Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ansamycin antibiotic, geldanamycin, targets the hsp 90 protein chaperone and promotes ubiquitin-dependent proteasomal degradation of its numerous client proteins. Bortezomib is a specific and potent proteasome inhibitor. Both bortezomib and the geldanamycin analogue, 17-N-allylamino-17-demethoxy geldanamycin, are in separate clinical trials as new anticancer drugs. We hypothesized that destabilization of hsp 90 client proteins with geldanamycin, while blocking their degradation with bortezomib, would promote the accumulation of aggregated, ubiquitinated, and potentially cytotoxic proteins. Indeed, geldanamycin plus bortezomib inhibited MCF-7 tumor cell proliferation significantly more than either drug alone. Importantly, while control cells were unaffected, human papillomavirus E6 and E7 transformed fibroblasts were selectively sensitive to geldanamycin plus bortezomib. Geldanamycin alone slightly increased protein ubiquitination, but when geldanamycin was combined with bortezomib, protein ubiquitination was massively increased, beyond the amount stabilized by bortezomib alone. In geldanamycin plus bortezomib-treated cells, ubiquitinated proteins were mostly detergent insoluble, indicating that they were aggregated. Individually, both geldanamycin and bortezomib induced hsp 90, hsp 70, and GRP78 stress proteins, but the drug combination superinduced these chaperones and caused them to become detergent insoluble. Geldanamycin plus bortezomib also induced the formation of abundant, perinuclear vacuoles, which were neither lysosomes nor autophagosomes and did not contain engulfed cytosolic ubiquitin or hsp 70. Fluorescence marker experiments indicated that these vacuoles were endoplasmic reticulum derived and that their formation was prevented by cycloheximide, suggesting a role for protein synthesis in their genesis. These observations support a mechanism whereby the geldanamycin plus bortezomib combination simultaneously disrupts hsp 90 and proteasome function, promotes the accumulation of aggregated, ubiquitinated proteins, and results in enhanced antitumor activity.
Mol Cancer Ther 2004 May
PMID:Simultaneous inhibition of hsp 90 and the proteasome promotes protein ubiquitination, causes endoplasmic reticulum-derived cytosolic vacuolization, and enhances antitumor activity. 1514 Oct 13

Hrd1p in yeast plays an important role in endoplasmic reticulum-associated degradation (ERAD). In the present study, we used an in vivo model of hypoxia-ischemia in mice to study the expression of murine HRD1. Hypoxia-ischemia induced a significant increase in mRNA levels of genes including GRP78, CHOP and MyD116, the expression of which are specifically activated under conditions associated with ER dysfunction. The level of mHRD1 mRNA was significantly increased after ischemia. Interestingly, induction of mHRD1 was elevated at a later time point (12-48 h) in the ischemic cortex, whereas it increased at an earlier time point (3-12 h) in the injured striatum. We also examined the changes of mHRD1 mRNA expression in neuroblastoma Neuro2a and primary glial cells exposed to hypoxia/reoxygenation. The expression of mHRD1 mRNA was remarkably up-regulated in glial cells subjected to 24 h hypoxia, whereas no significant changes were observed in Neuro2a cells under hypoxia/reoxygenation. In addition, the levels of mHRD1 mRNA were markedly elevated in glial cells exposed to treatment with tunicamycin (Tm, an ER stress inducer). These findings suggest that hypoxia-ischemia triggers ER dysfunction and mHRD1 may play a role in ischemia-induced ER dysfunction.
Brain Res Mol Brain Res 2004 Nov 04
PMID:Induction of murine HRD1 in experimental cerebral ischemia. 1551 74

The mechanisms involved in the cytotoxic action of oxysterols in the pathogenesis of atherosclerosis still remain poorly understood. Among the major oxysterols present in oxidized low-density lipoprotein, we show here that 7-ketocholesterol (7-Kchol) induces oxidative stress and/or apoptotic events in human aortic smooth muscle cells (SMCs). This specific effect of 7-Kchol is mediated by a robust upregulation (threefold from the basal level) of Nox-4, a reactive oxygen species (ROS)-generating NAD(P)H oxidase homologue. This effect was highlighted by silencing Nox-4 expression with a specific small interfering RNA, which significantly reduced the 7-Kchol-induced production of ROS and abolished apoptotic events. Furthermore, the 7-Kchol activating pathway included an early triggering of endoplasmic reticulum stress, as assessed by transient intracellular Ca(2+) oscillations, and the induction of the expression of the cell death effector CHOP and of GRP78/Bip chaperone via the activation of IRE-1, all hallmarks of the unfolded protein response (UPR). We also showed that 7-Kchol activated the IRE-1/Jun-NH(2)-terminal kinase (JNK)/AP-1 signaling pathway to promote Nox-4 expression. Silencing of IRE-1 and JNK inhibition downregulated Nox-4 expression and subsequently prevented the UPR-dependent cell death induced by 7-Kchol. These findings demonstrate that Nox-4 plays a key role in 7-Kchol-induced SMC death, which is consistent with the hypothesis that Nox-4/oxysterols are involved in the pathogenesis of atherosclerosis.
Mol Cell Biol 2004 Dec
PMID:NAD(P)H oxidase Nox-4 mediates 7-ketocholesterol-induced endoplasmic reticulum stress and apoptosis in human aortic smooth muscle cells. 1557 75

Hippocalcin is a neuronal calcium binding protein, but its physiological function in brain is unknown. We show here that hippocampal neurons from hippocalcin-deficient mice are more vulnerable to degeneration, particularly using thapsigargin, elevating intracellular calcium. Caspase-12 was activated in neurons lacking hippocalcin, while calpain was unchanged. Neuronal viability was accompanied by endoplasmic reticulum (ER) stress and a change in the relative induction of the ER chaperone, BiP/GRP78. Neuronal apoptosis inhibitor protein (NAIP), known to interact with hippocalcin, was not altered, but hippocampal neurons from gene-deleted mice were more sensitive to excitotoxicity caused by kainic acid. In addition, an age-dependent increase in neurodegeneration occurred in the gene-deleted mice, showing that hippocalcin contributes to neuronal viability during aging.
Mol Cell Neurosci 2005 Jan
PMID:Hippocalcin protects against caspase-12-induced and age-dependent neuronal degeneration. 1560 44

The unfolded protein response is an evolutionarily conserved mechanism whereby cells respond to stress conditions that target the endoplasmic reticulum (ER). The transcriptional activation of the promoter of GRP78/BiP, a prosurvival ER chaperone, has been used extensively as an indicator of the onset of the UPR. YY1, a constitutively expressed multifunctional transcription factor, activates the Grp78 promoter only under ER stress conditions. Previously, in vivo footprinting analysis revealed that the YY1 binding site of the ER stress response element of the Grp78 promoter exhibits ER stress-induced changes in occupancy. Toward understanding the underlying mechanisms of these unique phenomena, we performed chromatin immunoprecipitation analyses, revealing that YY1 only occupies the Grp78 promoter upon ER stress and is mediated in part by the nuclear form of ATF6. We show that YY1 is an essential coactivator of ATF6 and uncover their specific interactive domains. Using small interfering RNA against YY1 and insertional mutation of the gene encoding ATF6alpha, we provide direct evidence that YY1 and ATF6 are required for optimal stress induction of Grp78. We also discovered enhancement of the ER-stressed induction of the Grp78 promoter through the interaction of YY1 with the arginine methyltransferase PRMT1 and evidence of its action through methylation of the arginine 3 residue on histone H4. Furthermore, we detected ER stress-induced binding of the histone acetyltransferase p300 to the Grp78 promoter and histone H4 acetylation. A model for the ER stress-mediated transcription factor binding and chromatin modifications at the Grp78 promoter leading to its activation is proposed.
Mol Cell Biol 2005 Jun
PMID:Endoplasmic reticulum stress induction of the Grp78/BiP promoter: activating mechanisms mediated by YY1 and its interactive chromatin modifiers. 1589 57

Epithelial cells of the thick ascending limb of Henle's loop (TALH cells) play a major role in the urinary concentrating mechanism. They are normally exposed to variable and often very high osmotic stress, which is particularly due to high sodium and chloride reabsorption and very low water permeability of the luminal membrane. It is already established that elevation of the activity of aldose reductase and hence an increase in intracellular sorbitol are indispensable for the osmotic adaptation and stability of the TALH cells. To identify new molecular factors potentially associated with the osmotic stress-resistant phenotype in kidney cells, TALH cells exhibiting low or high levels of resistance to osmotic stress were characterized using proteomic tools. Two-dimensional gel analysis showed a total number of 40 proteins that were differentially expressed in TALH cells under osmotic stress. Twenty-five proteins were overexpressed, whereas 15 proteins showed a down-regulation. Besides the sorbitol pathway enzyme aldose reductase, whose expression was 15 times increased, many other metabolic enzymes like glutathione S-transferase, malate dehydrogenase, lactate dehydrogenase, alpha enolase, glyceraldehyde-3-phosphate dehydrogenase, and triose-phosphate isomerase were up-regulated. Among the cytoskeleton proteins and cytoskeleton-associated proteins vimentin, cytokeratin, tropomyosin 4, and annexins I, II, and V were up-regulated, whereas tubulin and tropomyosins 1, 2, and 3 were down-regulated. The heat shock proteins alpha-crystallin chain B, HSP70, and HSP90 were found to be overexpressed. In contrast to the results in oxidative stress the endoplasmic reticulum stress proteins like glucose-regulated proteins (GRP78, GRP94, and GRP96), calreticulin, and protein-disulfide isomerase were down-regulated under hypertonic stress.
Mol Cell Proteomics 2005 Oct
PMID:Proteomic analysis of cellular response to osmotic stress in thick ascending limb of Henle's loop (TALH) cells. 1597 15

Regulated intramembrane proteolysis of the factors SREBP and ATF6 represents a central control mechanism in sterol homeostasis and stress response within the endoplasmic reticulum. Here, we compare localization of ATF6-related bZip factors CREB4, CREB-H, Luman, and OASIS. These factors contain the defining features of a bZip domain, a predicted transmembrane domain and an adjacent cleavage site for the Golgi protease S1P, with conserved features which indicate that it represents a specific subclass of S1P sites. Each factor localizes to the endoplasmic reticulum (ER), but a population of CREB4 was also observed in the Golgi. Deletion of the transmembrane domain in CREB4 resulted in efficient nuclear accumulation. An N-terminal variant of CREB4 containing the BZIp domain potently activated expression from a target gene containing ATF6 binding sites and from the promoter for the ER chaperone GRP78/BIP. CREB4 was cleaved in a site-specific manner in response to brefeldin A disruption of the Golgi or by coexpression with S1P but only after deletion or substitution of its C-terminal lumenal domain. Thus, S1P cleavage of CREB4 may be suppressed by a determinant in the C-terminal region. Dithiothreitol induced more complete transport of CREB4 to the Golgi, but not cleavage. Together, the data identify at least one additional bZip factor whose localization responds to ER stress, and we propose a model based on these results that indicates additional levels of control of this novel class of transcription factors.
Mol Biol Cell 2006 Jan
PMID:CREB4, a transmembrane bZip transcription factor and potential new substrate for regulation and cleavage by S1P. 1623 96

We present the first identification of transient folding intermediates of endogenous thyroglobulin (Tg; a large homodimeric secretory glycoprotein of thyrocytes), which include mixed disulfides with endogenous oxidoreductases servicing Tg folding needs. Formation of disulfide-linked Tg adducts with endoplasmic reticulum (ER) oxidoreductases begins cotranslationally. Inhibition of ER glucosidase activity blocked formation of a subgroup of Tg adducts containing ERp57 while causing increased Tg adduct formation with protein disulfide isomerase (PDI), delayed adduct resolution, perturbed oxidative folding of Tg monomers, impaired Tg dimerization, increased Tg association with BiP/GRP78 and GRP94, activation of the unfolded protein response, increased ER-associated degradation of a subpopulation of Tg, partial Tg escape from ER quality control with increased secretion of free monomers, and decreased overall Tg secretion. These data point towards mixed disulfides with the ERp57 oxidoreductase in conjunction with calreticulin/calnexin chaperones acting as normal early Tg folding intermediates that can be "substituted" by PDI adducts only at the expense of lower folding efficiency with resultant ER stress.
Mol Cell Biol 2005 Nov
PMID:Mixed-disulfide folding intermediates between thyroglobulin and endoplasmic reticulum resident oxidoreductases ERp57 and protein disulfide isomerase. 1626 May 97

The UDP-glucose:glycoprotein glucosyltransferase (UGT) is a central player of glycoprotein quality control in the endoplasmic reticulum (ER). UGT reglucosylation of nonnative glycopolypeptides prevents their release from the calnexin cycle and secretion. Here, we compared the fate of a glycoprotein with a reversible, temperature-dependent folding defect in cells with and without UGT1. Upon persistent misfolding, tsO45 G was slowly released from calnexin and entered a second level of retention-based ER quality control by forming BiP/GRP78-associated disulfide-bonded aggregates. This correlated with loss in the ability to correct misfolding. Deletion of UGT1 did not affect the stringency of ER quality control. Rather, it accelerated release from calnexin and transfer to the second ER quality control level, but it did so after an unexpectedly long lag, showing that cycling in the calnexin chaperone system is not frenetic, as claimed by existing models, and is fully activated only upon persistent glycoprotein misfolding.
Mol Cell 2005 Nov 23
PMID:Persistent glycoprotein misfolding activates the glucosidase II/UGT1-driven calnexin cycle to delay aggregation and loss of folding competence. 1630 15

Monocrotaline (MCT) causes pulmonary hypertension in the rat by a mechanism characterized by megalocytosis (enlarged cells with enlarged endoplasmic reticulum and Golgi and a cell cycle arrest) of pulmonary arterial endothelial (PAEC), arterial smooth muscle, and type II alveolar epithelial cells. In cell culture, although megalocytosis is associated with a block in entry into mitosis in both lung endothelial and epithelial cells, DNA synthesis is stimulated in endothelial but inhibited in epithelial cells. The molecular mechanism(s) for this dichotomy are unclear. While MCTP-treated PAEC and lung epithelial (A549) cells both showed an increase in the "promitogenic" transcription factor STAT3 levels and in the IL-6-induced nuclear pool of PY-STAT3, this was transcriptionally inactive in A549 but not in PAEC cells. This lack of transcriptional activity of STAT3 in A549 cells correlated with the cytoplasmic sequestration of the STAT3 coactivators CBP/p300 and SRC1/NcoA in A549 cells but not in PAEC. Both cell types displayed a Golgi trafficking block, loss of caveolin-1 rafts, and increased nuclear Ire1alpha, but an incomplete unfolded protein response (UPR) with little change in levels of UPR-induced chaperones including GRP78/BiP. There were discordant alterations in cell cycle regulatory proteins in the two cell types such as increase in levels of both cyclin D1 and p21 simultaneously, but with a decrease in cdc2/cdk1, a kinase required for entry into mitosis. While both cell types showed increased cytoplasmic geminin, the DNA synthesis-initiating protein Cdt1 was predominantly nuclear in PAEC but remained cytoplasmic in A549 cells, consistent with the stimulation of DNA synthesis in the former but an inhibition in the latter cell type. Thus differences in cell type-specific alterations in subcellular trafficking of critical regulatory molecules (such as CBP/p300, SRC1/NcoA, Cdt1) likely account for the dichotomy of the effects of MCTP on DNA synthesis in endothelial and epithelial cells.
Am J Physiol Lung Cell Mol Physiol 2006 Jun
PMID:Discordant regulatory changes in monocrotaline-induced megalocytosis of lung arterial endothelial and alveolar epithelial cells. 1641 77


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>