Induction of the Unfolded Protein Response Drives Enhanced Metabolism and Chemoresistance in Glioma Cells

Abstract

The unfolded protein response (UPR) is an endoplasmic reticulum (ER)-based cytoprotective mechanism acting to prevent pathologies accompanying protein aggregation. It is frequently active in tumors, but relatively unstudied in gliomas. We hypothesized that UPR stress effects on glioma cells might protect tumors from additional exogenous stress (ie, chemotherapeutics), postulating that protection was concurrent with altered tumor cell metabolism. Using human brain tumor cell lines, xenograft tumors, human samples and gene expression databases, we determined molecular features of glioma cell UPR induction/activation, and here report a detailed analysis of UPR transcriptional/translational/metabolic responses. Immunohistochemistry, Western and Northern blots identified elevated levels of UPR transcription factors and downstream ER chaperone targets in gliomas. Microarray profiling revealed distinct regulation of stress responses between xenograft tumors and parent cell lines, with gene ontology and network analyses linking gene expression to cell survival and metabolic processes. Human glioma samples were examined for levels of the ER chaperone GRP94 by immunohistochemistry and for other UPR components by Western blotting. Gene and protein expression data from patient gliomas correlated poor patient prognoses with increased expression of ER chaperones, UPR target genes, and metabolic enzymes (glycolysis and lipogenesis). NMR-based metabolomic studies revealed increased metabolic outputs in glucose uptake with elevated glycolytic activity as well as increased phospholipid turnover. Elevated levels of amino acids, antioxidants, and cholesterol were also evident upon UPR stress; in particular, recurrent tumors had overall higher lipid outputs and elevated specific UPR arms. Clonogenicity studies following temozolomide treatment of stressed or unstressed cells demonstrated UPR-induced chemoresistance. Our data characterize the UPR in glioma cells and human tumors, and link the UPR to chemoresistance possibly via enhanced metabolism. Given the role of the UPR in the balance between cell survival and apoptosis, targeting the UPR and/or controlling metabolic activity may prove beneficial for malignant glioma therapeutics.

The Unfolded Protein Response in Glioblastomas: Targetable Or Trouble?

“…Tumors will invoke the UPR to counteract the detrimental environmental effects (often of the tumor's own making) [10]. Ultimately, the benefits of the stress response outweigh the risks (e.g., apoptosis) [11] and the tumor's engagement of the UPR becomes ‘fixed’ [12]. This is logical in a cellular situation where there is need for dynamic cell surface and extracellular/microenvironmental remodeling [13,14] to promote angiogenesis or tumor cell migration/invasion/metastasis.…”

“…Shown is an immunohistochemical stain for CHOP on 5 μm paraffin sections of a D245MG GBM xenograft tumor (IHC details are in Epple et al . [12]). Counterstain is hematoxylin/eosin (resulting in blue nuclear staining, while brown staining is for the CHOP protein).…”

Endoplasmic Reticulum Stress–Activated Cell Reprogramming in Oncogenesis

“…Bidirectional regulation between the UPR and DNA-damage responses has been shown in various experimental systems (112)(113)(114)(115)(116), suggesting a dynamic feed-forward homeostatic regulation that controls the stability of the proteome and genome. Studies in yeast uncovered a relevant function of IRE1p in maintaining the stability of the genome ( 117,118 ).…”

Anti-Leukemic Activity of Shikonin: Role of ERP57 in Shikonin Induced Apoptosis in Acute Myeloid Leukemia

“…AML is still an incurable disease and innovative treatment strategies are urgently needed [3]. Unfolded protein response (UPR) is one of the factors playing an important role in chemoresistance in cancer cells [4,5]. UPR is an evolutionary conserved mechanism and is activated to compensate the adverse effects of protein accumulation in the endoplasmic reticulum (ER), following the induction of ER stress [6].…”

“…However, severe and prolonged ER stress may leads to apoptosis rather than being cytoprotective [14]. The collective activities of PERK, IRE1 and ATF6 leads to increased expression of effector stress response (XBP-1,ATF4and ATF6) and proapoptotic transcription factor (CHOP) additionally enhancing the expression of ER resident chaperones, such as GRP78 and GRP94 [4,15].…”