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Rossi AM, Riley AM, Dupont G, Rahman T, Potter BVL, Taylor CW. Quantal Ca 2+ release mediated by very few IP 3 receptors that rapidly inactivate allows graded responses to IP 3. Cell Rep 2021; 37:109932. [PMID: 34731613 DOI: 10.1016/j.celrep.2021.109932] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 07/16/2021] [Accepted: 10/12/2021] [Indexed: 11/22/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are intracellular Ca2+ channels that link extracellular stimuli to Ca2+ signals. Ca2+ release from intracellular stores is "quantal": low IP3 concentrations rapidly release a fraction of the stores. Ca2+ release then slows or terminates without compromising responses to further IP3 additions. The mechanisms are unresolved. Here, we synthesize a high-affinity partial agonist of IP3Rs and use it to demonstrate that quantal responses do not require heterogenous Ca2+ stores. IP3Rs respond incrementally to IP3 and close after the initial response to low IP3 concentrations. Comparing functional responses with IP3 binding shows that only a tiny fraction of a cell's IP3Rs mediate incremental Ca2+ release; inactivation does not therefore affect most IP3Rs. We conclude, and test by simulations, that Ca2+ signals evoked by IP3 pulses arise from rapid activation and then inactivation of very few IP3Rs. This allows IP3Rs to behave as increment detectors mediating graded Ca2+ release.
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Chavkin C, Cohen JH, Land BB. Repeated Administration of Norbinaltorphimine Produces Cumulative Kappa Opioid Receptor Inactivation. Front Pharmacol 2019; 10:88. [PMID: 30787880 PMCID: PMC6373456 DOI: 10.3389/fphar.2019.00088] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 01/21/2019] [Indexed: 12/20/2022] Open
Abstract
Kappa receptor activation by dynorphins contributes to the anxiogenic, dysphoric, and cognitive disrupting effects of repeated stress, suggesting that kappa receptor antagonists might have therapeutic utility in the treatment of stress disorders. Three classes of kappa antagonists have been distinguished: non-selective, selective-competitive (readily reversible), and non-competitive (receptor-inactivating); however, which would be the most effective medication has not been established. To assess the utility of receptor inactivating antagonists, we tested the effects of a range of doses in both male and female mice. As previously established, the antinociceptive effects of the kappa agonist U50,488 were blocked by a single injection of the long-acting antagonist norbinatorphimine (norBNI) (10 mg/kg i.p.) in male mice. Ten to 20-fold lower doses of norBNI were ineffective after a single administration, but daily administration of 1.0 or 0.5 mg/kg for 5 days completely blocked U50,488 antinociceptive effects. Daily administration of 0.1 mg/kg norBNI produced slowly accumulating inhibition and completely blocked the antinociceptive effect of U50,488 after 20–30 days. Estrogen reduces female sensitivity to kappa opioid effects, but 30 days of 0.1 mg/kg norBNI completely blocked U50,488 analgesia in ovariectomized mice. Receptor inactivation in both male and female mice treated for 30 days with 0.1 mg/kg norBNI persisted for at least 1-week. These results suggest that receptor-inactivating kappa antagonists are effective in both males and females when given at 100-fold lower doses than typically administered in preclinical studies. The enhanced safety of this low-dosing protocol has important clinical implications if receptor inactivating kappa antagonists advance in medication development.
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Affiliation(s)
- Charles Chavkin
- Department of Pharmacology, University of Washington, Seattle, WA, United States
| | - Joshua H Cohen
- Department of Pharmacology, University of Washington, Seattle, WA, United States
| | - Benjamin B Land
- Department of Pharmacology, University of Washington, Seattle, WA, United States
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Wang R, Liu M, Yuan M, Oses-Prieto JA, Cai X, Sun Y, Burlingame AL, Wang ZY, Tang W. The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switched off by Dephosphorylation Mediated by Cytoplasm-Localized PP2A B' Subunits. Mol Plant 2016; 9:148-157. [PMID: 26517938 DOI: 10.1016/j.molp.2015.10.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2015] [Revised: 09/27/2015] [Accepted: 10/19/2015] [Indexed: 06/05/2023]
Abstract
Brassinosteroid (BR) binding activates the receptor kinase BRI1 by inducing heterodimerization with its co-receptor kinase BAK1; however, the mechanisms that reversibly inactivate BRI1 remain unclear. Here we show that cytoplasm-localized protein phosphatase 2A (PP2A) B' regulatory subunits interact with BRI1 to mediate its dephosphorylation and inactivation. Loss-of-function and overexpression experiments showed that a group of PP2A B' regulatory subunits, represented by B'η, negatively regulate BR signaling by decreasing BRI1 phosphorylation. BR increases the expression levels of these B' subunits, and B'η interacts preferentially with phosphorylated BRI1, suggesting that the dynamics of BR signaling are modulated by the PP2A-mediated feedback inactivation of BRI1. Compared with PP2A B'α and B'β, which promote BR responses by dephosphorylating the downstream transcription factor BZR1, the BRI1-inactivating B' subunits showed similar binding to BRI1 and BZR1 but distinct subcellular localization. Alteration of the nuclear/cytoplasmic localization of the B' subunits revealed that cytoplasmic PP2A dephosphorylates BRI1 and inhibits the BR response, whereas nuclear PP2A dephosphorylates BZR1 and activates the BR response. Our findings not only identify the PP2A regulatory B subunits that mediate the binding and dephosphorylation of BRI1, but also demonstrate that the subcellular localization of PP2A specifies its substrate selection and distinct effects on BR signaling.
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Affiliation(s)
- Ruiju Wang
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China
| | - Mengmeng Liu
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China
| | - Min Yuan
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China
| | - Juan A Oses-Prieto
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA
| | - Xingbo Cai
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China
| | - Ying Sun
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China
| | - Alma L Burlingame
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA
| | - Zhi-Yong Wang
- Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA
| | - Wenqiang Tang
- Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
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