The ubiquitin conjugation system is required for ligand-induced endocytosis and degradation of the growth hormone receptor.
The ubiquitin-dependent protein degradation system has recently been implicated in downregulation of signal transducing receptors. Growth hormone receptor (GHR) cDNA was transfected into Chinese hamster ovary cells, which exhibit a temperature-sensitive defect in ubiquitin conjugation (CHO-ts20), as well as into wild-type cells (CHO-E36). Upon binding of growth hormone (GH), two GHR polypeptides dimerize and initiate signal transduction. In CHO-E36 and in CHO-ts20 at the permissive temperature the GHR was ubiquitinated and degraded in a GH-dependent fashion. However, at the non-permissive temperature in CHO-ts20 cells, neither GH-dependent uptake nor degradation of the GHR was observed, while in CHO-E36 cells both GHR uptake and degradation were accelerated. Incubation of CHO-E36 cells with inhibitors of endosomal/lysosomal function (NH4Cl, bafilomycin A1) markedly reduced ligand-induced GHR degradation. Our results indicate that a functional ubiquitin conjugating system is required for GH-induced endocytosis and that degradation of both the exoplasmic and cytoplasmic portions of the GHR occurs within the endosomal/lysosomal compartment.
Strous
G J
GJ
Department of Cell Biology, Faculty of Medicine and Institute of Biomembranes, Utrecht University, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
van Kerkhof
P
P
Govers
R
R
Ciechanover
A
A
Schwartz
A L
AL
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D020126:Brefeldin A; D006224:Cricetinae; D003412:Cricetulus; D003517:Cyclopentanes / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis / Q000187:drug effects; D018942:Macrolides; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014452:Ubiquitins / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D003517:Cyclopentanes; D018076:DNA, Complementary; D018942:Macrolides; D011500:Protein Synthesis Inhibitors; D011986:Receptors, Somatotropin; D014452:Ubiquitins; D020126:Brefeldin A; C040929:bafilomycin A1