Proparathyroid hormone-related protein is associated with the chaperone protein BiP and undergoes proteasome-mediated degradation.
Parathyroid hormone-related peptide (PTHrP) is an important causal factor for hypercalcemia associated with malignancy. In addition to the endocrine functions attributed to secretory forms of the peptide, PTHrP also plays a local role as a mediator of cellular growth and differentiation presumably at least in part through intracellular pathways. In studying the post-translational regulation of PTHrP, we observed that PTHrP was conjugated to multiple ubiquitin moieties. We report here that the proteasome is responsible for the degradation of the endoplasmic reticulum-associated precursor, pro-PTHrP. Cells expressing prepro-PTHrP and exposed to lactacystin accumulate pro-PTHrP assessed by anti-pro specific antibodies. Brefeldin A-treated cells also accumulate pro-PTHrP suggesting that degradation does not occur in the endoplasmic reticulum (ER) lumen. Subcellular fractionation of both lactacystin and brefeldin A-treated cells indicated that accumulated pro-PTHrP resides in microsomal fractions with a portion of the protein exposed to the cytosolic side of the ER membrane as assessed by protease protection experiments. Immunoprecipitation and Western blot analysis identified pro-PTHrP in association with the ER molecular chaperone protein BiP. We conclude that pro-PTHrP from the ER can gain access to the cytoplasmic side of the ER membrane where it can undergo ubiquitination and degradation by the proteasome.
Meerovitch
K
K
Calcium Research Laboratory, Department of Medicine, McGill University, Montreal, Quebec H3A 1A1, Canada.
Wing
S
S
Goltzman
D
D
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D020126:Brefeldin A; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003517:Cyclopentanes / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D006868:Hydrolysis; D018942:Macrolides; D018832:Molecular Chaperones / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D003517:Cyclopentanes; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018942:Macrolides; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D044162:Parathyroid Hormone-Related Protein; D011498:Protein Precursors; D011506:Proteins; C067713:lactacystin; D020126:Brefeldin A; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine