Interferon selectively inhibits the expression of mitochondrial genes: a novel pathway for interferon-mediated responses

Uncovering strain- and age-dependent innate immune responses to SARS-CoV-2 infection in air-liquid-interface cultured nasal epithelia

Continuous assessment of the impact of SARS-CoV-2 on the host at the cell-type level is crucial for understanding key mechanisms involved in host defense responses to viral infection. We investigated host response to ancestral-strain and Alpha-variant SARS-CoV-2 infections within air-liquid-interface human nasal epithelial cells from younger adults (26-32 Y) and older children (12-14 Y) using single-cell RNA-sequencing. Ciliated and secretory-ciliated cells formed the majority of highly infected cell-types, with the latter derived from ciliated lineages. Strong innate immune responses were observed across lowly infected and uninfected bystander cells and heightened in Alpha-infection. Alpha highly infected cells showed increased expression of protein-refolding genes compared with ancestral-strain-infected cells in children. Furthermore, oxidative phosphorylation-related genes were down-regulated in bystander cells versus infected and mock-control cells, underscoring the importance of these biological functions for viral replication. Overall, this study highlights the complexity of cell-type-, age- and viral strain-dependent host epithelial responses to SARS-CoV-2.

Baltic Sea coastal sediment-bound eukaryotes have increased year-round activities under predicted climate change related warming

Climate change related warming is a serious environmental problem attributed to anthropogenic activities, causing ocean water temperatures to rise in the coastal marine ecosystem since the last century. This particularly affects benthic microbial communities, which are crucial for biogeochemical cycles. While bacterial communities have received considerable scientific attention, the benthic eukaryotic community response to climate change remains relatively overlooked. In this study, sediments were sampled from a heated (average 5°C increase over the whole year for over 50 years) and a control (contemporary conditions) Baltic Sea bay during four different seasons across a year. RNA transcript counts were then used to investigate eukaryotic community changes under long-term warming. The composition of active species in the heated and control bay sediment eukaryotic communities differed, which was mainly attributed to salinity and temperature. The family level RNA transcript alpha diversity in the heated bay was higher during May but lower in November, compared with the control bay, suggesting altered seasonal activity patterns and dynamics. In addition, structures of the active eukaryotic communities varied between the two bays during the same season. Hence, this study revealed that long-term warming can change seasonality in eukaryotic diversity patterns. Relative abundances and transcript expression comparisons between bays suggested that some taxa that now have lower mRNA transcripts numbers could be favored by future warming. Furthermore, long-term warming can lead to a more active metabolism in these communities throughout the year, such as higher transcript numbers associated with diatom energy production and protein synthesis in the heated bay during winter. In all, these data can help predict how future global warming will affect the ecology and metabolism of eukaryotic community in coastal sediments.

Mitochondrial RNA stimulates beige adipocyte development in young mice

Childhood obesity is a serious public health crisis and a critical factor that determines future obesity prevalence. Signals affecting adipocyte development in early postnatal life have a strong potential to trigger childhood obesity; however, these signals are still poorly understood. We show here that mitochondrial (mt)RNA efflux stimulates transcription of nuclear-encoded genes for mitobiogenesis and thermogenesis in adipocytes of young mice and human infants. While cytosolic mtRNA is a potential trigger of the interferon (IFN) response, young adipocytes lack such a response to cytosolic mtRNA due to the suppression of IFN regulatory factor (IRF)7 expression by vitamin D receptor signalling. Adult and obese adipocytes, however, strongly express IRF7 and mount an IFN response to cytosolic mtRNA. In turn, suppressing IRF7 expression in adult adipocytes restores mtRNA-induced mitobiogenesis and thermogenesis and eventually mitigates obesity. Retrograde mitochondrion-to-nucleus signalling by mtRNA is thus a mechanism to evoke thermogenic potential during early adipocyte development and to protect against obesity.

The immune system as a driver of mitochondrial disease pathogenesis: a review of evidence

BACKGROUND

Genetic mitochondrial diseases represent a significant challenge to human health. These diseases are extraordinarily heterogeneous in clinical presentation and genetic origin, and often involve multi-system disease with severe progressive symptoms. Mitochondrial diseases represent the most common cause of inherited metabolic disorders and one of the most common causes of inherited neurologic diseases, yet no proven therapeutic strategies yet exist. The basic cell and molecular mechanisms underlying the pathogenesis of mitochondrial diseases have not been resolved, hampering efforts to develop therapeutic agents.

MAIN BODY

In recent pre-clinical work, we have shown that pharmacologic agents targeting the immune system can prevent disease in the Ndufs4(KO) model of Leigh syndrome, indicating that the immune system plays a causal role in the pathogenesis of at least this form of mitochondrial disease. Intriguingly, a number of case reports have indicated that immune-targeting therapeutics may be beneficial in the setting of genetic mitochondrial disease. Here, we summarize clinical and pre-clinical evidence suggesting a key role for the immune system in mediating the pathogenesis of at least some forms of genetic mitochondrial disease.

CONCLUSIONS

Significant clinical and pre-clinical evidence indicates a key role for the immune system as a significant in the pathogenesis of at least some forms of genetic mitochondrial disease.

Potential Anticarcinogenic Effects From Plasma of Older Adults After Exercise Training: An Exploratory Study

Aim: To evaluate the impact of exercise training plasma on in vitro prostate cancer cell viability and proliferation.

Methods: PC3 prostate cancer cells were incubated with plasma obtained from young men with high and low physical fitness (PF) (high PF, n = 5; low PF, n = 5) and with the plasma collected from institutionalized older adults (n = 8) before and after multimodal exercise training. Cell viability and proliferation, mitochondria membrane polarization, reactive oxygen species (ROS) generation, and apoptosis were evaluated after the cell treatment with plasma. Systemic cytokines were evaluated in the plasma of institutionalized older adults submitted to an exercise training protocol.

Results: Plasma from high-PF men lowers both cell viability and proliferation after the incubation time. PC3 cells also presented lower cell viability and diminished rates of cell proliferation after the incubation with post-training plasma samples of the older adults. The incubation of PC3 cells with post-training plasma of older adults depolarized the mitochondrial membrane potential and increased mitochondrial reactive oxygen species production. Post-training plasma did not change apoptosis or necrosis rates in the PC3 cell line. Multimodal exercise training increased the plasma levels of IL-2, IL-10, IFN-α, and FGF-1 and decreased TNF-α concentrations in institutionalized older adults.

Conclusion: Adaptations in blood factors of institutionalized older adults may alter cell viability and proliferation by targeting mitochondrial ROS in a prostate cancer cell line.

Immune system cells from COVID-19 patients display compromised mitochondrial-nuclear expression co-regulation and rewiring toward glycolysis

Mitochondria are pivotal for bioenergetics, as well as in cellular response to viral infections. Nevertheless, their role in COVID-19 was largely overlooked. Here, we analyzed available bulk RNA-seq datasets from COVID-19 patients and corresponding healthy controls (three blood datasets, N = 48 healthy, 119 patients; two respiratory tract datasets, N = 157 healthy, 524 patients). We found significantly reduced mtDNA gene expression in blood, but not in respiratory tract samples from patients. Next, analysis of eight single-cells RNA-seq datasets from peripheral blood mononuclear cells, nasopharyngeal samples, and Bronchoalveolar lavage fluid (N = 1,192,243 cells), revealed significantly reduced mtDNA gene expression especially in immune system cells from patients. This is associated with elevated expression of nuclear DNA-encoded OXPHOS subunits, suggesting compromised mitochondrial-nuclear co-regulation. This, together with elevated expression of ROS-response genes and glycolysis enzymes in patients, suggest rewiring toward glycolysis, thus generating beneficial conditions for SARS-CoV-2 replication. Our findings underline the centrality of mitochondrial dysfunction in COVID-19.

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mtDNA gene expression is downregulated in COVID-19 blood, but not in respiratory tract

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Decreased mtDNA gene expression disrupts mito-nuclear coordination

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mtDNA is downregulated and rewired toward glycolysis especially in immune system cells

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Mitochondrial dysfunction is central to the etiology of COVID19

Structural characterization of a polysaccharide from Lycium barbarum and its neuroprotective effect against β-amyloid peptide neurotoxicity

A water-soluble polysaccharide, designated as LBP-3, was isolated and purified from Lycium barbarum. Chemical analysis indicated that LBP-3 was composed of arabinose and galactose at a molar ratio of 1.00:1.56. The average molecular weight of LBP-3 was 6.74 × 104 Da. The structural features of LBP-3 were investigated by Fourier-transform infrared spectroscopy (FT-IR), methylation, and nuclear magnetic resonance (NMR). LBP-3 is a highly branched polysaccharide with a backbone of 1, 3-linked β-Galp, which is partially substituted at C-6. The branches contain 1, 5-linked α-Araf, 1, 6-linked β-Galp, 1, 3-linked α-Araf, and 1, 4-linked α-Araf. In vitro studies revealed that LBP-3 induced a concentration-dependent decrease in the levels of Aβ42/Aβ40 in N2a/APP695 cells. Proteomic analysis was conducted to investigate the potential molecular mechanism underlying the neuroprotective effect of LBP-3, and the results suggested that LBP-3 might have the potential for the treatment of AD.

Innate Viral Sensor MDA5 and Coxsackievirus Interplay in Type 1 Diabetes Development

Type 1 diabetes (T1D) is a polygenic autoimmune disease characterized by immune-mediated destruction of insulin-producing β-cells. The concordance rate for T1D in monozygotic twins is ≈30-50%, indicating that environmental factors also play a role in T1D development. Previous studies have demonstrated that enterovirus infections such as coxsackievirus type B (CVB) are associated with triggering T1D. Prior to autoantibody development in T1D, viral RNA and antibodies against CVB can be detected within the blood, stool, and pancreata. An innate pathogen recognition receptor, melanoma differentiation-associated protein 5 (MDA5), which is encoded by the IFIH1 gene, has been associated with T1D onset. It is unclear how single nucleotide polymorphisms in IFIH1 alter the structure and function of MDA5 that may lead to exacerbated antiviral responses contributing to increased T1D-susceptibility. Binding of viral dsRNA via MDA5 induces synthesis of antiviral proteins such as interferon-alpha and -beta (IFN-α/β). Viral infection and subsequent IFN-α/β synthesis can lead to ER stress within insulin-producing β-cells causing neo-epitope generation, activation of β-cell-specific autoreactive T cells, and β-cell destruction. Therefore, an interplay between genetics, enteroviral infections, and antiviral responses may be critical for T1D development.

Interferon alpha: The key trigger of type 1 diabetes

IFNα is a cytokine essential to a vast array of immunologic processes. Its induction early in the innate immune response provides a priming mechanism that orchestrates numerous subsequent pathways in innate and adaptive immunity. Despite its beneficial effects in viral infections IFNα has been reported to be associated with several autoimmune diseases including autoimmune thyroid disease, systemic lupus erythematosus, rheumatoid arthritis, primary biliary cholangitis, and recently emerged as a major cytokine that triggers Type 1 Diabetes. In this review, we dissect the role of IFNα in T1D, focusing on the potential pathophysiological mechanisms involved. Evidence from human and mouse studies indicates that IFNα plays a key role in enhancing islet expression of HLA-I in patients with T1D, thereby increasing autoantigen presentation and beta cell activation of autoreactive cytotoxic CD8 T-lymphocytes. The binding of IFNα to its receptor induces the secretion of chemokines, attracting monocytes, T lymphocytes, and NK cells to the infected tissue triggering autoimmunity in susceptible individuals. Furthermore, IFNα impairs insulin production through the induction of endoplasmic reticulum stress as well as by impairing mitochondrial function. Due to its central role in the early phases of beta cell death, targeting IFNα and its pathways in genetically predisposed individuals may represent a potential novel therapeutic strategy in the very early stages of T1D.

PRDM16 represses the type I interferon response in adipocytes to promote mitochondrial and thermogenic programing

Brown adipose has the potential to counteract obesity, and thus, identifying signaling pathways that regulate the activity of this tissue is of great clinical interest. PRDM16 is a transcription factor that activates brown fat-specific genes while repressing white fat and muscle-specific genes in adipocytes. Whether PRDM16 also controls other gene programs to regulate adipocyte function was unclear. Here, we identify a novel role for PRDM16 in suppressing type I interferon (IFN)-stimulated genes (ISGs), including Stat1, in adipocytes in vitro and in vivo Ectopic activation of type I IFN signaling in brown adipocytes induces mitochondrial dysfunction and reduces uncoupling protein 1 (UCP1) expression. Prdm16-deficient adipose displays an exaggerated response to type I IFN, including higher STAT1 levels and reduced mitochondrial gene expression. Mechanistically, PRDM16 represses ISGs through binding to promoter regions of these genes and blocking the activating function of IFN regulatory factor 1 (IRF1). Together, these data indicate that PRDM16 diminishes responsiveness to type I IFN in adipose cells to promote thermogenic and mitochondrial function.

Human Cytomegalovirus Infection Upregulates the Mitochondrial Transcription and Translation Machineries

Infection with human cytomegalovirus (HCMV) profoundly affects cellular metabolism. Like in tumor cells, HCMV infection increases glycolysis, and glucose carbon is shifted from the mitochondrial tricarboxylic acid cycle to the biosynthesis of fatty acids. However, unlike in many tumor cells, where aerobic glycolysis is accompanied by suppression of mitochondrial oxidative phosphorylation, HCMV induces mitochondrial biogenesis and respiration. Here, we affinity purified mitochondria and used quantitative mass spectrometry to determine how the mitochondrial proteome changes upon HCMV infection. We found that the mitochondrial transcription and translation systems are induced early during the viral replication cycle. Specifically, proteins involved in biogenesis of the mitochondrial ribosome were highly upregulated by HCMV infection. Inhibition of mitochondrial translation with chloramphenicol or knockdown of HCMV-induced ribosome biogenesis factor MRM3 abolished the HCMV-mediated increase in mitochondrially encoded proteins and significantly impaired viral growth under bioenergetically restricting conditions. Our findings demonstrate how HCMV manipulates mitochondrial biogenesis to support its replication.

IMPORTANCE

Human cytomegalovirus (HCMV), a betaherpesvirus, is a leading cause of morbidity and mortality during congenital infection and among immunosuppressed individuals. HCMV infection significantly changes cellular metabolism. Akin to tumor cells, in HCMV-infected cells, glycolysis is increased and glucose carbon is shifted from the tricarboxylic acid cycle to fatty acid biosynthesis. However, unlike in tumor cells, HCMV induces mitochondrial biogenesis even under aerobic glycolysis. Here, we have affinity purified mitochondria and used quantitative mass spectrometry to determine how the mitochondrial proteome changes upon HCMV infection. We find that the mitochondrial transcription and translation systems are induced early during the viral replication cycle. Specifically, proteins involved in biogenesis of the mitochondrial ribosome were highly upregulated by HCMV infection. Inhibition of mitochondrial translation with chloramphenicol or knockdown of HCMV-induced ribosome biogenesis factor MRM3 abolished the HCMV-mediated increase in mitochondrially encoded proteins and significantly impaired viral growth. Our findings demonstrate how HCMV manipulates mitochondrial biogenesis to support its replication.

Interferons, signal transduction pathways, and the central nervous system

The interferon (IFN) family of cytokines participates in the development of innate and acquired immune defenses against various pathogens and pathogenic stimuli. Discovered originally as a proteinaceous substance secreted from virus-infected cells that afforded immunity to neighboring cells from virus infection, these cytokines are now implicated in various human pathologies, including control of tumor development, cell differentiation, and autoimmunity. It is now believed that the IFN system (IFN genes and the genes induced by them, and the factors that regulate these processes) is a generalized alarm of cellular stress, including DNA damage. IFNs exert both beneficial and deleterious effects on the central nervous system (CNS). Our knowledge of the IFN-regulated processes in the CNS is far from being clear. In this article, we reviewed the current understanding of IFN signal transduction pathways and gene products that might have potential relevance to diseases of the CNS.

Human polynucleotide phosphorylase (hPNPaseold-35): should I eat you or not--that is the question?

RNA degradation plays a fundamental role in maintaining cellular homeostasis whether it occurs as a surveillance mechanism eliminating aberrant mRNAs or during RNA processing to generate mature transcripts. 3'-5' exoribonucleases are essential mediators of RNA decay pathways, and one such evolutionarily conserved enzyme is polynucleotide phosphorylase (PNPase). The human homologue of this fascinating enzymatic protein (hPNPaseold-35) was cloned a decade ago in the context of terminal differentiation and senescence through a novel "overlapping pathway screening" approach. Since then, significant insights have been garnered about this exoribonuclease and its repertoire of expanding functions. The objective of this review is to provide an up-to-date perspective of the recent discoveries made relating to hPNPaseold-35 and the impact they continue to have on our comprehension of its expanding and diverse array of functions.

Multi-tasking: nuclear transcription factors with novel roles in the mitochondria

Coordinated responses between the nucleus and mitochondria are essential for the maintenance of homeostasis. For over 15 years, pools of nuclear transcription factors (TFs), such as p53 and nuclear hormone receptors, have been observed in the mitochondria. The contribution of the mitochondrial pool of these TFs to their well-defined biological actions is in some cases clear and in others not well understood. Recently, a small mitochondrial pool of the TF signal transducer and activator of transcription factor 3 (STAT3) was shown to modulate the activity of the electron transport chain (ETC). The mitochondrial function of STAT3 encompasses both its biological actions in the heart as well as its oncogenic effects. This review highlights advances in our understanding of how mitochondrial pools of nuclear TFs may influence the function of this organelle.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

Mitochondrial involvement in drug-induced liver injury

Mitochondrial dysfunction is a major mechanism of liver injury. A parent drug or its reactive metabolite can trigger outer mitochondrial membrane permeabilization or rupture due to mitochondrial permeability transition. The latter can severely deplete ATP and cause liver cell necrosis, or it can instead lead to apoptosis by releasing cytochrome c, which activates caspases in the cytosol. Necrosis and apoptosis can trigger cytolytic hepatitis resulting in lethal fulminant hepatitis in some patients. Other drugs severely inhibit mitochondrial function and trigger extensive microvesicular steatosis, hypoglycaemia, coma, and death. Milder and more prolonged forms of drug-induced mitochondrial dysfunction can also cause macrovacuolar steatosis. Although this is a benign liver lesion in the short-term, it can progress to steatohepatitis and then to cirrhosis. Patient susceptibility to drug-induced mitochondrial dysfunction and liver injury can sometimes be explained by genetic or acquired variations in drug metabolism and/or elimination that increase the concentration of the toxic species (parent drug or metabolite). Susceptibility may also be increased by the presence of another condition, which also impairs mitochondrial function, such as an inborn mitochondrial cytopathy, beta-oxidation defect, certain viral infections, pregnancy, or the obesity-associated metabolic syndrome. Liver injury due to mitochondrial dysfunction can have important consequences for pharmaceutical companies. It has led to the interruption of clinical trials, the recall of several drugs after marketing, or the introduction of severe black box warnings by drug agencies. Pharmaceutical companies should systematically investigate mitochondrial effects during lead selection or preclinical safety studies.

Interferon-stimulated gene ISG12b1 inhibits adipogenic differentiation and mitochondrial biogenesis in 3T3-L1 cells

Microarray analysis was performed to find a new group of genes or pathways that might be important in adipocyte development and metabolism. Among them, a mouse interferon-stimulated gene 12b1 (ISG12b1) is expressed at a 400-fold higher level in adipocytes compared with stromal-vascular cells. It is predominantly expressed in adipose tissue among other tissues we tested. Developmentally, ISG12b1 mRNA expression was initially inhibited followed by a dramatic induction during both in vivo and in vitro adipogenic differentiation. Adenovirus-mediated overexpression of ISG12b1 inhibited adipogenic differentiation in 3T3-L1 cells as shown by decreased lipid staining with Oil-Red-O and reduction in adipogenic marker proteins including peroxisome proliferator-activated receptor-gamma (PPARgamma), and CCAAT/enhancer-binding protein-alpha (C/EBPalpha). Our bioinformatics analysis for the predicted localization of ISG12b1 protein suggested the mitochondrial localization, which was confirmed by the colocalization of hemagglutinin-tagged ISG12b1 protein with mitochondrial marker MitoTracker. In addition, ISG12b1 protein was exclusively detected in protein extract from the fractionated mitochondria by Western blot analysis. Furthermore, overexpression of ISG12b1 in adipocytes reduced mitochondrial DNA content and gene expression of mitochondrial transcription factor A (mtTFA), nuclear respiratory factor 1 (NRF1), and cytochrome oxidase II, suggesting an inhibitory role of ISG12b1 in mitochondrial biogenesis and function. Activation of mitochondrial biogenesis and function by treatment with PPARgamma and PPARalpha agonists in 3T3-L1 cells and cold exposure in mice induced mitochondrial transcription factors and reduced ISG12 expression. These data demonstrated that mitochondrial-localized ISG12b1 protein inhibits adipocyte differentiation and mitochondrial biogenesis and function, implying the important role of mitochondrial function in adipocyte development and associated diseases.

Response characteristics of the mitochondrial DNA genome in developmental health and disease

This review focuses on mitochondrial biology in mammalian development; specifically, the dynamics of information transfer from nucleus to mitochondrion in the regulation of mitochondrial DNA genomic expression, and the reverse signaling of mitochondrion to nucleus as an adaptive response to the environment. Data from recent studies suggest that the capacity of embryonic cells to react to oxygenation involves a tradeoff between factors that influence prenatal growth/development and postnatal growth/function. For example, mitochondrial DNA replication and metabolic set points in nematodes may be determined by mitochondrial activity early in life. The mitochondrial drug PK11195, a ligand of the peripheral benzodiazepine receptor, has antiteratogenic and antidisease action in several developmental contexts in mice. Protein malnutrition during early life in rats can program mitochondrial DNA levels in adult tissues and, in humans, epidemiological data suggest an association between impaired fetal growth and insulin resistance. Taken together, these findings raise the provocative hypothesis that environmental programming of mitochondrial status during early life may be linked with diseases that manifest during adulthood. Genetic defects that affect mitochondrial function may involve the mitochondrial DNA genome directly (maternal inheritance) or indirectly (Mendelian inheritance) through nuclear-coded mitochondrial proteins. In a growing number of cases, the depletion of, or deletion in, mitochondrial DNA is seen to be secondary to mutation of key nuclear-coded mitochondrial proteins that affect mitochondrial DNA replication, expression, or stability. These defects of intergenomic regulation may disrupt the normal cross-talk or structural compartmentation of signals that ultimately regulate mitochondrial DNA integrity and copy number, leading to depletion of mitochondrial DNA.

Altered gene expression in liver from a murine model of hyperhomocysteinemia

Cystathionine beta-synthase (CBS) deficiency causes severe hyperhomocysteinemia and other signs of homocystinuria syndrome, in particular a premature atherosclerosis with multiple thrombosis. However, the molecular mechanisms by which homocysteine could interfere with normal cell function are poorly understood in a whole organ like the liver, which is central to the catabolism of homocysteine. We used a combination of differential display and cDNA arrays to analyze differential gene expression in association with elevated hepatic homocysteine levels in CBS-deficient mice, a murine model of hyperhomocysteinemia. Expression of several genes was found to be reproducibly abnormal in the livers of heterozygous and homozygous CBS-deficient mice. We report altered expression of genes encoding ribosomal protein S3a and methylthioadenosine phosphorylase, suggesting such cellular growth and proliferation perturbations may occur in homozygous CBS-deficient mice liver. Many up- or down-regulated genes encoded cytochromes P450, evidence of perturbations of the redox potential in heterozygous and homozygous CBS-deficient mice liver. The expression of various genes involved in severe oxidative processes was also abnormal in homozygous CBS-deficient mice liver. Among them, the expression of heme oxygenase 1 gene was increased, concomitant with overexpression of heme oxygenase 1 at the protein level. Commensurate with the difference in hepatic mRNA paraoxonase 1 abundance, the mean hepatic activity of paraoxonase 1, an enzyme that protects low density lipoprotein from oxidation, was 3-fold lower in homozygous CBS-deficient mice. Heterozygous CBS-deficient mice, when fed a hyperhomocysteinemic diet, have also reduced PON1 activity, which demonstrates the effect of hyperhomocysteinemia in the paraoxonase 1 activity.

Human polynucleotide phosphorylase, hPNPase, is localized in mitochondria

The human gene encoding a polynucleotide phosphorylase (hPNPase) has been recently identified as strongly up-regulated in two processes leading to irreversible arrest of cell division: progeroid senescence and terminal differentiation. Here, we demonstrate that the hPNPase is localized in mitochondria. Our finding suggests the involvement of mitochondrial RNA metabolism in cellular senescence.

Neutralizing interferon alpha as a therapeutic approach to autoimmune diseases

Therapeutic antibodies directed against tumor necrosis factor alpha (TNF-alpha) for the treatment of rheumatoid arthritis, and against the human EGF receptor-2 (HER2) receptor for the treatment of breast cancer have provided significant clinical benefit for the patients. The success of these antibodies has also provided strong support for the possibility that increased activity of cytokines or growth factors is causally implicated in a variety of human diseases. Interferon alpha (IFN-alpha) is induced by viruses (linked by epidemiological studies to autoimmune diseases), has significant direct effects on both epithelial cells and the immune system, and then can be further induced by the autoantibodies and apoptotic cells generated by the actions of IFN-alpha. The direct and deleterious impact on target tissues, the ability to induce an autoimmune response, and the potential for a self-sustaining cycle of induction and damage suggests that IFN-alpha could be a pivotal factor in the development of autoimmune diseases. This review will evaluate the rationale for, possible approaches to, and safety concerns associated with, targeting interferon alpha (IFN-alpha) as a therapeutic strategy for the treatment of autoimmune diseases. While the approach may be applicable to several autoimmune diseases, there will be an emphasis on systemic lupus erythematosus and insulin dependent diabetes mellitus.

Depletion of mitochondrial DNA in the skeletal muscle of two cirrhotic patients with severe asthenia

Qualitative and quantitative alterations of mitochondrial DNA (mtDNA) in the skeletal muscle from two patients with cirrhosis and severe asthenia have been studied. The 4977 bp (mtDNA(4977)) and the 7436 bp (mtDNA(7436)) mtDNA deletions, as well as other mtDNA deletions, revealed by long extension PCR (LX-PCR), were found in the two patients, whereas the 10,422 bp (mtDNA(10,422)) mtDNA deletion was absent. Altogether, the qualitative alterations of mtDNA in cirrhotic patients with severe asthenia were comparable to those of age-matched healthy individuals. The mtDNA content, on the contrary, was substantially decreased in both patients with respect to control. Such mtDNA depletion might be explained by an increased, disease-related, oxidative damage to mtDNA, which probably affects the replication of the mitochondrial genome as already suggested in other oxidative stress-associated diseases.

The 2-5A/RNase L/RNase L inhibitor (RLI) [correction of (RNI)] pathway regulates mitochondrial mRNAs stability in interferon alpha-treated H9 cells

Interferon alpha (IFNalpha) belongs to a cytokine family that exhibits antiviral properties, immuno-modulating effects, and antiproliferative activity on normal and neoplasic cells in vitro and in vivo. IFNalpha exerts antitumor action by inducing direct cytotoxicity against tumor cells. This toxicity is at least partly due to induction of apoptosis. Although the molecular basis of the inhibition of cell growth by IFNalpha is only partially understood, there is a direct correlation between the sensitivity of cells to the antiproliferative action of IFNalpha and the down-regulation of their mitochondrial mRNAs. Here, we studied the role of the 2-5A/RNase L system and its inhibitor RLI in this regulation of the mitochondrial mRNAs by IFNalpha. We found that a fraction of cellular RNase L and RLI is localized in the mitochondria. Thus, we down-regulated RNase L activity in human H9 cells by stably transfecting (i) RNase L antisense cDNA or (ii) RLI sense cDNA constructions. In contrast to control cells, no post-transcriptional down-regulation of mitochondrial mRNAs and no cell growth inhibition were observed after IFNalpha treatment in these transfectants. These results demonstrate that IFNalpha exerts its antiproliferative effect on H9 cells at least in part via the degradation of mitochondrial mRNAs by RNase L.

Preservation of RNA for functional genomic studies: a multidisciplinary tumor bank protocol

Few human tumors are collected such that RNA is preserved for molecular analysis. Completion of the Human Genome Project will soon result in the identification of more than 100,000 new genes. Consequently, increasing attention is being diverted to identifying the function of these newly described genes. Here we describe a multidisciplinary tumor bank procurement protocol that preserves both the integrity of tissue for pathologic diagnosis, and the RNA for molecular analyses. Freshly excised normal skin was obtained from five patients undergoing wound reconstruction following Mohs micrographic surgery for cutaneous neoplasia. Tissues treated for 24 hours with RNAlater were compared histologically and immunohistochemically to tissues not treated with RNAlater. Immunohistochemical stains studied included: CD45, CEA, cytokeratin AE1/3, vimentin, S-100, and CD34 on formalin-fixed, paraffin embedded tissue and CD45 staining of frozen tissue. Slides were blinded and evaluated independently by three pathologists. The histologic and immunohistochemical parameters of tissue stored in RNAlater were indistinguishable from tissue processed in standard fashion with the exception of S-100 stain which failed to identify melanocytes or Langerhan's cells within the epidermis in any of the RNAlater-treated tissues. Interestingly, nerve trunks within the dermis stained appropriately for S-100. Multiple non-cutaneous autopsy tissues were treated with RNAlater, formalin, liquid nitrogen (LN2), and TRIzol Reagent. The pathologists were unable to distinguish between tissues treated with RNAlater, formalin, or frozen in LN2, but could easily distinguish tissues treated with TRIzol Reagent because of extensive cytolysis. RNA was isolated from a portion of the tissue treated with RNAlater and used for molecular studies including Northern blotting and microarray analysis. RNA was adequate for Northern blot analysis and mRNA purified from RNAlater-treated tissues consistently provided excellent templates for reverse transcription and subsequent microarray analysis. We conclude that tissues treated with RNAlater before routine processing are indistinguishable histologically and immunohistochemically from tissues processed in routine fashion and that the RNA isolated from these tissues is of high quality and can be used for molecular studies. Based on this study, we developed a multidisciplinary tumor bank procurement protocol in which fresh tissue from resection specimens are routinely stored in RNAlater at the time of preliminary dissection. Thus, precious human tissue can be utilized for functional genomic studies without compromising the tissue's diagnostic and prognostic qualities.

Alterations in mitochondria and mtTFA in response to LPS-induced differentiation of B-cells

Stimulation of immune cells results in altered cell function and metabolism, which must be recognized by and coordinated with energy production from mitochondria. Mitochondria contain their own DNA genome encoding 13 polypeptides that combine with nuclear-derived subunits to create functional enzyme complexes of the electron transport chain. Therefore, coordination of mitochondrial and nuclear transcription is necessary to achieve a sustained elevation in mitochondrial ATP production. Pre-B-lymphocytes stimulated with lipopolysaccharide exhibit increased activity levels of the mitochondrial enzymes, succinate dehydrogenase and cytochrome c oxidase. Immunoblot analyses of purified mitochondria indicate an increase in the mitochondrial transcription factor (mtTFA) levels in mitochondria induced by cell stimulation. This increase is consistent with increased mtTFA production in the cytoplasm. In addition, mitochondrial protein extracts indicate an increase in protein binding to a mtTFA-DNA binding site from the mitochondrial genome, subsequent to cell stimulation. These results indicate that mitochondrial activity changes during B-lymphocyte stimulation, and mtTFA may contribute to the coordination of respiration with cellular energy demand.

The augmenter of liver regeneration induces mitochondrial gene expression in rat liver and enhances oxidative phosphorylation capacity of liver mitochondria

BACKGROUND

The mammalian augmenter of liver regeneration gene encodes a protein involved in the unique process of liver regeneration. The augmenter of liver regeneration respective protein stimulates hepatocyte proliferation in hepatectomized rats and inhibits cytotoxic activity of liver-derived Natural Killer cells from intact rats. Augmenter of liver regeneration protein shares homology with a Saccharomyces Cerevisiae protein essential for the viability, oxidative phosphorylation and cell-division cycle.

AIMS

To demonstrate if augmenter of liver regeneration protein, like the homologous in the yeast, plays a role in the regulation of biogenesis of mitochondria.

METHODS

Augmenter of liver regeneration protein was injected in intact rats and, in the hepatic tissue, the expression of two genes located in two different regions of the mitochondrial genome, mitochondrial ATPase 6/8, and ND1 subunit, and of a nuclear gene, mitochondrial Transcription Factor A, were considered. In addition, cytochrome content and oxidative phosphorylation capacity of liver-derived mitochondria were evaluated.

RESULTS

The augmenter of liver regeneration protein administration induces an increase in the mitochondrial gene expression and enhances cytochrome content and oxidative phosphorylation capacity of liver-derived mitochondria.

CONCLUSIONS

The present data demonstrate a comparable role in the regulation of mitochondria biogenesis in the eukaryotic cell like the yeast protein. This phenomenon could be part of the complex mechanism through which augmenter of liver regeneration regulates hepatocyte proliferation.

Differential expression of sense and antisense transcripts of the mitochondrial DNA region coding for ATPase 6 in fetal and adult porcine brain: identification of novel unusually assembled mitochondrial RNAs

The mammalian mitochondrial genome is a double-stranded circular DNA molecule, which is transcribed from both strands as polycistronic RNAs, which are further processed to yield the mature polyadenylated mRNAs, rRNAs and tRNAs. We compared the gene expression patterns of foetal and adult porcine brains and identified a sequence tag from the ATPase 6 region of the mitochondrial genome which, in adult brain, was more abundant in the sense (H-strand) form, but, in foetal brain, more abundant in the antisense form (L-strand). By means of solution hybridisation/S1 nuclease protection assay, Northern blotting, and PCR based techniques, we demonstrated that the ATPase 6 region of the porcine mitochondrial genome is transcribed as co-existing, stable sense and antisense RNAs. Furthermore, we identified sense and antisense transcripts from this region consisting of inversely assembled fragments joined together at a direct repeat of 7 nucleotides. Our results suggest that transcription and post-transcriptional processing of mitochondrial RNAs are much more complex than presently thought.

Nitric oxide production and mitochondrial dysfunction during rat thymocyte apoptosis

Production of nitric oxide (NO) by mitochondrial membranes as methemoglobin formation sensitive to N(G)-methyl-l-arginine inhibition and mitochondrial O(2) consumption in metabolic states 3 and 4 and the respiratory control (state 3/state 4) were measured at early stages of rat thymocyte apoptosis. Programmed cell death was induced by addition of methylprednisolone and etoposide to thymocyte suspensions. Increased NO production by mitochondrial membranes was observed after 30 min of methylprednisolone and etoposide addition and was accompanied by mitochondrial respiratory impairment as an early phenomenon in apoptotic thymocytes. The respiratory control in isolated mitochondria from untreated thymocytes was 4.2 +/- 0.2 and decreased to 3.1 +/- 0.2 and 1.9 +/- 0.3 after 1 h of methylprednisolone and etoposide treatment, respectively. The low mitochondrial respiratory control was accompanied by a marked decrease in GSH and cytochrome c content. Moreover, an inhibitory effect in the amount of apoptosis due to thymocyte pretreatment with N(G)-methyl-l-arginine and N(omega)-nitro-(l)-arginine (l-NNA), indicate that nitric oxide production is closely involved in the signaling of rat thymocyte apoptosis.

Oxidative insult specifically decreases levels of a mitochondrial transcript

The effects of oxidative insult, applied with hydrogen peroxide, on gene transcript levels in a human lymphocyte cell line (Molt-17) were investigated using mRNA differential display. Several cDNA fragments corresponding to putatively up- or down-regulated transcripts were isolated. One of these was found to hybridize to two discrete transcripts on Northern blots of Molt-17 cell RNA. The more abundant transcript, that has previously been demonstrated to correspond to the mRNA for mitochondrial ATPase subunits 8 and 6, was unaffected by the hydrogen peroxide treatment. In contrast, levels of the rarer, larger transcript were consistently reduced in a rapid, sustained, and dose-dependent manner following hydrogen peroxide treatment. Prior supplementation of the cells with beta carotene provided some protection against the reduction in levels of this transcript following hydrogen peroxide treatment. In contrast, vitamins C and E had no effect at the concentrations tested. We have now cloned the cDNA corresponding to this stress-responsive transcript and demonstrated that it is an incompletely processed product of the mitochondrial genome encompassing ATPase subunits 8 and 6 plus the adjacent gene for cytochrome c oxidase subunit 3. This decrease in one specific mitochondrial transcript may represent a novel mechanism for differential expression of mitochondrially-encoded genes.

Age-associated changes in mitochondrial mRNA expression and translation in the Wistar rat heart

The purpose of this research is to determine possible causes and mechanisms involved in the age-associated decline in mitochondrial activity. We have focused on cytochrome c oxidase because it is comprised of both nuclear and mitochondrial-encoded subunits and may provide some insight into the coordination of the two genomes. In agreement with previous reports, we show an approximate 30% decrease in cardiac cytochrome c oxidase activity at 24 months compared to 6 months with no change in the activity of the nuclear encoded citrate synthase of the mitochondrial matrix. The rate of the mitochondrial protein synthesis as shown by [35S]methionine incorporation decreased approximately 35% in the 24-month-old rat compared to the 6-month-old rat. The decrease in protein synthesis was associated with a 30-50% reduction in the levels of most individually radiolabeled translation products including the COX subunits and specifically, a 23% decrease in COX1 protein steady-state levels according to Western analysis. Similarly, there was a decrease in the mRNA steady-state levels of both nuclear and mitochondrial-encoded subunits of cytochrome c oxidase. These results suggest that a number of different mechanisms are involved in the age-associated decrease in heart mitochondrial activity and these are discussed.

Isolation and characterization of all-trans-retinoic acid-responsive genes in the rat testis

By way of differential screening of testis cDNA libraries from vitamin A-deficient (VAD) rats before and after administration of all-trans retinoic acid (ATRA), genes, the transcription of which was influenced by ATRA, were isolated. Most clones with an increased transcription encoded different subunits of the same mitochondrial protein complex, cytochrome c oxidase (COX). The mRNA expression of COX increased by a factor 3.9 +/- 1.5 (mean +/- SD, n = 4). This increased expression seems to reflect an increased energy demand in the ATRA-supplemented VAD testis. Also, one gene was isolated, the transcription of which was reduced to about 70% by ATRA. This gene, sulfated glycoprotein 2 (Sgp-2), is a major secretion product of Sertoli cells, the function of which is still unknown. The effect of ATRA on Sgp-2 expression may be direct, since the promoter of Sgp-2 contains a putative ATRA-responsive element (RARE).

Interferons suppress mitochondrial gene transcription by depleting mitochondrial transcription factor A (mtTFA)

Mitochondrial gene transcription activity in organello was suppressed after culturing HeLa cells with 1000 U/ml of interferon-alpha (IFN-alpha) or IFN-gamma for 18 h. The suppression was associated with reduced levels of mitochondrial gene transcripts. Northern blot analysis of HeLa cell RNA showed marked reduction of the mRNA encoding for mitochondrial transcription factor A (mtTFA). Immunoblotting with antiserum directed against recombinant mtTFA showed a reduced level of the protein as well. Consistently, gel-retardation assay of mitochondrial extract showed reduced level of functional mtTFA, which is known to bind to both heavy and light strand promoters of bidirectionally transcribed mitochondrial DNA. We suggest that depletion of mtTFA is a pathway through which IFNs depress the mitochondrial respiration.

2-Chloro-2'-deoxyadenosine, an antileukemic drug, has an early effect on cellular mitochondrial function

2-Chloro-2'-deoxyadenosine [CldAdo (cladribine)], a novel effective antileukemic agent, was examined for its effects on cellular mitochondrial function and DNA content after long term (< or = 7-day) incubation of cultured CCRF-CEM human leukemia cells. Dideoxycytidine (ddC), which is known to have a delayed effect on mitochondrial DNA content, was used as a positive control to monitor mitochondrial dysfunction. CldAdo at 6-16 nM was toxic to cells within 24 hr, which is in contrast to 300 nM ddC, which had no effect on cell growth for the first 4 days of treatment. Cellular lactic acid production was used to monitor concomitant perturbations in oxidative phosphorylation during drug treatment. Unlike the delayed increase in lactate observed with ddC exposure, CldAdo-treated cells exhibited a 2-2.4-fold increase in lactate levels after 2 days of exposure to 16 nM CldAdo. By days 4 and 7, however, lactate production returned to control levels. Shorter incubations with CldAdo revealed that lactate levels began to increase within 12 hr of drug exposure, paralleling cytotoxicity. We also examined mitochondrial DNA content during drug treatment by competitive polymerase chain reaction. ddC (300 nM) reduced mitochondrial DNA levels from approximately 1000 copies/untreated cell to approximately 130 copies/cell after 7 days of exposure. In contrast, cytotoxic doses of CldAdo had little or no effect on mitochondrial DNA content during the 1-week incubation. Thus, the early CldAdo-induced perturbation of mitochondrial function was not associated with a loss of mitochondrial DNA per cell. In addition, no evidence of DNA laddering, indicative of cellular apoptosis, was detected at these dosage levels and treatment times.

Interferon-beta prevents the upregulation of interleukin-8 expression in human melanoma cells

The constitutive expression of interleukin-8 (IL-8) by human melanoma cells correlates with their metastatic potential. The exposure of human melanoma cells to the inflammatory cytokines IL-1 beta or tumor necrosis factor-alpha (TNF-alpha) upregulated IL-8 expression in a time-dependent and concentration-dependent manner. This enhanced expression of IL-8 was inhibited by cycloheximide or actinomycin-D. Treatment of melanoma cells with interferon (IFN) alpha, beta, or gamma did not affect the constitutive expression of IL-8, but IFN-alpha and IFN-beta blocked the upregulation of IL-8 expression in cells treated with IL-1 beta or TNF-alpha subsequent to or simultaneously with the IFN. These data suggest that the expression of IL-8 in human melanoma cells can be upregulated by inflammatory cytokines and that IFN-alpha and IFN-beta can counterregulate this stimulation.

Inhibition of mitochondrial function by interferon

We showed previously that type I interferon causes a down-regulation of mitochondrial gene expression. We show here that IFN treatment leads to functional impairment of mitochondria. Western blot analysis indicated that interferon treatment reduces the steady-state level of cytochrome b in murine L-929 cells. Interferon produced a reduction in cytochrome c oxidase and NADH-cytochrome c reductase activities of isolated mitochondria as well as inhibiting electron transport in isolated mitochondria and in intact cells. Several mitochondrial mRNAs are affected by interferon treatment in human Daudi lymphoblastoid cells, which are highly sensitive to the antiproliferative effects of interferon. Electron transport in Daudi cells was also inhibited by interferon both in intact cells and isolated mitochondria with a dose response identical to that for the antiproliferative response. In contrast, a Daudi strain resistant to the antiproliferative effects of interferon showed no down-regulation of mRNA expression and no inhibition of electron transport. Possibly as a consequence of the inhibitory effect on mitochondrial gene expression, treatment with interferon causes a reduction in cellular ATP levels. The inhibition of cellular growth by interferon may thus be partly a consequence of a reduction in cellular ATP levels.

Effect of interferon therapy on bone marrow morphology in chronic myeloid leukemia: a cytochemical and immunohistochemical study of trephine biopsies

The effect of interferon (IFN) therapy on bone marrow features in chronic myeloid leukemia (CML) has been studied on successive trephine biopsies (mean interval 13 +/- 8 months) by cytochemical and immunohistochemical methods in combination with morphometry and in comparison with a control group of patients who received monotherapy by busulfan (BU). Following IFN administration (IFN-alpha frequently in combination with IFN-gamma), there was a decrease in neutrophil granulopoiesis accompanied by a significant expansion of erythroid precursors and increased numbers of hemosiderin-laden macrophages. These changes corresponded with the hematologic response in 21 of the 25 patients investigated. Numbers of megakaryocytes and reticulin/collagen fiber density increased during treatment. Most conspicuously, in responding patients atypical micromegakaryocytes, usually characterizing CML, were partially replaced by normal-sized cells of this lineage. These features are in keeping with the assumption of a reappearance of the normal hematopoietic cell clone as the result of IFN therapy, which was not found in the BU-treated control group. On the other hand, a relevant subpopulation of micromegakaryocytes (about 30%) was still maintained. This result probably relates to the failure to improve myelofibrosis more effectively. Analysis of cell proliferation (proliferating cell nuclear antigen-PCNA) and apoptosis (in situ end labeling) revealed a reduction in PCNA labeling and increased numbers of cells undergoing programmed death. Identification of the activated subset of macrophages (alpha-D-galactosyl residues expression) by appropriate lectin histochemistry disclosed an increase in the number of GSA-I binding cells. These findings were exclusively limited to IFN administration and reflect an inhibitory effect of IFN on cell proliferation and stimulation of programmed cell death. The latter phenomenon probably results in increased phagocytosis of clonally transformed myeloid cells by GSA-I-positive (activated) macrophages.

Antisense manganese superoxide dismutase mRNA inhibits the antiviral action of interferon-gamma and interferon-alpha

Manganese superoxide dismutase (MnSOD) is induced by interferon-gamma (IFN-gamma) in various cell lines. To determine whether MnSOD plays a role in the antiviral action of IFN-gamma, we employed an antisense strategy to inhibit the expression of MnSOD in the human melanoma cell line, A375. Three antisense-containing clones that exhibited reduced induction of MnSOD were investigated with respect to their response to the antiviral protective effects of IFN-gamma and IFN-alpha. We observed a striking decrease in the ability of IFN-gamma to protect antisense clones from vesicular stomatitis virus infection (VSV). The IFN-alpha induced antiviral state was also impaired, but to a lesser degree than was observed with IFN-gamma. We excluded the possibility that these effects were caused by a higher sensitivity of the antisense cells to VSV itself and found that the antisense clones actually were less sensitive to VSV. Therefore, we conclude that MnSOD is involved in the establishment of the IFN-gamma-induced antiviral state and to a lesser degree in the antiviral actions of IFN-gamma.

The role of interferon in the therapy of malignant lymphoma

As a single agent, interferon-alpha (IFN-alpha) can induce remissions, mostly partial, in a large fraction of patients with indolent lymphomas, including the low grade B-cell lymphomas and cutaneous T-cell lymphoma. In aggressive lymphomas, IFN has minimal activity, and in Hodgkin's disease the limited available experience suggests only modest activity. In indolent B-cell lymphomas, IFN has been integrated with chemotherapy in several large trials: the majority of these trials indicate a favorable impact on failure-free survival; a survival benefit of IFN has been reported by the French-Belgian group. Updated results are now available from a previously reported trial from the MD Anderson Cancer Center that also indicate an apparent survival benefit when IFN is used in conjunction with chemotherapy in patients with indolent B-cell lymphoma.

The interleukin-2 receptor down-regulates the expression of cytochrome P450 in cultured rat hepatocytes

BACKGROUND & AIMS

Interleukin (IL) 2 is used in advanced cancers, but its effects on cytochrome P450 remain unknown. Other cytokines down-regulate hepatic cytochrome P450, but it is not known whether this involves cytokine receptors. The aim of this study was to determine whether the IL-2 receptor is expressed on hepatocytes and whether its activation by IL-2 depresses cytochrome P450 in cultured rat hepatocytes.

METHODS

A monoclonal antibody specific for the rat IL-2 receptor alpha chain was used to label the receptor, whereas effects on cytochrome P450 were determined after 24 hours of culture with human recombinant IL-2 (5000 U/mL).

RESULTS

The presence of the IL-2 receptor in hepatocytes was shown by immunoblots, flow cytometry, and scanning confocal microscopy. IL-2 caused a 46% decrease in total cytochrome P450; a 35%, 35%, 36%, 26%, and 56% decrease in immunoreactive cytochrome P4501A1, 2B, 2C11, 2D1, and 3A, respectively; and a marked decrease in cytochrome P4503A2 and 2C11 messenger RNAs. Addition to the culture medium of the anti-receptor antibody or the tyrosine kinase inhibitor genistein prevented the IL-2-mediated decrease in cytochrome P450.

CONCLUSIONS

IL-2 down-regulates the expression of cytochrome P450 genes in cultured rat hepatocytes by interacting with its receptor expressed on hepatocytes.

A sensitive biological assay for interferons

Several assays are available for interferons that either measure activity (bioassays) or protein mass (ELISAs). Bioassays generally require the use of viruses and some means of determining cell killing. Many investigators lack the expertise to work with potentially harmful viral agents and eschew this approach in favor of an ELISA assay based on a specific antibody or, to obtain the high level of sensitivity usually required, a combination of antibodies. Such immunological assays, while relatively easy, are expensive and detect protein mass which is not a reliable index of biological activity. I describe here a bioassay based on induction of a reporter gene linked to an interferon (IFN)-responsive promoter element. Production of the reporter gene product is dose-dependent in the range of 1 to approximately 100 U/ml of IFN and sensitivity is comparable to standard cytopathic effect assays. The assay can be modified to quantitate or detect other IFNs and could be applied to other cytokines.