Subtilase cytotoxin activates PERK, IRE1 and ATF6 endoplasmic reticulum stress-signalling pathways

Maganty

Journal of Cell Science

et al. 2012

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SummaryER stress leads to upregulation of multiple folding and quality control components, known as the unfolded protein response (UPR). Glucose Regulated Protein 78 (GRP78) (also known as binding immunoglobulin protein, BiP, and HSPA5) and GRP94 are often upregulated coordinately as part of this homeostatic response. Given that endoplasmic reticulum (ER) chaperones have distinct sets of clients, we asked how cells respond to ablation of individual chaperones. The cellular responses to silencing BiP, GRP94, HSP47, PDIA6 and OS-9, were distinct. When BiP was silenced, a widespread UPR was observed, but when GRP94 was either inhibited or depleted by RNA interference (RNAi), the expression of only some genes was induced, notably those encoding BiP and protein disulfide isomerase A6 (PDIA6). Silencing of HSP47 or OS-9 did not lead to any compensatory induction of other genes. The selective response to GRP94 depletion was distinct from a typical ER stress response, both because other UPR target genes were not affected and because the canonical UPR signaling branches were not activated. The response to silencing of GRP94 did not preclude further UPR induction when chemical stress was imposed. Importantly, re-expression of wild-type GRP94 in the silenced cells prevented the upregulation of BiP and PDIA6, whereas re-expression of an ATPase-deficient GRP94 mutant did not, indicating that cells monitor the activity state of GRP94. These findings suggest that cells are able to distinguish among folding resources and generate distinct responses.

Section: The Response To Grp94 Ablation Is Not Mediated By Upr Signalingmentioning

confidence: 81%

Limitation of individual folding resources in the ER leads to outcomes distinct from the unfolded protein response

Maganty

Journal of Cell Science

et al. 2012

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Biological & Pharmaceutical Bulletin

“…1D). CHOP is a pro-apoptotic transcription factor that is induced mainly by PERK, 21) while EDEM1 and ERdj4 are responsible for the induction of ERAD, expression of which is mediated through the XBP1 pathway. 22,23) Thus, these data suggest that GRP78 siRNA activates both survival and apoptotic pathways in RENCA.…”

Section: Discussionmentioning

confidence: 99%

Inhibition of Cancer Cell Growth by GRP78 siRNA Lipoplex <i>via</i> Activation of Unfolded Protein Response

Matsumura

Sakai

Kawakami

et al. 2014

Proteasome inhibitors are a novel class of molecular-targeted anti-cancer drugs that suppress the degradation of malfolded proteins, trigger endoplasmic reticulum (ER) stress, and activate apoptosis signals. Glucose-regulated protein 78 (GRP78), a major ER chaperone, is one of the most important molecules for transduction of unfolded protein response (UPR) signals. In accordance with past findings that expression of GRP78 is elevated in cancer cells and helps to resist stress-induced apoptosis, GRP78 knockdown could be effective in anticancer therapy. We tested this hypothesis and found that transfection of small interfering RNA (siRNA) targeting GRP78 inhibited the growth of RENCA renal carcinoma cells, in association with elevated gene expression of UPR downstream signaling molecules (CHOP, EDEM1, and ERdj4 mRNA). In addition, the combinatorial effect of GRP78 siRNA with ER stress inducers (tunicamycin, MG132, and 2-deoxyglucose) on survival was measured. Combination of GRP78 siRNA and the ER stress inducers more extensively reduced cell viability than combination with scrambled siRNA. Besides RENCA, B16BL6 melanoma cells were also shown to be sensitive to GRP78 siRNA. These results suggest that GRP78 knockdown might be an effective strategy for cancer therapy targeting UPR-induced apoptosis.Key words glucose-regulated protein 78; small interfering RNA; apoptosis; unfolded protein response; endoplasmic reticulum stress; cancer cellThe endoplasmic reticulum (ER) is responsible for protein synthesis, conformational maturation, and quality control of correctly folded proteins. In cancer cells, protein synthesis and by-product disposal are elevated, therefore, disruption of ER functions is believed to be a promising approach for cancer therapy. Proteasome inhibitors, which are a novel class of molecular-targeted anti-cancer drugs, suppress the degradation of malfolded proteins and trigger ER stress, which leads to the activation of the unfolded protein response (UPR) and subsequent apoptotic signals.1,2) Bortezomib was the first approved proteasome inhibitor, and is used for the treatment of relapsed multiple myeloma 3) and mantle cell lymphoma. 4) A second generation of proteasome inhibitors are now under development to improve drug efficacy and compliance. 5)Molecular chaperones are key factors involved in unfolded protein accumulation. Glucose-regulated protein 78 (GRP78) is known as a stress-inducible ER chaperone protein and serves as an ER stress signal regulator.6) Under unstressed conditions, GRP78 associates with ER transmembrane sensor proteins, such as protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme-1 (IRE1) and activating transcription factor 6 (ATF6), 7,8) and these interactions maintain them in an inactive form. However, accumulation of unfolded proteins results in the detachment of GRP78 from the sensor proteins and the subsequent activation of the unfolded protein response (UPR), which results in general translational attenuation, up-regulation of chaperones a...

The Journal of Immunology

“…GRP78 is one of the most abundant ER chaperons and its knockdown leads to selective induction of UPR (35). Recently, we identified SubAB as a specific inhibitor of GRP78 by rapid cleavage of this protein between two leucine residues at positions 416 and 417 (12).…”

Section: Involvement Of Upr In the Suppressive Effects Of Csa And Fk5mentioning

confidence: 99%

Suppression of NF-κB by Cyclosporin A and Tacrolimus (FK506) via Induction of the C/EBP Family: Implication for Unfolded Protein Response

Hiramatsu

Hayakawa

et al. 2009

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Immunosuppressive agents cyclosporin A (CsA) and tacrolimus (FK506) inhibit cytokine production by activated lymphocytes through interfering with calcineurin. However, little is known about their effects on the function of nonlymphoid cells. We found that, in renal tubular cells, induction of MCP-1 by inflammatory cytokines was blunted by CsA and FK506. This suppression was correlated with induction of unfolded protein response (UPR) evidenced by endogenous and exogenous indicators. The induction of UPR by these agents was reversible and observed generally in other nonimmune cells. Furthermore, administration with CsA in reporter mice caused rapid, systemic induction of UPR in vivo. In TNF-α-treated cells, suppression of MCP-1 by CsA or FK506 was associated with blunted responses of NF-κB, the crucial regulator of MCP-1. The suppression of NF-κB was reproduced by other inducers of UPR including AB5 subtilase cytotoxin, tunicamycin, thapsigargin, and A23187. CsA and FK506, as well as other UPR inducers, caused up-regulation of C/EBP family members, especially C/EBPβ and CHOP (C/EBP homologous protein), and overexpression of either C/EBPβ or CHOP significantly attenuated TNF-α-triggered NF-κB activation. Furthermore, down-regulation of C/EBPβ by small interfering RNA substantially reversed the suppressive effect of CsA on TNF-α-induced MCP-1 expression. These results suggested that CsA and FK506 confer insensitiveness to TNF-α on resident cells through UPR-dependent induction of the C/EBP family members.