Thrombin Promotes Sustained Signaling and Inflammatory Gene Expression through the CDC25 and Ras-associating Domains of Phospholipase Cε

Phospholipase C-epsilon (PLC epsilon) plays a critical role in G-protein-coupled receptor-mediated inflammation. In addition to its ability to generate the second messengers inositol 1,4,5-trisphosphate and diacylglycerol, PLC epsilon, unlike the other phospholipase C family members, is activated in a sustained manner. We hypothesized that the ability of PLC epsilon to function as a guanine nucleotide exchange factor (GEF) for Rap1 supports sustained downstream signaling via feedback of Rap1 to the enzyme Ras-associating (RA2) domain. Using gene deletion and adenoviral rescue, we demonstrate that both the GEF (CDC25 homology domain) and RA2 domains of PLC epsilon are required for long term protein kinase D (PKD) activation and subsequent induction of inflammatory genes. PLC epsilon localization is largely intracellular and its compartmentalization could contribute to its sustained activation. Here we show that localization of PLC epsilon to the Golgi is required for activation of PKD in this compartment as well as for subsequent induction of inflammatory genes. These data provide a molecular mechanism by which PLC epsilon mediates sustained signaling and by which astrocytes mediate pathophysiological inflammatory responses.