Abstract
Hyperhomocysteinemia, a risk factor for vascular disease, injures endothelial cells through undefined mechanisms. We previously identified several homocysteine-responsive genes in cultured human vascular endothelial cells, including the endoplasmic reticulum (ER)-resident molecular chaperone GRP78/BiP. Here, we demonstrate that homocysteine induces the ER stress response and leads to the expression of a novel protein, Herp, containing a ubiquitin-like domain at the N terminus. mRNA expression of Herp was strongly up-regulated by inducers of ER stress, including mercaptoethanol, tunicamycin, A23187, and thapsigargin. The ER stress-dependent induction of Herp was also observed at the protein level. Immunochemical analyses using Herp-specific antibodies indicated that Herp is a 54-kDa, membrane-associated ER protein. Herp is the first integral membrane protein regulated by the ER stress response pathway. Both the N and C termini face the cytoplasmic side of the ER; this membrane topology makes it unlikely that Herp acts as a molecular chaperone for proteins in the ER, in contrast to GRP78 and other ER stress-responsive proteins. Herp may, therefore, play an unknown role in the cellular survival response to stress.
MeSH terms
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Amino Acid Sequence
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Animals
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Base Sequence
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Calcimycin / pharmacology
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Cells, Cultured
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Cloning, Molecular
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Endoplasmic Reticulum / drug effects
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Endoplasmic Reticulum / physiology*
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Endoplasmic Reticulum Chaperone BiP
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Endothelium, Vascular / drug effects
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Endothelium, Vascular / physiology*
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Gene Expression Regulation / drug effects
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Gene Expression Regulation / physiology*
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Humans
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Intracellular Membranes / physiology
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Intracellular Membranes / ultrastructure
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Membrane Proteins / biosynthesis
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Membrane Proteins / chemistry
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Membrane Proteins / genetics*
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Mercaptoethanol / pharmacology
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Mice
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Molecular Sequence Data
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Protein Biosynthesis
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Protein Conformation
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RNA, Messenger / genetics
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Recombinant Proteins / biosynthesis
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Recombinant Proteins / chemistry
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Sequence Alignment
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Sequence Homology, Amino Acid
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Thapsigargin / pharmacology
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Transcription, Genetic* / drug effects
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Tunicamycin / pharmacology
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Ubiquitins / chemistry*
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Umbilical Veins
Substances
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Endoplasmic Reticulum Chaperone BiP
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HERPUD1 protein, human
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HSPA5 protein, human
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Herpud1 protein, mouse
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Hspa5 protein, mouse
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Membrane Proteins
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RNA, Messenger
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Recombinant Proteins
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Ubiquitins
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Tunicamycin
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Calcimycin
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Mercaptoethanol
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Thapsigargin
Associated data
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GENBANK/AB034989
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GENBANK/AB034991