Macrophage transcription factor TonEBP promotes systemic lupus erythematosus and kidney injury via damage-induced signaling pathways.

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by autoreactive B cells and dysregulation of many other types of immune cells including myeloid cells. Lupus nephritis (LN) is a common target organ manifestations of SLE. Tonicity-responsive enhancer-binding protein (TonEBP, also known as nuclear factor of activated T-cells 5 (NFAT5)), was initially identified as a central regulator of cellular responses to hypertonic stress and is a pleiotropic stress protein involved in a variety of immunometabolic diseases. To explore the role of TonEBP, we examined kidney biopsy samples from patients with LN. Kidney TonEBP expression was found to be elevated in these patients compared to control patients - in both kidney cells and infiltrating immune cells. Kidney TonEBP mRNA was elevated in LN and correlated with mRNAs encoding inflammatory cytokines and the degree of proteinuria. In a pristane-induced SLE model in mice, myeloid TonEBP deficiency blocked the development of SLE and LN. In macrophages, engagement of various toll-like receptors (TLRs) that respond to damage-associated molecular patterns induced TonEBP expression via stimulation of its promoter. Intracellular signaling downstream of the TLRs was dependent on TonEBP. Therefore, TonEBP can act as a transcriptional cofactor for NF-κB, and activated mTOR-IRF3/7 via protein-protein interactions. Additionally, TonEBP-deficient macrophages displayed elevated efferocytosis and animals with myeloid deficiency of TonEBP showed reduced Th1 and Th17 differentiation, consistent with macrophages defective in TLR signaling. Thus, our data show that myeloid TonEBP may be an attractive therapeutic target for SLE and LN.

TonEBP recognizes R-loops and initiates m6A RNA methylation for R-loop resolution.

R-loops are three-stranded, RNA-DNA hybrid, nucleic acid structures produced due to inappropriate processing of newly transcribed RNA or transcription-replication collision (TRC). Although R-loops are important for many cellular processes, their accumulation causes genomic instability and malignant diseases, so these structures are tightly regulated. It was recently reported that R-loop accumulation is resolved by methyltransferase-like 3 (METTL3)-mediated m6A RNA methylation under physiological conditions. However, it remains unclear how R-loops in the genome are recognized and induce resolution signals. Here, we demonstrate that tonicity-responsive enhancer binding protein (TonEBP) recognizes R-loops generated by DNA damaging agents such as ultraviolet (UV) or camptothecin (CPT). Single-molecule imaging and biochemical assays reveal that TonEBP preferentially binds a R-loop via both 3D collision and 1D diffusion along DNA in vitro. In addition, we find that TonEBP recruits METTL3 to R-loops through the Rel homology domain (RHD) for m6A RNA methylation. We also show that TonEBP recruits RNaseH1 to R-loops through a METTL3 interaction. Consistent with this, TonEBP or METTL3 depletion increases R-loops and reduces cell survival in the presence of UV or CPT. Collectively, our results reveal an R-loop resolution pathway by TonEBP and m6A RNA methylation by METTL3 and provide new insights into R-loop resolution processes.

Microglial TonEBP mediates LPS-induced inflammation and memory loss as transcriptional cofactor for NF-κB and AP-1.

BACKGROUND: Microglia are brain-resident myeloid cells involved in the innate immune response and a variety of neurodegenerative diseases. In macrophages, TonEBP is a transcriptional cofactor of NF-κB which stimulates the transcription of pro-inflammatory genes in response to LPS. Here, we examined the role of microglial TonEBP. METHODS: We used microglial cell line, BV2 cells. TonEBP was knocked down using lentiviral transduction of shRNA. In animals, TonEBP was deleted from myeloid cells using a line of mouse with floxed TonEBP. Cerulenin was used to block the NF-κB cofactor function of TonEBP. RESULTS: TonEBP deficiency blocked the LPS-induced expression of pro-inflammatory cytokines and enzymes in association with decreased activity of NF-κB in BV2 cells. We found that there was also a decreased activity of AP-1 and that TonEBP was a transcriptional cofactor of AP-1 as well as NF-κB. Interestingly, we found that myeloid-specific TonEBP deletion blocked the LPS-induced microglia activation and subsequent neuronal cell death and memory loss. Cerulenin disrupted the assembly of the TonEBP/NF-κB/AP-1/p300 complex and suppressed the LPS-induced microglial activation and the neuronal damages in animals. CONCLUSIONS: TonEBP is a key mediator of microglial activation and neuroinflammation relevant to neuronal damage. Cerulenin is an effective blocker of the TonEBP actions.

Tonicity-responsive enhancer-binding protein promotes hepatocellular carcinogenesis, recurrence and metastasis.

OBJECTIVES: Hepatocellular carcinoma (HCC) is a common cancer with high rate of recurrence and mortality. Diverse aetiological agents and wide heterogeneity in individual tumours impede effective and personalised treatment. Tonicity-responsive enhancer-binding protein (TonEBP) is a transcriptional cofactor for the expression of proinflammatory genes. Although inflammation is intimately associated with the pathogenesis of HCC, the role of TonEBP is unknown. We aimed to identify function of TonEBP in HCC. DESIGN: Tumours with surrounding hepatic tissues were obtained from 296 patients with HCC who received completion resection. TonEBP expression was analysed by quantitative reverse transcription-quantitative real-time PCR (RT-PCR) and immunohfistochemical analyses of tissue microarrays. Mice with TonEBP haplodeficiency, and hepatocyte-specific and myeloid-specific TonEBP deletion were used along with HCC and hepatocyte cell lines. RESULTS: TonEBP expression is higher in tumours than in adjacent non-tumour tissues in 92.6% of patients with HCC regardless of aetiology associated. The TonEBP expression in tumours and adjacent non-tumour tissues predicts recurrence, metastasis and death in multivariate analyses. TonEBP drives the expression of cyclo-oxygenase-2 (COX-2) by stimulating the promoter. In mouse models of HCC, three common sites of TonEBP action in response to diverse aetiological agents leading to tumourigenesis and tumour growth were found: cell injury and inflammation, induction by oxidative stress and stimulation of the COX-2 promoter. CONCLUSIONS: TonEBP is a key component of the common pathway in tumourigenesis and tumour progression of HCC in response to diverse aetiological insults. TonEBP is involved in multiple steps along the pathway, rendering it an attractive therapeutic target as well as a prognostic biomarker.

Tonicity-Responsive Enhancer-Binding Protein Mediates Hyperglycemia-Induced Inflammation and Vascular and Renal Injury.

Diabetic nephropathy (DN) has become the single leading cause of ESRD in developed nations. Bearing in mind the paucity of effective treatment for DN and progressive CKD, novel targets for treatment are sorely needed. We previously reported that increased activity of tonicity-responsive enhancer-binding protein (TonEBP) in monocytes was associated with early DN in humans. We now extend these findings by testing the hypotheses that TonEBP in macrophages promotes hyperglycemia-mediated proinflammatory activation and chronic renal inflammation leading to DN and CKD, and TonEBP genetic variability in humans is associated with inflammatory, renal, and vascular function-related phenotypes. In a mouse model of DN, compared with the wild-type phenotype, TonEBP haplodeficiency associated with reduced activation of macrophages by hyperglycemia, fewer macrophages in the kidney, lower renal expression of proinflammatory genes, and attenuated DN. Furthermore, in a cohort of healthy humans, genetic variants within TonEBP associated with renal function, BP, and systemic inflammation. One of the genetic variants associated with renal function was replicated in a large population-based cohort. These findings suggest that TonEBP is a promising target for minimizing diabetes- and stress-induced inflammation and renovascular injury.

Macrophage migration inhibitory factor mediates the antidepressant actions of voluntary exercise.

Voluntary exercise is known to have an antidepressant effect. However, the underlying mechanism for this antidepressant action of exercise remains unclear, and little progress has been made in identifying genes that are directly involved. We have identified macrophage migration inhibitory factor (MIF) by analyzing existing mRNA microarray data and confirmed the augmented expression of selected genes under two experimental conditions: voluntary exercise and electroconvulsive seizure. A proinflammatory cytokine, MIF is expressed in the central nervous system and involved in innate and adaptive immune responses. A recent study reported that MIF is involved in antidepressant-induced hippocampal neurogenesis, but the mechanism remains elusive. In our data, tryptophan hydroxylase 2 (Tph2) and brain-derived neurotrophic factor (Bdnf) expression were induced after MIF treatment in vitro, as well as during both exercise and electroconvulsive seizure in vivo. This increment of Tph2 was accompanied by increases in the levels of total serotonin in vitro. Moreover, the MIF receptor CD74 and the ERK1/2 pathway mediate the MIF-induced Tph2 and Bdnf gene expression as well as serotonin content. Experiments in Mif(-/-) mice revealed depression-like behaviors and a blunted antidepressant effect of exercise, as reflected by changes in Tph2 and Bdnf expression in the forced swim test. In addition, administration of recombinant MIF protein produced antidepressant-like behavior in rats in the forced swim test. Taken together, these results suggest a role of MIF in mediating the antidepressant action of exercise, probably by enhancing serotonin neurotransmission and neurotrophic factor-induced neurogenesis in the brain.

One-hit kill: On the inactivation of RNA viruses by ultraviolet (UV)-C-induced genomic damage.

Large scale outbreaks of infectious respiratory disease have repeatedly plagued the globe over the last 100 years. The scope and strength of the outbreaks are getting worse as pathogenic RNA viruses are rapidly evolving and highly evasive to vaccines and anti-viral drugs. Germicidal UV-C is considered as a robust agent to disinfect RNA viruses regardless of their evolution. While genomic damage by UV-C has been known to be associated with viral inactivation, the precise relationship between the damage and inactivation remains unsettled as genomic damage has been analyzed in small areas, typically under 0.5 kb. In this study, we assessed genomic damage by the reduced efficiency of reverse transcription of regions of up to 7.2 kb. Our data seem to indicate that genomic damage was directly proportional to the size of the genome, and a single hit of damage was sufficient for inactivation of RNA viruses. The high efficacy of UV-C is already effectively adopted to inactivate airborne RNA viruses.

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

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.

PDZ domain-containing 1 (PDZK1) protein regulates phospholipase C-ß3 (PLC-ß3)-specific activation of somatostatin by forming a ternary complex with PLC-ß3 and somatostatin receptors.

Phospholipase C-ß (PLC-ß) is a key molecule in G protein-coupled receptor (GPCR)-mediated signaling. Many studies have shown that the four PLC-ß subtypes have different physiological functions despite their similar structures. Because the PLC-ß subtypes possess different PDZ-binding motifs, they have the potential to interact with different PDZ proteins. In this study, we identified PDZ domain-containing 1 (PDZK1) as a PDZ protein that specifically interacts with PLC-ß3. To elucidate the functional roles of PDZK1, we next screened for potential interacting proteins of PDZK1 and identified the somatostatin receptors (SSTRs) as another protein that interacts with PDZK1. Through these interactions, PDZK1 assembles as a ternary complex with PLC-ß3 and SSTRs. Interestingly, the expression of PDZK1 and PLC-ß3, but not PLC-ß1, markedly potentiated SST-induced PLC activation. However, disruption of the ternary complex inhibited SST-induced PLC activation, which suggests that PDZK1-mediated complex formation is required for the specific activation of PLC-ß3 by SST. Consistent with this observation, the knockdown of PDZK1 or PLC-ß3, but not that of PLC-ß1, significantly inhibited SST-induced intracellular Ca(2+) mobilization, which further attenuated subsequent ERK1/2 phosphorylation. Taken together, our results strongly suggest that the formation of a complex between SSTRs, PDZK1, and PLC-ß3 is essential for the specific activation of PLC-ß3 and the subsequent physiologic responses by SST.

Wedelolactone inhibits adipogenesis through the ERK pathway in human adipose tissue-derived mesenchymal stem cells.

Wedelolactone is an herbal medicine that is used to treat septic shock, hepatitis and venom poisoning. Although in differentiated and cancer cells, wedelolactone has been identified as anti-inflammatory, growth inhibitory, and pro-apoptotic, the effects of wedelolactone on stem cell differentiation remain largely unknown. Here, we report that wedelolactone inhibits the adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hAMSCs). Wedelolactone reduced the formation of lipid droplets and the expression of adipogenesis-related proteins, such as CCAAT enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein aP2 (aP2). Wedelolactone mediated this process by sustaining ERK activity. In addition, inhibition of ERK activity with PD98059 resulted in reversion of the wedelolactone-mediated inhibition of adipogenic differentiation. Taken together, these results indicate that wedelolactone inhibits adipogenic differentiation through ERK pathway and suggest a novel inhibitory effect of wedelolactone on adipogenic differentiation in hAMSCs.

TonEBP in Myeloid Cells Promotes Obesity-Induced Insulin Resistance and Inflammation Through Adipose Tissue Remodeling.

The phenotypic and functional plasticity of adipose tissue macrophages (ATMs) during obesity plays a crucial role in orchestration of adipose and systemic inflammation. Tonicity-responsive enhancer binding protein (TonEBP) (also called NFAT5) is a stress protein that mediates cellular responses to a range of metabolic insults. Here, we show that myeloid cell-specific TonEBP depletion reduced inflammation and insulin resistance in mice with high-fat diet-induced obesity but did not affect adiposity. This phenotype was associated with a reduced accumulation and a reduced proinflammatory phenotype of metabolically activated macrophages, decreased expression of inflammatory factors related to insulin resistance, and enhanced insulin sensitivity. TonEBP expression was elevated in the ATMs of obese mice, and Sp1 was identified as a central regulator of TonEBP induction. TonEBP depletion in macrophages decreased induction of insulin resistance-related genes and promoted induction of insulin sensitivity-related genes under obesity-mimicking conditions and thereby improved insulin signaling and glucose uptake in adipocytes. mRNA expression of TonEBP in peripheral blood mononuclear cells was positively correlated with blood glucose levels in mice and humans. These findings suggest that TonEBP in macrophages promotes obesity-associated systemic insulin resistance and inflammation, and downregulation of TonEBP may induce a healthy metabolic state during obesity.

PARP1-mediated PARylation of TonEBP prevents R-loop-associated DNA damage.

Lack of coordination between the DNA replication and transcription machineries can increase the frequency of transcription-replication conflicts, leading ultimately to DNA damage and genomic instability. A major source of these conflicts is the formation of R-loops, which consist of a transcriptionally generated RNA-DNA hybrid and the displaced single-stranded DNA. R-loops play important physiological roles and have been implicated in human diseases. Although these structures have been extensively studied, many aspects of R-loop biology and R-loop-mediated genome instability remain unclear. We found that in cancer cells, tonicity-responsive enhancer-binding protein (TonEBP, also called NFAT5) interacted with PARP1 and localized to R-loops in response to DNA-damaging agent camptothecin (CPT), which is associated with R-loop formation. PARP1-mediated PARylation was required for recruitment of TonEBP to the sites of R-loop-associated DNA damage. Loss of TonEBP increased levels of R-loop accumulation and DNA damage, and promoted cell death in response to CPT. These findings suggest that TonEBP mediates resistance to CPT-induced cell death by preventing R-loop accumulation in cancer cells.

Intrinsic nitric oxide and superoxide production regulates descending vasa recta contraction.

Descending vasa recta (DVR) are 12- to 15-µm microvessels that supply the renal medulla with blood flow. We examined the ability of intrinsic nitric oxide (NO) and reactive oxygen species (ROS) generation to regulate their vasoactivity. Nitric oxide synthase (NOS) inhibition with N(ω)-nitro-l-arginine methyl ester (l-NAME; 100 µmol/l), or asymmetric N(G),N(G)-dimethyl-l-arginine (ADMA; 100 µmol/l), constricted isolated microperfused DVR by 48.82 ± 4.34 and 27.91 ± 2.91%, respectively. Restoring NO with sodium nitroprusside (SNP; 1 mmol/l) or application of 8-Br-cGMP (100 µmol/l) reversed DVR vasoconstriction by l-NAME. The superoxide dismutase mimetic Tempol (1 mmol/l) and the NAD(P)H inhibitor apocynin (100, 1,000 µmol/l) also blunted ADMA- or l-NAME-induced vasoconstriction, implicating a role for concomitant generation of ROS. A role for ROS generation was also supported by an l-NAME-associated rise in oxidation of dihydroethidium that was prevented by Tempol or apocynin. To test whether H(2)O(2) might play a role, we examined its direct effects. From 1 to 100 µmol/l, H(2)O(2) contracted DVR whereas at 1 mmol/l it was vasodilatory. The H(2)O(2) scavenger polyethylene glycol-catalase reversed H(2)O(2) (10 µmol/l)-induced vasoconstriction; however, it did not affect l-NAME-induced contraction. Finally, the previously known rise in DVR permeability to (22)Na and [(3)H]raffinose that occurs with luminal perfusion was not prevented by NOS blockade. We conclude that intrinsic production of NO and ROS can modulate DVR vasoactivity and that l-NAME-induced vasoconstriction occurs, in part, by modulating superoxide concentration and not through H(2)O(2) generation. Intrinsic NO production does not affect DVR permeability to hydrophilic solutes.

The evolving role of TonEBP as an immunometabolic stress protein.

Tonicity-responsive enhancer-binding protein (TonEBP), which is also known as nuclear factor of activated T cells 5 (NFAT5), was discovered 20 years ago as a transcriptional regulator of the cellular response to hypertonic (hyperosmotic salinity) stress in the renal medulla. Numerous studies since then have revealed that TonEBP is a pleiotropic stress protein that is involved in a range of immunometabolic diseases. Some of the single-nucleotide polymorphisms (SNPs) in TONEBP introns are cis-expression quantitative trait loci that affect TONEBP transcription. These SNPs are associated with increased risk of type 2 diabetes mellitus, diabetic nephropathy, inflammation, high blood pressure and abnormal plasma osmolality, indicating that variation in TONEBP expression might contribute to these phenotypes. In addition, functional studies have shown that TonEBP is involved in the pathogenesis of rheumatoid arthritis, atherosclerosis, diabetic nephropathy, acute kidney injury, hyperlipidaemia and insulin resistance, autoimmune diseases (including type 1 diabetes mellitus and multiple sclerosis), salt-sensitive hypertension and hepatocellular carcinoma. These pathological activities of TonEBP are in contrast to the protective actions of TonEBP in response to hypertonicity, bacterial infection and DNA damage induced by genotoxins. An emerging theme is that TonEBP is a stress protein that mediates the cellular response to a range of pathological insults, including excess caloric intake, inflammation and oxidative stress.

TonEBP Promotes ß-Cell Survival under ER Stress by Enhancing Autophagy.

The endoplasmic reticulum (ER) stress response and autophagy are important cellular responses that determine cell fate and whose dysregulation is implicated in the perturbation of homeostasis and diseases. Tonicity-responsive enhancer-binding protein (TonEBP, also called NFAT5) is a pleiotropic stress protein that mediates both protective and pathological cellular responses. Here, we examined the role of TonEBP in ß-cell survival under ER stress. We found that TonEBP increases ß-cell survival under ER stress by enhancing autophagy. The level of TonEBP protein increased under ER stress due to a reduction in its degradation via the ubiquitin-proteasome pathway. In response to ER stress, TonEBP increased autophagosome formations and suppressed the accumulation of protein aggregates and ß-cell death. The Rel-homology domain of TonEBP interacted with FIP200, which is essential for the initiation of autophagy, and was required for autophagy and cell survival upon exposure to ER stress. Mice in which TonEBP was specifically deleted in pancreatic endocrine progenitor cells exhibited defective glucose homeostasis and a loss of islet mass. Taken together, these findings demonstrate that TonEBP protects against ER stress-induced ß-cell death by enhancing autophagy.

Serial optical coherence microscopy for label-free volumetric histopathology.

The observation of histopathology using optical microscope is an essential procedure for examination of tissue biopsies or surgically excised specimens in biological and clinical laboratories. However, slide-based microscopic pathology is not suitable for visualizing the large-scale tissue and native 3D organ structure due to its sampling limitation and shallow imaging depth. Here, we demonstrate serial optical coherence microscopy (SOCM) technique that offers label-free, high-throughput, and large-volume imaging of ex vivo mouse organs. A 3D histopathology of whole mouse brain and kidney including blood vessel structure is reconstructed by deep tissue optical imaging in serial sectioning techniques. Our results demonstrate that SOCM has unique advantages as it can visualize both native 3D structures and quantitative regional volume without introduction of any contrast agents.

TonEBP in dendritic cells mediates pro-inflammatory maturation and Th1/Th17 responses.

Dendritic cells (DCs) are potent antigen-presenting cells that link the innate and adaptive immune responses; as such they play pivotal roles in initiation and progression of rheumatoid arthritis (RA). Here, we report that the tonicity-responsive enhancer-binding protein (TonEBP or NFAT5), a Rel family protein involved in the pathogenesis of autoimmune disease and inflammation, is required for maturation and function of DCs. Myeloid cell-specific TonEBP deletion reduces disease severity in a murine model of collagen-induced arthritis; it also inhibits maturation of DCs and differentiation of pathogenic Th1 and Th17 cells in vivo. Upon stimulation by TLR4, TonEBP promotes surface expression of major histocompatibility complex class II and co-stimulatory molecules via p38 mitogen-activated protein kinase. This is followed by DC-mediated differentiation of pro-inflammatory Th1 and Th17 cells. Taken together, these findings provide mechanistic basis for the pathogenic role of TonEBP in RA and possibly other autoimmune diseases.

Tonicity-responsive enhancer-binding protein promotes stemness of liver cancer and cisplatin resistance.

BACKGROUND: High recurrence and chemoresistance drive the high mortality in hepatocellular carcinoma (HCC). Although cancer stem cells are considered to be the source of recurrent and chemoresistant tumors, they remain poorly defined in HCC. Tonicity-responsive enhancer binding protein (TonEBP) is elevated in almost all HCC tumors and associated with recurrence and death. We aimed to identify function of TonEBP in stemness and chemoresistance of liver cancer. METHODS: Tumors obtained from 280 HCC patients were analyzed by immunohistochemical analyses. Stemness and chemoresistance of liver CSCs (LCSCs) were investigated using cell culture. Tumor-initiating activity was measured by implanting LCSCs into BALB/c nude mice. FINDINGS: Expression of TonEBP is higher in LCSCs in HCC cell lines and correlated with markers of LCSCs whose expression is significantly associated with poor prognosis of HCC patients. TonEBP mediates ATM-mediated activation of NF-κB, which stimulates the promoter of a key stem cell transcription factor SOX2. As expected, TonEBP is required for the tumorigenesis and self-renewal of LSCSs. Cisplatin induces the recruitment of the ERCC1/XPF dimer to the chromatin in a TonEBP-dependent manner leading to DNA repair and cisplatin resistance. The cisplatin-induced inflammation in LSCSs is also dependent on the TonEBP-ERCC1/XPF complex, and leads to enhanced stemness via the ATM-NF-κB-SOX2 pathway. In HCC patients, tumor expression of ERCC1/XPF predicts recurrence and death in a TonEBP-dependent manner. INTERPRETATION: TonEBP promotes stemness and cisplatin resistance of HCC via ATM-NF-κB. TonEBP is a key regulator of LCSCs and a promising therapeutic target for HCC and its recurrence.

Transcriptional Regulator TonEBP Mediates Oxidative Damages in Ischemic Kidney Injury.

TonEBP (tonicity-responsive enhancer binding protein) is a transcriptional regulator whose expression is elevated in response to various forms of stress including hyperglycemia, inflammation, and hypoxia. Here we investigated the role of TonEBP in acute kidney injury (AKI) using a line of TonEBP haplo-deficient mice subjected to bilateral renal ischemia followed by reperfusion (I/R). In the TonEBP haplo-deficient animals, induction of TonEBP, oxidative stress, inflammation, cell death, and functional injury in the kidney in response to I/R were all reduced. Analyses of renal transcriptome revealed that genes in several cellular pathways including peroxisome and mitochondrial inner membrane were suppressed in response to I/R, and the suppression was relieved in the TonEBP deficiency. Production of reactive oxygen species (ROS) and the cellular injury was reproduced in a renal epithelial cell line in response to hypoxia, ATP depletion, or hydrogen peroxide. The knockdown of TonEBP reduced ROS production and cellular injury in correlation with increased expression of the suppressed genes. The cellular injury was also blocked by inhibitors of necrosis. These results demonstrate that ischemic insult suppresses many genes involved in cellular metabolism leading to local oxidative stress by way of TonEBP induction. Thus, TonEBP is a promising target to prevent AKI.

TonEBP Regulates PCNA Polyubiquitination in Response to DNA Damage through Interaction with SHPRH and USP1.

Polyubiquitination of proliferating cell nuclear antigen (PCNA) regulates the error-free template-switching mechanism for the bypass of DNA lesions during DNA replication. PCNA polyubiquitination is critical for the maintenance of genomic integrity; however, the underlying mechanism is poorly understood. Here, we demonstrate that tonicity-responsive enhancer-binding protein (TonEBP) regulates PCNA polyubiquitination in response to DNA damage. TonEBP was recruited to DNA damage sites with bulky adducts and sequentially recruited E3 ubiquitin ligase SHPRH, followed by deubiquitinase USP1, to DNA damage sites, in correlation with the dynamics of PCNA polyubiquitination. Similarly, TonEBP was found to be required for replication fork protection in response to DNA damage. The Rel-homology domain of TonEBP, which encircles DNA, was essential for the interaction with SHPRH and USP1, PCNA polyubiquitination, and cell survival after DNA damage. The present findings suggest that TonEBP is an upstream regulator of PCNA polyubiquitination and of the DNA damage bypass pathway.