Critically ill COVID-19 patients with neutralizing autoantibodies against type I interferons have increased risk of herpesvirus disease.

Autoantibodies neutralizing the antiviral action of type I interferons (IFNs) have been associated with predisposition to severe Coronavirus Disease 2019 (COVID-19). Here, we screened for such autoantibodies in 103 critically ill COVID-19 patients in a tertiary intensive care unit (ICU) in Switzerland. Eleven patients (10.7%), but no healthy donors, had neutralizing anti-IFNα or anti-IFNα/anti-IFNω IgG in plasma/serum, but anti-IFN IgM or IgA was rare. One patient had non-neutralizing anti-IFNα IgG. Strikingly, all patients with plasma anti-IFNα IgG also had anti-IFNα IgG in tracheobronchial secretions, identifying these autoantibodies at anatomical sites relevant for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Longitudinal analyses revealed patient heterogeneity in terms of increasing, decreasing, or stable anti-IFN IgG levels throughout the length of hospitalization. Notably, presence of anti-IFN autoantibodies in this critically ill COVID-19 cohort appeared to predict herpesvirus disease (caused by herpes simplex viruses types 1 and 2 (HSV-1/-2) and/or cytomegalovirus (CMV)), which has been linked to worse clinical outcomes. Indeed, all 7 tested COVID-19 patients with anti-IFN IgG in our cohort (100%) suffered from one or more herpesviruses, and analysis revealed that these patients were more likely to experience CMV than COVID-19 patients without anti-IFN autoantibodies, even when adjusting for age, gender, and systemic steroid treatment (odds ratio (OR) 7.28, 95% confidence interval (CI) 1.14 to 46.31, p = 0.036). As the IFN system deficiency caused by neutralizing anti-IFN autoantibodies likely directly and indirectly exacerbates the likelihood of latent herpesvirus reactivations in critically ill patients, early diagnosis of anti-IFN IgG could be rapidly used to inform risk-group stratification and treatment options. Trial Registration: ClinicalTrials.gov Identifier: NCT04410263.

Sec61 Inhibitor Apratoxin S4 Potently Inhibits SARS-CoV-2 and Exhibits Broad-Spectrum Antiviral Activity.

There is a pressing need for host-directed therapeutics that elicit broad-spectrum antiviral activities to potentially address current and future viral pandemics. Apratoxin S4 (Apra S4) is a potent Sec61 inhibitor that prevents cotranslational translocation of secretory proteins into the endoplasmic reticulum (ER), leading to anticancer and antiangiogenic activity both in vitro and in vivo. Since Sec61 has been shown to be an essential host factor for viral proteostasis, we tested Apra S4 in cellular models of viral infection, including SARS-CoV-2, influenza A virus, and flaviviruses (Zika, West Nile, and Dengue virus). Apra S4 inhibited viral replication in a concentration-dependent manner and had high potency particularly against SARS-CoV-2 and influenza A virus, with subnanomolar activity in human cells. Characterization studies focused on SARS-CoV-2 revealed that Apra S4 impacted a post-entry stage of the viral life-cycle. Transmission electron microscopy revealed that Apra S4 blocked formation of stacked double-membrane vesicles, the sites of viral replication. Apra S4 reduced dsRNA formation and prevented viral protein production and trafficking of secretory proteins, especially the spike protein. Given the potent and broad-spectrum activity of Apra S4, further preclinical evaluation of Apra S4 and other Sec61 inhibitors as antivirals is warranted.

Restriction factor screening identifies RABGAP1L-mediated disruption of endocytosis as a host antiviral defense.

Host interferons (IFNs) powerfully restrict viruses through the action of several hundred IFN-stimulated gene (ISG) products, many of which remain uncharacterized. Here, using RNAi screening, we identify several ISG restriction factors with previously undescribed contributions to IFN-mediated defense. Notably, RABGAP1L, a Tre2/Bub2/Cdc16 (TBC)-domain-containing protein involved in regulation of small membrane-bound GTPases, robustly potentiates IFN action against influenza A viruses (IAVs). Functional studies reveal that the catalytically active TBC domain of RABGAP1L promotes antiviral activity, and the RABGAP1L proximal interactome uncovered its association with proteins involved in endosomal sorting, maturation, and trafficking. In this regard, RABGAP1L overexpression is sufficient to disrupt endosomal function during IAV infection and restricts an early post-attachment, but pre-fusion, stage of IAV cell entry. Other RNA viruses that enter cells primarily via endocytosis are also impaired by RABGAP1L, while entry promiscuous SARS-CoV-2 is resistant. Our data highlight virus endocytosis as a key target for host defenses.

BRD9 is a druggable component of interferon-stimulated gene expression and antiviral activity.

Interferon (IFN) induction of IFN-stimulated genes (ISGs) creates a formidable protective antiviral state. However, loss of appropriate control mechanisms can result in constitutive pathogenic ISG upregulation. Here, we used genome-scale loss-of-function screening to establish genes critical for IFN-induced transcription, identifying all expected members of the JAK-STAT signaling pathway and a previously unappreciated epigenetic reader, bromodomain-containing protein 9 (BRD9), the defining subunit of non-canonical BAF (ncBAF) chromatin-remodeling complexes. Genetic knockout or small-molecule-mediated degradation of BRD9 limits IFN-induced expression of a subset of ISGs in multiple cell types and prevents IFN from exerting full antiviral activity against several RNA and DNA viruses, including influenza virus, human immunodeficiency virus (HIV1), and herpes simplex virus (HSV1). Mechanistically, BRD9 acts at the level of transcription, and its IFN-triggered proximal association with the ISG transcriptional activator, STAT2, suggests a functional localization at selected ISG promoters. Furthermore, BRD9 relies on its intact acetyl-binding bromodomain and unique ncBAF scaffolding interaction with GLTSCR1/1L to promote IFN action. Given its druggability, BRD9 is an attractive target for dampening ISG expression under certain autoinflammatory conditions.

Combined computational and cellular screening identifies synergistic inhibition of SARS-CoV-2 by lenvatinib and remdesivir.

Rapid repurposing of existing drugs as new therapeutics for COVID-19 has been an important strategy in the management of disease severity during the ongoing SARS-CoV-2 pandemic. Here, we used high-throughput docking to screen 6000 compounds within the DrugBank library for their potential to bind and inhibit the SARS-CoV-2 3 CL main protease, a chymotrypsin-like enzyme that is essential for viral replication. For 19 candidate hits, parallel in vitro fluorescence-based protease-inhibition assays and Vero-CCL81 cell-based SARS-CoV-2 replication-inhibition assays were performed. One hit, diclazuril (an investigational anti-protozoal compound), was validated as a SARS-CoV-2 3 CL main protease inhibitor in vitro (IC50 value of 29 µM) and modestly inhibited SARS-CoV-2 replication in Vero-CCL81 cells. Another hit, lenvatinib (approved for use in humans as an anti-cancer treatment), could not be validated as a SARS-CoV-2 3 CL main protease inhibitor in vitro, but serendipitously exhibited a striking functional synergy with the approved nucleoside analogue remdesivir to inhibit SARS-CoV-2 replication, albeit this was specific to Vero-CCL81 cells. Lenvatinib is a broadly-acting host receptor tyrosine kinase (RTK) inhibitor, but the synergistic effect with remdesivir was not observed with other approved RTK inhibitors (such as pazopanib or sunitinib), suggesting that the mechanism-of-action is independent of host RTKs. Furthermore, time-of-addition studies revealed that lenvatinib/remdesivir synergy probably targets SARS-CoV-2 replication subsequent to host-cell entry. Our work shows that combining computational and cellular screening is a means to identify existing drugs with repurposing potential as antiviral compounds. Future studies could be aimed at understanding and optimizing the lenvatinib/remdesivir synergistic mechanism as a therapeutic option.

Manipulation of the unfolded protein response: A pharmacological strategy against coronavirus infection.

Coronavirus infection induces the unfolded protein response (UPR), a cellular signalling pathway composed of three branches, triggered by unfolded proteins in the endoplasmic reticulum (ER) due to high ER load. We have used RNA sequencing and ribosome profiling to investigate holistically the transcriptional and translational response to cellular infection by murine hepatitis virus (MHV), often used as a model for the Betacoronavirus genus to which the recently emerged SARS-CoV-2 also belongs. We found the UPR to be amongst the most significantly up-regulated pathways in response to MHV infection. To confirm and extend these observations, we show experimentally the induction of all three branches of the UPR in both MHV- and SARS-CoV-2-infected cells. Over-expression of the SARS-CoV-2 ORF8 or S proteins alone is itself sufficient to induce the UPR. Remarkably, pharmacological inhibition of the UPR greatly reduced the replication of both MHV and SARS-CoV-2, revealing the importance of this pathway for successful coronavirus replication. This was particularly striking when both IRE1α and ATF6 branches of the UPR were inhibited, reducing SARS-CoV-2 virion release (~1,000-fold). Together, these data highlight the UPR as a promising antiviral target to combat coronavirus infection.

An antiviral trap made of protein nanofibrils and iron oxyhydroxide nanoparticles.

Minimizing the spread of viruses in the environment is the first defence line when fighting outbreaks and pandemics, but the current COVID-19 pandemic demonstrates how difficult this is on a global scale, particularly in a sustainable and environmentally friendly way. Here we introduce and develop a sustainable and biodegradable antiviral filtration membrane composed of amyloid nanofibrils made from food-grade milk proteins and iron oxyhydroxide nanoparticles synthesized in situ from iron salts by simple pH tuning. Thus, all the membrane components are made of environmentally friendly, non-toxic and widely available materials. The membrane has outstanding efficacy against a broad range of viruses, which include enveloped, non-enveloped, airborne and waterborne viruses, such as SARS-CoV-2, H1N1 (the influenza A virus strain responsible for the swine flu pandemic in 2009) and enterovirus 71 (a non-enveloped virus resistant to harsh conditions, such as highly acidic pH), which highlights a possible role in fighting the current and future viral outbreaks and pandemics.

SARS-CoV-2 variants reveal features critical for replication in primary human cells.

Since entering the human population, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2; the causative agent of Coronavirus Disease 2019 [COVID-19]) has spread worldwide, causing >100 million infections and >2 million deaths. While large-scale sequencing efforts have identified numerous genetic variants in SARS-CoV-2 during its circulation, it remains largely unclear whether many of these changes impact adaptation, replication, or transmission of the virus. Here, we characterized 14 different low-passage replication-competent human SARS-CoV-2 isolates representing all major European clades observed during the first pandemic wave in early 2020. By integrating viral sequencing data from patient material, virus stocks, and passaging experiments, together with kinetic virus replication data from nonhuman Vero-CCL81 cells and primary differentiated human bronchial epithelial cells (BEpCs), we observed several SARS-CoV-2 features that associate with distinct phenotypes. Notably, naturally occurring variants in Orf3a (Q57H) and nsp2 (T85I) were associated with poor replication in Vero-CCL81 cells but not in BEpCs, while SARS-CoV-2 isolates expressing the Spike D614G variant generally exhibited enhanced replication abilities in BEpCs. Strikingly, low-passage Vero-derived stock preparation of 3 SARS-CoV-2 isolates selected for substitutions at positions 5/6 of E and were highly attenuated in BEpCs, revealing a key cell-specific function to this region. Rare isolate-specific deletions were also observed in the Spike furin cleavage site during Vero-CCL81 passage, but these were rapidly selected against in BEpCs, underscoring the importance of this site for SARS-CoV-2 replication in primary human cells. Overall, our study uncovers sequence features in SARS-CoV-2 variants that determine cell-specific replication and highlights the need to monitor SARS-CoV-2 stocks carefully when phenotyping newly emerging variants or potential variants of concern.

Structure and dsRNA-binding activity of the Birnavirus Drosophila X Virus VP3 protein.

The Birnavirus multifunctional protein VP3 plays an essential role coordinating the virus life cycle, interacting with the capsid protein VP2, with the RNA-dependent RNA polymerase VP1 and with the dsRNA genome. Furthermore, the role of this protein in controlling host cell responses triggered by dsRNA and preventing gene silencing has been recently demonstrated. Here we report the X-ray structure and dsRNA-binding activity of the N-terminal domain of Drosophila X virus (DXV) VP3. The domain folds in a bundle of three α-helices and arranges as a dimer, exposing to the surface a well-defined cluster of basic residues. Site directed mutagenesis combined with Electrophoretic Mobility Shift Assays (EMSA) and Surface Plasmon Resonance (SPR) revealed that this cluster, as well as a flexible and positively charged region linking the first and second globular domains of DXV VP3, are essential for dsRNA-binding. Also, RNA silencing studies performed in insect cell cultures confirmed the crucial role of this VP3 domain for the silencing suppression activity of the protein.IMPORTANCE The Birnavirus moonlighting protein VP3 plays crucial roles interacting with the dsRNA genome segments to form stable ribonucleoprotein complexes and controlling host cell immune responses, presumably by binding to and shielding the dsRNA from recognition by the host silencing machinery. The structural, biophysical and functional data presented in this work has identified the N-terminal domain of VP3 as responsible for the dsRNA-binding and silencing suppression activities of the protein in Drosophila X virus.

Antiviral Activity of Type I, II, and III Interferons Counterbalances ACE2 Inducibility and Restricts SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), is a recently emerged respiratory coronavirus that has infected >23 million people worldwide with >800,000 deaths. Few COVID-19 therapeutics are available, and the basis for severe infections is poorly understood. Here, we investigated properties of type I (ß), II (γ), and III (λ1) interferons (IFNs), potent immune cytokines that are normally produced during infection and that upregulate IFN-stimulated gene (ISG) effectors to limit virus replication. IFNs are already in clinical trials to treat COVID-19. However, recent studies highlight the potential for IFNs to enhance expression of host angiotensin-converting enzyme 2 (ACE2), suggesting that IFN therapy or natural coinfections could exacerbate COVID-19 by upregulating this critical virus entry receptor. Using a cell line model, we found that beta interferon (IFN-ß) strongly upregulated expression of canonical antiviral ISGs, as well as ACE2 at the mRNA and cell surface protein levels. Strikingly, IFN-λ1 upregulated antiviral ISGs, but ACE2 mRNA was only marginally elevated and did not lead to detectably increased ACE2 protein at the cell surface. IFN-γ induced the weakest ISG response but clearly enhanced surface expression of ACE2. Importantly, all IFN types inhibited SARS-CoV-2 replication in a dose-dependent manner, and IFN-ß and IFN-λ1 exhibited potent antiviral activity in primary human bronchial epithelial cells. Our data imply that type-specific mechanisms or kinetics shape IFN-enhanced ACE2 transcript and cell surface levels but that the antiviral action of IFNs against SARS-CoV-2 counterbalances any proviral effects of ACE2 induction. These insights should aid in evaluating the benefits of specific IFNs, particularly IFN-λ, as repurposed therapeutics.IMPORTANCE Repurposing existing, clinically approved, antiviral drugs as COVID-19 therapeutics is a rapid way to help combat the SARS-CoV-2 pandemic. Interferons (IFNs) usually form part of the body's natural innate immune defenses against viruses, and they have been used with partial success to treat previous new viral threats, such as HIV, hepatitis C virus, and Ebola virus. Nevertheless, IFNs can have undesirable side effects, and recent reports indicate that IFNs upregulate the expression of host ACE2 (a critical entry receptor for SARS-CoV-2), raising the possibility that IFN treatments could exacerbate COVID-19. Here, we studied the antiviral- and ACE2-inducing properties of different IFN types in both a human lung cell line model and primary human bronchial epithelial cells. We observed differences between IFNs with respect to their induction of antiviral genes and abilities to enhance the cell surface expression of ACE2. Nevertheless, all the IFNs limited SARS-CoV-2 replication, suggesting that their antiviral actions can counterbalance increased ACE2.

The Envelope Gene of Transmitted HIV-1 Resists a Late Interferon Gamma-Induced Block.

Type I interferon (IFN) signaling engenders an antiviral state that likely plays an important role in constraining HIV-1 transmission and contributes to defining subsequent AIDS pathogenesis. Type II IFN (IFN-γ) also induces an antiviral state but is often primarily considered to be an immunomodulatory cytokine. We report that IFN-γ stimulation can induce an antiviral state that can be both distinct from that of type I interferon and can potently inhibit HIV-1 in primary CD4+ T cells and a number of human cell lines. Strikingly, we find that transmitted/founder (TF) HIV-1 viruses can resist a late block that is induced by type II IFN, and the use of chimeric IFN-γ-sensitive/resistant viruses indicates that interferon resistance maps to the env gene. Simultaneously, in vitro evolution also revealed that just a single amino acid substitution in the envelope can confer substantial resistance to IFN-mediated inhibition. Thus, the env gene of transmitted HIV-1 confers resistance to a late block that is phenotypically distinct from blocks previously described to be resisted by env and is therefore mediated by unknown IFN-γ-stimulated factor(s) in human CD4+ T cells and cell lines. This important unidentified block could play a key role in constraining HIV-1 transmission.IMPORTANCE The human immune system can hinder invading pathogens through interferon (IFN) signaling. One consequence of this signaling is that cells enter an antiviral state, increasing the levels of hundreds of defenses that can inhibit the replication and spread of viruses. The majority of HIV-1 infections result from a single virus particle (the transmitted/founder) that makes it past these defenses and colonizes the host. Thus, the founder virus is hypothesized to be a relatively interferon-resistant entity. Here, we show that certain HIV-1 envelope genes have the unanticipated ability to resist specific human defenses mediated by different types of interferons. Strikingly, the envelope gene from a founder HIV-1 virus is far better at evading these defenses than the corresponding gene from a common HIV-1 lab strain. Thus, these defenses could play a role in constraining the transmission of HIV-1 and may select for transmitted viruses that are resistant to this IFN-mediated inhibition.

Host and viral determinants of Mx2 antiretroviral activity.

Myxovirus resistance 2 (Mx2/MxB) has recently been uncovered as an effector of the anti-HIV-1 activity of type I interferons (IFNs) that inhibits HIV-1 at an early stage postinfection, after reverse transcription but prior to proviral integration into host DNA. The mechanistic details of Mx2 antiviral activity are not yet understood, but a few substitutions in the HIV-1 capsid have been shown to confer resistance to Mx2. Through a combination of in vitro evolution and unbiased mutagenesis, we further map the determinants of sensitivity to Mx2 and reveal that multiple capsid (CA) surfaces define sensitivity to Mx2. Intriguingly, we reveal an unanticipated sensitivity determinant within the C-terminal domain of capsid. We also report that Mx2s derived from multiple primate species share the capacity to potently inhibit HIV-1, whereas selected nonprimate orthologs have no such activity. Like TRIM5α, another CA targeting antiretroviral protein, primate Mx2s exhibit species-dependent variation in antiviral specificity against at least one extant virus and multiple HIV-1 capsid mutants. Using a combination of chimeric Mx2 proteins and evolution-guided approaches, we reveal that a single residue close to the N terminus that has evolved under positive selection can determine antiviral specificity. Thus, the variable N-terminal region can define the spectrum of viruses inhibited by Mx2. Importance: Type I interferons (IFNs) inhibit the replication of most mammalian viruses. IFN stimulation upregulates hundreds of different IFN-stimulated genes (ISGs), but it is often unclear which ISGs are responsible for inhibition of a given virus. Recently, Mx2 was identified as an ISG that contributes to the inhibition of HIV-1 replication by type I IFN. Thus, Mx2 might inhibit HIV-1 replication in patients, and this inhibitory action might have therapeutic potential. The mechanistic details of how Mx2 inhibits HIV-1 are currently unclear, but the HIV-1 capsid protein is the likely viral target. Here, we determine the regions of capsid that specify sensitivity to Mx2. We demonstrate that Mx2 from multiple primates can inhibit HIV-1, whereas Mx2 from other mammals (dogs and sheep) cannot. We also show that primate variants of Mx2 differ in the spectrum of lentiviruses they inhibit and that a single residue in Mx2 can determine this antiviral specificity.

The VP3 factor from viruses of Birnaviridae family suppresses RNA silencing by binding both long and small RNA duplexes.

RNA silencing is directly involved in antiviral defense in a wide variety of eukaryotic organisms, including plants, fungi, invertebrates, and presumably vertebrate animals. The study of RNA silencing-mediated antiviral defences in vertebrates is hampered by the overlap with other antiviral mechanisms; thus, heterologous systems are often used to study the interplay between RNA silencing and vertebrate-infecting viruses. In this report we show that the VP3 protein of the avian birnavirus Infectious bursal disease virus (IBDV) displays, in addition to its capacity to bind long double-stranded RNA, the ability to interact with double-stranded small RNA molecules. We also demonstrate that IBDV VP3 prevents the silencing mediated degradation of a reporter mRNA, and that this silencing suppression activity depends on its RNA binding ability. Furthermore, we find that the anti-silencing activity of IBDV VP3 is shared with the homologous proteins expressed by both insect- and fish-infecting birnaviruses. Finally, we show that IBDV VP3 can functionally replace the well-characterized HCPro silencing suppressor of Plum pox virus, a potyvirus that is unable to infect plants in the absence of an active silencing suppressor. Altogether, our results support the idea that VP3 protects the viral genome from host sentinels, including those of the RNA silencing machinery.

The infectious bursal disease virus RNA-binding VP3 polypeptide inhibits PKR-mediated apoptosis.

Infectious bursal disease virus (IBDV) is an avian pathogen responsible for an acute immunosuppressive disease that causes major losses to the poultry industry. Despite having a bipartite dsRNA genome, IBDV, as well as other members of the Birnaviridae family, possesses a single capsid layer formed by trimers of the VP2 capsid protein. The capsid encloses a ribonucleoprotein complex formed by the genome associated to the RNA-dependent RNA polymerase and the RNA-binding polypeptide VP3. A previous report evidenced that expression of the mature VP2 IBDV capsid polypeptide triggers a swift programmed cell death response in a wide variety of cell lines. The mechanism(s) underlying this effect remained unknown. Here, we show that VP2 expression in HeLa cells activates the double-stranded RNA (dsRNA)-dependent protein kinase (PKR), which in turn triggers the phosphorylation of the eukaryotic initiation factor 2α (eIF2α). This results in a strong blockade of protein synthesis and the activation of an apoptotic response which is efficiently blocked by coexpression of a dominant negative PKR polypeptide. Our results demonstrate that coexpression of the VP3 polypeptide precludes phosphorylation of both PKR and eIF2α and the onset of programmed cell death induced by VP2 expression. A mutation blocking the capacity of VP3 to bind dsRNA also abolishes its capacity to prevent PKR activation and apoptosis. Further experiments showed that VP3 functionally replaces the host-range vaccinia virus (VACV) E3 protein, thus allowing the E3 deficient VACV deletion mutant WRΔE3L to grow in non-permissive cell lines. According to results presented here, VP3 can be categorized along with other well characterized proteins such us VACV E3, avian reovirus sigmaA, and influenza virus NS1 as a virus-encoded dsRNA-binding polypeptide with antiapoptotic properties. Our results suggest that VP3 plays a central role in ensuring the viability of the IBDV replication cycle by preventing programmed cell death.

Superoxide anions are involved in doxorubicin-induced ERK activation in hepatocyte cultures.

Doxorubicin (DOX), an antineoplastic agent widely used for the treatment of cancer, belongs to the anthracycline family of antitumor antibiotics. DOX may undergo one-electron reduction to the corresponding semiquinone free radical by flavin-containing reductases. Under aerobic conditions, the semiquinone radical reacts rapidly with oxygen to generate superoxide anion, undergoing redox cycling. At moderate concentrations, reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. We have shown that DOX increased phosphorylation of enzymes comprising mitogen-activated protein (MAP) kinase cascades in primary hepatocyte cultures, and that this action was independent of oxidant damage. In particular, extracellular signal-regulated kinase (ERK) was phosphorylated by the drug treatment. In this work, we have determined the possible involvement of particular free radicals in DOX-induced ERK phosphorylation in hepatocyte cultures by using specific free radical scavengers. The levels of ERK phosphorylation were measured by Western blot analysis with an anti-Thr202/Tyr204-phosphorylated p44/p42 MAPK antibody. Deferoxamine (DFO; iron chelator), catalase (hydrogen peroxide-removing enzyme), or alpha-tocopherol (peroxyl-radical scavenger) did not affect DOX-increased ERK phosphorylation levels. However, the cell-permeable superoxide dismutase mimetic MnTBAP and the flavin-containing enzyme inhibitor diphenyleneiodonium reverted DOX-induced effects. These results suggest that superoxide anions, probably generated by DOX metabolism, are involved in the effects of the anthracycline on the MAP kinase cascade activation.

Doxorubicin-induced MAPK activation in hepatocyte cultures is independent of oxidant damage.

Doxorubicin (DOX) is a potent anticancer drug, whose clinical use is limited on account of its toxicity. DOX cytotoxic effects have been associated with reactive oxygen species (ROS) generated during drug metabolism. ROS induce signaling cascades leading to changes in the phosphorylation status of target proteins, which are keys for cell survival or apoptosis. The mitogen-activated protein kinase (MAPK) cascades are routes activated in response to oxidative stress. In this work, the effects of DOX on cytotoxicity, indicators of oxidative stress (malondialdehyde -MDA- and GSH), and the phosphorylation status of extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38 kinases were analyzed in primary cultures of rat hepatocytes. DOX (1-50 microM) did not modify lactate dehydrogenase (LDH) release into the medium, the levels of MDA (determined by high-performance liquid chromatography [HPLC]) or the intracellular GSH during the incubation time up to 6 h. GSH levels from mitochondria extracted by Percoll gradient from cultured hepatocytes were not modified by DOX, thus excluding its depletion or any impaired mitochondrial uptake. Characterization of proteins by Western blot analysis revealed that DOX increased phosphorylation of p38 kinases and JNK1 and JNK2 in a dose- and time-dependent manner. DOX also increased ERK2 phosphorylation at latter time points. In conclusion, DOX triggers activation of ERK, JNK, and p38 kinases in primary cultures of rat hepatocytes independently of oxidant damage.