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J. Exp. Med.,
Volume 187, Number 8, April 20, 1998 1343-1348
By

From the * Department of Oncology, Institute of Medical Science, The University of Tokyo, Tokyo
108-8639, Japan; and the B cells from young lyn
Department of Biophysics and Biochemistry, Graduate School of Science,
The University of Tokyo, Tokyo 113-0033, Japan
/
mice are hyperresponsive to anti-IgM-induced proliferation, suggesting involvement of Lyn in negative regulation of B cell antigen receptor (BCR)-mediated
signaling. Here we show that tyrosine phosphorylation of Fc
RIIB and CD22 coreceptors,
which are important for feedback suppression of BCR-induced signaling, was severely impaired in lyn
/
B cells upon their coligation with the BCR. Hypophosphorylation on tyrosine
residues of these molecules resulted in failure of recruiting the tyrosine phosphatase SHP-1 and
inositol phosphatase SHIP, SH2-containing potent inhibitors of BCR-induced B cell activation, to the coreceptors. Consequently, lyn
/
B cells exhibited defects in suppressing BCR-induced Ca2+ influx and proliferation. Thus, Lyn is critically important in tyrosine phosphorylation of the coreceptors, which is required for feedback suppression of B cell activation.
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