title: Endocytosis and degradation of the growth hormone receptor are proteasome-dependent.
abstract: The ubiquitin conjugation system is involved in ligand-induced endocytosis of the growth hormone receptor (GHR) via a cytosolic 10-amino acid ubiquitin-dependent endocytosis motif. Herein, we demonstrate that the proteasome is also involved in growth hormone receptor down-regulation. Ligand-induced degradation was blocked in the presence of specific proteasomal inhibitors. In addition, growth hormone (GH) internalization was inhibited, whereas the transferrin receptor cycle remained unaffected. A truncated GHR entered the cells independent of proteasome action. In addition, we show that GH internalization is independent of the presence of lysine residues in the cytosolic domain of the receptor, whereas its internalization can still be inhibited by proteasomal inhibitors. Thus, GHR internalization requires proteasome action in addition to an active ubiquitin conjugation system, but ubiquitination of the GHR itself seems not to be required.
authors.affiliation: Department of Cell Biology, University Medical Center Utrecht and Institute of Biomembranes, Heidelberglaan 100, AZU-G02.525, 3584CX Utrecht, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: van Kerkhof
authors.forename: R
authors.initials: R
authors.lastname: Govers
authors.forename: C M
authors.initials: CM
authors.lastname: Alves dos Santos
authors.forename: G J
authors.initials: GJ
authors.lastname: Strous
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D013006:Growth Hormone / Q000493:pharmacokinetics; D008024:Ligands; D008239:Lysine / Q000378:metabolism; D016296:Mutagenesis; D010447:Peptide Hydrolases / Q000378:metabolism*; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014168:Transferrin / Q000378:metabolism
chemical_list: D015853:Cysteine Proteinase Inhibitors; D008024:Ligands; D011986:Receptors, Somatotropin; D014168:Transferrin; C067713:lactacystin; D013006:Growth Hormone; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D008239:Lysine; D000111:Acetylcysteine