CD45 modulates phosphorylation of both autophosphorylation and negative regulatory tyrosines of Lyn in B cells.
CD45 is a tyrosine phosphatase that is required for normal B cell receptor (BCR)-mediated signaling. It has been shown that Src-family tyrosine kinases such as Lyn could be a potential substrate for CD45. In vitro studies indicate that activities of Src family tyrosine kinases are regulated by tyrosine phosphorylation; C-terminal phosphorylation is inhibitory, and autophosphorylation is stimulatory. We report here that both autophosphorylation and C-terminal negative regulatory tyrosines of Lyn were hyperphosphorylated in CD45-deficient DT40 B cells. In this mutant cell, BCR-induced protein-tyrosine phosphorylation and calcium mobilization were severely compromised, as seen in Lyn-deficient cells. Consistent with this observation, Lyn activation upon receptor ligation was profoundly decreased in CD45-deficient cells. Taken together, our results suggest that dephosphorylation of tyrosine residues at both autophosphorylation and negative regulatory sites is mediated by CD45 in vivo, and that dephosphorylation of C-terminal tyrosine is a prerequisite for participation of Lyn in BCR signaling.
Yanagi
S
S
Section of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06510-8023, USA. kurosaki@mxr.meshnet.or.jp
Sugawara
H
H
Kurosaki
M
M
Sabe
H
H
Yamamura
H
H
Kurosaki
T
T
D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D002451:Cell Compartmentation; D002478:Cells, Cultured; D002645:Chickens; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D010449:Peptide Mapping; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D015398:Signal Transduction; D019061:src-Family Kinases / Q000378:metabolism*
D019000:Phosphotyrosine; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D017493:Leukocyte Common Antigens; D002118:Calcium