Desensitization and endocytosis mechanisms of ghrelin-activated growth hormone secretagogue receptor 1a

Endocrinology. 2004 Feb;145(2):930-40. doi: 10.1210/en.2003-0974. Epub 2003 Oct 23.


In this study, a sequential analysis of pathways involved in the regulation of GH secretagogue receptor subtype 1a (GHSR-1a) signaling has been undertaken to characterize the process of rapid desensitization that is observed after ghrelin binding. This process was evaluated by studying the binding of [(125)I]ghrelin, measurement of intracellular calcium mobilization, and confocal microscopy. The results indicate that GHSR-1a is mainly localized at the plasma membrane under unstimulated conditions and rapidly desensitizes after stimulation. The agonist-dependent desensitization is not mediated by protein kinase C because phorbol ester, phorbol-12-myristate-13-acetate, failed to block the ghrelin-induced calcium response. The ghrelin/GHSR-1a complex progressively disappears from the plasma membrane after 20 min exposure to ghrelin and accumulates in the perinuclear region after 60 min. Colocalization of the internalized GHSR-1a with the early endosome marker (EEA1) after 20 min exposure to ghrelin suggests that endocytosis occurs via clathrin-coated pits, which is consistent with the lack of internalization of this receptor observed after potassium depletion. Different from other G protein-coupled receptors, GHSR-1a showed slow recycling. Surface binding slowly recovered after agonist treatment and returned to control levels within 360 min. Furthermore, inhibition of vacuolar H(+)-ATPases prevented recycling of the receptor, suggesting that the nondissociation of the ligand/receptor complex is responsible for this effect. The GHSR-1a internalization may explain the characteristic physiological responses mediated by this receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CHO Cells
  • Calcium / metabolism
  • Cell Line
  • Clathrin-Coated Vesicles / physiology
  • Cricetinae
  • Embryo, Mammalian
  • Endocytosis*
  • Enzyme Activation
  • Ghrelin
  • Green Fluorescent Proteins
  • Humans
  • Inositol 1,4,5-Trisphosphate / metabolism
  • Iodine Radioisotopes
  • Kidney
  • Luminescent Proteins / genetics
  • Microscopy, Confocal
  • Peptide Hormones / metabolism
  • Peptide Hormones / pharmacology*
  • Phosphatidylinositol 4,5-Diphosphate / metabolism
  • Phosphatidylinositol Diacylglycerol-Lyase / metabolism
  • Protein Kinase C / metabolism
  • Radioligand Assay
  • Receptors, G-Protein-Coupled / drug effects
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Receptors, Ghrelin
  • Recombinant Fusion Proteins
  • Transfection


  • Ghrelin
  • Iodine Radioisotopes
  • Luminescent Proteins
  • Peptide Hormones
  • Phosphatidylinositol 4,5-Diphosphate
  • Receptors, G-Protein-Coupled
  • Receptors, Ghrelin
  • Recombinant Fusion Proteins
  • Green Fluorescent Proteins
  • Inositol 1,4,5-Trisphosphate
  • Protein Kinase C
  • Phosphatidylinositol Diacylglycerol-Lyase
  • Calcium