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G-protein-coupled OX1 Orexin/hcrtr-1 Hypocretin Receptors Induce Caspase-dependent and -independent Cell Death through p38 Mitogen-/Stress-activated Protein Kinase
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Physiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Physiology.
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2006 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 281, 834-842 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the signaling of OX1 receptors to cell death using Chinese hamster ovary cells as a model system. OX1 receptor stimulation with orexin-A caused a delayed cell death independently of cytosolic Ca2+ elevation. The classical mitogen-activated protein kinase (MAPK) pathways, ERK and p38, were strongly activated by orexin-A. p38 was essential for induction of cell death, whereas the ERK pathway appeared protective. A pathway often implicated in the p38-mediated cell death, activation of p53, did not mediate the cell death, as there was no stabilization of p53 or increase in p53-dependent transcriptional activity, and dominant-negative p53 constructs did not inhibit cell demise. Under basal conditions, orexin-A-induced cell death was associated with compact chromatin condensation and it required de novo gene transcription and protein synthesis, the classical hallmarks of programmed (apoptotic) cell death. However, though the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)fluoromethyl ketone (Z-VAD-fmk) fully inhibited the caspase activity, it did not rescue the cells from orexin-A-induced death. In the presence of Z-VAD-fmk, orexin-A-induced cell death was still dependent on p38 and de novo protein synthesis, but it no longer required gene transcription. Thus, caspase inhibition causes activation of alternative, gene transcription-independent death pathway. In summary, the present study points out mechanisms for orexin receptor-mediated cell death and adds to our general understanding of the role of G-protein-coupled receptor signaling in cell death by suggesting a pathway from G-protein-coupled receptors to cell death via p38 mitogen-/stress-activated protein kinase independent of p53 and caspase activation.

Place, publisher, year, edition, pages
2006. Vol. 281, 834-842 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-93310DOI: 10.1074/jbc.M508603200OAI: oai:DiVA.org:uu-93310DiVA: diva2:166751
Available from: 2005-09-01 Created: 2005-09-01 Last updated: 2013-09-20Bibliographically approved
In thesis
1. Orexin Receptors in Recombinant CHO Cells: Signaling to Short- and Long-Term Cell Responses
Open this publication in new window or tab >>Orexin Receptors in Recombinant CHO Cells: Signaling to Short- and Long-Term Cell Responses
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recently discovered neuropeptides orexins (orexin-A and -B) act as endogenous ligands for G-protein-coupled receptors called OX1 and OX2 receptors. Our previous studies have established model systems for investigation of the pharmacology and signaling of these receptors in recombinant CHO cells. OX1 receptor-expressing CHO cells were mainly utilized in this thesis.

Orexin-A and -B activate both OX1 and OX2 receptors. However, orexin-B is less potent in activating OX1 receptors than orexin-A, whereas the peptides are equipotent on OX2 receptors. We have performed mutagenesis on orexin-A to investigate the basis for this selectivity. We show that OX2 receptor is generally less affected by the mutations and thus OX2 receptor appears to have less strict requirements for ligand binding, likely explaining the lack of difference in affinity/potency between orexin-A and orexin-B on OX2 receptor.

The other studies focus on orexin receptor signaling. OX1 receptors are shown to regulate adenylyl cyclase both in positive and negative manner, activate different MAP-kinases (ERK1/2 and p38) and induce cell death after long-lasting stimulation. Adenylyl cyclase regulation occurs likely through three different G-protein families, Gi, Gs and Gq. For ERK1/2, several downstream pathways, such as Ras, Src, PI3-kinase and protein kinase C (PKC) are implicated. OX1 receptor-mediated activation of ERK is suggested to be cytoprotective whereas p38 MAP-kinase induces programmed cell death.

Three particularly interesting findings were made. Firstly, novel PKC δ (delta) is suggested to regulate adenylyl cyclase, whereas conventional and atypical PKCs are involved in activation of ERK. Secondly, adenylyl cyclase and ERK activation is fully dependent on extracellular Ca2+. Further experiments suggest that the previously discovered receptor-operated Ca2+ influx is not affecting the downstream effectors of orexin receptors but that it instead enables orexin receptors to couple to several signal cascades. Thirdly, upon inhibition of caspases, classical mediators of programmed cell death, OX1 receptor-mediated cell death is not reversed, but instead the pathways to death are altered so de novo gene transcription is no longer required for cell death.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 92 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 56
Keyword
Neurosciences, orexins, cell signaling, Neurovetenskap
National Category
Neurology
Identifiers
urn:nbn:se:uu:diva-5890 (URN)91-554-6300-2 (ISBN)
Public defence
2005-09-22, B42, Biomedicinskt centrum (BMC), Husargatan 3, Uppsala, 09:00
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Supervisors
Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved

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