Misfolded growth hormone causes fragmentation of the Golgi apparatus and disrupts endoplasmic reticulum-to-Golgi traffic.
In some individuals with autosomal dominant isolated growth hormone deficiency, one copy of growth hormone lacks amino acids 32-71 and is severely misfolded. We transfected COS7 cells with either wild-type human growth hormone or Delta 32-71 growth hormone and investigated subcellular localization of growth hormone and other proteins. Delta 32-71 growth hormone was retained in the endoplasmic reticulum, whereas wild-type hormone accumulated in the Golgi apparatus. When cells transfected with wild-type or Delta 32-71 growth hormone were dually stained for growth hormone and the Golgi markers beta-COP, membrin or 58K, wild-type growth hormone was colocalized with the Golgi markers, but beta-COP, membrin and 58K immunoreactivity was highly dispersed or undetectable in cells expressing Delta 32-71 growth hormone. Examination of alpha-tubulin immunostaining showed that the cytoplasmic microtubular arrangement was normal in cells expressing wild-type growth hormone, but microtubule-organizing centers were absent in nearly all cells expressing Delta 32-71 growth hormone. To determine whether Delta 32-71 growth hormone would alter trafficking of a plasma membrane protein, we cotransfected the cells with the thyrotropin-releasing hormone (TRH) receptor and either wild-type or Delta 32-71 growth hormone. Cells expressing Delta 32-71 growth hormone, unlike those expressing wild-type growth hormone, failed to show normal TRH receptor localization or binding. Expression of Delta 32-71 growth hormone also disrupted the trafficking of two secretory proteins, prolactin and secreted alkaline phosphatase. Delta 32-71 growth hormone only weakly elicited the unfolded protein response as indicated by induction of BiP mRNA. Pharmacological induction of the unfolded protein response partially prevented deletion mutant-induced Golgi fragmentation and partially restored normal TRH receptor trafficking. The ability of some misfolded proteins to block endoplasmic reticulum-to-Golgi traffic may explain their toxic effects on host cells and suggests possible strategies for therapeutic interventions.
Graves
T K
TK
Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA. Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510, USA.
Patel
S
S
Dannies
P S
PS
Hinkle
P M
PM
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015415:Biomarkers; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D020756:Coatomer Protein / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006056:Golgi Apparatus / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D006360:Heat-Shock Proteins; D019382:Human Growth Hormone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007202:Indicators and Reagents; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D022101:Microtubule-Organizing Center / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D017510:Protein Folding; D021381:Protein Transport / Q000502:physiology*; D050766:Qb-SNARE Proteins; D018025:Receptors, Thyrotropin-Releasing Hormone / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D015415:Biomarkers; D002352:Carrier Proteins; D002843:Chromatin; D020756:Coatomer Protein; D000091342:Endoplasmic Reticulum Chaperone BiP; C491344:GOSR2 protein, human; D006360:Heat-Shock Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D050766:Qb-SNARE Proteins; D018025:Receptors, Thyrotropin-Releasing Hormone; D014415:Tunicamycin; D019382:Human Growth Hormone; D049452:Green Fluorescent Proteins; D011388:Prolactin; D000469:Alkaline Phosphatase