Premium
ITIM‐dependent endocytosis of CD33‐related Siglecs: role of intracellular domain, tyrosine phosphorylation, and the tyrosine phosphatases, Shp1 and Shp2
Author(s) -
Walter Roland B.,
Raden Brian W.,
Zeng Rong,
Häusermann Peter,
Bernstein Irwin D.,
Cooper Jonathan A.
Publication year - 2008
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1189/jlb.0607388
Subject(s) - biology , protein tyrosine phosphatase , sh2 domain , microbiology and biotechnology , proto oncogene tyrosine protein kinase src , endocytosis , tyrosine phosphorylation , endocytic cycle , syk , tyrosine , receptor tyrosine kinase , phosphorylation , immunoreceptor tyrosine based activation motif , internalization , phosphotyrosine binding domain , amphiphysin , biochemistry , tyrosine kinase , signal transduction , dynamin , receptor
The leukocyte CD33‐related sialic acid‐binding Ig‐like lectins (Siglecs) are implicated in glycan recognition and host defense against and pathogenicity of sialylated pathogens. Recent studies have shown endocytosis by CD33‐related Siglecs, which is implicated in clearance of sialylated antigens and antigen presentation and makes targeted immunotherapy possible. Using CD33 as a paradigm, we have now investigated the reasons underlying the comparatively slow rate of endocytosis of these receptors. We show that endocytosis is largely limited and determined by the intracellular domain while the extracellular and transmembrane domains play a minor role. Tyrosine phosphorylation, most likely through Src family kinases, increases uptake of CD33 depending on the integrity of the two cytoplasmic immunoreceptor tyrosine‐based inhibitory motifs (ITIMs). Simultaneous depletion of the protein tyrosine phosphatases, Src homology‐2‐containing tyrosine phosphatase 1 (Shp1) and Shp2, which bind to phosphorylated CD33, increases internalization of CD33 slightly in some cell lines, whereas depletion of spleen tyrosine kinase (Syk) has no effect, implying that Shp1 and Shp2 can dephosphorylate the ITIMs or mask binding of the phosphorylated ITIMs to an endocytic adaptor. Our studies show that restraint of CD33 internalization through the intracellular domain is relieved partly when the ITIMs are phosphorylated and show that Shp1 and Shp2 can modulate this process.