Abstract
ATF6, a member of the leucine zipper protein family, can constitutively induce the promoter of glucose-regulated protein (grp) genes through activation of the endoplasmic reticulum (ER) stress element (ERSE). To understand the mechanism of grp78 induction by ATF6 in cells subjected to ER calcium depletion stress mediated by thapsigargin (Tg) treatment, we discovered that ATF6 itself undergoes Tg stress-induced changes. In nonstressed cells, ATF6, which contains a putative short transmembrane domain, is primarily associated with the perinuclear region. Upon Tg stress, the ATF6 protein level dropped initially but quickly recovered with the additional appearance of a faster-migrating form. This new form of ATF6 was recovered as soluble nuclear protein by biochemical fractionation, correlating with enhanced nuclear localization of ATF6 as revealed by immunofluorescence. Optimal ATF6 stimulation requires at least two copies of the ERSE and the integrity of the tripartite structure of the ERSE. Of primary importance is a functional NF-Y complex and a high-affinity NF-Y binding site that confers selectivity among different ERSEs for ATF6 inducibility. In addition, we showed that YY1 interacts with ATF6 and in Tg-treated cells can enhance ATF6 activity. The ERSE stimulatory activity of ATF6 exhibits properties distinct from those of human Ire1p, an upstream regulator of the mammalian unfolded protein response. The requirement for a high-affinity NF-Y site for ATF6 but not human Ire1p activity suggests that they stimulate the ERSE through diverse pathways.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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3T3 Cells / drug effects
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3T3 Cells / metabolism
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Activating Transcription Factor 6
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Animals
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Basic-Leucine Zipper Transcription Factors
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CCAAT-Enhancer-Binding Proteins
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COS Cells / drug effects
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COS Cells / metabolism
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Carrier Proteins / genetics
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Carrier Proteins / metabolism
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DNA-Binding Proteins / drug effects
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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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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Endoribonucleases
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Enzyme Inhibitors / pharmacology
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Erythroid-Specific DNA-Binding Factors
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Heat-Shock Proteins*
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Humans
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Membrane Glycoproteins / metabolism
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Membrane Proteins*
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Mice
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism
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Promoter Regions, Genetic
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Protein Serine-Threonine Kinases / metabolism
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Repressor Proteins / metabolism
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Response Elements
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Saccharomyces cerevisiae Proteins*
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Stress, Physiological
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Thapsigargin / pharmacology*
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Transcription Factors / drug effects
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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YY1 Transcription Factor
Substances
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ATF6 protein, human
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Activating Transcription Factor 6
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Atf6 protein, mouse
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Basic-Leucine Zipper Transcription Factors
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CCAAT-Enhancer-Binding Proteins
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Carrier Proteins
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DNA-Binding Proteins
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Endoplasmic Reticulum Chaperone BiP
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Enzyme Inhibitors
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Erythroid-Specific DNA-Binding Factors
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HAC1 protein, S cerevisiae
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HSPA5 protein, human
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Heat-Shock Proteins
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Hspa5 protein, mouse
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Membrane Glycoproteins
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Membrane Proteins
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Molecular Chaperones
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Repressor Proteins
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Saccharomyces cerevisiae Proteins
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Transcription Factors
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YY1 Transcription Factor
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YY1 protein, human
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Yy1 protein, mouse
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Thapsigargin
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ERN2 protein, human
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Ern2 protein, mouse
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Protein Serine-Threonine Kinases
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Endoribonucleases