Characterization of Stanniocalcin 2, a Novel Target of the Mammalian Unfolded Protein Response with Cytoprotective Properties

ABSTRACT Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces a highly conserved homeostatic response in all eukaryotic cells, termed the unfolded-protein response (UPR). Here we describe the characterization of stanniocalcin 2 (STC2), a mammalian homologue of a calcium- and phosphate-regulating hormone first identified in fish, as a novel target of the UPR. Expression of STC2 gene is rapidly upregulated in cultured cells after exposure to tunicamycin and thapsigargin, by ATF4 after activation of the ER-resident kinase PERK. In addition, STC2 expression is also activated in neuronal cells by oxidative stress and hypoxia but not by several cellular stresses unrelated to the UPR. In contrast, expression of another homologue, STC1, is only upregulated by hypoxia independent of PERK or ATF4 expression. In vivo studies revealed that rat cortical neurons rapidly upregulate STC2 after transient middle cerebral artery occlusion. Finally, siRNA-mediated inhibition of STC2 expression renders N2a neuroblastoma cells and HeLa cells significantly more vulnerable to apoptotic cell death after treatment with thapsigargin, and overexpression of STC2 attenuated thapsigargin-induced cell death. Consequently, induced STC2 expression is an essential feature of survival component of the UPR.

Download Full-text

P3-195 Characterization of stanniocalcin 2, a novel target of the mammalian unfolded protein response with cytoprotective properties

Neurobiology of Aging ◽

10.1016/s0197-4580(04)81347-2 ◽

2004 ◽

Vol 25 ◽

pp. S411

Author(s):

Daisuke Ito ◽

John R. Walker ◽

Charlie S. Thompson ◽

Isabella Moroz ◽

Margaret L. Veselits ◽

...

Keyword(s):

Unfolded Protein Response ◽

Unfolded Protein ◽

Stanniocalcin 2 ◽

Novel Target ◽

Protein Response

Download Full-text

Simvastatin Induces Unfolded Protein Response and Enhances Temozolomide-Induced Cell Death in Glioblastoma Cells

Cells ◽

10.3390/cells9112339 ◽

2020 ◽

Vol 9 (11) ◽

pp. 2339

Author(s):

Sanaz Dastghaib ◽

Shahla Shojaei ◽

Zohreh Mostafavi-Pour ◽

Pawan Sharma ◽

John B. Patterson ◽

...

Keyword(s):

Cell Death ◽

Unfolded Protein Response ◽

Apoptotic Cell ◽

Primary Brain Tumor ◽

Initiation Factor ◽

Autophagic Flux ◽

Unfolded Protein ◽

Eif2α Phosphorylation ◽

Protein Response ◽

U87 Cells

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor with a very poor survival rate. Temozolomide (TMZ) is the common chemotherapeutic agent used for GBM treatment. We recently demonstrated that simvastatin (Simva) increases TMZ-induced apoptosis via the inhibition of autophagic flux in GBM cells. Considering the role of the unfolded protein response (UPR) pathway in the regulation of autophagy, we investigated the involvement of UPR in Simva–TMZ-induced cell death by utilizing highly selective IRE1 RNase activity inhibitor MKC8866, PERK inhibitor GSK-2606414 (PERKi), and eIF2α inhibitor salubrinal. Simva–TMZ treatment decreased the viability of GBM cells and significantly increased apoptotic cell death when compared to TMZ or Simva alone. Simva–TMZ induced both UPR, as determined by an increase in GRP78, XBP splicing, eukaryote initiation factor 2α (eIF2α) phosphorylation, and inhibited autophagic flux (accumulation of LC3β-II and inhibition of p62 degradation). IRE1 RNase inhibition did not affect Simva–TMZ-induced cell death, but it significantly induced p62 degradation and increased the microtubule-associated proteins light chain 3 (LC3)β-II/LC3β-I ratio in U87 cells, while salubrinal did not affect the Simva–TMZ induced cytotoxicity of GBM cells. In contrast, protein kinase RNA-like endoplasmic reticulum kinase (PERK) inhibition significantly increased Simva–TMZ-induced cell death in U87 cells. Interestingly, whereas PERK inhibition induced p62 accumulation in both GBM cell lines, it differentially affected the LC3β-II/LC3β-I ratio in U87 (decrease) and U251 (increase) cells. Simvastatin sensitizes GBM cells to TMZ-induced cell death via a mechanism that involves autophagy and UPR pathways. More specifically, our results imply that the IRE1 and PERK signaling arms of the UPR regulate Simva–TMZ-mediated autophagy flux inhibition in U251 and U87 GBM cells.

Download Full-text

The unfolded protein response and its potential role in Huntington ́s disease elucidated by a systems biology approach

F1000Research ◽

10.12688/f1000research.6358.1 ◽

2015 ◽

Vol 4 ◽

pp. 103 ◽

Cited By ~ 16

Author(s):

Ravi Kiran Reddy Kalathur ◽

Joaquin Giner-Lamia ◽

Susana Machado ◽

Kameshwar R S Ayasolla ◽

Matthias E. Futschik

Keyword(s):

Cell Death ◽

Unfolded Protein Response ◽

Potential Role ◽

Apoptotic Cell ◽

Fatal Outcome ◽

Neuronal Cell ◽

Misfolded Proteins ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

Huntington ́s disease (HD) is a progressive, neurodegenerative disease with a fatal outcome. Although the disease-causing gene (huntingtin) has been known for over 20 years, the exact mechanisms leading to neuronal cell death are still controversial. One potential mechanism contributing to the massive loss of neurons observed in the brain of HD patients could be the unfolded protein response (UPR) activated by accumulation of misfolded proteins in the endoplasmic reticulum (ER). As an adaptive response to counter-balance accumulation of un- or misfolded proteins, the UPR upregulates transcription of chaperones, temporarily attenuates new translation, and activates protein degradation via the proteasome. However, persistent ER stress and an activated UPR can also cause apoptotic cell death. Although different studies have indicated a role for the UPR in HD, the evidence remains inconclusive. Here, we present extensive bioinformatic analyses that revealed UPR activation in different experimental HD models based on transcriptomic data. Accordingly, we have identified 58 genes, including RAB5A, HMGB1, CTNNB1, DNM1, TUBB, TSG101, EEF2, DYNC1H1 and SLC12A5 that provide a potential link between UPR and HD. To further elucidate the potential role of UPR as a disease-relevant process, we examined its connection to apoptosis based on molecular interaction data, and identified a set of 40 genes including ADD1, HSP90B1, IKBKB, IKBKG, RPS3A and LMNB1, which seem to be at the crossroads between these two important cellular processes.

Download Full-text

Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death

Biochemical Journal ◽

10.1042/bj20111004 ◽

2011 ◽

Vol 441 (2) ◽

pp. 685-696 ◽

Cited By ~ 14

Author(s):

Deborah L. Duricka ◽

R. Lane Brown ◽

Michael D. Varnum

Keyword(s):

Cell Death ◽

Er Stress ◽

Unfolded Protein Response ◽

Apoptotic Cell ◽

Cone Photoreceptor ◽

Loss Of Function ◽

Cellular Mechanisms ◽

Unfolded Protein ◽

Degradation Rates ◽

Protein Response

Mutations that perturb the function of photoreceptor CNG (cyclic nucleotide-gated) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the ER (endoplasmic reticulum) is known to cause ER stress and trigger the UPR (unfolded protein response), an evolutionarily conserved cellular programme that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared with wild-type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones {TUDCA (tauroursodeoxycholate sodium salt), 4-PBA (sodium 4-phenylbutyrate) and the cGMP analogue CPT-cGMP [8-(4-chlorophenylthio)-cGMP]} differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER-stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization-defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.

Download Full-text