B-CELL ANTIGEN RECEPTOR CROSS-LINKING INDUCES TYROSINE PHOSPHORYLATION AND MEMBRANE TRANSLOCATION OF A MULTIMERIC SHC COMPLEX THAT IS AUGMENTED BY CD19 CO-LIGATION
Ac. Lankester et al., B-CELL ANTIGEN RECEPTOR CROSS-LINKING INDUCES TYROSINE PHOSPHORYLATION AND MEMBRANE TRANSLOCATION OF A MULTIMERIC SHC COMPLEX THAT IS AUGMENTED BY CD19 CO-LIGATION, European Journal of Immunology, 24(11), 1994, pp. 2818-2825
The SH2 domain-containing transforming Shc protein has been implicated
in mitogenic signaling via several surface receptors through p21(ras)
. Following tyrosine phosphorylation by either receptor or non-recepto
r tyrosine kinases, She may interact with the adaptor protein Grb2, wh
ich is linked to Sos1, a guanine nucleotide exchange factor for human
ras. Ligation of the antigen receptor complex on B cells (BCR) is know
n to activate various intracellular signaling pathways, which may accu
mulate in mitogenic responses. With respect to the initial steps, the
activation of BCR-associated non-receptor tyrosine kinases appears to
be indispensible. In this report we show that She proteins become tyro
sine phosphorylated after BCR ligation on both transformed and normal
human B cells. This is accompanied by the association of She with Grb2
proteins and a yet unidentified 145-kDa tyrosine phosphorylated prote
in. Subcellular fractionation revealed that this activation-induced mu
ltimeric Shc complex rapidly translocates towards the plasma membrane.
Co-ligation of the BCR with the CD19 molecule results in a marked inc
rease of these events, whereas CD19 cross-linking alone does not induc
e Shc tyrosine phosphorylation or translocation. Thus, in B cells the
Shc complex may represent a molecular junction between the BCR and the
mitogenic p21(ras) cascade.