Phosphoprotein associated with glycosphingolipid-enriched microdomains (PAG), a novel ubiquitously expressed transmembrane adaptor protein, binds the protein tyrosine kinase csk and is involved in regulation of T cell activation.
According to a recently proposed hypothesis, initiation of signal transduction via immunoreceptors depends on interactions of the engaged immunoreceptor with glycosphingolipid-enriched membrane microdomains (GEMs). In this study, we describe a novel GEM-associated transmembrane adaptor protein, termed phosphoprotein associated with GEMs (PAG). PAG comprises a short extracellular domain of 16 amino acids and a 397-amino acid cytoplasmic tail containing ten tyrosine residues that are likely phosphorylated by Src family kinases. In lymphoid cell lines and in resting peripheral blood alpha/beta T cells, PAG is expressed as a constitutively tyrosine-phosphorylated protein and binds the major negative regulator of Src kinases, the tyrosine kinase Csk. After activation of peripheral blood alpha/beta T cells, PAG becomes rapidly dephosphorylated and dissociates from Csk. Expression of PAG in COS cells results in recruitment of endogenous Csk, altered Src kinase activity, and impaired phosphorylation of Src-specific substrates. Moreover, overexpression of PAG in Jurkat cells downregulates T cell receptor-mediated activation of the transcription factor nuclear factor of activated T cells. These findings collectively suggest that in the absence of external stimuli, the PAG-Csk complex transmits negative regulatory signals and thus may help to keep resting T cells in a quiescent state.
Brdicka
T
T
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 14220 Prague, Czech Republic.
Pavlistová
D
D
Leo
A
A
Bruyns
E
E
Korínek
V
V
Angelisová
P
P
Scherer
J
J
Shevchenko
A
A
Hilgert
I
I
Cerný
J
J
Drbal
K
K
Kuramitsu
Y
Y
Kornacker
B
B
Horejsí
V
V
Schraven
B
B
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D017252:CD3 Complex / Q000378:metabolism; D000081247:CSK Tyrosine-Protein Kinase; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D006028:Glycosphingolipids / Q000378:metabolism*; D006801:Humans; D008213:Lymphocyte Activation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology*; D019061:src-Family Kinases
D048868:Adaptor Proteins, Signal Transducing; D017252:CD3 Complex; D018076:DNA, Complementary; D006028:Glycosphingolipids; D008565:Membrane Proteins; C498710:PAG1 protein, human; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human