Complementary cell-based high-throughput screens identify novel modulators of the unfolded protein response.

Carmen and Ann Adams Department of Pediatrics, Division of Hematology/Oncology, Wayne State University, 421 E. Canfield, Detroit, MI 48201, USA.
Journal of Biomolecular Screening (Impact Factor: 2.01). 08/2011; 16(8):825-35. DOI: 10.1177/1087057111414893
Source: PubMed

ABSTRACT Despite advances toward understanding the prevention and treatment of many cancers, patients who suffer from oral squamous cell carcinoma (OSCC) confront a survival rate that has remained unimproved for more than 2 decades, indicating our ability to treat them pharmacologically has reached a plateau. In an ongoing effort to improve the clinical outlook for this disease, we previously reported that an essential component of the mechanism by which the proteasome inhibitor bortezomib (PS-341, Velcade) induced apoptosis in OSCC required the activation of a terminal unfolded protein response (UPR). Predicated on these studies, the authors hypothesized that high-throughput screening (HTS) of large diverse chemical libraries might identify more potent or selective small-molecule activators of the apoptotic arm of the UPR to control or kill OSCC. They have developed complementary cell-based assays using stably transfected CHO-K1 cell lines that individually assess the PERK/eIF2α/CHOP (apoptotic) or the IRE1/XBP1 (adaptive) UPR subpathways. An 66 K compound collection was screened at the University of Michigan Center for Chemical Genomics that included a unique library of prefractionated natural product extracts. The mycotoxin methoxycitrinin was isolated from a natural extract and found to selectively activate the CHOP-luciferase reporter at 80 µM. A series of citrinin derivatives was isolated from these extracts, including a unique congener that has not been previously described. In an effort to identify more potent compounds, the authors examined the ability of citrinin and the structurally related mycotoxins ochratoxin A and patulin to activate the UPR. Strikingly, it was found that patulin at 2.5 to 10 µM induced a terminal UPR in a panel of OSCC cells that was characterized by an increase in CHOP, GADD34, and ATF3 gene expression and XBP1 splicing. A luminescent caspase assay and the induction of several BH3-only genes indicated that patulin could induce apoptosis in OSCC cells. These data support the use of this complementary HTS strategy to identify novel modulators of UPR signaling and tumor cell death.

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Available from: Giselle Tamayo, Jul 18, 2015
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    • "ER stress-induced apoptosis is an important pathogenic factor in a number of widespread diseases, including diabetes, neurodegenerative diseases, atherosclerosis, and renal disease (Tabas and Ron 2011). Because of the UPR's central role in determining cell fate, there have been multiple studies to identify small molecules modulators to exploit the UPR for therapeutic benefit (Fribley et al. 2011; Papandreou et al. 2011; Volkmann et al. 2011; Cross et al. 2012; Mimura et al. 2012). "
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    ABSTRACT: Secretory and transmembrane proteins enter the endoplasmic reticulum (ER) as unfolded proteins and exit as either folded proteins in transit to their target organelles or as misfolded proteins targeted for degradation. The unfolded protein response (UPR) maintains the protein-folding homeostasis within the ER, ensuring that the protein-folding capacity of the ER meets the load of client proteins. Activation of the UPR depends on three ER stress sensor proteins, Ire1, PERK, and ATF6. Although the consequences of activation are well understood, how these sensors detect ER stress remains unclear. Recent evidence suggests that yeast Ire1 directly binds to unfolded proteins, which induces its oligomerization and activation. BiP dissociation from Ire1 regulates this oligomeric equilibrium, ultimately modulating Ire1's sensitivity and duration of activation. The mechanistic principles of ER stress sensing are the focus of this review.
    Cold Spring Harbor perspectives in biology 02/2013; 5(3). DOI:10.1101/cshperspect.a013169 · 8.23 Impact Factor
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    ABSTRACT: The unfolded protein response, also known as endoplasmic reticulum (ER) stress, has been implicated in numerous human diseases, including atherosclerosis, cancer, diabetes, and neurodegenerative disorders. Protein misfolding activates one or more of the three ER transmembrane sensors to initiate a complex network of signaling that transiently suppresses protein translation while also enhancing protein folding and proteasomal degradation of misfolded proteins to ensure full recovery from ER stress. Gene disruption studies in mice have provided critical insights into the role of specific signaling components and pathways in the differing responses of animal tissues to ER stress. These studies have emphasized an important contribution of translational repression to sustained insulin synthesis and β-cell viability in experimental models of type-2 diabetes. This has focused attention on the recently discovered small-molecule inhibitors of eIF2α phosphatases that prolong eIF2α phosphorylation to reduce cell death in several animal models of human disease. These compounds show significant cytoprotection in cellular and animal models of neurodegenerative disorders, highlighting a potential strategy for future development of drugs to treat human protein misfolding disorders.
    Progress in molecular biology and translational science 01/2012; 106:75-106. DOI:10.1016/B978-0-12-396456-4.00005-5 · 3.11 Impact Factor
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    ABSTRACT: Abstract The endoplasmic reticulum (ER) orchestrates the production of membrane-bound and secreted proteins. However, its capacity to process the synthesis and folding of protein is limited. Protein overload and the accumulation of misfolded proteins in the ER trigger an adaptive response known as the ER-stress response that is mediated by specific ER-anchored signaling pathways. This response regulates cell functions aimed at restoring cellular homeostasis or at promoting apoptosis of irreparably damaged cells. Activation or deregulation of ER-signaling pathways has been associated with various diseases including cancer. Here we discuss how tumors engage ER-signaling pathways to promote tumorigenesis and how manipulation of this process by anticancer drugs may contribute to cancer treatment.
    Acta oncologica (Stockholm, Sweden) 06/2012; 51(7):822-30. DOI:10.3109/0284186X.2012.689113 · 3.71 Impact Factor
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