title: Contributions of protein kinases and β-arrestin to termination of protease-activated receptor 2 signaling.
abstract: Activated Gq protein-coupled receptors (GqPCRs) can be desensitized by phosphorylation and β-arrestin binding. The kinetics and individual contributions of these two mechanisms to receptor desensitization have not been fully distinguished. Here, we describe the shut off of protease-activated receptor 2 (PAR2). PAR2 activates Gq and phospholipase C (PLC) to hydrolyze phosphatidylinositol 4,5-bisphosphate (PIP2) into diacylglycerol and inositol trisphosphate (IP3). We used fluorescent protein-tagged optical probes to monitor several consequences of PAR2 signaling, including PIP2 depletion and β-arrestin translocation in real time. During continuous activation of PAR2, PIP2 was depleted transiently and then restored within a few minutes, indicating fast receptor activation followed by desensitization. Knockdown of β-arrestin 1 and 2 using siRNA diminished the desensitization, slowing PIP2 restoration significantly and even adding a delayed secondary phase of further PIP2 depletion. These effects of β-arrestin knockdown on PIP2 recovery were prevented when serine/threonine phosphatases that dephosphorylate GPCRs were inhibited. Thus, PAR2 may continuously regain its activity via dephosphorylation when there is insufficient β-arrestin to trap phosphorylated receptors. Similarly, blockers of protein kinase C (PKC) and G protein-coupled receptor kinase potentiated the PIP2 depletion. In contrast, an activator of PKC inhibited receptor activation, presumably by augmenting phosphorylation of PAR2. Our interpretations were strengthened by modeling. Simulations supported the conclusions that phosphorylation of PAR2 by protein kinases initiates receptor desensitization and that recruited β-arrestin traps the phosphorylated state of the receptor, protecting it from phosphatases. Speculative thinking suggested a sequestration of phosphatidylinositol 4-phosphate 5 kinase (PIP5K) to the plasma membrane by β-arrestin to explain why knockdown of β-arrestin led to secondary depletion of PIP2. Indeed, artificial recruitment of PIP5K removed the secondary loss of PIP2 completely. Altogether, our experimental and theoretical approaches demonstrate roles and dynamics of the protein kinases, β-arrestin, and PIP5K in the desensitization of PAR2.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Seung-Ryoung
authors.initials: SR
authors.lastname: Jung
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Jong Bae
authors.initials: JB
authors.lastname: Seo
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Yi
authors.initials: Y
authors.lastname: Deng
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Asbury
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Bertil
authors.initials: B
authors.lastname: Hille
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195 Department of Physics, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, Republic of Korea koh@uw.edu.
authors.forename: Duk-Su
authors.initials: DS
authors.lastname: Koh
mesh_terms: D057809:HEK293 Cells; D006801:Humans; D010716:Phosphatidylinositols / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D044464:Receptor, PAR-2 / Q000378:metabolism*; D015398:Signal Transduction; D000071557:beta-Arrestins / Q000378:metabolism*
chemical_list: D010716:Phosphatidylinositols; D044464:Receptor, PAR-2; D000071557:beta-Arrestins; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D011493:Protein Kinase C