Calcium Transduces Plasma Membrane Receptor Signals to Produce Diacylglycerol at Golgi Membranes

Protein kinase C and protein kinase D are potently activated by agonist-evoked increases in diacylglycerol. Using live cell-imaging probes for kinase activity, we have shown that both kinases are robustly activated at the Golgi following stimulation of Gq-coupled receptor signaling pathways, displaying activation signatures at the Golgi that are distinct from those at the plasma membrane. Here we report that Ca2+ is the mediator that allows signals received at the plasma membrane to activate these two protein kinases at the Golgi. Specifically, using fluorescence resonance energy transfer-based reporters to image diacylglycerol production, we show that Ca2+ is necessary and sufficient to elevate diacylglycerol levels at the Golgi. First, raising intracellular Ca2+ by treating cells with thapsigargin induces diacylglycerol production at the Golgi. Second, chelation of intracellular Ca2+ prevents UTP-stimulated increases in diacylglycerol at the Golgi. Thus, agonist-evoked increases in intracellular Ca2+ cause increases in Golgi diacylglycerol, allowing this intracellular membrane to serve as a platform for signaling by protein kinases C and D.