secretion where it seems to play
a key role in the sorting and targeting of secreted proteins
to the correct destination. Some surface receptors recycle between
the cell surface and the TGN, suggesting that the TGN is also
important in endocytic pathways.
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