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Abstract

Protein kinase C (PKC)-δ is a diacylglycerol-dependent, calcium-independent novel PKC isoform and has been demonstrated to exert negative regulatory functions in B lymphocytes as well as in mast cells. Whereas in mast cells PKC-δ functionally interacts with the high-affinity receptor for IgE, FcεR1, no such association has been described for the B cell antigen receptor (BCR). In this report, for the first time, we demonstrate the interaction of PKC-δ with different classes of BCR by means of affinity purification and native protein complex analysis. Using a C-terminally truncated Ig-α as well as non-phosphorylated and phosphorylated peptides representing C-terminal regions of Ig-α, the dependence of this BCR/PKC-δ interaction on tyrosine-phosphorylated Ig-α is shown. Finally, splenocytes from PKC-δ-deficient mice are found to exert reduced phosphorylation of PKD (a.k.a. PKC-μ) in response to BCR engagement, suggesting the early, membrane-proximal activation of an attenuating kinase complex including PKC-δ and PKD.