title: OX1 orexin/hypocretin receptor activation of phospholipase D.
abstract: OBJECTIVE
  Orexin receptors potently signal to lipid messenger systems, and our previous studies have suggested that PLD would be one of these. We thus wanted to verify this by direct measurements and clarify the molecular mechanism of the coupling.
  
  
  METHODS
  Orexin receptor-mediated PLD activation was investigated in CHO cells stably expressing human OX(1)  orexin receptors using [(14) C]-oleic acid-prelabelling and the transphosphatidylation assay.
  
  
  RESULTS
  Orexin stimulation strongly increased PLD activity - even more so than the phorbol ester TPA (12-O-tetradecanoyl-phorbol-13-acetate), a highly potent activator of PLD. Both orexin and TPA responses were mediated by PLD1. Orexin-A and -B showed approximately 10-fold difference in potency, and the concentration-response curves were biphasic. Using pharmacological inhibitors and activators, both orexin and TPA were shown to signal to PLD1 via the novel PKC isoform, PKCδ. In contrast, pharmacological or molecular biological inhibitors of Rho family proteins RhoA/B/C, cdc42 and Rac did not inhibit the orexin (or the TPA) response, nor did the molecular biological inhibitors of PKD. In addition, neither cAMP elevation, Gα(i/o)  nor Gβγ seemed to play an important role in the orexin response.
  
  
  CONCLUSIONS
  Stimulation of OX(1)  receptors potently activates PLD (probably PLD1) in CHO cells and this is mediated by PKCδ but not other PKC isoforms, PKDs or Rho family G-proteins. At present, the physiological significance of orexin-induced PLD activation is unknown, but this is not the first time we have identified PKCδ in orexin signalling, and thus some specific signalling cascade may exist between orexin receptors and PKCδ.
authors: Biochemistry and Cell Biology, Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland.
authors: M H
authors: MH
authors: Jäntti
authors: J
authors: J
authors: Putula
authors: P
authors: P
authors: Somerharju
authors: M A
authors: MA
authors: Frohman
authors: J P
authors: JP
authors: Kukkonen
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D001583:Benzoxazoles / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology; D009287:Naphthyridines; D009479:Neuropeptides / Q000494:pharmacology; D064446:Orexin Receptors; D000068797:Orexins; D010739:Phospholipase D / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018013:Receptors, Neuropeptide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014508:Urea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C420062:1-(2-methylbenzoxazol-6-yl)-3-(1,5)naphthyridin-4-yl urea; D000098:Acetophenones; D001578:Benzopyrans; D001583:Benzoxazoles; C000596229:HCRT protein, human; D047908:Intracellular Signaling Peptides and Proteins; D009287:Naphthyridines; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D047428:Protein Kinase Inhibitors; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D014508:Urea; C085746:rottlerin; D051745:Protein Kinase C-delta; D010739:Phospholipase D; D013755:Tetradecanoylphorbol Acetate