Selective activation of TACI by syndecan-2.
B-lymphocyte homeostasis and function are regulated by complementary actions of the TNFR family members TACI, BCMA, and BAFF-R, which are expressed by mature B cells. How these receptors are differentially activated is not entirely understood, because the primary ligand BAFF binds to all three. We searched for alternative ligands for TACI using recombinant TACI-Fc fusion protein as a probe and identified syndecan-2 as a new binding partner. TACI binding appears to require heparan sulfate posttranslational modifications of syndecan-2, because free heparin or pretreatment with heparitinase blocked the interaction. Syndecan-2 bound TACI but bound neither BAFF-R nor BCMA. Transfected cells expressing syndecan-2 activated signaling through TACI, as indicated by an NFAT-specific reporter. Syndecan-1 and syndecan-4 were also able to induce TACI signaling in a similar manner. This is the first identification of ligands that selectively activate TACI without simultaneously triggering BCMA or BAFF-R. This finding may help explain the alternative outcomes of signaling from this family of receptors in B cells.[1]References
- Selective activation of TACI by syndecan-2. Bischof, D., Elsawa, S.F., Mantchev, G., Yoon, J., Michels, G.E., Nilson, A., Sutor, S.L., Platt, J.L., Ansell, S.M., von Bulow, G., Bram, R.J. Blood (2006) [Pubmed]
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