Katerina Leonova - Academia.edu (original) (raw)
Papers by Katerina Leonova
Experimental and Molecular Therapeutics
Experimental and Molecular Therapeutics
Cell Metabolism
Highlights d SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway d ... more Highlights d SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway d Wild-type aged mice accumulate L1 cDNA and display type I interferon response d Reverse-transcriptase inhibitors rescue type I interferon response and DNA damage d Reverse-transcriptase inhibitors extend lifespan and improve health of SIRT6 KO mice
The Journal of clinical investigation, 2018
Polyamine inhibition for cancer therapy is, conceptually, an attractive approach but has yet to m... more Polyamine inhibition for cancer therapy is, conceptually, an attractive approach but has yet to meet success in the clinical setting. The aryl hydrocarbon receptor (AHR) is the central transcriptional regulator of the xenobiotic response. Our study revealed that AHR also positively regulates intracellular polyamine production via direct transcriptional activation of 2 genes, ODC1 and AZIN1, which are involved in polyamine biosynthesis and control, respectively. In patients with multiple myeloma (MM), AHR levels were inversely correlated with survival, suggesting that AHR inhibition may be beneficial for the treatment of this disease. We identified clofazimine (CLF), an FDA-approved anti-leprosy drug, as a potent AHR antagonist and a suppressor of polyamine biosynthesis. Experiments in a transgenic model of MM (Vk*Myc mice) and in immunocompromised mice bearing MM cell xenografts revealed high efficacy of CLF comparable to that of bortezomib, a first-in-class proteasome inhibitor use...
Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly el... more Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly elevated LINE1 (L1) activity. Here we report that SIRT6 deficient cells and tissues accumulate abundant cytoplasmic L1 cDNA which triggers massive type I interferon response via activation of cGAS. Remarkably, nucleoside reverse transcriptase inhibitors (NRTIs), which inhibit L1 retrotransposition, significantly improved health and lifespan of SIRT6 knockout mice and completely rescued type I interferon response. In tissue culture, inhibition of L1 with siRNA or NRTIs abrogated type I interferon response, in addition to a significant reduction of DNA damage markers. These results indicate that L1 activation contributes to the pathologies of SIRT6 knockout mice. Similarly, L1 transcription, cytoplasmic cDNA copy number and type I interferons were elevated in the wild type aged mice. As sterile inflammation is a hallmark of aging we propose that modulating L1 activity may be an important str...
eLife, Jan 5, 2018
Cellular responses to the loss of genomic stability are well-established, while how mammalian cel... more Cellular responses to the loss of genomic stability are well-established, while how mammalian cells respond to chromatin destabilization is largely unknown. We previously found that DNA demethylation on p53-deficient background leads to transcription of repetitive heterochromatin elements, followed by an interferon response, a phenomenon we named TRAIN (Transcription of Repeats Activates INterferon). Here, we report that curaxin, an anticancer small molecule, destabilizing nucleosomes via disruption of histone/DNA interactions, also induces TRAIN. Furthermore, curaxin inhibits oncogene-induced transformation and tumor growth in mice in an interferon-dependent manner, suggesting that anticancer activity of curaxin, previously attributed to p53-activation and NF-kappaB-inhibition, may also involve induction of interferon response to epigenetic derepression of the cellular 'repeatome'. Moreover, we observed that another type of drugs decondensing chromatin, HDAC inhibitor, also...
Aging
Constitutive p16 Ink4a expression, along with senescence-associated β-galactosidase (SAβG), are c... more Constitutive p16 Ink4a expression, along with senescence-associated β-galactosidase (SAβG), are commonly accepted biomarkers of senescent cells (SCs). Recent reports attributed improvement of the healthspan of aged mice following p16 Ink4a-positive cell killing to the eradication of accumulated SCs. However, detection of p16 Ink4a /SAβG-positive macrophages in the adipose tissue of old mice and in the peritoneal cavity of young animals following injection of alginate-encapsulated SCs has raised concerns about the exclusivity of these markers for SCs. Here we report that expression of p16 Ink4a and SAβG in macrophages is acquired as part of a physiological response to immune stimuli rather than through senescence, consistent with reports that p16 Ink4a plays a role in macrophage polarization and response. Unlike SCs, p16 Ink4a /SAβG-positive macrophages can be induced in p53-null mice. Macrophages, but not mesenchymal SCs, lose both markers in response to M1-[LPS, IFN-α, Poly(I:C)] and increase their expression in response to M2-inducing stimuli (IL-4, IL-13). Moreover, interferon-inducing agent Poly(I:C) dramatically reduced p16 Ink4a expression in vivo in our alginate bead model and in the adipose tissue of aged mice. These observations suggest that the antiaging effects following eradication of p16 Ink4a-positive cells may not be solely attributed to SCs but also to non-senescent p16 Ink4a /SAβG-positive macrophages.
Aging, 2017
The development of healthspan-extending pharmaceuticals requires quantitative estimation of age-r... more The development of healthspan-extending pharmaceuticals requires quantitative estimation of age-related progressive physiological decline. In humans, individual health status can be quantitatively assessed by means of a frailty index (FI), a parameter which reflects the scale of accumulation of age-related deficits. However, adaptation of this methodology to animal models is a challenging task since it includes multiple subjective parameters. Here we report a development of a quantitative non-invasive procedure to estimate biological age of an individual animal by creating physiological frailty index (PFI). We demonstrated the dynamics of PFI increase during chronological aging of male and female NIH Swiss mice. We also demonstrated acceleration of growth of PFI in animals placed on a high fat diet, reflecting aging acceleration by obesity and provide a tool for its quantitative assessment. Additionally, we showed that PFI could reveal anti-aging effect of mTOR inhibitor rapatar (bioavailable formulation of rapamycin) prior to registration of its effects on longevity. PFI revealed substantial sex-related differences in normal chronological aging and in the efficacy of detrimental (high fat diet) or beneficial (rapatar) aging modulatory factors. Together, these data introduce PFI as a reliable, noninvasive, quantitative tool suitable for testing potential anti-aging pharmaceuticals in pre-clinical studies.
Methods in molecular biology (Clifton, N.J.), 2017
Metabolic flux analysis (MFA) is a comprehensive technique that allows researchers to create a ma... more Metabolic flux analysis (MFA) is a comprehensive technique that allows researchers to create a map of cellular metabolic state. This method is extensively studied in the literature in the context of the metabolism of various cancer cells, and it normally utilizes a labeled substrate that is absorbed by the cells, the levels of the incorporation are measured by mass spectrometry (MS) within the pool of metabolites and computational estimation is performed. Here, we propose the use of this assay to study metabolic changes that occur in oncogene-induced senescence (OIS) of normal human fibroblasts (Wi38) versus those in the state of proliferation/quiescence.
Aging, 2016
Senescent cells (SCs) have been considered a source of age-related chronic sterile systemic infla... more Senescent cells (SCs) have been considered a source of age-related chronic sterile systemic inflammation and a target for anti-aging therapies. To understand mechanisms controlling the amount of SCs, we analyzed the phenomenon of rapid clearance of human senescent fibroblasts implanted into SCID mice, which can be overcome when SCs were embedded into alginate beads preventing them from immunocyte attack. To identify putative SC killers, we analyzed the content of cell populations in lavage and capsules formed around the SC-containing beads. One of the major cell types attracted by secretory factors of SCs was a subpopulation of macrophages characterized by p16(Ink4a) gene expression and β-galactosidase activity at pH6.0 (β-gal(pH6)), thus resembling SCs. Consistently, mice with p16(Ink4a) promoter-driven luciferase, developed bright luminescence of their peritoneal cavity within two weeks following implantation of SCs embedded in alginate beads. p16(Ink4a)/β-gal(pH6)-expressing cell...
Proceedings of the National Academy of Sciences, 2015
Recent studies have demonstrated abundant transcription of a set of noncoding RNAs (ncRNAs) prefe... more Recent studies have demonstrated abundant transcription of a set of noncoding RNAs (ncRNAs) preferentially within tumors as opposed to normal tissue. Using an approach from statistical physics, we quantify global transcriptome-wide motif use for the first time, to our knowledge, in human and murine ncRNAs, determining that most have motif use consistent with the coding genome. However, an outlier subset of tumor-associated ncRNAs, typically of recent evolutionary origin, has motif use that is often indicative of pathogen-associated RNA. For instance, we show that the tumor-associated human repeat human satellite repeat II (HSATII) is enriched in motifs containing CpG dinucleotides in AU-rich contexts that most of the human genome and human adapted viruses have evolved to avoid. We demonstrate that a key subset of these ncRNAs functions as immunostimulatory “self-agonists” and directly activates cells of the mononuclear phagocytic system to produce proinflammatory cytokines. These nc...
Aging, 2012
The down-regulation of dominant oncogenes, including C-MYC, in tumor cells often leads to the ind... more The down-regulation of dominant oncogenes, including C-MYC, in tumor cells often leads to the induction of senescence via mechanisms that are not completely identified. In the current study, we demonstrate that MYC-depleted melanoma cells undergo extensive DNA damage that is caused by the underexpression of thymidylate synthase (TS) and ribonucleotide reductase (RR) and subsequent depletion of deoxyribonucleoside triphosphate pools. Simultaneous genetic inhibition of TS and RR in melanoma cells induced DNA damage and senescence phenotypes very similar to the ones caused by MYC-depletion. Reciprocally, overexpression of TS and RR in melanoma cells or addition of deoxyribo-nucleosides to culture media substantially inhibited DNA damage and senescence-associated phenotypes caused by C-MYC depletion. Our data demonstrate the essential role of TS and RR in C-MYC-dependent suppression of senescence in melanoma cells.
Proceedings of the National Academy of Sciences, 2013
Large parts of mammalian genomes are transcriptionally inactive and enriched with various classes... more Large parts of mammalian genomes are transcriptionally inactive and enriched with various classes of interspersed and tandem repeats. Here we show that the tumor suppressor protein p53 cooperates with DNA methylation to maintain silencing of a large portion of the mouse genome. Massive transcription of major classes of short, interspersed nuclear elements (SINEs) B1 and B2, both strands of near-centromeric satellite DNAs consisting of tandem repeats, and multiple species of noncoding RNAs was observed in p53-deficient but not in p53 wild-type mouse fibroblasts treated with the DNA demethylating agent 5-aza-2'-deoxycytidine. The abundance of these transcripts exceeded the level of β-actin mRNA by more than 150-fold. Accumulation of these transcripts, which are capable of forming double-stranded RNA (dsRNA), was accompanied by a strong, endogenous, apoptosis-inducing type I IFN response. This phenomenon, which we named "TRAIN" (for "transcription of repeats activates interferon"), was observed in spontaneous tumors in two models of cancer-prone mice, presumably reflecting naturally occurring DNA hypomethylation and p53 inactivation in cancer. These observations suggest that p53 and IFN cooperate to prevent accumulation of cells with activated repeats and provide a plausible explanation for the deregulation of IFN function frequently seen in tumors. Overall, this work reveals roles for p53 and IFN that are key for genetic stability and therefore relevant to both tumorigenesis and the evolution of species. interferon alpha-beta receptor | RNA sequencing | epigenetic repression |
Proceedings of the National Academy of Sciences, 2013
Molecular Cell, 2014
Reactive oxygen species (ROS) activate NF-E2related transcription factor 2 (Nrf2), a key transcri... more Reactive oxygen species (ROS) activate NF-E2related transcription factor 2 (Nrf2), a key transcriptional regulator driving antioxidant gene expression and protection from oxidant injury. Here, we report that in response to elevation of intracellular ROS above a critical threshold, Nrf2 stimulates expression of transcription Kruppel-like factor 9 (Klf9), resulting in further Klf9-dependent increases in ROS and subsequent cell death. We demonstrated that Klf9 independently causes increased ROS levels in various types of cultured cells and in mouse tissues and is required for pathogenesis of bleomycin-induced pulmonary fibrosis in mice. Mechanistically, Klf9 binds to the promoters and alters the expression of several genes involved in the metabolism of ROS, including suppression of thioredoxin reductase 2, an enzyme participating in ROS clearance. Our data reveal an Nrf2-dependent feedforward regulation of ROS and identify Klf9 as a ubiquitous regulator of oxidative stress and lung injury. RESULTS Klf9 Expression Is Induced by Oxidative Stress Recently, we have shown that Klf9 expression is induced by proteotoxic stress (Mannava et al., 2012). To identify other types of stress increasing Klf9 expression, we treated NIH 3T3 mouse fibroblasts for 8 hr with sublethal amounts of chemical agents
Experimental and Molecular Therapeutics
Experimental and Molecular Therapeutics
Cell Metabolism
Highlights d SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway d ... more Highlights d SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway d Wild-type aged mice accumulate L1 cDNA and display type I interferon response d Reverse-transcriptase inhibitors rescue type I interferon response and DNA damage d Reverse-transcriptase inhibitors extend lifespan and improve health of SIRT6 KO mice
The Journal of clinical investigation, 2018
Polyamine inhibition for cancer therapy is, conceptually, an attractive approach but has yet to m... more Polyamine inhibition for cancer therapy is, conceptually, an attractive approach but has yet to meet success in the clinical setting. The aryl hydrocarbon receptor (AHR) is the central transcriptional regulator of the xenobiotic response. Our study revealed that AHR also positively regulates intracellular polyamine production via direct transcriptional activation of 2 genes, ODC1 and AZIN1, which are involved in polyamine biosynthesis and control, respectively. In patients with multiple myeloma (MM), AHR levels were inversely correlated with survival, suggesting that AHR inhibition may be beneficial for the treatment of this disease. We identified clofazimine (CLF), an FDA-approved anti-leprosy drug, as a potent AHR antagonist and a suppressor of polyamine biosynthesis. Experiments in a transgenic model of MM (Vk*Myc mice) and in immunocompromised mice bearing MM cell xenografts revealed high efficacy of CLF comparable to that of bortezomib, a first-in-class proteasome inhibitor use...
Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly el... more Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly elevated LINE1 (L1) activity. Here we report that SIRT6 deficient cells and tissues accumulate abundant cytoplasmic L1 cDNA which triggers massive type I interferon response via activation of cGAS. Remarkably, nucleoside reverse transcriptase inhibitors (NRTIs), which inhibit L1 retrotransposition, significantly improved health and lifespan of SIRT6 knockout mice and completely rescued type I interferon response. In tissue culture, inhibition of L1 with siRNA or NRTIs abrogated type I interferon response, in addition to a significant reduction of DNA damage markers. These results indicate that L1 activation contributes to the pathologies of SIRT6 knockout mice. Similarly, L1 transcription, cytoplasmic cDNA copy number and type I interferons were elevated in the wild type aged mice. As sterile inflammation is a hallmark of aging we propose that modulating L1 activity may be an important str...
eLife, Jan 5, 2018
Cellular responses to the loss of genomic stability are well-established, while how mammalian cel... more Cellular responses to the loss of genomic stability are well-established, while how mammalian cells respond to chromatin destabilization is largely unknown. We previously found that DNA demethylation on p53-deficient background leads to transcription of repetitive heterochromatin elements, followed by an interferon response, a phenomenon we named TRAIN (Transcription of Repeats Activates INterferon). Here, we report that curaxin, an anticancer small molecule, destabilizing nucleosomes via disruption of histone/DNA interactions, also induces TRAIN. Furthermore, curaxin inhibits oncogene-induced transformation and tumor growth in mice in an interferon-dependent manner, suggesting that anticancer activity of curaxin, previously attributed to p53-activation and NF-kappaB-inhibition, may also involve induction of interferon response to epigenetic derepression of the cellular 'repeatome'. Moreover, we observed that another type of drugs decondensing chromatin, HDAC inhibitor, also...
Aging
Constitutive p16 Ink4a expression, along with senescence-associated β-galactosidase (SAβG), are c... more Constitutive p16 Ink4a expression, along with senescence-associated β-galactosidase (SAβG), are commonly accepted biomarkers of senescent cells (SCs). Recent reports attributed improvement of the healthspan of aged mice following p16 Ink4a-positive cell killing to the eradication of accumulated SCs. However, detection of p16 Ink4a /SAβG-positive macrophages in the adipose tissue of old mice and in the peritoneal cavity of young animals following injection of alginate-encapsulated SCs has raised concerns about the exclusivity of these markers for SCs. Here we report that expression of p16 Ink4a and SAβG in macrophages is acquired as part of a physiological response to immune stimuli rather than through senescence, consistent with reports that p16 Ink4a plays a role in macrophage polarization and response. Unlike SCs, p16 Ink4a /SAβG-positive macrophages can be induced in p53-null mice. Macrophages, but not mesenchymal SCs, lose both markers in response to M1-[LPS, IFN-α, Poly(I:C)] and increase their expression in response to M2-inducing stimuli (IL-4, IL-13). Moreover, interferon-inducing agent Poly(I:C) dramatically reduced p16 Ink4a expression in vivo in our alginate bead model and in the adipose tissue of aged mice. These observations suggest that the antiaging effects following eradication of p16 Ink4a-positive cells may not be solely attributed to SCs but also to non-senescent p16 Ink4a /SAβG-positive macrophages.
Aging, 2017
The development of healthspan-extending pharmaceuticals requires quantitative estimation of age-r... more The development of healthspan-extending pharmaceuticals requires quantitative estimation of age-related progressive physiological decline. In humans, individual health status can be quantitatively assessed by means of a frailty index (FI), a parameter which reflects the scale of accumulation of age-related deficits. However, adaptation of this methodology to animal models is a challenging task since it includes multiple subjective parameters. Here we report a development of a quantitative non-invasive procedure to estimate biological age of an individual animal by creating physiological frailty index (PFI). We demonstrated the dynamics of PFI increase during chronological aging of male and female NIH Swiss mice. We also demonstrated acceleration of growth of PFI in animals placed on a high fat diet, reflecting aging acceleration by obesity and provide a tool for its quantitative assessment. Additionally, we showed that PFI could reveal anti-aging effect of mTOR inhibitor rapatar (bioavailable formulation of rapamycin) prior to registration of its effects on longevity. PFI revealed substantial sex-related differences in normal chronological aging and in the efficacy of detrimental (high fat diet) or beneficial (rapatar) aging modulatory factors. Together, these data introduce PFI as a reliable, noninvasive, quantitative tool suitable for testing potential anti-aging pharmaceuticals in pre-clinical studies.
Methods in molecular biology (Clifton, N.J.), 2017
Metabolic flux analysis (MFA) is a comprehensive technique that allows researchers to create a ma... more Metabolic flux analysis (MFA) is a comprehensive technique that allows researchers to create a map of cellular metabolic state. This method is extensively studied in the literature in the context of the metabolism of various cancer cells, and it normally utilizes a labeled substrate that is absorbed by the cells, the levels of the incorporation are measured by mass spectrometry (MS) within the pool of metabolites and computational estimation is performed. Here, we propose the use of this assay to study metabolic changes that occur in oncogene-induced senescence (OIS) of normal human fibroblasts (Wi38) versus those in the state of proliferation/quiescence.
Aging, 2016
Senescent cells (SCs) have been considered a source of age-related chronic sterile systemic infla... more Senescent cells (SCs) have been considered a source of age-related chronic sterile systemic inflammation and a target for anti-aging therapies. To understand mechanisms controlling the amount of SCs, we analyzed the phenomenon of rapid clearance of human senescent fibroblasts implanted into SCID mice, which can be overcome when SCs were embedded into alginate beads preventing them from immunocyte attack. To identify putative SC killers, we analyzed the content of cell populations in lavage and capsules formed around the SC-containing beads. One of the major cell types attracted by secretory factors of SCs was a subpopulation of macrophages characterized by p16(Ink4a) gene expression and β-galactosidase activity at pH6.0 (β-gal(pH6)), thus resembling SCs. Consistently, mice with p16(Ink4a) promoter-driven luciferase, developed bright luminescence of their peritoneal cavity within two weeks following implantation of SCs embedded in alginate beads. p16(Ink4a)/β-gal(pH6)-expressing cell...
Proceedings of the National Academy of Sciences, 2015
Recent studies have demonstrated abundant transcription of a set of noncoding RNAs (ncRNAs) prefe... more Recent studies have demonstrated abundant transcription of a set of noncoding RNAs (ncRNAs) preferentially within tumors as opposed to normal tissue. Using an approach from statistical physics, we quantify global transcriptome-wide motif use for the first time, to our knowledge, in human and murine ncRNAs, determining that most have motif use consistent with the coding genome. However, an outlier subset of tumor-associated ncRNAs, typically of recent evolutionary origin, has motif use that is often indicative of pathogen-associated RNA. For instance, we show that the tumor-associated human repeat human satellite repeat II (HSATII) is enriched in motifs containing CpG dinucleotides in AU-rich contexts that most of the human genome and human adapted viruses have evolved to avoid. We demonstrate that a key subset of these ncRNAs functions as immunostimulatory “self-agonists” and directly activates cells of the mononuclear phagocytic system to produce proinflammatory cytokines. These nc...
Aging, 2012
The down-regulation of dominant oncogenes, including C-MYC, in tumor cells often leads to the ind... more The down-regulation of dominant oncogenes, including C-MYC, in tumor cells often leads to the induction of senescence via mechanisms that are not completely identified. In the current study, we demonstrate that MYC-depleted melanoma cells undergo extensive DNA damage that is caused by the underexpression of thymidylate synthase (TS) and ribonucleotide reductase (RR) and subsequent depletion of deoxyribonucleoside triphosphate pools. Simultaneous genetic inhibition of TS and RR in melanoma cells induced DNA damage and senescence phenotypes very similar to the ones caused by MYC-depletion. Reciprocally, overexpression of TS and RR in melanoma cells or addition of deoxyribo-nucleosides to culture media substantially inhibited DNA damage and senescence-associated phenotypes caused by C-MYC depletion. Our data demonstrate the essential role of TS and RR in C-MYC-dependent suppression of senescence in melanoma cells.
Proceedings of the National Academy of Sciences, 2013
Large parts of mammalian genomes are transcriptionally inactive and enriched with various classes... more Large parts of mammalian genomes are transcriptionally inactive and enriched with various classes of interspersed and tandem repeats. Here we show that the tumor suppressor protein p53 cooperates with DNA methylation to maintain silencing of a large portion of the mouse genome. Massive transcription of major classes of short, interspersed nuclear elements (SINEs) B1 and B2, both strands of near-centromeric satellite DNAs consisting of tandem repeats, and multiple species of noncoding RNAs was observed in p53-deficient but not in p53 wild-type mouse fibroblasts treated with the DNA demethylating agent 5-aza-2'-deoxycytidine. The abundance of these transcripts exceeded the level of β-actin mRNA by more than 150-fold. Accumulation of these transcripts, which are capable of forming double-stranded RNA (dsRNA), was accompanied by a strong, endogenous, apoptosis-inducing type I IFN response. This phenomenon, which we named "TRAIN" (for "transcription of repeats activates interferon"), was observed in spontaneous tumors in two models of cancer-prone mice, presumably reflecting naturally occurring DNA hypomethylation and p53 inactivation in cancer. These observations suggest that p53 and IFN cooperate to prevent accumulation of cells with activated repeats and provide a plausible explanation for the deregulation of IFN function frequently seen in tumors. Overall, this work reveals roles for p53 and IFN that are key for genetic stability and therefore relevant to both tumorigenesis and the evolution of species. interferon alpha-beta receptor | RNA sequencing | epigenetic repression |
Proceedings of the National Academy of Sciences, 2013
Molecular Cell, 2014
Reactive oxygen species (ROS) activate NF-E2related transcription factor 2 (Nrf2), a key transcri... more Reactive oxygen species (ROS) activate NF-E2related transcription factor 2 (Nrf2), a key transcriptional regulator driving antioxidant gene expression and protection from oxidant injury. Here, we report that in response to elevation of intracellular ROS above a critical threshold, Nrf2 stimulates expression of transcription Kruppel-like factor 9 (Klf9), resulting in further Klf9-dependent increases in ROS and subsequent cell death. We demonstrated that Klf9 independently causes increased ROS levels in various types of cultured cells and in mouse tissues and is required for pathogenesis of bleomycin-induced pulmonary fibrosis in mice. Mechanistically, Klf9 binds to the promoters and alters the expression of several genes involved in the metabolism of ROS, including suppression of thioredoxin reductase 2, an enzyme participating in ROS clearance. Our data reveal an Nrf2-dependent feedforward regulation of ROS and identify Klf9 as a ubiquitous regulator of oxidative stress and lung injury. RESULTS Klf9 Expression Is Induced by Oxidative Stress Recently, we have shown that Klf9 expression is induced by proteotoxic stress (Mannava et al., 2012). To identify other types of stress increasing Klf9 expression, we treated NIH 3T3 mouse fibroblasts for 8 hr with sublethal amounts of chemical agents