Cutting Edge: Feed-Forward Activation of Phospholipase C gamma 2 via C2 Domain-Mediated Binding to SLP65

Ag-mediated B cell stimulation relies on phospholipase C gamma 2 (PLC gamma 2) for Ca2+ mobilization. Enzymatic activity of PLC gamma 2 is triggered upon Src homology 2 domain-mediated binding to the tyrosine-phosphorylated adaptor SLP65. However, SLP65 phosphorylation outlasts the elevation of cytosolic Ca2+ concentration suggesting additional levels of PLC gamma 2 regulation. We show in this article that the functionality of the PLC gamma 2/SLP65 complex is controlled by the weakly characterized C2 domain of PLC gamma 2. Usually C2 domains bind membrane lipids, but that of PLC gamma 2 docks in a Ca2+-regulated manner to a distinct phosphotyrosine of SLP65. Hence, early Ca2+ fluxing provides feed-forward signal amplification by promoting anchoring of the PLC gamma 2 C2 domain to phospho-SLP65. As the cellular Ca2+ resources become exhausted, the concomitant decline of Ca2+ dampens the C2-phosphotyrosine interaction so that PLC gamma 2 activation terminates despite sustained SLP65 phosphorylation.