title: A method to increase the number of growth hormone receptors at the surface of cells.
abstract: The number of growth hormone receptors (GHRs) per cell are regulated and this feature plays a major role in the hormone responsiveness of the body. We previously observed in transfected Chinese hamster lung cells that GHR availability is determined by three factors: endocytosis (75%), shedding (10%), and other undetermined mechanisms (15%). The endocytosis depends on an active ubiquitin conjugation system. In addition, this process is ligand-independent. Here, we show that this principle is useful to increase the abundance of GHRs at the cell surface of cells using a combination of inhibitors. In theory, an inhibitor that targets the ubiquitin conjugation specific for the GHR, would suffice, as almost 80% of the removal rate depends on this mechanism. As the molecular mechanism is unknown yet, we used a general inhibitor of proteasome action. Unfortunately, such an inhibitor stimulates the shedding process severalfold. Our data show that the combination of a general proteasome inhibitor and a matrix metalloprotease inhibitor results in an almost twofold increase in functional GHRs at the cell surface, and generate new perspectives to increase the sensitivity of cells for growth hormone.
authors.affiliation: Department of Cell Biology and Institute of Biomembranes, University Medical Centre Utrecht, Heidelberglaan 100, AZU-G02.525, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: van Kerkhof
authors.forename: Erica
authors.initials: E
authors.lastname: Vallon
authors.forename: Ger J
authors.initials: GJ
authors.lastname: Strous
mesh_terms: D016475:3T3 Cells / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D013006:Growth Hormone / Q000378:metabolism; D006801:Humans; D008024:Ligands; D061965:Matrix Metalloproteinase Inhibitors; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D015853:Cysteine Proteinase Inhibitors; D008024:Ligands; D061965:Matrix Metalloproteinase Inhibitors; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D011986:Receptors, Somatotropin; D025801:Ubiquitin; D013006:Growth Hormone; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex