Abstract
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 G(q)-coupled receptor signaling pathways, displaying activation signatures at the Golgi that are distinct from those at the plasma membrane. Here we report that Ca(2+) 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 Ca(2+) is necessary and sufficient to elevate diacylglycerol levels at the Golgi. First, raising intracellular Ca(2+) by treating cells with thapsigargin induces diacylglycerol production at the Golgi. Second, chelation of intracellular Ca(2+) prevents UTP-stimulated increases in diacylglycerol at the Golgi. Thus, agonist-evoked increases in intracellular Ca(2+) cause increases in Golgi diacylglycerol, allowing this intracellular membrane to serve as a platform for signaling by protein kinases C and D.
Highlights
Diacylglycerol (DAG)2 is a ubiquitous lipid second messenger generated following activation of numerous G-protein-coupled receptor (GPCR) and tyrosine kinase receptors
Increasing Intracellular Ca2ϩ Is Sufficient to Increase DAG Levels at the Golgi—Previously, we demonstrated that increasing intracellular Ca2ϩ by treating cells with thapsigargin causes a rapid increase in plasma membrane DAG production (5)
Because we have shown that the Golgi serves as a platform for robust Protein kinase C (PKC) and protein kinase D (PKD) activation following agonist stimulation (6),3 we asked whether Ca2ϩ is the mediator that stimulates DAG production at Golgi membranes, too
Summary
Diacylglycerol (DAG)2 is a ubiquitous lipid second messenger generated following activation of numerous G-protein-coupled receptor (GPCR) and tyrosine kinase receptors. We demonstrate that Ca2ϩ is both necessary and sufficient to increase Golgi-localized DAG levels downstream of GPCR signaling from the plasma membrane.
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