The SH2-containing inositol 5'-phosphatase, SHIP1, negatively regulates signal transduction from the B cell antigen receptor (BCR). The mode of coupling between SHIP1 and the BCR has not been elucidated so far. In comparison to wild-type cells, B cells expressing a mutant IgD- or IgM-BCR containing a C-terminally truncated Ig-α respond to pervanadate stimulation with markedly reduced tyrosine phosphorylation of SHIP1 and augmented activation of protein kinase B. This indicates that SHIP1 is capable of interacting with the C-terminus of Ig-α. Employing a system of fluorescence resonance energy transfer in S2 cells, we can clearly demonstrate interaction between the SH2-domain of SHIP1 and Ig-α. Furthermore, a fluorescently labeled SH2-domain of SHIP1 translocates to the plasma membrane in an Ig-α-dependent manner. Interestingly, whereas the SHIP1 SH2-domain can be pulled-down with phospho-peptides corresponding to the immunoreceptor tyrosine-based activation motif (ITAM) of Ig-α from detergent lysates, no interaction between full-length SHIP1 and the phosphorylated Ig-α ITAM can be observed. Further studies show that the SH2-domain of SHIP1 can bind to the C-terminus of the SHIP1 molecule, most probably by inter- as well as intra-molecular means, and that this interaction regulates the association between different forms of SHIP1 and Ig-α.
Signal transduction by the B cell antigen receptor (BCR) regulates development, survival and clonal expansion of B cells. The BCR complex comprises the membrane‐bound immunoglobulin molecule (mIg) and the Ig‐α/Ig‐β heterodimer, and was shown to form oligomeric structures. In pervanadate (PV)‐treated B cells, multiple proteins are tyrosine phosphorylated upon expression of the BCR, indicating that the BCR can signal in an antigen‐independent fashion. We analyzed the signal transduction from BCR mutants which either have an altered heavy chain transmembrane region or lack theIg‐α cytoplasmic tail. In comparison to cells expressing the wild‐type receptors, those with a mutant BCR respond to PV treatment with reduced and retarded tyrosine phosphorylation of substrateproteins. Conversely, the cells with mutant BCR are more sensitive to stimulation with low doses of antigen. These data suggest that a correctly assembled BCR complex is important for antigen‐independent signaling and setting the threshold for antigen‐dependent BCR activation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.