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Nelson Fausto

Publications and source records attributed to Nelson Fausto.

At least 19 recordsLinked to original sources
PubMed2007

Transforming growth factor-beta differentially regulates oval cell and hepatocyte proliferation.

UNLABELLED: Oval cells are hepatocytic precursors that proliferate in late-stage cirrhosis and that give rise to a subset of human hepatocellular carcinomas. Although liver regeneration typically occurs through replication of existing hepatocytes, oval cells proliferate only when hepatocyte proliferation is inhibited. Transforming growth factor-beta (TGF-beta) is a key inhibitory cytokine for hepatocytes, both in vitro and in vivo. Because TGF-beta levels are elevated in chronic liver injury when oval cells arise, we hypothesized that oval cells may be less responsive to the growth inhibitory effects of this cytokine. To examine TGF-beta signaling in vivo in oval cells, we analyzed livers of rats fed a choline-deficient, ethionine-supplemented (CDE) diet for phospho-Smad2. Phospho-Smad2 was detected in more than 80% of hepatocytes, but staining was substantially reduced in oval cells. Ki67 staining, in contrast, was significantly more common in oval cells than hepatocytes. To understand the inverse relationship between TGF-beta signaling and proliferation in oval cells and hepatocytes, we examined TGF-beta signaling in vitro. TGF-beta caused marked growth inhibition in primary hepatocytes and the AML12 hepatocyte cell line. Two oval cell lines, LE/2 and LE/6, were less responsive. The greater sensitivity of the hepatocytes to TGF-beta-induced growth inhibition may result from the absence of Smad6 in these cells. CONCLUSION: Our results indicate that oval cells, both in vivo and in vitro, are less sensitive to TGF-beta-induced growth inhibition than hepatocytes. These findings further suggest an underlying mechanism for the proliferation of oval cells in an environment inhibitory to hepatocytic proliferation.

Animals↗
PubMed2006

Distinct Wnt signaling pathways have opposing roles in appendage regeneration.

In contrast to mammals, lower vertebrates have a remarkable capacity to regenerate complex structures damaged by injury or disease. This process, termed epimorphic regeneration, involves progenitor cells created through the reprogramming of differentiated cells or through the activation of resident stem cells. Wnt/beta-catenin signaling regulates progenitor cell fate and proliferation during embryonic development and stem cell function in adults, but its functional involvement in epimorphic regeneration has not been addressed. Using transgenic fish lines, we show that Wnt/beta-catenin signaling is activated in the regenerating zebrafish tail fin and is required for formation and subsequent proliferation of the progenitor cells of the blastema. Wnt/beta-catenin signaling appears to act upstream of FGF signaling, which has recently been found to be essential for fin regeneration. Intriguingly, increased Wnt/beta-catenin signaling is sufficient to augment regeneration, as tail fins regenerate faster in fish heterozygous for a loss-of-function mutation in axin1, a negative regulator of the pathway. Likewise, activation of Wnt/beta-catenin signaling by overexpression of wnt8 increases proliferation of progenitor cells in the regenerating fin. By contrast, overexpression of wnt5b (pipetail) reduces expression of Wnt/beta-catenin target genes, impairs proliferation of progenitors and inhibits fin regeneration. Importantly, fin regeneration is accelerated in wnt5b mutant fish. These data suggest that Wnt/beta-catenin signaling promotes regeneration, whereas a distinct pathway activated by wnt5b acts in a negative-feedback loop to limit regeneration.

Adult Stem Cells↗
PubMed2006

Distinct cellular responses differentiating alcohol- and hepatitis C virus-induced liver cirrhosis.

BACKGROUND: Little is known at the molecular level concerning the differences and/or similarities between alcohol and hepatitis C virus induced liver disease. Global transcriptional profiling using oligonucleotide microarrays was therefore performed on liver biopsies from patients with cirrhosis caused by either chronic alcohol consumption or chronic hepatitis C virus (HCV). RESULTS: Global gene expression patterns varied significantly depending upon etiology of liver disease, with a greater number of differentially regulated genes seen in HCV-infected patients. Many of the gene expression changes specifically observed in HCV-infected cirrhotic livers were expectedly associated with activation of the innate antiviral immune response. We also compared severity (CTP class) of cirrhosis for each etiology and identified gene expression patterns that differentiated ethanol-induced cirrhosis by class. CTP class A ethanol-cirrhotic livers showed unique expression patterns for genes implicated in the inflammatory response, including those related to macrophage activation and migration, as well as lipid metabolism and oxidative stress genes. CONCLUSION: Stages of liver cirrhosis could be differentiated based on gene expression patterns in ethanol-induced, but not HCV-induced, disease. In addition to genes specifically regulating the innate antiviral immune response, mechanisms responsible for differentiating chronic liver damage due to HCV or ethanol may be closely related to regulation of lipid metabolism and to effects of macrophage activation on deposition of extracellular matrix components.

Cytokines↗
PubMed2006

Decreased aquaporin expression leads to increased resistance to apoptosis in hepatocellular carcinoma.

Cells undergoing apoptosis are characterized by decreased cell size due to changes in intracellular ion concentration and rapid, aquaporin (AQP)-dependent water movement out of the cell, events required for the activation of pro-apoptotic enzymes. The current study demonstrates AQP 8 and 9 expression is significantly decreased in hepatocellular carcinoma (HCC) versus normal liver. Isolation of hepatic tumor cells (H4IIE) and hepatocytes confirmed a lack of water movement across the H4IIE cell membrane via AQPs and identified an inherent resistance of H4IIE cells to apoptotic stimuli. In contrast, hepatocytes rapidly responded to osmotic challenge through AQP-dependent water movement and underwent cell death following apoptotic stimulation.

Animals↗
PubMed2006

Reactive oxygen species derived from NADPH oxidase system is not essential for liver regeneration after partial hepatectomy.

BACKGROUND: There is suggestive evidence that reactive oxygen species may play a role in the initiation of liver regeneration via a kupffer cell-mediated mechanism involving TNFa and NF-kappa B. In mammalian cells, a major source of reactive oxygen species derives from the membrane-bound NADPH oxidase system (no protein de novo synthesis is required) and it is known that the low levels of oxidants produced through NADPH oxidase play a role in liver cell proliferation because of peroxisome proliferators. METHODS: We used knockout mice lacking Cybb: subunit of NADPH oxidase to determine whether signaling at the start of liver regeneration after partial hepatectomy (PH) involves reactive oxygen species produced through NADPH oxidase and to analyze in more detail the abnormalities caused by lack of its component, which is required for the initiation of liver regeneration. RESULTS: Lack of Cybb had little effect on NF-kappa B and STAT3 binding, and no effect in TNFa and interleukin-6 production after PH. Cybb KO mice had normal liver structure and similar levels of hepatocyte DNA replication as those of wild type mice. CONCLUSIONS: We conclude that NADPH oxidase is not necessary for liver regeneration after PH. It is likely that there is a potential pathway not including NADPH oxidase to activate NF-kappa B and STAT3 binding for the initiation of liver regeneration after PH.

Animals↗
PubMed2006

Acetaminophen-induced liver injury is attenuated in male glutamate-cysteine ligase transgenic mice.

Acetaminophen overdose is a leading cause of drug-related acute liver failure in the United States. Glutathione, a tripeptide antioxidant protects cells against oxidative damage from reactive oxygen species and plays a crucial role in the detoxification of xenobiotics, including acetaminophen. Glutathione is synthesized in a two-step enzymatic reaction. Glutamate-cysteine ligase carries out the rate-limiting and first step in glutathione synthesis. We have generated C57Bl/6 mice that conditionally overexpress glutamate-cysteine ligase, and report here their resistance to acetaminophen-induced liver injury. Indices of liver injury included histopathology and serum alanine aminotransferase activity. Male transgenic mice induced to overexpress glutamate-cysteine ligase exhibited resistance to acetaminophen-induced liver injury when compared with acetaminophen-treated male mice carrying, but not expressing glutamate-cysteine ligase transgenes, or to female glutamate-cysteine ligase transgenic mice. We conclude that glutamate-cysteine ligase activity is an important factor in determining acetaminophen-induced liver injury in C57Bl/6 male mice. Because people are known to vary in their glutamate-cysteine ligase activity, this enzyme may also be an important determinant of sensitivity to acetaminophen-induced liver injury in humans.

Acetaminophen↗
PubMed2006

Reciprocal and coordinate regulation of serum amyloid A versus apolipoprotein A-I and paraoxonase-1 by inflammation in murine hepatocytes.

OBJECTIVE: During inflammation, the serum amyloid A (SAA) content of HDL increases, whereas apolipoprotein A-I (apoA-I) and paraoxonase-1 (PON-1) decrease. It remains unclear whether SAA physically displaces apoA-I or if these changes derive from coordinated but inverse transcriptional regulation of the HDL apolipoprotein genes. Because cytokines stimulate the hepatic expression of inflammatory markers, we investigated their role in regulating SAA, apoA-I, and PON-1 expression. METHODS AND RESULTS: A cytokine mixture (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, and IL-6) simultaneously induced SAA and repressed apoA-I and PON-1 expression levels. These effects were partially inhibited in cells pretreated with either nuclear factor kappaB (NF-kappaB) inhibitors (pyrrolidine dithiocarbamate, SN50, and overexpression of super-repressor inhibitor kappaB) or after exposure to the peroxisome proliferator-activated receptor-alpha (PPARalpha) ligands (WY-14643 and fenofibrate). Consistent with these findings, the basal level of SAA was increased, whereas apoA-I and PON-1 decreased in primary hepatocytes from PPARalpha-deficient mice as compared with wild-type mice. Moreover, neither WY-14643 nor fenofibrate had any effect on SAA, apoA-I, or PON-1 expression in the absence of PPARalpha. CONCLUSIONS: These results suggest that cytokines increase the expression of SAA through NF-kappaB transactivation, while simultaneously decreasing the expression of apoA-I and PON-1 by inhibiting PPARalpha activation. Inflammation may convert HDL de novo into a more proatherogenic form by coordinate but inverse transcriptional regulation in the liver, rather than by physical displacement of apoA-I by SAA.

Animals↗
PubMed2006

Identification of a specific gene expression pattern associated with HCV-induced pathogenesis in HCV- and HCV/HIV-infected individuals.

Gene expression profiling was performed on liver biopsies from 28 patients (12 HCV and 16 HCV/HIV infected) in an attempt to understand the mechanisms of HCV liver disease in the presence and absence of HIV coinfection. The data were compared with clinical observations and a gene expression database obtained for transplant HCV-infected samples. This is the first report of functional genomics being used to compare intrahepatic gene expression profiles of HCV- and HCV/HIV-infected individuals. Significantly, the intrahepatic global gene expression profiles do not differ between HCV- and HCV/HIV-infected individuals. However, a subset of patients was identified who share a specific pattern of gene expression, termed the enhanced gene expression (EGE) pattern. Specifically, the EGE (+) patients show a dramatic decreased expression of multiple genes associated with the FAS-apoptosis pathway and increased expression of lymphocyte adhesion molecules and lymphocyte-specific genes. The EGE (+) patients also have partially impaired Type I and II IFN-mediated antiviral responses, including a lack of induction of the anti-fibrogenic cytokine IFN-gamma. Importantly, the pattern of gene expression observed in EGE (+) patients has similarities to patients who developed fibrosis within 1 year of receiving a liver transplant.

Female↗
PubMed2006

Cytosolic heat shock proteins and heme oxygenase-1 are preferentially induced in response to specific and localized intramitochondrial damage by tetrafluoroethylcysteine.

Previously, S-(1,1,2,2-tetrafluoroethyl)-l-cysteine (TFEC) was shown to mediate cytotoxicity by covalently modifying a well-defined group of intramitochondrial proteins including aconitase, alpha-ketoglutarate dehydrogenase (alphaKGDH) subunits, heat shock protein 60 (HSP60) and mitochondrial HSP70 (mtHSP70). To investigate the cellular responses to this mitochondrial damage, microarray analysis of TFEC treated murine hepatocytes of the TAMH cell line was carried out. Results of these studies revealed a HSP response that was significantly stronger than other well-characterized hepatotoxicants including acetaminophen, diquat and rotenone. Specifically, cytosolic HSP25, HSP40, HSP70, HSP105 and microsomal HSP32 (HO-1) were strongly upregulated within the first few hours of TFEC treatment, while little change was observed among other HSPs that are predominantly localized in the mitochondria and endoplasmic reticulum (ER). Post-translational modification of HSP25 was also observed with the appearance of a unique DTT-resistant immunoreactive band at about 50kDa, a putative dimer. The biological significance of HSP responses to TFEC-induced toxicity were subsequently demonstrated using the "gain of function" pretreatment: heat shock. Overall, we report an atypical HSP induction profile that does not conform to changes expected of a classical temperature shock. Furthermore, despite a well-defined intramitochondrial origin of toxicity, TFEC rapidly evokes an early and strong upregulation of cytosolic stress proteins. The cytoprotective effects of such HSP responses suggest a plausible role in modulating the progression of TFEC-induced cellular injury.

Cell Line↗
PubMed2006

Proinflammatory cytokine production in liver regeneration is Myd88-dependent, but independent of Cd14, Tlr2, and Tlr4.

TNF and IL-6 are considered to be important to the initiation or priming phase of liver regeneration. However, the signaling pathways that lead to the production of these cytokines after partial hepatectomy (PH) have not been identified. Enteric-derived LPS appears to be important to liver regeneration, possibly by stimulating proinflammatory cytokine production after surgery. To determine whether LPS signaling pathways are involved in the regulation of the proinflammatory cytokines TNF and IL-6 during the priming phase of liver regeneration, we performed PH on mice lacking the TLRs Tlr4 and Tlr2, the LPS coreceptor, Cd14, and Myd88, an adapter protein involved in most TLR and IL-1R pathways. In MyD88 knockout (KO) mice after PH, both liver Tnf mRNA and circulating IL-6 levels were severely depressed compared with heterozygous or wild-type mice. Activation of STAT-3 and three STAT-3 responsive genes, Socs3, Cd14, and serum amyloid A2 were also blocked. In contrast, Tlr4, Tlr2, and Cd14 KO mice showed no deficits in the production of IL-6. Surprisingly, none of these KO mice showed any delay in hepatocyte replication. These data indicate that the LPS receptor TLR4, as well as TLR2 and CD14, do not play roles in regulating cytokine production or DNA replication after PH. In contrast, MyD88-dependent pathways appear to be responsible for TNF, IL-6, and their downstream signaling pathways.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Liver regeneration.

During liver regeneration after partial hepatectomy, normally quiescent hepatocytes undergo one or two rounds of replication to restore the liver mass by a process of compensatory hyperplasia. A large number of genes are involved in liver regeneration, but the essential circuitry required for the process may be categorized into three networks: cytokine, growth factor and metabolic. There is much redundancy within each network, and intricate interactions exist between them. Thus, loss of function from a single gene rarely leads to complete blockage of liver regeneration. The innate immune system plays an important role in the initiation of liver regeneration after partial hepatectomy, and new cytokines and receptors that participate in initiation mechanisms have been identified. Hepatocytes primed by these agents readily respond to growth factors and enter the cell cycle. Presumably, the increased metabolic demands placed on hepatocytes of the regenerating liver are linked to the machinery needed for hepatocyte replication, and may function as a sensor that calibrates the regenerative response according to body demands. In contrast to the regenerative process after partial hepatectomy, which is driven by the replication of existing hepatocytes, liver repopulation after acute liver failure depends on the differentiation of progenitor cells. Such cells are also present in chronic liver diseases, but their contribution to the production of hepatocytes in those conditions is unknown. Most of the new knowledge about the molecular and cellular mechanisms of liver regeneration is both conceptually important and directly relevant to clinical problems.

Animals↗
PubMed2006

Gene expression patterns that correlate with hepatitis C and early progression to fibrosis in liver transplant recipients.

BACKGROUND & AIMS: Liver transplant recipients infected with hepatitis C virus (HCV) develop recurrent hepatitis soon after transplantation and, in some cases, progress to fibrosis within the first 2 years. Our goals were to identify molecular processes influencing the liver disease progression and to find potential gene markers of early fibrosis. METHODS: We performed gene expression profiling on serial liver biopsy specimens obtained from 13 (11 infected and 2 uninfected) transplant recipients within the first year after transplantation at 0, 3, 6, and 12 months. The data were compared with clinical observations and with a gene expression database obtained for 55 nontransplant HCV-infected and uninfected liver samples. RESULTS: We identified several specific gene expression patterns. The first pattern was unique for the transplant recipients regardless of their infection status. The corresponding genes encoded stress response proteins and blood proteins involved in coagulation that were differentially expressed in response to posttransplantation graft recovery. The second pattern was specific to HCV-infected samples and included up-regulation of genes encoding components of the interferon-mediated antiviral response and immune system (antigen presentation, cytotoxic response). This up-regulation pattern was absent or suppressed in the patients who developed early fibrosis, indicating that the disease progression might result from an impaired liver response to infection. Finally, we identified gene expression patterns that were specific for 12-month biopsy specimens in all 4 HCV-infected patients who developed early fibrosis. CONCLUSIONS: The identified gene expression patterns may prove useful for diagnostic and prognostic applications in HCV-infected patients, including predicting early progression to fibrosis.

Adult↗
PubMed2005

Effect of ethanol on innate antiviral pathways and HCV replication in human liver cells.

Alcohol abuse reduces response rates to IFN therapy in patients with chronic hepatitis C. To model the molecular mechanisms behind this phenotype, we characterized the effects of ethanol on Jak-Stat and MAPK pathways in Huh7 human hepatoma cells, in HCV replicon cell lines, and in primary human hepatocytes. High physiological concentrations of acute ethanol activated the Jak-Stat and p38 MAPK pathways and inhibited HCV replication in several independent replicon cell lines. Moreover, acute ethanol induced Stat1 serine phosphorylation, which was partially mediated by the p38 MAPK pathway. In contrast, when combined with exogenously applied IFN-alpha, ethanol inhibited the antiviral actions of IFN against HCV replication, involving inhibition of IFN-induced Stat1 tyrosine phosphorylation. These effects of alcohol occurred independently of i) alcohol metabolism via ADH and CYP2E1, and ii) cytotoxic or cytostatic effects of ethanol. In this model system, ethanol directly perturbs the Jak-Stat pathway, and HCV replication. Infection with Hepatitis C virus is a significant cause of morbidity and mortality throughout the world. With a propensity to progress to chronic infection, approximately 70% of patients with chronic viremia develop histological evidence of chronic liver diseases including chronic hepatitis, cirrhosis, and hepatocellular carcinoma. The situation is even more dire for patients who abuse ethanol, where the risk of developing end stage liver disease is significantly higher as compared to HCV patients who do not drink 12.Recombinant interferon alpha (IFN-alpha) therapy produces sustained responses (ie clearance of viremia) in 8-12% of patients with chronic hepatitis C 3. Significant improvements in response rates can be achieved with IFN plus ribavirin combination 456 and pegylated IFN plus ribavirin 78 therapies. However, over 50% of chronically infected patients still do not clear viremia. Moreover, HCV-infected patients who abuse alcohol have extremely low response rates to IFN therapy 9, but the mechanisms involved have not been clarified.MAPKs play essential roles in regulation of differentiation, cell growth, and responses to cytokines, chemokines and stress. The core element in MAPK signaling consists of a module of 3 kinases, named MKKK, MKK, and MAPK, which sequentially phosphorylate each other 10. Currently, four MAPK modules have been characterized in mammalian cells: Extracellular Regulated Kinases (ERK1 and 2), Stress activated/c-Jun N terminal kinase (SAPK/JNK), p38 MAP kinases, and ERK5 11. Interestingly, ethanol modulates MAPKs 12. However, information on how ethanol affects MAPKs in the context of innate antiviral pathways such as the Jak-Stat pathway in human cells is extremely limited. When IFN-alpha binds its receptor, two receptor associated tyrosine kinases, Tyk2 and Jak1 become activated by phosphorylation, and phosphorylate Stat1 and Stat2 on conserved tyrosine residues 13. Stat1 and Stat2 combine with the IRF-9 protein to form the transcription factor interferon stimulated gene factor 3 (ISGF-3), which binds to the interferon stimulated response element (ISRE), and induces transcription of IFN-alpha-induced genes (ISG). The ISGs mediate the antiviral effects of IFN. The transcriptional activities of Stats 1, 3, 4, 5a, and 5b are also regulated by serine phosphorylation 14. Phosphorylation of Stat1 on a conserved serine amino acid at position 727 (S727), results in maximal transcriptional activity of the ISGF-3 transcription factor complex 15. Although cross-talk between p38 MAPK and the Jak-Stat pathway is essential for IFN-induced ISRE transcription, p38 does not participate in IFN induction of Stat1 serine phosphorylation 1416171819. However, cellular stress responses induced by stimuli such as ultraviolet light do induce p38 MAPK mediated Stat1 S727 phosphorylation 18. In the current report, we postulated that alcohol and HCV proteins modulate MAPK and Jak-Stat pathways in human liver cells. To begin to address these issues, we characterized the interaction of acute ethanol on Jak-Stat and MAPK pathways in Huh7 cells, HCV replicon cells lines, and primary human hepatocytes.

Cell Line, Tumor↗
PubMed2005

Nrf2 activation involves an oxidative-stress independent pathway in tetrafluoroethylcysteine-induced cytotoxicity.

Tetrafluoroethylcysteine (TFEC), a metabolite of the industrial gas tetrafluoroethylene, can cause both nephrotoxicity and limited hepatotoxicity in animal models, and this is associated with the covalent modification of specific intramitochondrial proteins including heat shock protein 60 (HSP60), mitochondrial HSP70 (mtHSP70), aspartate aminotransferase (AST), aconitase, and alpha-ketoglutarate dehydrogenase (alphaKGDH). Using the murine TAMH cell line as a useful in vitro model for TFEC toxicity, we demonstrate a rapid and sustained induction of Nrf2, a member of the "cap-and-collar" transcription factor family, following exposure to cytotoxic concentrations of TFEC. A functional correlate was also established with the rapid translocation of cytosolic Nrf2 into the nucleus. In addition, transcriptional and translational upregulation of known Nrf2 regulated genes including glutamate cysteine ligase (GCL), both catalytic and modulatory subunits, heme oxygenase-1, and glutathione S-transferase (GST) isoforms were detected. While Nrf2 activation is often linked to perturbation of cellular thiol status and/or oxidative stress, we were unable to detect any significant depletion of cellular glutathione or oxidation of mitochondrial membrane cardiolipin or increases in reactive oxygen species (ROS). These data suggest Nrf2 activation is likely independent of classical oxidative stress or, at best, a result of a transient, low-level redox stress. Moreover, supporting evidence indicates an early endoplasmic reticular (ER) stress response after TFEC treatment, with a time-dependent upregulation of the ER responsive genes gadd34, gadd45, gadd153, and ndr1 . These findings suggest an alternative pathway for Nrf2 activation, i.e., Nrf2 phosphorylation through ER-mediated protein kinases such as PKR-like endoplasmic reticular kinase (PERK). Overall, the results implicate a role for Nrf2 in the cellular response to TFEC toxicity and suggest a previously unrecognized role for the ER in this model of mitochondrially initiated cytotoxicity.

Adenosine Triphosphate↗
PubMed2005

Platelet-derived growth factor C induces liver fibrosis, steatosis, and hepatocellular carcinoma.

Members of the platelet-derived growth factor (PDGF) ligand family are known to play important roles in wound healing and fibrotic disease. We show that both transient and stable expression of PDGF-C results in the development of liver fibrosis consisting of the deposition of collagen in a pericellular and perivenular pattern that resembles human alcoholic and nonalcoholic fatty liver disease. Fibrosis in PDGF-C transgenic mice, as demonstrated by staining and hydroxyproline content, is preceded by activation and proliferation of hepatic stellate cells, as shown by collagen, alpha-smooth muscle actin and glial fibrillary acidic protein staining and between 8 and 12 months of age is followed by the development of liver adenomas and hepatocellular carcinomas. The hepatic expression of a number of known profibrotic genes, including type beta1 TGF, PDGF receptors alpha and beta, and tissue inhibitors of matrix metalloproteinases-1 and -2, increased by 4 weeks of age. Increased PDGF receptor alpha and beta protein levels were associated with activation of extracellular regulated kinase-1 and -2 and protein kinase B. At 9 months of age, PDGF-C transgenic mice had enlarged livers associated with increased fibrosis, steatosis, cell dysplasia, and hepatocellular carcinomas. These studies indicate that hepatic expression of PDGF-C induces a number of profibrotic pathways, suggesting that this growth factor may act as an initiator of fibrosis. Moreover, PDGF-C transgenic mice represent a unique model for the study of hepatic fibrosis progressing to tumorigenesis.

Animals↗
PubMed2005

BCL-xL overexpression effectively protects against tetrafluoroethylcysteine-induced intramitochondrial damage and cell death.

S-(1,1,2,2-Tetrafluoroethyl)-L-cysteine (TFEC), a major metabolite of the industrial gas tetrafluoroethylene, has been shown to mediate nephrotoxicity by necrosis. TFEC-induced cell death is associated with an early covalent modification of specific intramitochondrial proteins; including aconitase, alpha-ketoglutarate dehydrogenase (KGDH) subunits, HSP60 and HSP70. Previous studies have indicated that the TAMH line accurately models TFEC-induced in vivo cell death with dose- and time-dependent inhibitions of both KGDH and aconitase activities. Here, we show that the molecular pathway leading to TFEC-mediated cell death is associated with an early cytosolic to mitochondrial translocation of BAX, a pro-apoptotic member of the BCL-2 family. Immunoblot analyses indicated movement of BAX (21 kDa) to the mitochondrial fraction after exposure to a cytotoxic concentration of TFEC (250 microM). Subsequent cytochrome c release from mitochondria was also demonstrated, but only a modest increase in caspase activities was observed, suggesting a degeneration of early apoptotic signals into secondary necrosis. Significantly, TAMH cells overexpressing BCL-xL preserved cell viability even to supratoxicological concentrations of TFEC (< or =600 microM), and this cytoprotection was associated with decreased HSP70i upregulation, indicating suppression of TFEC-induced proteotoxicity. Hence, TFEC-induced necrotic cell death in the TAMH cell line is mediated by BAX and antagonized by the anti-apoptotic BCL-2 family member, BCL-xL.

Cell Death↗
PubMed2005

Hepatitis B virus pre-S2 mutant upregulates cyclin A expression and induces nodular proliferation of hepatocytes.

Naturally occurring mutants with a deletion in the pre-S2 region of the large surface protein (Delta S2-LHBs) are prevalent in serum and livers of patients with chronic hepatitis B virus (HBV) infection associated with cirrhosis. The Delta S2-LHBs protein is retained in the endoplasmic reticulum (ER) and may induce ER stress. One interesting observation is the consistently clustered distribution of hepatocytes expressing Delta S2-LHBs. In this study, complementary DNA microarray analysis identified cyclin A and several groups of genes as being significantly upregulated by Delta S2-LHBs in the HuH-7 cell line. This observation was confirmed in liver tissues. The induction of cyclin A expression may occur via the specific transactivator function of Delta S2-LHBs independent of ER stress. In the presence of Delta S2-LHBs, hepatocytes sustained cyclin A expression and cell cycle progression under ER stress and displayed increased BrdU incorporation with multinuclear formation. Furthermore, Delta S2-LHBs could enhance anchorage-independent cell growth in a nontransformed human hepatocyte line and induced nodular proliferation of hepatocytes in transgenic mice. In conclusion, these in vitro and in vivo data support a role for Delta S2-LHBs in the hepatocyte hyperplasia and a likely role in the process of HBV-related tumorigenesis.

Animals↗