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

Phospholipase C-epsilon (PLCϵ) 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, PLCϵ, unlike the other phospholipase C family members, is activated in a sustained manner. We hypothesized that the ability of PLCϵ 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 PLCϵ are required for long term protein kinase D (PKD) activation and subsequent induction of inflammatory genes. PLCϵ localization is largely intracellular and its compartmentalization could contribute to its sustained activation. Here we show that localization of PLCϵ 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 PLCϵ mediates sustained signaling and by which astrocytes mediate pathophysiological inflammatory responses. Background: PLCϵ activation is sustained but the underlying regulatory mechanisms are unknown. Results: PLCϵ gene deletion and rescue demonstrate that Rap1 activation by the CDC25 domain and regulation via the RA2 domain sustain thrombin-mediated PLCϵ and PKD activation and inflammatory gene expression. Conclusion: Unique domains and compartmentalization of PLCϵ allow for sustained GPCR signaling. Significance: Targeting these PLCϵ domains could ameliorate pathophysiological inflammation.