ERK1/2-dependent bestrophin-3 expression prevents ER-stress-induced cell death in renal epithelial cells by reducing CHOP

Renal epithelial cells regulate the destructive activity of macrophages and participate in the progression of kidney diseases. Critically, the Unfolded Protein Response (UPR), which is activated in renal epithelial cells in the course of kidney injury, is required for the optimal differentiation and activation of macrophages. Given that macrophages are key regulators of renal inflammation and fibrosis, we suppose that the identification of mediators that are released by renal epithelial cells under Endoplasmic Reticulum (ER) stress and transmitted to macrophages is a critical issue to address. Signals leading to a paracrine transmission of ER stress (TERS) from a donor cell to a recipient cells could be of paramount importance to understand how ER-stressed cells shape the immune microenvironment. Critically, the vast majority of studies that have examined TERS used thaspigargin as an inducer of ER stress in donor cells in cellular models. By using multiple sources of ER stress, we evaluated if human renal epithelial cells undergoing ER stress can transmit the UPR to human monocyte-derived macrophages and if such TERS can modulate the inflammatory profiles of these cells. Our results indicate that carry-over of thapsigargin is a confounding factor in chemically based TERS protocols classically used to induce ER Stress in donor cells. Hence, such protocols are not suitable to study the TERS phenomenon and to identify its mediators. In addition, the absence of TERS transmission in more physiological models of ER stress indicates that cell-to-cell UPR transmission is not a universal feature in cultured cells.

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ERK pathway mediates P2X7 expression and cell death in renal interstitial fibroblasts exposed to necrotic renal epithelial cells

AJP Renal Physiology ◽

10.1152/ajprenal.00215.2011 ◽

2011 ◽

Vol 301 (3) ◽

pp. F650-F659 ◽

Cited By ~ 19

Author(s):

Murugavel Ponnusamy ◽

Na Liu ◽

Rujun Gong ◽

Haidong Yan ◽

Shougang Zhuang

Keyword(s):

Cell Death ◽

Epithelial Cells ◽

Signaling Pathway ◽

P2x7 Receptor ◽

Transcriptional Factor ◽

Erk Pathway ◽

Signaling Mechanism ◽

Renal Epithelial Cells ◽

Extracellular Signal ◽

Dose Dependent

We recently reported that necrotic renal proximal epithelial cells (RPTC) stimulate the expression of P2X7 receptor in renal fibroblasts and that P2X7 receptor mediates deleterious epithelial-fibroblast cross talk. The present study was carried out to investigate the signaling mechanism of necrotic RPTC-induced P2X7 expression in cultured renal interstitial fibroblasts (NRK-49F). Exposure of NRK-49F to necrotic RPTC supernatant (RPTC-Sup) induced a time- and dose-dependent phosphorylation of several signaling pathways including extracellular signal-regulated kinases (ERK1/2), p38, c-Jun N-terminal kinases (JNKs), and AKT in NRK-49F. Pharmacological inhibition of ERK1/2, but not p38, JNK, and AKT pathways, blocked RPTC-Sup-induced P2X7 expression and renal interstitial fibroblast death. Knockdown of ERK1/2 or MEK1, a direct upstream activator of ERK1/2, also reduced RPTC-Sup-induced P2X7 expression and cell death of renal fibroblasts. Conversely, overexpression of MEK1 enhanced these responses. Upon necrotic RPTC exposure, phosphorylation of Elk1, a transcriptional factor targeted by ERK1/2, was increased in NRK-49F, and knockdown of Elk1 by siRNA remarkably reduced RPTC-Sup-induced P2X7 expression as well as renal fibroblast death. Furthermore, silencing of MEK1 inhibited Elk1 phosphorylation in response to necrotic RPTC, whereas overexpression of MEK1 increased Elk1 phosphorylation. Taken together, these data reveal that necrotic RPTC induces P2X7 expression in renal fibroblasts through activation of the MEK1-ERK1/2-Elk1 signaling pathway.

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A role for c-myc in chemically induced renal-cell death.

Molecular and Cellular Biology ◽

10.1128/mcb.17.11.6755 ◽

1997 ◽

Vol 17 (11) ◽

pp. 6755-6764 ◽

Cited By ~ 23

Author(s):

Y Zhan ◽

J L Cleveland ◽

J L Stevens

Keyword(s):

Cell Death ◽

Epithelial Cells ◽

Apoptotic Cell ◽

Tubular Damage ◽

Transactivation Domain ◽

Apoptotic Pathway ◽

Toxicant Exposure ◽

Renal Epithelial Cells ◽

Cell Death Pathway

A variety of genes, including c-myc, are activated by chemical toxicants in vivo and in vitro. Although enforced c-myc expression induces apoptosis after withdrawing survival factors, it is not clear if activation of the endogenous c-myc gene is an apoptotic signal after toxicant exposure. The renal tubular epithelium is a target for many toxicants. c-myc expression is activated by tubular damage. In quiescent LLC-PK1 renal epithelial cells, c-myc but not max or mad mRNA is induced by the nephrotoxicant S-(1,2-dichlorovinyl)-L-cysteine (DCVC). The kinetics of DCVC-induced c-myc expression and apoptosis suggested an association between cell death and prolonged activation of c-myc expression after toxicant exposure. Accordingly, prolonged activation of an estrogen receptor-Myc fusion construct, but not a construct in which a c-Myc transactivation domain had been deleted, was sufficient to induce apoptosis in LLC-PK1 cells. Moreover, under conditions in which necrosis was the predominant cell death pathway caused by DCVC in parental cells, overexpressing c-myc biased the cell death pathway toward apoptosis. DCVC also induced ornithine decarboxylase (odc) mRNA and activated the odc promoter. Activation of the odc promoter by DCVC required consensus c-Myc-Max binding sites in odc intron 1. Inhibiting ODC activity with alpha-difluoromethylornithine delayed DCVC-induced cell death. Therefore, odc is a target gene in the DCVC apoptotic pathway involving c-myc activation and contributes to apoptosis. Finally, a structurally related cytotoxic but nongenotoxic analog of DCVC did not induce c-myc and did not activate the odc promoter or induce apoptosis. The data support the hypothesis that activation of apoptotic cell death in quiescent renal epithelial cells involves induction of c-myc. This is the first study to demonstrate that c-myc induction by a specific nephrotoxicant leads to gene activation and cell death.

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Multiple cell death pathways are independently activated by lethal hypertonicity in renal epithelial cells

AJP Cell Physiology ◽

10.1152/ajpcell.00384.2012 ◽

2013 ◽

Vol 305 (10) ◽

pp. C1011-C1020 ◽

Cited By ~ 5

Author(s):

Soo Youn Choi ◽

Whaseon Lee-Kwon ◽

Hwan Hee Lee ◽

Jun Ho Lee ◽

Satoru Sanada ◽

...

Keyword(s):

Cell Death ◽

Epithelial Cells ◽

Cytochrome C ◽

Cathepsin B ◽

Extrinsic Pathway ◽

Renal Epithelial Cells ◽

Caspase Inhibitors ◽

Cell Death Pathways ◽

Cell Death Pathway ◽

Multiple Cell

When hypertonicity is imposed with sufficient intensity and acuteness, cells die. Here we investigated the cellular pathways involved in death using a cell line derived from renal epithelium. We found that hypertonicity rapidly induced activation of an intrinsic cell death pathway—release of cytochrome c and activation of caspase-3 and caspase-9—and an extrinsic pathway—activation of caspase-8. Likewise, a lysosomal pathway of cell death characterized by partial lysosomal rupture and release of cathepsin B from lysosomes to the cytosol was also activated. Relationships among the pathways were examined using specific inhibitors. Caspase inhibitors did not affect cathepsin B release into the cytosol by hypertonicity. In addition, cathepsin B inhibitors and caspase inhibitors did not affect hypertonicity-induced cytochrome c release, suggesting that the three pathways were independently activated. Combined inhibition of caspases and cathepsin B conferred significantly more protection from hypertonicity-induced cell death than inhibition of caspase or cathepsin B alone, indicating that all the three pathways contributed to the hypertonicity-induced cell death. Similar pattern of sensitivity to the inhibitors was observed in two other cell lines derived from renal epithelia. We conclude that multiple cell death pathways are independently activated early in response to lethal hypertonic stress in renal epithelial cells.

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