Cutting edge: Fyn is essential for tyrosine phosphorylation of Csk-binding protein/phosphoprotein associated with glycolipid-enriched microdomains in lipid rafts in resting T cells.
In resting T cells, Csk is constitutively localized in lipid rafts by virtue of interaction with a phosphorylated adaptor protein, Csk-binding protein (Cbp)/phosphoprotein associated with glycolipid-enriched microdomains, and sets an activation threshold in TCR signaling. In this study, we examined a kinase responsible for Cbp phosphorylation in T cell membrane rafts. By analyzing T cells from Fyn-/- mice, we clearly demonstrated that Fyn, but not Lck, has its kinase activity in membrane rafts, and plays a critical role in Cbp phosphorylation, Cbp-Csk interaction, and Csk kinase activity. Naive CD44(low)CD62 ligand(high) T cells were substantially reduced in Fyn-/- mice, presumably due to the inhibition of Cbp phosphorylation. Thus, Fyn mediates Cbp-Csk interaction and recruits Csk to rafts by phosphorylating Cbp. Csk recruited to rafts would then be activated and inhibit the kinase activity of Lck to keep resting T cells in a quiescent state. Our results elucidate a negative regulatory role for Fyn in proximal TCR signaling in lipid rafts.
Yasuda
Koubun
K
Department of Oncogenesis, Graduate School of Medicine, Osaka University, Osaka, Japan.
Nagafuku
Masakazu
M
Shima
Takaki
T
Okada
Masato
M
Yagi
Takeshi
T
Yamada
Takenao
T
Minaki
Yasuko
Y
Kato
Akiko
A
Tani-Ichi
Shizue
S
Hamaoka
Toshiyuki
T
Kosugi
Atsushi
A
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D006017:Glycolipids / Q000378:metabolism; D006801:Humans; D016130:Immunophenotyping; D036341:Intercellular Signaling Peptides and Proteins; D007399:Interphase / Q000235:genetics / Q000276:immunology*; D019169:Jurkat Cells; D018655:Lymphocyte Count; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism; D021962:Membrane Microdomains / Q000201:enzymology / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src); D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D014443:Tyrosine / Q000037:antagonists & inhibitors / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D006017:Glycolipids; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C498710:PAG1 protein, human; C408344:Pag protein, mouse; C498709:Pag1 protein, mouse; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; C086603:Matk protein, mouse; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; C494960:Fyn protein, mouse; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src)