(−)‐ Epigallocatechin‐3‐gallate induces GRP78 accumulation in the ER and shifts mesothelioma constitutive UPR into proapoptotic ER stress

Abstract

GRP78 is a molecular chaperone of the endoplasmic reticulum (ER) that aids proper folding of nascent polypeptides. When unfolded proteins accumulate, GRP78 triggers unfolded protein response (UPR), involving activation of transcription factors like XBP1 and CHOP that may restore cell homeostasis. Increased expression of GRP78 and mild UPR can be constitutive in cancer cells, hindering apoptosis, and promoting cell survival, for example, by GRP78 relocation to the plasma membrane that activates MAPK and PI3 K/AKT pathways. These processes are thought to favor the insurgence of chemoresistance and worsen patient outcome. We have previously shown that (-)-epigallocatechin-3-gallate (EGCG) enhances ROS production and alters Ca homeostasis in cell lines deriving from therapy-recalcitrant malignant mesothelioma (MMe). We consider here the EGCG impact on GRP78 and downstream factors by using qRT-PCR, Western blot, immunofluorescence, caspase assays, GRP78 siRNA silencing, and cell surface ELISA. MMe cells were found to display mild constitutive UPR, as shown by increased levels of GRP78, and presence of the protein at the cell surface, linked to AKT activation. Exposure to EGCG further increased GRP78 in the ER, and induced ATF4, spliced XBP1, CHOP, and EDEM expressions, combined with a reduction of cell surface GRP78 and a rise in caspase 3 and 8 activities. We propose that GRP78 accumulation in the ER, caused by EGCG, converts constitutive UPR of MMe cells into proapoptotic ER stress. This argues for a possible therapeutic use of EGCG in the treatment of MMe as a co-drug able to abolish chemoresistance to conventional drugs at tolerable doses.

Norcantharidin inhibits proliferation and promotes apoptosis via c‐Met/Akt/mTOR pathway in human osteosarcoma cells

“…There is also evidence that the induction of ER stress proteins plays a role in apoptosis in various cancer cells . GRP78 functions as a molecular chaperone and is a major regulator of ER stress, as it maintains the integrity of the ER and controls the activation of unfolded protein response (UPR) signaling molecules . The UPR involves 3 proteins (i.e.…”

“…17 GRP78 functions as a molecular chaperone and is a major regulator of ER stress, as it maintains the integrity of the ER and controls the activation of unfolded protein response (UPR) signaling molecules. 30 The UPR involves 3 proteins (i.e. inositol-requiring enzyme-1, activating transcription factor 6 and protein kinase R-like ER kinase [PERK]), that respond to the accumulation of unfolded proteins as part of a survival response.…”

Naturally occurring anti-cancer compounds: shining from Chinese herbal medicine

“…ER stress-induced apoptosis, PERK and eIF2α phosphorylation by EGCG are suppressed in PARP16-deficient hepatocellular carcinoma QGY-7703 cells, so EGCG mediates apoptosis through ER stress, which is dependent on PARP16 [105]. Similarly, EGCG causes 78-kDa glucose-regulated protein (GRP78) accumulation in the ER, which up-regulates ER stress markers such as activating transcription factor 4 (ATF-4), X-box binding protein 1 (XBP-1) and C/EBP homologous protein (CHOP), and shifts into pro-apoptotic ER stress, leading to increased caspase-3 and -8 activities [107]. Furthermore, it suppresses cell migration and invasion by blocking tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), MMP-2/c-Jun N-terminal kinase (JNK) and transforming growth factor-β (TGF-β) pathways [85,93,100].…”

In vitro anticancer activity of methanolic extract of Granulocystopsis sp., a microalgae from an oligotrophic oasis in the Chihuahuan desert

“…No. 10009135) (Martinotti, Ranzato & Burlando, 2018) according to the manufacturer's instructions. Three independent experiments were performed with three technical replicates each.…”