A negative-feedback function of PKC in the formation and accumulation of signaling-active B cell receptor microclusters within B cell immunological synapse.

Advanced live cell imaging studies suggested that B cell activation is initiated by the formation of BCR microclusters and subsequent B cell IS upon BCR and antigen recognition. PKC family member PKC is highly expressed in B cells and plays an important role in the initiation of B cell activation. Here, we reported an inhibitory function of PKC through a negative-feedback manner in B cell activation. Compared with WT (PKC-WT) or the constitutively active (PKC-NPS) form of PKC, DN PKC (PKC-DN) unexpectedly enhanced the accumulation of BCR microclusters into the B cell IS, leading to the recruitment of an excessive amount of pSyk, pPLC-2, and pBLNK signaling molecules into the membrane-proximal BCR signalosome. Enhanced calcium mobilization responses in the decay phase were also observed in B cells expressing PKC-DN. Mechanistic studies showed that this negative-feedback function of PKC works through the induction of an inhibitory form of pBtk at S180 (pBtk-S180). Indeed, the capability of inducing the formation of an inhibitory pBtk-S180 is in the order of PKC-NPS > PKC-WT > PKC-DN. Thus, these results improve our comprehensive understanding on the positive and negative function of PKCβ in the fine tune of B cell activation.