Critical role for Epac1 in inflammatory pain controlled by GRK2-mediated phosphorylation of Epac1.

Abstract

cAMP signaling plays a key role in regulating pain sensitivity. Here, we uncover a previously unidentified molecular mechanism in which direct phosphorylation of the exchange protein directly activated by cAMP 1 (EPAC1) by G protein kinase 2 (GRK2) suppresses Epac1-to-Rap1 signaling, thereby inhibiting persistent inflammatory pain. Epac1(-/-) mice are protected against inflammatory hyperalgesia in the complete Freund's adjuvant (CFA) model. Moreover, the Epac-specific inhibitor ESI-09 inhibits established CFA-induced mechanical hyperalgesia without affecting normal mechanical sensitivity. At the mechanistic level, CFA increased activity of the Epac target Rap1 in dorsal root ganglia of WT, but not of Epac1(-/-), mice. Using sensory neuron-specific overexpression of GRK2 or its kinase-dead mutant in vivo, we demonstrate that GRK2 inhibits CFA-induced hyperalgesia in a kinase activity-dependent manner. In vitro, GRK2 inhibits Epac1-to-Rap1 signaling by phosphorylation of Epac1 at Ser-108 in the Disheveled/Egl-10/pleckstrin domain. This phosphorylation event inhibits agonist-induced translocation of Epac1 to the plasma membrane, thereby reducing Rap1 activation. Finally, we show that GRK2 inhibits Epac1-mediated sensitization of the mechanosensor Piezo2 and that Piezo2 contributes to inflammatory mechanical hyperalgesia. Collectively, these findings identify a key role of Epac1 in chronic inflammatory pain and a molecular mechanism for controlling Epac1 activity and chronic pain through phosphorylation of Epac1 at Ser-108. Importantly, using the Epac inhibitor ESI-09, we validate Epac1 as a potential therapeutic target for chronic pain.

• Authors: Pooja Singhmar, XiaoJiao Huo, Niels Eijkelkamp, Susana Rojo Berciano, Faiza Baameur, Fang C Mei, Yingmin Zhu, Xiaodong Cheng, David Hawke, Federico Mayor Jr, Cristina Murga, Cobi J Heijnen, Annemieke Kavelaars
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 113 Issue 11 Pg. 3036-41 (Mar 15 2016) ISSN: 1091-6490 [Electronic] United States
• PMID: 26929333 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Epac protein, mouse
• Guanine Nucleotide Exchange Factors
• Ion Channels
• Nerve Tissue Proteins
• Piezo2 protein, mouse
• Phosphoserine
• Freund's Adjuvant
• GRK2 protein, mouse
• G-Protein-Coupled Receptor Kinase 2
• rap1 GTP-Binding Proteins

Topics

• Amino Acid Sequence
• Animals
• Chronic Disease
• Freund's Adjuvant (toxicity)
• G-Protein-Coupled Receptor Kinase 2 (physiology)
• Ganglia, Spinal (physiopathology)
• Guanine Nucleotide Exchange Factors (deficiency, genetics, physiology)
• Hyperalgesia (etiology, physiopathology)
• Inflammation (chemically induced, complications)
• Ion Channels (physiology)
• Mechanoreceptors (physiology)
• Mice
• Mice, Knockout
• Molecular Sequence Data
• Nerve Tissue Proteins (physiology)
• Nociception (physiology)
• Pain (etiology, physiopathology)
• Pain Threshold (physiology)
• Phosphorylation
• Phosphoserine (metabolism)
• Protein Interaction Mapping
• Protein Processing, Post-Translational
• Protein Structure, Tertiary
• Signal Transduction
• rap1 GTP-Binding Proteins (physiology)