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AP‐3 Adaptor Functions in Targeting P‐Selectin to Secretory Granules in Endothelial Cells
Author(s) -
Daugherty Brandy L.,
Straley Kimberly S.,
Sanders John M.,
Phillips J. William,
Disdier Magali,
McEver Rodger P.,
Green Samuel A.
Publication year - 2001
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1034/j.1600-0854.2001.002006406.x
Subject(s) - microbiology and biotechnology , endosome , signal transducing adaptor protein , biology , granule (geology) , p selectin , protein targeting , lysosome , platelet activation , platelet , signal transduction , immunology , biochemistry , membrane protein , intracellular , paleontology , membrane , enzyme
P‐selectin, a cell adhesion protein participating in the early stages of inflammation, contains multiple sorting signals that regulate its cell surface expression. Targeting to secretory granules regulates delivery of P‐selectin to the cell surface. Internalization followed by sorting from early to late endosomes mediates rapid removal of P‐selectin from the surface. We show here that the P‐selectin cytoplasmic domain bound AP‐2 and AP‐3 adaptor complexes in vitro . The amino acid substitution L768A, which abolishes endosomal sorting and impairs granule targeting of P‐selectin, reduced binding of AP‐3 adaptors but not AP‐2 adaptors. Turnover of P‐selectin was 2.4‐fold faster than turnover of transferrin receptor in AP‐3‐deficient mocha fibroblasts, similar to turnover of these two proteins in AP‐3‐competent cells, demonstrating that AP‐3 function is not required for endosomal sorting. However, sorting P‐selectin to secretory granules was defective in endothelial cells from AP‐3‐deficient pearl mice, demonstrating a role for AP‐3 adaptors in granule assembly in endothelial cells. P‐selectin sorting to platelet α‐granules was normal in pearl mice, consistent with earlier evidence that granule targeting of P‐selectin is mechanistically distinct in endothelial cells and platelets. These observations establish that AP‐3 adaptor functions in assembly of conventional secretory granules, in addition to lysosomes and the ‘lysosome‐like’ secretory granules of platelets and melanocytes.