Obestatin does not activate orphan G protein-coupled receptor GPR39.
Recently, the ligand of the orphan G protein-coupled receptor GPR39 has been identified as obestatin, a 23-amino acid peptide derived from the ghrelin precursor protein. We used two methods to study the possible activation of GPR39 by obestatin: cAMP measurements based on a luminescent reporter gene and a fluorometric Ca(2+) flux method. The former was similar to that reported in the original publication of Zhang et al. [J.V. Zhang, P.G. Ren, O. Avsian-Kretchmer, C.W. Luo, R. Rauch, C. Klein, Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake, Science 310 (2005) 996-999]. The latter method used promiscuous as well as chimaeric G-proteins commonly used to couple orphan G protein-coupled receptors to the phospholipase C pathway, that leads to intracellular Ca(2+) rise. We could, however, not demonstrate activation of the GPR39 receptor by obestatin via any of these signal transduction pathways. We could activate GPR39 by high concentrations of Zn(2+), demonstrating cell surface expression of a functional receptor that could elicit a Ca(2+) response. The Zn(2+) response was not affected by obestatin. The identity of the native ligand for GPR39 remains to be elucidated.
Lauwers
Erwin
E
Laboratory of Developmental Physiology, Genomics, and Proteomics, Katholieke Universiteit Leuven, Naamsestraat 59, B-3000 Leuven, Belgium. Erwin.Lauwers@med.kuleuven.be
Landuyt
Bart
B
Arckens
Lutgarde
L
Schoofs
Liliane
L
Luyten
Walter
W
D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D054439:Ghrelin; D006801:Humans; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism*; D036361:Peptide Hormones / Q000008:administration & dosage*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
C495797:GPR39 protein, human; D054439:Ghrelin; D036361:Peptide Hormones; D043562:Receptors, G-Protein-Coupled; C505799:obestatin, human