Vwf. Chan et al., DEFECTIVE NEGATIVE REGULATION OF ANTIGEN RECEPTOR SIGNALING IN LYN-DEFICIENT B-LYMPHOCYTES, Current biology, 8(10), 1998, pp. 545-553
Background: To elucidate the role of the Src family kinase Lyn in B ce
ll receptor (BCR) signaling, we and others previously generated lyn(-/
-)mice and analyzed their B cell responses. Although the initiation of
BCR signaling in lyn(-/-)B cells is delayed, BCR-induced ERK2 activat
ion and proliferation are enhanced, As the co-receptors Fc gamma RIIb1
and CD22 have been shown to be negative regulators of BCR signaling,
we have now examined their functional roles in lyn(-/-)B cells. Result
s: B cells from lyn(-/-)mice have increased expression of the protein
product of the early response gene egr-1, enhanced activation of Jun N
-terminal kinase (JNK), and elevated calcium responses upon BCR cross-
linking. Tyrosine phosphorylation of Fc gamma RIIb1 in lyn(-/-)B cells
was reduced but negative regulation of the BCR signal by Fc gamma RII
b1 was only modestly impaired. In contrast, tyrosine phosphorylation o
f CD22 was greatly decreased in lyn(-/-)B cells, correlating with the
inability of CD22 to downregulate the BCR-induced calcium response in
these cells. Surprisingly, CD22 remains capable of regulating the ERK2
and JNK pathways in lyn(-/-)B cells, which may relate to the small re
sidual increase in BCR-induced CD22 phosphorylation. Conclusions: BCR
signal initiation and negative regulation by Fc gamma RIIb1 is not cri
tically dependent on Lyn. In contrast, Lyn plays a particularly import
ant role in the tyrosine phosphorylation of CD22 and in the consequent
inhibition of BCR-induced calcium influx. The net result of the Lyn d
eficiency in B cells is hyperresponsiveness to antigen stimulation, wh
ich may explain the autoimmunity observed in lyn(-/-)mice. (C) Current
Biology Ltd ISSN 0960-9822.