H-ras-transformed NRK-52E renal epithelial cells have altered growth, morphology, and cytoskeletal structure that correlates with renal cell carcinoma in vivo

Epithelial–Fibroblast Crosstalk Protects against Acidosis-Induced Inflammatory and Fibrotic Alterations

Pathogenesis of chronic kidney disease (CKD) is accompanied by extracellular acidosis inflammation, fibrosis and epithelial-to-mesenchymal transition (EMT). The aim of this study was to assess the influence of acidosis on tubule epithelial cells (NRK-52E) and fibroblasts (NRK-49F) in dependence of cellular crosstalk. NRK-52E and NRK-49F were used in mono- and co-cultures, and were treated with acidic media (pH 6.0) for 48 h. The intracellular proteins were measured by Western blot. Secreted proteins were measured by ELISA. Distribution of E-cadherin was assessed by immunofluorescence and epithelial barrier function by FITC-dextran diffusion. Inflammation: Acidosis led to an increase in COX-2 in NRK-52E and TNF in NRK-49F in monoculture. In co-culture, this effect was reversed. EMT: Acidosis led to an increase in vimentin protein in both cell lines, whereas in co-culture, the effect was abolished. In NRK-52E, the E-cadherin expression was unchanged, but subcellular E-cadherin showed a disturbed distribution, and cellular barrier function was decreased. Fibrosis: Monoculture acidosis led to an increased secretion of collagen I and fibronectin in NRK-52E and collagen I in NRK-49F. In co-culture, the total collagen I secretion was unchanged, and fibronectin secretion was decreased. Intercellular crosstalk between epithelial cells and fibroblasts has a protective function regarding the development of acidosis-induced damage.

Use of in vitro metabolomics in NRK cells to help predicting nephrotoxicity and differentiating the MoA of nephrotoxicants

We describe a strategy using an in vitro metabolomics assay with tubular rat NRK-52E cells to investigate the Modes of Action (MoAs) of nephrotoxic compounds. Chemicals were selected according to their MoAs based on literature information: acetaminophen, 4-aminophenol and S-(trichlorovinyl-)L-cysteine (TCVC), (covalent protein binding); gentamycin, vancomycin, polymycin B and CdCl₂ (lysosomal overload) and tenofovir and cidofovir (mitochondrial DNA-interaction). After treatment and harvesting of the cells, intracellular endogenous metabolites were quantified relative to vehicle control. Metabolite patterns were evaluated in a purely data-driven pattern generation process excluding published information. This strategy confirmed the assignment of the chemicals to the respective MoA except for TCVC and CdCl₂. Finally, TCVC was defined as unidentified and CdCl₂ was reclassified to the MoA "covalent protein binding". Hierarchical cluster analysis of 58 distinct metabolites from the patterns enabled a clear visual separation of chemicals in each MoA. The assay reproducibility was very good and metabolic responses were consistent. These results support the use of metabolome analysis in NRK-52E cells as a suitable tool for understanding and investigating the MoA of nephrotoxicants. This assay could enable the early identification of nephrotoxic compounds and finally reduce animal testing.

Perfluorooctanesulfonate Mediates Renal Tubular Cell Apoptosis through PPARgamma Inactivation

Perfluorinated chemicals (PFCs) are ubiquitously distributed in the environments including stainless pan-coating, raincoat, fire extinguisher, and semiconductor products. The PPAR family has been shown to contribute to the toxic effects of PFCs in thymus, immune and excretory systems. Herein, we demonstrated that perfluorooctanesulfonate (PFOS) caused cell apoptosis through increasing ratio of Bcl-xS/xL, cytosolic cytochrome C, and caspase 3 activation in renal tubular cells (RTCs). In addition, PFOS increased transcription of inflammatory cytokines (i.e., TNFα, ICAM1, and MCP1) by NFκB activation. Conversely, PFOS reduced the mRNA levels of antioxidative enzymes, such as glutathione peroxidase, catalase, and superoxide dismutase, as a result of reduced PPARγ transactivational activity by using reporter and chromatin immuoprecipitation (ChIP) assays. PFOS reduced the protein interaction between PPARγ and PPARγ coactivator-1 alpha (PGC1α) by PPARγ deacetylation through Sirt1 upregulation, of which the binding of PPARγ and PGC1α to a peroxisome proliferator response element (PPRE) in the promoter regions of these antioxidative enzymes was alleviated in the ChIP assay. Furthermore, Sirt1 also deacetylated p53 and then increased the binding of p53 to Bax, resulting in increased cytosolic cytochrome C. The effect of PPARγ inactivation by PFOS was validated using the PPARγ antagonist GW9662, whereas the adverse effects of PFOS were prevented by PPARγ overexpression and activators, rosiglitozone and L-carnitine, in RTCs. The in vitro finding of protective effect of L-carnitine was substantiated in vivo using Balb/c mice model subjected to PFOS challenge. Altogether, we provide in vivo and in vitro evidence for the protective mechanism of L-carnitine in eliminating PFOS-mediated renal injury, at least partially, through PPARγ activation.

L-carnitine protects against carboplatin-mediated renal injury: AMPK- and PPARα-dependent inactivation of NFAT3

We have previously shown that carboplatin induces inflammation and apoptosis in renal tubular cells (RTCs) through the activation of the nuclear factor of activated T cells-3 (NFAT3) protein by reactive oxygen species (ROS), and that the ROS-mediated activation of NFAT3 is prevented by N-acetyl cysteine and heme oxygenase-1 treatment. In the current study, we investigated the underlying molecular mechanisms of the protective effect of L-carnitine on carboplatin-mediated renal injury. Balb/c mice and RTCs were used as model systems. Carboplatin-induced apoptosis in RTCs was examined using terminal-deoxynucleotidyl-transferase-mediated dUTP nick end labeling. We evaluated the effects of the overexpression of the peroxisome-proliferator-activated receptor alpha (PPARα) protein, the knockdown of PPARα gene, and the blockade of AMPK activation and PPARα to investigate the underlying mechanisms of the protective effect of L-carnitine on carboplatin-mediated renal injury. Carboplatin reduced the nuclear translocation, phosphorylation, and peroxisome proliferator responsive element transactivational activity of PPARα. These carboplatin-mediated effects were prevented by L-carnitine through a mechanism dependent on AMPK phosphorylation and subsequent PPARα activation. The activation of PPARα induced cyclooxygenase 2 (COX-2) and prostacyclin (PGI2) synthase expression that formed a positive feedback loop to further activate PPARα. The coimmunoprecipitation of the nuclear factor (NF) κB proteins increased following the induction of PPARα by L-carnitine, which reduced NFκB transactivational activity and cytokine expression. The in vivo study showed that the inactivation of AMPK suppressed the protective effect of L-carnitine in carboplatin-treated mice, indicating that AMPK phosphorylation is required for PPARα activation in the L-carnitine-mediated protection of RTC apoptosis caused by carboplatin. The results of our study provide molecular evidence that L-carnitine prevents carboplatin-mediated apoptosis through AMPK-mediated PPARα activation.

Increased immunogenicity is an integral part of the heat shock response following renal ischemia

Renal ischemia increases tubular immunogenicity predisposing to increased risk of kidney allograft rejection. Ischemia-reperfusion not only disrupts cellular homeostasis but also induces the cytoprotective heat shock response that also plays a major role in cellular immune and defense processes. This study therefore tested the hypothesis that upregulation of renal tubular immunogenicity is an integral part of the heat shock response after renal ischemia. Expressions of 70 kDa heat shock protein (Hsp70), major histocompatibility complex (MHC) class II, and intercellular adhesion molecule-1 (ICAM-1) were assessed in normal rat kidney (NRK) cells following ATP depletion (antimycin A for 3 h) and heat (42°C for 24 h). In vitro, transient Hsp70 transfection and heat shock factor-1 (HSF-1) transcription factor decoy treatment were performed. In vivo, ischemic renal cortex was investigated in Sprague-Dawley rats following unilateral renal artery clamping for 45 min and 24 h recovery. Upregulation of Hsp70 was closely and significantly correlated with upregulation of MHC class II and/or ICAM-1 following ATP depletion and heat injury. Bioinformatics analysis searching the TRANSFAC database predicted HSF-1 binding sites in these genes. HSF-1 decoy significantly reduced the expression of immunogenicity markers in stressed NRK cells. In the in vivo rat model of renal ischemia, concordant upregulation of MHC class II molecules and Hsp70 suggests biological relevance of this link. The results demonstrate that upregulation of renal tubular immunogenicity is an integral part of the heat shock response after renal ischemia. Bioinformatic analysis predicted a molecular link to tubular immunogenicity at the level of the transcription factor HSF-1 that was experimentally verified by HSF-1 decoy treatment. Future studies in HSF-1 knockout mice are needed.

Calcineurin inhibitors activate the proto-oncogene Ras and promote protumorigenic signals in renal cancer cells

The development of cancer is a major problem in immunosuppressed patients, particularly after solid organ transplantation. We have recently shown that calcineurin inhibitors (CNI) used to treat transplant patients may play a critical role in the rapid progression of renal cancer. To examine the intracellular signaling events for CNI-mediated direct tumorigenic pathway(s), we studied the effect of CNI on the activation of proto-oncogenic Ras in human normal renal epithelial cells (REC) and renal cancer cells (786-0 and Caki-1). We found that CNI treatment significantly increased the level of activated GTP-bound form of Ras in these cells. In addition, CNI induced the association of Ras with one of its effector molecules, Raf, but not with Rho and phosphatidylinositol 3-kinase; CNI treatment also promoted the phosphorylation of the Raf kinase inhibitory protein and the downregulation of carabin, all of which may lead to the activation of the Ras-Raf pathway. Blockade of this pathway through either pharmacologic inhibitors or gene-specific small interfering RNA significantly inhibited CNI-mediated augmented proliferation of renal cancer cells. Finally, it was observed that CNI treatment increased the growth of human renal tumors in vivo, and the Ras-Raf pathway is significantly activated in the tumor tissues of CNI-treated mice. Together, targeting the Ras-Raf pathway may prevent the development/progression of renal cancer in CNI-treated patients.

Uranium(VI) complexation in cell culture medium: influence of speciation on Normal Rat Kidney (NRK-52E) cell accumulation

Uranium bioavailability and toxicity are closely linked to the metal's speciation in solution. However in biological fluids or in media classically used for cell culture – and subsequently for in vitro cell exposure –, uranium is rarely present as free-ion since these media contain non-negligible concentrations of potential ligands such as phosphate and bicarbonate but also co-ions such as calcium which can cause U(VI) complexes precipitation. The chemical form of uranium that is internalized in cells and interferes with biological processes is of major concern. Uranium toxicity and accumulation were evaluated in vitro on NRK-52E cells, model for rat renal proximal tubule. Uranium intracellular accumulation begins after 12 h exposure to 600 μM U(VI); toxicity appears as soon as cells accumulated 25 to 30 mg U/g protein. Modification of uranium speciation in the exposure medium induces great changes in toxicity and cell accumulation. Comparison of toxicity and accumulation results to theoretical uranium speciation, calculated with the J-Chess computer program, shows that free-ion concentration can not explain the total uranium intracellular accumulation. Low molecular weight U(VI) complexes, such as UO2(CO3)3 4− but also UO2PO4 − could be implicated in U(VI) cellular accumulation and toxicity.

Isolation of ORCTL3 in a novel genetic screen for tumor-specific apoptosis inducers

We have established a systematic high-throughput screen for genes that cause cell death specifically in transformed tumor cells. In a first round of screening cDNAs are detected that induce apoptosis in a transformed human cell line. Positive genes are subsequently tested in a synthetic lethal screen in normal cells versus their isogenic counterparts that have been transformed by a particular oncogene. In this way, ORCTL3 was found to be inactive in normal rat kidney cells (NRK), but to induce apoptosis in NRK cells transformed by oncogenic H-ras. ORCTL3 also causes cell death in v-src-transformed cells and in various human tumor cell lines but not in normal cells or untransformed cell lines. While ORCTL3 is a member of the organic-cation transporter gene family, our data indicate that this gene induces apoptosis independently of its putative transporter activity. Rather, various lines of evidence suggest that ORCTL3 brings about apoptosis via an ER stress mediated mechanism. Finally, we detected ORCTL3 to be down-regulated in human kidney tumors.

Synthesis and evaluation of antitumor activity of novel N-acyllavendamycin analogues and quinoline-5,8-diones

A series of 7-N-acyllavendamycins with zero, one or two substituents at the C-2', C-3', and C-11' were synthesized through short and efficient methods. Pictet-Spengler condensation of 7-N-acylamino-2-formylquinoline-5,8-diones with tryptamine or tryptophans produced the desired lavendamycins. Screening data on a panel of three ras oncogene-transformed cell lines and the non-transformed parent cell line showed that a significant number of these analogues are potent antitumor agents and appear to be particularly active against K-ras transformed cells. Compared with the corresponding quinolinediones, these novel lavendamycins are much more inhibitory toward the transformed cells indicating that the beta-carboline moiety of the lavendamycin analogues plays an important role in its potency and selective toxicity.

Identification of thrombospondin 1 (TSP-1) as a novel mediator of cell injury in kidney ischemia

Thrombospondin 1 (TSP-1) is a matricellular protein that inhibits angiogenesis and causes apoptosis in vivo and in vitro in several cancerous cells and tissues. Here we identify TSP-1 as the molecule with the highest induction level at 3 hours of IR injury in rat and mouse kidneys subjected to ischemia/reperfusion (IR) injury using the DNA microarray approach. Northern hybridizations demonstrated that TSP-1 expression was undetectable at baseline, induced at 3 and 12 hours, and returned to baseline levels at 48 hours of reperfusion. Immunocytochemical staining identified the injured proximal tubules as the predominant sites of expression of TSP-1 in IR injury and showed colocalization of TSP-1 with activated caspase-3. Addition of purified TSP-1 to normal kidney proximal tubule cells or cells subjected to ATP depletion in vitro induced injury as demonstrated by cytochrome c immunocytochemical staining and caspase-3 activity. The deleterious role of TSP-1 in ischemic kidney injury was demonstrated directly in TSP-1 null mice, which showed significant protection against IR injury-induced renal failure and tubular damage. We propose that TSP-1 is a novel regulator of ischemic damage in the kidney and may play an important role in the pathophysiology of ischemic kidney failure.

Role of ERK1/2 and p38 mitogen-activated protein kinases in the regulation of thrombospondin-1 by TGF-beta1 in rat proximal tubular cells and mouse fibroblasts

Thrombospondin-1 (TSP-1) inhibits angiogenesis and activates latent TGF-beta1, both of which are strongly associated with progression of renal disease. Recently, it was reported that Smad2 but not Smad3 regulates TSP-1 expression in response to TGF-beta1 in rat tubular epithelial cells as well as in mouse fibroblasts. This study investigated the role of ERK1/2 and p38 mitogen-activated protein kinases (MAPK). TGF-beta1 activated both ERK1/2 and p38 in the rat proximal tubular cell line NRK52E. Blocking ERK1/2 and p38 inhibited TGF-beta1-induced TSP-1 mRNA and protein expression. Next, the cross-talk between Smad2 and ERK1/2 or p38 was examined. Whereas blocking of ERK1/2 or p38 failed to inhibit TGF-beta1-induced Smad2 activation, inhibition of Smad2 by Smad7 overexpression inhibited the phosphorylation of ERK1/2 but not p38 in response to TGF-beta1. Similar results were observed using mouse fibroblasts from Smad2 knockout embryos, in that TGF-beta1 was able to activate p38 but not ERK1/2 in this cell line. In conclusion, TSP-1 expression is regulated by both ERK1/2 and p38 MAPK in rat proximal tubular cells and mouse fibroblasts in response to TGF-beta1. The ERK1/2 activation is dependent on Smad2 activation, whereas the p38 activation occurs independent of Smad2. Because TSP-1 is a major antiangiogenic molecule and an activator of TGF-beta1, this provides an important insight to the mechanism by which TGF-beta1 may mediate interstitial fibrosis and progressive renal disease.

Comparative Analysis of Caspase Activation and Apoptosis in Renal Tubular Epithelial Cells and Renal Cell Carcinomas

BACKGROUND/AIMS

Treatment of renal cell carcinoma (RCC) is limited by its resistance to conventional chemotherapies. This may occur, in part, from resistance to apoptosis. The role of caspase activation in apoptosis resistance in treated RCCs was investigated.

METHODS

Two human RCC cell lines (ACHN and SN12K1) and renal tubular epithelial cells (HK2) were treated with 5-fluorouracil (0.2-20 microg/ml) or cisplatin (1-100 microM). Activation of caspase-3 and -2 was analysed and compared with levels of apoptosis. Caspase function was analysed using pan-caspase inhibition (z-VAD-fmk) and caspase-2 inhibition (z-VDVAD-fmk).

RESULTS

RCC apoptosis was significantly lower (p < 0.05) than in HK2s after treatment, confirming their chemoresistance. Pro-caspase-3 (32 kDa) was detected in all cell lines. Cleaved caspase-3 (19 kDa) was not detected by Western immunoblots in treated RCCs and only minimal activated caspase-3 was detected in treated RCCs using immunohistochemistry. All cells had pro-caspase-2 (48 kDa) and the activated form (33 kDa) appeared in all treated cells. Caspase inhibition caused a reduction in, but not negation of, therapy-induced apoptosis in HK2s and RCCs (p < 0.05 for HK2s and ACHN cells), indicating that a caspase activation pathway must occur in RCC apoptosis but this pathway does not act via caspase-3 cleavage. Inhibition of caspase-2 reduced apoptosis only in HK2s, indicating that the activated caspase-2, identified in treated RCCs, was not responsible for their apoptosis induction.

CONCLUSION

Specific differences in caspase-3 and -2 activation were identified in renal tubular epithelium and RCCs after chemotherapy. Identification of RCC-specific caspase inactivation or redundancy may explain, in part, the resistance of RCCs to cancer therapies and may be useful in targeting apoptotic pathways to overcome RCC resistance to treatment.

Studies on the mechanisms and kinetics of apoptosis induced by microinjection of cytochrome c in rat kidney tubule epithelial cells (NRK-52E)

Recent reports substantiating the role of cytochrome c in the induction of apoptosis led us to examine the kinetics and mechanisms involved in this process as an extension of our ongoing studies of cell injury and cell death. Microinjection of cytochrome c into NRK-52E kidney cells produced rapid apoptosis, which usually began within 30 minutes and reached a maximum of 60-70% by 3 hours. The changes that occurred included four phases: an initial shrinkage phase, an active phase, a spherical phase, and a necrotic phase. For morphological purposes, the progressive changes were followed by phase-contrast and fluorescence microscopy, transmission and scanning electron microscopy, and time-lapse video microscopy. Cells first showed shrinkage, then displayed multiple pseudopods, which rapidly extended and retracted, giving the cells a bosselated appearance. During this active phase there was chromatin condensation, mitochondria were swollen but retained membrane potential, and the endoplasmic reticulum was dilated. Within 2-4 hours, active-phase cells became spherical and smooth-surfaced but were still alive, the nuclei showed chromatin clumping, the mitochondria underwent high-amplitude swelling but retained membrane potential, the endoplasmic reticulum was highly dilated, and many large apical vacuoles were present. Elevation of [Ca(2+)](i) was seen at the late spherical phase, shortly before cell death. Pretreatment with the caspase 3 inhibitor (Ac-DEVD-CHO) prevented apoptosis, whereas overexpression of Bcl-2 did not. Depletion of cellular ATP by cyanide inhibition of energy metabolism prevented cytochrome c from inducing the active and later phases of apoptosis. The results clearly indicate that cytochrome c-induced apoptosis is a dynamic and energy-requiring process that has a distinct active and spherical phase before cell death.