Key Points
Cav-1–deficient T cells preferentially differentiate into Tregs, which translates into lower GVHD severity in mice. Reduced TCR:Lck clustering in Cav-1–deficient T cells is responsible for reduced TCR downstream signaling events promoting Treg differentiation.
Ag-triggered mast cell (MC) activation follows a bell-shaped dose-response curve. Reduced activation in response to supraoptimal Ag concentrations is thought to be due to preferential engagement of inhibitory-acting proteins like SHIP1, Lyn, and protein kinase C (PKC)-δ. We show in this study that short-term prestimulation with Steel factor (SF) prevents supraoptimal Ag inhibition, resulting in synergistic MC degranulation and IL-6 secretion. These events are preceded by synergistic phosphorylation/activation of numerous signaling proteins, e.g., Erk, p38, and LAT. However, these effects of prestimulation with SF appear not to be due to reduced engagement of the attenuator SHIP1. Pharmacological analyses suggest that the activation of conventional PKCs is important for this synergy. Specifically, although we found that the conventional PKC inhibitor, Gö6976, likely has some PKC-independent targets in MCs, it led us to further studies that established SF plus Ag-induced IL-6 secretion was severely impaired in PKC-β−/− MCs, but not PKC-α−/− MCs. Thus, PKC-β joins PI3K and Btk as important players in this synergistic MC activation.
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