Activation of the ubiquitin-proteasome system in doxorubicin cardiomyopathy

Implications of chronic moderate protein-deficiency malnutrition on doxorubicin pharmacokinetics and cardiotoxicity in early post-weaning stage

BACKGROUND

Malnutrition is a common problem in developing countries, and the impact of severe malnutrition on optimal treatment outcomes of chemotherapy in pediatric cancer patients is well documented. However, despite being a more prevalent and distinct entity, moderate malnutrition is until now unexplored for its effects on treatment outcomes.

AIMS

In this study we aimed to investigate the molecular basis of altered pharmacokinetics and cardiotoxicity of doxorubicin observed in early-life chronic moderate protein deficiency malnutrition.

MATERIALS AND METHODS

We developed an animal model of early-life moderate protein-deficiency malnutrition and validated it using clinical samples. This model was used to study pharmacokinetic and toxicity changes and was further utilized to study the molecular changes in liver and heart to get mechanistic insights.

KEY FINDINGS

Here we show that moderate protein-deficiency malnutrition in weanling rats causes changes in drug disposition in the liver by modification of hepatic ABCC3 and MRP2 transporters through the TNFα signalling axis. Furthermore, malnourished rats in repeat-dose doxorubicin toxicity study showed higher toxicity and mortality. A higher accumulation of doxorubicin in the heart was observed which was associated with alterations in cardiac metabolic pathways and increased cardiotoxicity.

SIGNIFICANCE

Our findings indicate that moderate malnutrition causes increased susceptibility towards toxic side effects of chemotherapy. These results may necessitate further investigations and new guidelines on the dosing of chemotherapy in moderately malnourished pediatric cancer patients.

Exploring Anthracycline-Induced Cardiotoxicity from the Perspective of Protein Quality Control

Anthracyclines are effective anticancer drugs; however, their use is restricted because of their dose-dependent, time-dependent and irreversible myocardial toxicity. The mechanism of anthracycline cardiotoxicity has been widely studied but remains unclear. Protein quality control is crucial to the stability of the intracellular environment and, ultimately, to the heart because cardiomyocytes are terminally differentiated. Two evolutionarily conserved mechanisms, autophagy, and the ubiquitin-proteasome system, synergistically degrade misfolded proteins and remove defective organelles. Recent studies demonstrated the importance of these mechanisms. Further studies will reveal the detailed metabolic pathway and metabolic control of the protein quality control mechanism integrated into anthracycline-induced cardiotoxicity. This review provides theoretical support for clinicians in the application and management of anthracyclines.

Doxorubicin-induced cardiotoxicity and risk factors

Doxorubicin (DOX) is an anthracycline antibiotic widely used as a chemotherapeutic agent to treat solid tumours and hematologic malignancies. Although useful in the treatment of cancers, the benefit of DOX is limited due to its cardiotoxic effect that is observed in a large number of patients. In the literature, there is evidence that the presence of various factors may increase the risk of developing DOX-induced cardiotoxicity. A better understanding of the role of these different factors in DOX-induced cardiotoxicity may facilitate the choice of the therapeutic approach in cancer patients suffering from various cardiovascular risk factors. In this review, we therefore discuss the latest findings in both preclinical and clinical research suggesting a link between DOX-induced cardiotoxicity and various risk factors including sex, age, ethnicity, diabetes, dyslipidaemia, obesity, hypertension, cardiovascular disease and co-medications.

DoxoDB: A Database for the Expression Analysis of Doxorubicin-Induced lncRNA Genes

Cancer and cardiovascular disease are the leading causes of death worldwide. Recent evidence suggests that these two life-threatening diseases share several features in disease progression, such as angiogenesis, fibrosis, and immune responses. This has led to the emergence of a new field called cardio-oncology. Doxorubicin is a chemotherapy drug widely used to treat cancer, such as bladder and breast cancer. However, this drug causes serious side effects, including acute ventricular dysfunction, cardiomyopathy, and heart failure. Based on this evidence, we hypothesize that comparing the expression profiles of cells and tissues treated with doxorubicin may yield new insights into the adverse effects of the drug on cellular activities. To test this hypothesis, we analyzed published RNA sequencing (RNA-seq) data from doxorubicin-treated cells to identify commonly differentially expressed genes, including long non-coding RNAs (lncRNAs) as they are known to be dysregulated in diseased tissues and cells. From our systematic analysis, we identified several doxorubicin-induced genes. To confirm these findings, we treated human cardiac fibroblasts with doxorubicin to record expression changes in the selected doxorubicin-induced genes and performed a loss-of-function experiment of the lncRNA MAP3K4-AS1. To further disseminate the analyzed data, we built the web database DoxoDB.

Hydrogen sulfide alleviates mitochondrial damage and ferroptosis by regulating OPA3-NFS1 axis in doxorubicin-induced cardiotoxicity

Ferroptosis is a major cause of cardiotoxicity induced by doxorubicin (DOX). Previous studies have shown that hydrogen sulfide (H₂S) inhibits ferroptosis in cardiomyocytes and myoblasts, but the underlying mechanism has not been fully elucidated. In this study, we investigated the role of H₂S in protecting against DOX-induced cardiotoxicity both in vivo and in vitro, and elucidated the potential mechanisms involved. We found that DOX downregulated the expression of glutathione peroxidase 4 (GPX4) and NFS1, and upregulated the expression of acyl-coenzyme A synthetase long-chain family member 4 (ACSL4) expression level, resulting in increased lipid peroxidation and ferroptosis. Additionally, DOX inhibited MFN2 expression and increased DRP1 and FIS1 expression, leading to abnormal mitochondrial structure and function. In contrast, exogenous H₂S inhibited DOX-induced ferroptosis by restoring GPX4 and NFS1 expression, and reducing lipid peroxidation in H9C2 cells. This effect was similar to that of the ferroptosis antagonist ferrostatin-1 (Fer-1) in protecting against DOX-induced cardiotoxicity. We further demonstrated that the protective effect of H₂S was mediated by the key mitochondrial membrane protein optic atrophy 3 (OPA3), which was downregulated by DOX and restored by exogenous H₂S. Overexpression of OPA3 alleviated DOX-induced mitochondrial dysfunction and ferroptosis both in vivo and in vitro. Mechanistically, NFS1 has an inhibitory effect on ferroptosis, and NFS1 deficiency increases the susceptibility of cardiomyocytes to ferroptosis. OPA3 is involved in the regulation of ferroptosis by interacting with NFS1. Post-translationally, DOX promoted OPA3 ubiquitination, while exogenous H₂S antagonized OPA3 ubiquitination by promoting OPA3 s-sulfhydration. In summary, our findings suggested that H₂S protects against DOX-induced cardiotoxicity by inhibiting ferroptosis via targeting the OPA3-NFS1 axis. This provides a potential therapeutic strategy for the treatment of DOX-induced cardiotoxicity.

Neprilysin Inhibition in the Prevention of Anthracycline-Induced Cardiotoxicity

Anthracycline-induced cardiotoxicity (AIC) poses a clinical challenge in the management of cancer patients. AIC is characterized by myocardial systolic dysfunction and remodeling, caused by cardiomyocyte DNA damage, oxidative stress, mitochondrial dysfunction, or renin-angiotensin-aldosterone system (RAAS) dysregulation. In the past decade, after positive results of a PARADIGM-HF trial, a new class of drugs, namely angiotensin receptor/neprilysin inhibitors (ARNi), was incorporated into the management of patients with heart failure with reduced ejection fraction. As demonstrated in a variety of preclinical studies of cardiovascular diseases, the cardioprotective effects of ARNi administration are associated with decreased oxidative stress levels, the inhibition of myocardial inflammatory response, protection against mitochondrial damage and endothelial dysfunction, and improvement in the RAAS imbalance. However, data on ARNi's effectiveness in the prevention of AIC remains limited. Several reports of ARNi administration in animal models of AIC have shown promising results, as ARNi prevented ventricular systolic dysfunction and electrocardiographic changes and ameliorated oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, and the inflammatory response associated with anthracyclines. There is currently an ongoing PRADAII trial aimed to assess the efficacy of ARNi in patients receiving breast cancer treatment, which is expected to be completed by late 2025.

Anthracycline-induced cardiotoxicity: targeting high-density lipoproteins to limit the damage?

Doxorubicin (DOX) is an anthracycline antibiotic frequently used against a wide range of cancers, including breast cancer. Although the drug is effective as a treatment against cancer, many patients develop heart failure (HF) months to years following their last treatment with DOX. The challenge in preventing DOX-induced cardiotoxicity is that symptoms present after damage has already occurred in the myocardium. Therefore, early biomarkers to assess DOX-induced cardiotoxicity are urgently needed. A better understanding of the mechanisms involved in the toxicity is important as this may facilitate the development of novel early biomarkers or therapeutic approaches. In this review, we discuss the role of high-density lipoprotein (HDL) particles and its components as possible key players in the early development of DOX-induced cardiotoxicity. HDL particles exist in different subclasses which vary in composition and biological functionality. Multiple cardiovascular risk factors are associated with a change in HDL subclasses, resulting in modifications of their composition and physiological functions. There is growing evidence in the literature suggesting that cancer affects HDL subclasses and that healthy HDL particles enriched with sphingosine-1-phosphate (S1P) and apolipoprotein A1 (ApoA1) protect against DOX-induced cardiotoxicity. Here, we therefore discuss associations and relationships between HDL, DOX and cancer and discuss whether assessing HDL subclass/composition/function may be considered as a possible early biomarker to detect DOX-induced cardiotoxicity.

Tripartite motif 25 ameliorates doxorubicin-induced cardiotoxicity by degrading p85α

Doxorubicin (DOX)-based chemotherapy is widely used to treat malignant tumors; however, the cardiotoxicity induced by DOX restricts its clinical usage. A therapeutic dose of DOX can activate ubiquitin-proteasome system. However, whether and how ubiquitin-proteasome system brings out DOX-induced cardiotoxicity remains to be investigated. Here we conducted a proteomics analysis of a DOX-induced cardiotoxicity model to screen the potentially ubiquitination-related molecules. Dysregulated TRIM25 was found to contribute to the cardiotoxicity. In vivo and in vitro cardiotoxicity experiments revealed that TRIM25 ameliorated DOX-induced cardiotoxicity. Electron microscopy and endoplasmic reticulum stress markers revealed that TRIM25 mitigated endoplasmic reticulum stress and apoptosis in DOX-induced cardiomyocytes. Mechanistically, the Co-immunoprecipitation assays and CHX pulse-chase experiment determined that TRIM25 affected p85α stability and promoted its ubiquitination and degradation. This leads to increase of nuclear translocation of XBP-1s, which mitigates endoplasmic reticulum stress. These findings reveal that TRIM25 may have a therapeutic role for DOX-induced cardiotoxicity.

Long non-coding RNA LALTOP promotes non-small cell lung cancer progression by stabilizing topoisomerase IIα mRNA

The long noncoding RNAs (lncRNAs) have been shown to actively participate in various biological processes including cancer progression. However, most lncRNAs still have undefined functions. In current work, we identified a novel lncRNA named LALTOP which displayed an oncogenic function in non-small cell lung cancer (NSCLC). LALTOP expression is increased in NSCLC tissues and cell lines. Moreover, LALTOP strongly promoted proliferation and migration of A549 and H1793 cells. RNA-RNA interaction assay showed that LALTOP bound and stabilized topoisomerase II alpha (Top2α) mRNA. Positive correlation can be found between LALTOP and Top2α mRNA expressions in clinical specimens. ASOs targeting LALTOP could markedly inhibit malignant phenotypes of NSCLC. Collectively, LALTOP may serve as an oncogenic lncRNA and enhances NSCLC progression. Targeting LALTOP has therapeutic potential for eradicating lung cancer cells.

Clarifying the pharmacological mechanisms of action of Shenfu Decoction on cardiovascular diseases using a network pharmacology approach

Since the molecular mechanisms underlying in the pathogenesis of cardiovascular diseases (CVD) are extremely complex and have not yet been elucidated in detail, CVD remain the leading cause of death worldwide. Traditional Chinese medicine involves the treatment of disease from an overall perspective, and its therapeutic effects on CVD have been demonstrated. However, the mechanisms contributing to the multiscale treatment of cardiovascular diseases at the systematic level remain unclear. Network pharmacology methods and a gene chip data analysis were integrated and applied in the present study, which was conducted to investigate the potential target genes and related pathways of Shenfu Decoction (SFD) for the treatment of myocardial injury. The gene chip analysis was initially performed, followed by network pharmacology to identify differentially expressed genes (DEG) and a functional enrichment analysis. Protein-protein networks were constructed and a module analysis was conducted. A network analysis was used to identify the target genes of SFD. Regarding the results obtained, 1134 DEG were identified using the STRING website. The module analysis revealed that nine hub genes exhibited ubiquitin-protein ligase activity. Therefore, SFD significantly alters the expression of ubiquitination-related genes and, thus, plays an important therapeutic role in the treatment of heart failure. In conclusion, hub genes may provide a more detailed understanding of the molecular mechanisms of action of as well as candidate targets for SFD therapy.

Phosphorylation Modifications Regulating Cardiac Protein Quality Control Mechanisms

Many forms of cardiac disease, including heart failure, present with inadequate protein quality control (PQC). Pathological conditions often involve impaired removal of terminally misfolded proteins. This results in the formation of large protein aggregates, which further reduce cellular viability and cardiac function. Cardiomyocytes have an intricately collaborative PQC system to minimize cellular proteotoxicity. Increased expression of chaperones or enhanced clearance of misfolded proteins either by the proteasome or lysosome has been demonstrated to attenuate disease pathogenesis, whereas reduced PQC exacerbates pathogenesis. Recent studies have revealed that phosphorylation of key proteins has a potent regulatory role, both promoting and hindering the PQC machinery. This review highlights the recent advances in phosphorylations regulating PQC, the impact in cardiac pathology, and the therapeutic opportunities presented by harnessing these modifications.

Possible Susceptibility Genes for Intervention against Chemotherapy-Induced Cardiotoxicity

Recent therapeutic advances have significantly improved the short- and long-term survival rates in patients with heart disease and cancer. Survival in cancer patients may, however, be accompanied by disadvantages, namely, increased rates of cardiovascular events. Chemotherapy-related cardiac dysfunction is an important side effect of anticancer therapy. While advances in cancer treatment have increased patient survival, treatments are associated with cardiovascular complications, including heart failure (HF), arrhythmias, cardiac ischemia, valve disease, pericarditis, and fibrosis of the pericardium and myocardium. The molecular mechanisms of cardiotoxicity caused by cancer treatment have not yet been elucidated, and they may be both varied and complex. By identifying the functional genetic variations responsible for this toxicity, we may be able to improve our understanding of the potential mechanisms and pathways of treatment, paving the way for the development of new therapies to target these toxicities. Data from studies on genetic defects and pharmacological interventions have suggested that many molecules, primarily those regulating oxidative stress, inflammation, autophagy, apoptosis, and metabolism, contribute to the pathogenesis of cardiotoxicity induced by cancer treatment. Here, we review the progress of genetic research in illuminating the molecular mechanisms of cancer treatment-mediated cardiotoxicity and provide insights for the research and development of new therapies to treat or even prevent cardiotoxicity in patients undergoing cancer treatment. The current evidence is not clear about the role of pharmacogenomic screening of susceptible genes. Further studies need to done in chemotherapy-induced cardiotoxicity.

Updates in Anthracycline-Mediated Cardiotoxicity

Cardiotoxicity is one of the main adverse effects of chemotheraphy, affecting the completion of cancer therapies and the short- and long-term quality of life. Anthracyclines are currently used to treat many cancers, including the various forms of leukemia, lymphoma, melanoma, uterine, breast, and gastric cancers. World Health Organization registered anthracyclines in the list of essential medicines. However, anthracyclines display a major cardiotoxicity that can ultimately culminate in congestive heart failure. Taking into account the growing rate of cancer survivorship, the clinical significance of anthracycline cardiotoxicity is an emerging medical issue. In this review, we focus on the key progenitor cells and cardiac cells (cardiomyocytes, fibroblasts, and vascular cells), focusing on the signaling pathways involved in cellular damage, and the clinical biomarkers in anthracycline-mediated cardiotoxicity.

Evaluation of the impact of the proteasome inhibitor on calcium channel expression in cardiomyocytes treated with doxorubicin

One of the less known mechanisms of doxorubicin action is the effect on the functioning of the ubiquitin-proteasome degradation system (UPS). So far, the role of impaired proteasome activity in the development of anthracycline cardiomyopathy has not been clarified. It has been shown, however, that doxorubicin decreases the expression of proteins, including the expression of the calcium channel. However, it has not been established whether the observed disturbances are due to the activation of the UPS system by doxorubicin, or due to inhibition of translation or transcription. Therefore, the aim of the study was to evaluate the mRNA and protein expression of plasmalemmal (NaCaX, L-type) and sarcoplasmic reticulum (SERCA2, RyR2) channels in rat embryonic cardiomyocytes treated with doxorubicin and the proteasome inhibitor – bortezomib. The study was conducted utilizing the rat cardiomyocyte H9C2 line that was treated with doxorubicin and bortezomib in different concentrations. After 24 hours incubation, mRNA and protein expression analysis followed. The study did not show any universal mechanism of doxorubicin influence on calcium channel expression. With regard to the Na/Ca exchanger, we saw that DOX decreased the protein level in a proteasome activitydependent manner. Moreover, we noted that the SERCA2 protein expression level was regulated by degradation intensity, however at the same time, no significant effect of doxorubicin on the level of this protein was demonstrated.

Analysis of defective protein ubiquitylation associated to adriamycin resistant cells

DNA damage activated by Adriamycin (ADR) promotes ubiquitin-proteasome system-mediated proteolysis by stimulating both the activity of ubiquitylating enzymes and the proteasome. In ADR-resistant breast cancer MCF7 (MCF7^ADR) cells, protein ubiquitylation is significantly reduced compared to the parental MCF7 cells. Here, we used tandem ubiquitin-binding entities (TUBEs) to analyze the ubiquitylation pattern observed in MCF7 or MCF7^ADR cells. While in MCF7, the level of total ubiquitylation increased up to six-fold in response to ADR, in MCF7^ADR cells only a two-fold response was found. To further explore these differences, we looked for cellular factors presenting ubiquitylation defects in MCF7^ADR cells. Among them, we found the tumor suppressor p53 and its ubiquitin ligase, Mdm2. We also observed a drastic decrease of proteins known to integrate the TUBE-associated ubiquitin proteome after ADR treatment of MCF7 cells, like histone H2AX, HMGB1 or β-tubulin. Only the proteasome inhibitor MG132, but not the autophagy inhibitor chloroquine partially recovers the levels of total protein ubiquitylation in MCF7^ADR cells. p53 ubiquitylation is markedly increased in MCF7^ADR cells after proteasome inhibition or a short treatment with the isopeptidase inhibitor PR619, suggesting an active role of these enzymes in the regulation of this tumor suppressor. Notably, MG132 alone increases apoptosis of MCF7^ADR and multidrug resistant ovarian cancer A2780DR1 and A2780DR2 cells. Altogether, our results highlight the use of ubiquitylation defects to predict resistance to ADR and underline the potential of proteasome inhibitors to treat these chemoresistant cells.

Molecular mechanism of doxorubicin-induced cardiomyopathy - An update

Doxorubicin is utilized for anti-neoplastic treatment for several decades. The utility of this drug is limited due to its side effects. Generally, doxorubicin toxicity is originated from the myocardium and then other organs are also ruined. The mechanism of doxorubicin is intercalated with the DNA and inhibits topoisomerase 2. There are various signalling mechanisms involved in doxorubicin cardiotoxicity. First and foremost, the doxorubicin-induced cardiotoxicity is due to oxidative stress. Cardiac mitochondrial damage is supposed after few hours following the revelation of doxorubicin. This has led important new uses for the mechanism of doxorubicin-induced cardiotoxicity and novel avenues of investigation to determine better pharmacotherapies and interventions for the impediment of cardiotoxicity. The idea of this review is to bring up to date the recent findings of the mechanism of doxorubicin cardiomyopathies such as calcium dysregulation, endoplasmic reticulum stress, impairment of progenitor cells, activation of immune, ubiquitous system and some other parameters.

Visfatin mediates doxorubicin resistance in human non-small-cell lung cancer via Akt-mediated up-regulation of ABCC1

OBJECTIVES

Non-small-cell lung cancer (NSCLC) is one of the leading causes of cancer deaths worldwide. Increasing levels of visfatin are correlated with worse clinical prognosis of NSCLC. However, the effects of visfatin on drug resistant are still not well illustrated.

MATERIALS AND METHODS

Effects of visfatin on drug resistant cells were checked by CCK-8 kit. Gene and protein variations were measured by real-time PCR and western blot analysis, respectively.

RESULTS

Our present data confirmed that expression of visfatin was significantly increased in NSCLC cells and tissues. In addition, protein and mRNA expression of visfatin were significantly elevated in doxorubicin (Dox) resistance of NSCLC cells when compared with their corresponding sensitivity parental cells. Overexpression of visfatin can down-regulate the Dox sensitivity of NSCLC cells and up-regulate the mRNA and protein expression of ABCC1, while has no effect on ABCB1. Knockdown of visfatin can down-regulate the expression of ABCC1 in Dox-resistant NSCLC cells. Visfatin can increase the phosphorylation and nuclear localization of Akt in NSCLC cells. LY294002 can decrease the expression of multidrug resistance protein-1 (MRP1) in NSCLC Dox-resistant cells. Chromatin immunoprecipitation assays showed that overexpression of visfatin can significantly increase the binding of Akt with the promoter of ABCC1 in both A549 and H1793 cells.

CONCLUSIONS

These data showed that visfatin can decrease Dox sensitivity of NSCLC cells via activation of Akt/MRP1. It indicated that inhibition of visfatin signals might be a promising therapeutic strategy for the management of chemoresistance of NSCLC patients.

Doxorubicin attenuates CHIP-guarded HSF1 nuclear translocation and protein stability to trigger IGF-IIR-dependent cardiomyocyte death

Doxorubicin (DOX) is one of the most effective antitumor drugs, but its cardiotoxicity has been a major concern for its use in cancer therapy for decades. Although DOX-induced cardiotoxicity has been investigated, the underlying mechanisms responsible for this cardiotoxicity have not been completely elucidated. Here, we found that the insulin-like growth factor receptor II (IGF-IIR) apoptotic signaling pathway was responsible for DOX-induced cardiotoxicity via proteasome-mediated heat shock transcription factor 1 (HSF1) degradation. The carboxyl-terminus of Hsp70 interacting protein (CHIP) mediated HSF1 stability and nuclear translocation through direct interactions via its tetratricopeptide repeat domain to suppress IGF-IIR expression and membrane translocation under physiological conditions. However, DOX attenuated the HSF1 inhibition of IGF-IIR expression by diminishing the CHIP–HSF1 interaction, removing active nuclear HSF1 and triggering HSF1 proteasomal degradation. Overexpression of CHIP redistributed HSF1 into the nucleus, inhibiting IGF-IIR expression and preventing DOX-induced cardiomyocyte apoptosis. Moreover, HSF1A, a small molecular drug that enhances HSF1 activity, stabilized HSF1 expression and minimized DOX-induced cardiac damage in vitro and in vivo. Our results suggest that the cardiotoxic effects of DOX result from the prevention of CHIP-mediated HSF1 nuclear translocation and activation, which leads to an upregulation of the IGF-IIR apoptotic signaling pathway. We believe that the administration of an HSF1 activator or agonist may further protect against the DOX-induced cell death of cardiomyocytes.

The regulatory mechanisms of myogenin expression in doxorubicin-treated rat cardiomyocytes

Doxorubicin, an anthracycline antibiotic, has been used as an anti-neoplastic drug for almost 60 years. However, the mechanism(s) by which anthracyclines cause irreversible myocardial injury remains unclear. In order to delineate possible molecular signals involved in the myocardial toxicity, we assessed candidate genes using mRNA expression profiling in the doxorubicin-treated rat cardiomyocyte H9c2 cell line. In the study, it was confirmed that myogenin, an important transcriptional factor for muscle terminal differentiation, was significantly reduced by doxorubicin in a dose-dependent manner using both RT-PCR and western blot analyses. Also, it was identified that the doxorubicin-reduced myogenin gene level could not be rescued by most cardio-protectants. Furthermore, it was demonstrated how the signaling of the decreased myogenin expression by doxorubicin was altered at the transcriptional, post-transcriptional and translational levels. Based on these findings, a working model was proposed for relieving doxorubicin-associated myocardial toxicity by down-regulating miR-328 expression and increasing voltage-gated calcium channel β1 expression, which is a repressor of myogenin gene regulation. In summary, this study provides several lines of evidence indicating that myogenin is the target for doxorubicin-induced cardio-toxicity and a novel therapeutic strategy for doxorubicin clinical applications based on the regulatory mechanisms of myogenin expression.

Hypoxia can impair doxorubicin resistance of non-small cell lung cancer cells by inhibiting MRP1 and P-gp expression and boosting the chemosensitizing effects of MRP1 and P-gp blockers

BACKGROUND

Non-small cell lung cancers (NSCLCs) frequently exhibit resistance to therapeutic drugs, which seriously hampers their treatment. Here, we set out to assess the roles of the multidrug resistance protein 1 (MRP1) and P-glycoprotein (P-gp) in the doxorubicin (DOX) resistance of NSCLC cells, as well as the putative therapeutic efficacy of MRP1 and P-gp blockers on DOX-treated NSCLC cells.

METHODS

The impact of DOX on cell survival, DOX efflux and MRP1 and P-gp expression was assessed in 5 different NSCLC-derived cell lines (parental CH27, A549, H1299, H460, and DOX resistant CH27) in the absence or presence of MK571 (MRP1 inhibitor) or Verapamil (P-gp inhibitor), under both normoxic and hypoxic conditions.

RESULTS

We found that in response to DOX treatment, NSCLC cells that express high levels of MRP1 and P-gp (such as CH27) showed a better DOX efflux and a higher DOX resistance. MK571 and Verapamil were found to abolish DOX resistance and to act as chemosensitizers for DOX therapy in all cell lines tested. We also found that hypoxia could inhibit MRP1 and P-gp expression in a HIF-1α-dependent manner, abolish DOX resistance and boost the chemosensitizer effect of MK571 and Verapamil on DOX treatment of all the NSCLC cells tested, except the DOX-resistant CH27 cells.

CONCLUSIONS

From our data we conclude that MRP1 and P-gp play critical roles in the DOX resistance of the NSCLC cells tested. MRP1 and P-gp targeted therapy using MK571, Verapamil, CoCl₂ or ambient hypoxia appeared to be promising in abolishing the DOX efflux and DOX resistance of the NSCLC cells. The putative therapeutic efficacies of MRP1 and/or P-gp blockers on NSCLC cells are worthy of note.

Mitochondria: Inadvertent targets in chemotherapy-induced skeletal muscle toxicity and wasting?

Chemotherapy has been associated with increased mitochondrial reactive oxygen species production, mitochondrial dysfunction and skeletal muscle atrophy leading to severe patient clinical complications including skeletal muscle fatigue, insulin resistance and wasting. The exact mechanisms behind this skeletal muscle toxicity are largely unknown, and as such co-therapies to attenuate chemotherapy-induced side effects are lacking. Here, we review the current literature describing the clinical manifestations and molecular origins of chemotherapy-induced myopathy with a focus on the mitochondria as the target organelle via which chemotherapeutic agents establish toxicity. We explore the likely mechanisms through which myopathy is induced, using the anthracycline doxorubicin, and the platinum-based alkylating agent oxaliplatin, as examples. Finally, we recommend directions for future research and outline the potential significance of these proposed directions.

Chemical Endoplasmic Reticulum Chaperone Alleviates Doxorubicin-Induced Cardiac Dysfunction

RATIONALE

Doxorubicin is an effective chemotherapeutic agent for cancer, but its use is often limited by cardiotoxicity. Doxorubicin causes endoplasmic reticulum (ER) dilation in cardiomyocytes, and we have demonstrated that ER stress plays important roles in the pathophysiology of heart failure.

OBJECTIVE

We evaluated the role of ER stress in doxorubicin-induced cardiotoxicity and examined whether the chemical ER chaperone could prevent doxorubicin-induced cardiac dysfunction.

METHODS AND RESULTS

We confirmed that doxorubicin caused ER dilation in mouse hearts, indicating that doxorubicin may affect ER function. Doxorubicin activated an ER transmembrane stress sensor, activating transcription factor 6, in cultured cardiomyocytes and mouse hearts. However, doxorubicin suppressed the expression of genes downstream of activating transcription factor 6, including X-box binding protein 1. The decreased levels of X-box binding protein 1 resulted in a failure to induce the expression of the ER chaperone glucose-regulated protein 78 which plays a major role in adaptive responses to ER stress. In addition, doxorubicin activated caspase-12, an ER membrane-resident apoptotic molecule, which can lead to cardiomyocyte apoptosis and cardiac dysfunction. Cardiac-specific overexpression of glucose-regulated protein 78 by adeno-associated virus 9 or the administration of the chemical ER chaperone 4-phenylbutyrate attenuated caspase-12 cleavage, and alleviated cardiac apoptosis and dysfunction induced by doxorubicin.

CONCLUSIONS

Doxorubicin activated the ER stress-initiated apoptotic response without inducing the ER chaperone glucose-regulated protein 78, further augmenting ER stress in mouse hearts. Cardiac-specific overexpression of glucose-regulated protein 78 or the administration of the chemical ER chaperone alleviated the cardiac dysfunction induced by doxorubicin and may facilitate the safe use of doxorubicin for cancer treatment.

HECT-Type Ubiquitin E3 Ligase ITCH Interacts With Thioredoxin-Interacting Protein and Ameliorates Reactive Oxygen Species-Induced Cardiotoxicity

Background

The homologous to the E6‐AP carboxyl terminus (HECT)–type ubiquitin E3 ligase ITCH is an enzyme that plays a pivotal role in posttranslational modification by ubiquitin proteasomal protein degradation. Thioredoxin‐interacting protein (TXNIP) is a negative regulator of the thioredoxin system and an endogenous reactive oxygen species scavenger. In the present study, we focused on the functional role of ubiquitin E3 ligase ITCH and its interaction with TXNIP to elucidate the mechanism of cardiotoxicity induced by reactive oxygen species, such as doxorubicin and hydrogen peroxide.

Methods and Results

Protein interaction between TXNIP and ITCH in cardiomyocyte was confirmed by immunoprecipitation assays. Overexpression of ITCH increased proteasomal TXNIP degradation and augmented thioredoxin activity, leading to inhibition of reactive oxygen species generation, p38 MAPK, p53, and subsequent intrinsic pathway cardiomyocyte apoptosis in reactive oxygen species–induced cardiotoxicity. Conversely, knockdown of ITCH using small interfering RNA inhibited TXNIP degradation and resulted in a subsequent increase in cardiomyocyte apoptosis. Next, we generated a transgenic mouse with cardiac‐specific overexpression of ITCH, called the ITCH‐Tg mouse. The expression level of TXNIP in the myocardium in ITCH‐Tg mice was significantly lower than WT littermates. In ITCH‐Tg mice, cardiac dysfunction and remodeling were restored compared with WT littermates after doxorubicin injection and myocardial infarction surgery. Kaplan–Meier analysis revealed that ITCH‐Tg mice had a higher survival rate than WT littermates after doxorubicin injection and myocardial infarction surgery.

Conclusion

We demonstrated, for the first time, that ITCH targets TXNIP for ubiquitin‐proteasome degradation in cardiomyocytes and ameliorates reactive oxygen species–induced cardiotoxicity through the thioredoxin system.

The role of frataxin in doxorubicin-mediated cardiac hypertrophy

Doxorubicin (DOX) is a highly effective anti-neoplastic agent; however, its cumulative dosing schedules are clinically limited by the development of cardiotoxicity. Previous studies have attributed the cause of DOX-mediated cardiotoxicity to mitochondrial iron accumulation and the ensuing reactive oxygen species (ROS) formation. The present study investigates the role of frataxin (FXN), a mitochondrial iron-sulfur biogenesis protein, and its role in development of DOX-mediated mitochondrial dysfunction. Athymic mice treated with DOX (5 mg/kg, 1 dose/wk with treatments, followed by 2-wk recovery) displayed left ventricular hypertrophy, as observed by impaired cardiac hemodynamic performance parameters. Furthermore, we also observed significant reduction in FXN expression in DOX-treated animals and H9C2 cardiomyoblast cell lines, resulting in increased mitochondrial iron accumulation and the ensuing ROS formation. This observation was paralleled in DOX-treated H9C2 cells by a significant reduction in the mitochondrial bioenergetics, as observed by the reduction of myocardial energy regulation. Surprisingly, similar results were observed in our FXN knockdown stable cell lines constructed by lentiviral technology using short hairpin RNA. To better understand the cardioprotective role of FXN against DOX, we constructed FXN overexpressing cardiomyoblasts, which displayed cardioprotection against mitochondrial iron accumulation, ROS formation, and reduction of mitochondrial bioenergetics. Lastly, our FXN overexpressing cardiomyoblasts were protected from DOX-mediated cardiac hypertrophy. Together, our findings reveal novel insights into the development of DOX-mediated cardiomyopathy.

Proteotoxicity and cardiac dysfunction

Baseline physiological function of the mammalian heart is under the constant threat of environmental or intrinsic pathological insults. Cardiomyocyte proteins are thus subject to unremitting pressure to function optimally, and this depends on them assuming and maintaining proper conformation. This review explores the multiple defenses a cell may use for its proteins to assume and maintain correct protein folding and conformation. There are multiple quality control mechanisms to ensure that nascent polypeptides are properly folded and mature proteins maintain their functional conformation. When proteins do misfold, either in the face of normal or pathological stimuli or because of intrinsic mutations or post-translational modifications, they must either be refolded correctly or recycled. In the absence of these corrective processes, they may become toxic to the cell. Herein, we explore some of the underlying mechanisms that lead to proteotoxicity. The continued presence and chronic accumulation of misfolded or unfolded proteins can be disastrous in cardiomyocytes because these misfolded proteins can lead to aggregation or the formation of soluble peptides that are proteotoxic. This in turn leads to compromised protein quality control and precipitating a downward spiral of the cell's ability to maintain protein homeostasis. Some underlying mechanisms are discussed and the therapeutic potential of interfering with proteotoxicity in the heart is explored.

Dissecting the Mechanisms of Doxorubicin and Oxidative Stress-Induced Cytotoxicity: The Involvement of Actin Cytoskeleton and ROCK1

We have recently reported that ROCK1 deficiency in mouse embryonic fibroblasts (MEF) has superior anti-apoptotic and pro-survival effects than antioxidants against doxorubicin, a chemotherapeutic drug. Although oxidative stress is the most widely accepted mechanism, our studies suggest that ROCK1-dependent actin cytoskeleton remodeling plays a more important role in mediating doxorubicin cytotoxicity on MEFs. To further explore the contributions of ROCK1-dependent actin cytoskeleton remodeling in response to stress, this study investigates the mechanistic differences between the cytotoxic effects of doxorubicin versus hydrogen peroxide (H2O2), with a focus on cytoskeleton alterations, apoptosis and necrosis induction. We found that both types of stress induce caspase activation but with different temporal patterns and magnitudes in MEFs: H2O2 induces the maximal levels (2 to 4-fold) of activation of caspases 3, 8, and 9 within 4 h, while doxorubicin induces much higher maximal levels (15 to 25-fold) of caspases activation at later time points (16-24 h). In addition, necrosis induced by H2O2 reaches maximal levels within 4 h while doxorubicin-induced necrosis largely occurs at 16-24 h secondary to apoptosis. Moreover, both types of stress induce actin cytoskeleton remodeling but with different characteristics: H2O2 induces disruption of stress fibers associated with cytosolic translocation of phosphorylated myosin light chain (p-MLC) from stress fibers, while doxorubicin induces cortical F-actin formation associated with cortical translocation of p-MLC from central stress fibers. Furthermore, N-acetylcysteine (an antioxidant) is a potent suppressor for H2O2-induced cytotoxic effects including caspase activation, necrosis, and cell detachment, but shows a much reduced inhibition on doxorubicin-induced changes. On the other hand, ROCK1 deficiency is a more potent suppressor for the cytotoxic effects induced by doxorubicin than by H2O2. These results support the notion that doxorubicin induces caspase activation, necrosis, and actin cytoskeleton alterations largely through ROCK1-dependent and oxidative stress-independent pathways.

The tell-tale heart: molecular and cellular responses to childhood anthracycline exposure

Since the modern era of cancer chemotherapy that began in the mid-1940s, survival rates for children afflicted with cancer have steadily improved from 10% to current rates that approach 80% (60). Unfortunately, many long-term survivors of pediatric cancer develop chemotherapy-related health effects; 25% are afflicted with a severe or life-threatening medical condition, with cardiovascular disease being a primary risk (96). Childhood cancer survivors have markedly elevated incidences of stroke, congestive heart failure (CHF), coronary artery disease, and valvular disease (96). Their cardiac mortality is 8.2 times higher than expected (93). Anthracyclines are a key component of most curative chemotherapeutic regimens used in pediatric cancer, and approximately half of all childhood cancer patients are exposed to them (78). Numerous epidemiologic and observational studies have linked childhood anthracycline exposure to an increased risk of developing cardiomyopathy and CHF, often decades after treatment. The acute toxic effects of anthracyclines on cardiomyocytes are well described; however, myocardial tissue is comprised of additional resident cell types, and events occurring in the cardiomyocyte do not fully explain the pathological processes leading to late cardiomyopathy and CHF. This review will summarize the current literature regarding the cellular and molecular responses to anthracyclines, with an important emphasis on nonmyocyte cardiac cell types as well as those that mediate the myocardial injury response.

Loss of urokinase receptor sensitizes cells to DNA damage and delays DNA repair

DNA damage induced by numerous exogenous or endogenous factors may have irreversible consequences on the cell leading to cell cycle arrest, senescence and cell death. The DNA damage response (DDR) is powerful signaling machinery triggered in response to DNA damage, to provide DNA damage recognition, signaling and repair. Most anticancer drugs induce DNA damage, and DNA repair in turn attenuates therapeutic efficiency of those drugs. Approaches delaying DNA repair are often used to increase efficiency of treatment. Recent data show that ubiquitin-proteasome system is essential for signaling and repair of DNA damage. However, mechanisms providing regulation of proteasome intracellular localization, activity, and recruitment to DNA damage sites are elusive. Even less investigated are the roles of extranuclear signaling proteins in these processes. In this study, we report the involvement of the serine protease urokinase-type plasminogen activator receptor (uPAR) in DDR-associated regulation of proteasome. We show that in vascular smooth muscle cells (VSMC) uPAR activates DNA single strand break repair signaling pathway. We provide evidence that uPAR is essential for functional assembly of the 26S proteasome. We further demonstrate that uPAR mediates DNA damage-induced phosphorylation, nuclear import, and recruitment of the regulatory subunit PSMD6 to proteasome. We found that deficiency of uPAR and PSMD6 delays DNA repair and leads to decreased cell survival. These data may offer new therapeutic approaches for diseases such as cancer, cardiovascular and neurodegenerative disorders.

Effects of short-term endurance exercise training on acute doxorubicin-induced FoxO transcription in cardiac and skeletal muscle

Doxorubicin (DOX) is a potent antitumor agent used in cancer treatment. Unfortunately, DOX can induce myopathy in both cardiac and skeletal muscle, which limits its clinical use. Importantly, exercise training has been shown to protect against DOX-mediated cardiac and skeletal muscle myopathy. However, the mechanisms responsible for this exercise-induced muscle protection remain elusive. These experiments tested the hypothesis that short-term exercise training protects against acute DOX-induced muscle toxicity, in part, due to decreased forkhead-box O (FoxO) transcription of atrophy genes. Rats (n = 6 per group) were assigned to sedentary or endurance exercise-trained groups and paired with either placebo or DOX treatment. Gene expression and protein abundance were measured in both cardiac and skeletal muscles to determine the impact of DOX and exercise on FoxO gene targets. Our data demonstrate that DOX administration amplified FoxO1 and FoxO3 mRNA expression and increased transcription of FoxO target genes [i.e., atrogin-1/muscle atrophy F-box (MaFbx), muscle ring finger-1 (MuRF-1), and BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3)] in heart and soleus muscles. Importantly, exercise training protected against DOX-induced increases of FoxO1 and MuRF-1 in cardiac muscle and also prevented the rise of FoxO3, MuRF-1, and BNIP3 in soleus muscle. Furthermore, our results indicate that exercise increased peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) in both the heart and soleus muscles. This is important because increased PGC-1α expression is known to suppress FoxO activity resulting in reduced expression of FoxO target genes. Together, these results are consistent with the hypothesis that exercise training protects against DOX-induced myopathy in both heart (FoxO1 and MuRF-1) and skeletal muscles (FoxO3, MuRF-1, and BNIP3).

Complications of chemotherapy, a basic science update

Anthracyclines, discovered 50 years ago, are antibiotics widely used as antineoplastic agents and are among the most successful anticancer therapies ever developed to treat a wide range of cancers, including hematological malignancies, soft tissue sarcomas and solid tumors. However, some anthracyclines, including doxorubicin, exhibit major signs of cardiotoxicity that may ultimately lead to heart failure (HF). Despite intensive research on doxorubicine-induced cardiotoxicity, the underlying mechanisms responsible for doxorubicin-induced cardiotoxicity have not been fully elucidated yet. Published literature so far has focused mostly on mitochondria dysfunction with consequent oxidative stress, Ca(2+) overload, and cardiomyocyte death as doxorubicin side effects, leading to heart dysfunction. This review focuses on the current understanding of the molecular mechanisms underlying doxorubicin-induced cardiomyocyte death (i.e.: cardiomyocyte death, mitochondria metabolism and bioenergetic alteration), but we will also point to new directions of possible mechanisms, suggesting potent prior or concomitant alterations of specific signaling pathways with molecular actors directly targeted by the anticancer drugs itself (i.e. calcium homeostasis or cAMP signaling cascade). The mechanisms of anticancer cardiac toxicity may be more complex than just mitochondria dysfunction. Partnership of both basic and clinical research is needed to promote new strategies in diagnosis, therapies with concomitant cardioprotection in order to achieve cancer treatment with acceptable cardiotoxicity along life span.

Urokinase receptor mediates doxorubicin-induced vascular smooth muscle cell senescence via proteasomal degradation of TRF2

The anthracycline doxorubicin is a widely used effective anti-cancer drug. However, its application and dosage are severely limited due to its cardiotoxicity. The exact mechanisms of doxorubicin-induced cardiotoxic side effects remain poorly understood. Even less is known about the impact of doxorubicin treatment on vascular damage. We found that low doses of doxorubicin induced a senescent response in human primary vascular smooth muscle cells (VSMC). We observed that expression of urokinase receptor (uPAR) was upregulated in response to doxorubicin. Furthermore, the level of uPAR expression played a decisive role in developing doxorubicin-induced senescence. uPAR silencing in human VSMC by means of RNA interference as well as uPAR knockout in mouse VSMC resulted in abrogation of doxorubicin-induced cellular senescence. On the contrary, uPAR overexpression promoted VSMC senescence. We further found that proteasomal degradation of telomeric repeat binding factor 2 (TRF2) mediates doxorubicin-induced VSMC senescence. Our results demonstrate that uPAR controls the ubiquitin-proteasome system in VSMC and regulates doxorubicin-induced TRF2 ubiquitination and proteasomal degradation via this mechanism. Therefore, VSMC senescence induced by low doses of doxorubicin may contribute to vascular damage upon doxorubicin treatment. uPAR-mediated TRF2 ubiquitination and proteasomal degradation are further identified as a molecular mechanism underlying this process.

MK5 is degraded in response to doxorubicin and negatively regulates doxorubicin-induced apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. The mechanisms by which hepatoma cells resist apoptosis induced by doxorubicin are largely unknown. MAPKAPK5 (MK5), also named as p38-regulated/activated protein kinase (PRAK), has been identified as a crucial mediator of skin tumorigenesis in mouse and colon cancerogenesis in human. Here, we describe a novel role of MK5 in doxorubicin-induced apoptosis in human hepatoma cells. Expression of MK5 was highly upregulated in hepatoma cell lines. Doxorubicin rather than other chemotherapeutic drugs reduced MK5 protein level in a time- and concentration-dependent manner in hepatoma cells (HepG2 and Hep3B). We further showed that MK5 degradation induced by doxorubicin was via the 26S proteasome. Remarkably, stable overexpression of MK5 led to decreased cleavage of caspase-3 and PARP and attenuated doxorubicin-induced apoptosis, while stable knockdown of endogenous MK5 sensitized hepatoma cells to doxorubicin, which was coupled with increased cleavage of caspase-3 and PARP. Taken together, our results firstly demonstrate that MK5 is degraded in response to doxorubicin and negatively regulates doxorubicin-induced apoptosis, providing novel insights into the molecular mechanism of doxorubicin resistance in hepatoma cells.

Effects of doxorubicin cancer therapy on autophagy and the ubiquitin-proteasome system in long-term cultured adult rat cardiomyocytes

The clinical use of anthracyclines in cancer therapy is limited by dose-dependent cardiotoxicity that involves cardiomyocyte injury and death. We have tested the hypothesis that anthracyclines affect protein degradation pathways in adult cardiomyocytes. To this aim, we assessed the effects of doxorubicin (Doxo) on apoptosis, autophagy and the proteasome/ubiquitin system in long-term cultured adult rat cardiomyocytes. Accumulation of poly-ubiquitinated proteins, increase of cathepsin-D-positive lysosomes and myofibrillar degradation were observed in Doxo-treated cardiomyocytes. Chymotrypsin-like activity of the proteasome was initially increased and then inhibited by Doxo over a time-course of 48 h. Proteasome 20S proteins were down-regulated by higher doses of Doxo. The expression of MURF-1, an ubiquitin-ligase specifically targeting myofibrillar proteins, was suppressed by Doxo at all concentrations measured. Microtubule-associated protein 1 light chain 3B (LC3)-positive punctae and both LC3-I and -II proteins were induced by Doxo in a dose-dependent manner, as confirmed by using lentiviral expression of green fluorescence protein bound to LC3 and live imaging. The lysosomotropic drug chloroquine led to autophagosome accumulation, which increased with concomitant Doxo treatment indicating enhanced autophagic flux. We conclude that Doxo causes a downregulation of the protein degradation machinery of cardiomyocytes with a resulting accumulation of poly-ubiquitinated proteins and autophagosomes. Although autophagy is initially stimulated as a compensatory response to cytotoxic stress, it is followed by apoptosis and necrosis at higher doses and longer exposure times. This mechanism might contribute to the late cardiotoxicity of anthracyclines by accelerated aging of the postmitotic adult cardiomyocytes and to the susceptibility of the aging heart to anthracycline cancer therapy.

Mechanisms and management of doxorubicin cardiotoxicity

Doxorubicin is an effective anti-tumor agent with a cumulative dose-dependent cardiotoxicity. In addition to its principal toxic mechanisms involving iron and redox reactions, recent studies have described new mechanisms of doxorubicin-induced cell death, including abnormal protein processing, hyper-activated innate immune responses, inhibition of neuregulin-1 (NRG1)/ErbB(HER) signalling, impaired progenitor cell renewal/cardiac repair, and decreased vasculogenesis. Although multiple mechanisms involved in doxorubicin cardiotoxicity have been studied, there is presently no clinically proven treatment established for doxorubicin cardiomyopathy. Iron chelator dexrazoxane, angiotensin converting enzyme (ACE) inhibitors, and β-blockade have been proposed as potential preventive strategies for doxorubicin cardiotoxicity. Novel approaches such as anti-miR-146 or recombinant NRG1 to increase cardiomyocyte resistance to toxicity may be of interest in the future.

A non-covalent interaction between small ubiquitin-like modifier-1 and Zac1 regulates Zac1 cellular functions

Zac1, a zinc-finger protein that regulates apoptosis and cell cycle arrest 1, such as p53, can induce cell-cycle arrest and apoptosis. The transactivation and coactivation functions of Zac1 may occur at non-promyelocytic leukemia nuclear body (PML-NB) sites in the presence of other PML-NB components, including ubiquitin-conjugating 9 (Ubc9). It is unclear whether post-translational modification of Zac1 by the small ubiquitin-like modifier SUMO plays a role in the coactivation functions of Zac1 for the regulation of the p21 gene. Mutagenesis experiments revealed that the two SUMO-binding lysine residues of Zac1, K237 and K424, repress the transactivation activity of Zac1. Studies using a SUMO-1 C-terminal di-glycine motif mutant that is deficient in the ability to form covalent bonds with lysines, SUMO-1 (GA), and a dominant-negative Ubc9 construct (C93S) indicated that SUMO-1 might regulate Zac1 transactivation and coactivation via a non-covalent interaction. Unlike the wild-type Zac1, which induced apoptosis, the Zac1 (K237/424R) double mutant had the ability to induce autophagy. The functional role of p21 remains to be investigated. SUMO-1 selectively suppressed the induction of the p21 gene and protein by wild-type Zac1 but not by the Zac1 (K237/424R) double mutant. Moreover, wild-type Ubc9 but not Ubc9 (C93S) further potentiated the suppression of SUMO-1 in all Zac1-induced p21 promoter activities. Our data reveal that p21 may be an important factor for the prevention of Zac1-induced apoptosis without affecting autophagosome formation. This work indicates that Zac1 functions are regulated, at least in part, via non-covalent interactions with SUMO-1 for the induction of p21, which is important for the modulation of apoptosis.

Apoptosis in Anthracycline Cardiomyopathy

Apoptosis is a tightly regulated physiologic process of programmed cell death that occurs in both normal and pathologic tissues. Numerous in vitro or in vivo studies have indicated that cardiomyocyte death through apoptosis and necrosis is a primary contributor to the progression of anthracycline-induced cardiomyopathy. There are now several pieces of evidence to suggest that activation of intrinsic and extrinsic apoptotic pathways contribute to anthracycline-induced apoptosis in the heart. Novel strategies were developed to address a wide variety of cardiotoxic mechanisms and apoptotic pathways by which anthracycline influences cardiac structure and function. Anthracycline-induced apoptosis provides a very valid representation of cardiotoxicity in the heart, an argument which has implications for the most appropriate animal models of damaged heart plus diverse pharmacological effects. In this review we describe various aspects of the current understanding of apoptotic cell death triggered by anthracycline. Differences in the sensitivity to anthracycline-induced apoptosis between young and adult hearts are also discussed.

Proteostasis and REDOX state in the heart

Force-generating contractile cells of the myocardium must achieve and maintain their primary function as an efficient mechanical pump over the life span of the organism. Because only half of the cardiomyocytes can be replaced during the entire human life span, the maintenance strategy elicited by cardiac cells relies on uninterrupted renewal of their components, including proteins whose specialized functions constitute this complex and sophisticated contractile apparatus. Thus cardiac proteins are continuously synthesized and degraded to ensure proteome homeostasis, also termed "proteostasis." Once synthesized, proteins undergo additional folding, posttranslational modifications, and trafficking and/or become involved in protein-protein or protein-DNA interactions to exert their functions. This includes key transient interactions of cardiac proteins with molecular chaperones, which assist with quality control at multiple levels to prevent misfolding or to facilitate degradation. Importantly, cardiac proteome maintenance depends on the cellular environment and, in particular, the reduction-oxidation (REDOX) state, which is significantly different among cardiac organelles (e.g., mitochondria and endoplasmic reticulum). Taking into account the high metabolic activity for oxygen consumption and ATP production by mitochondria, it is a challenge for cardiac cells to maintain the REDOX state while preventing either excessive oxidative or reductive stress. A perturbed REDOX environment can affect protein handling and conformation (e.g., disulfide bonds), disrupt key structure-function relationships, and trigger a pathogenic cascade of protein aggregation, decreased cell survival, and increased organ dysfunction. This review covers current knowledge regarding the general domain of REDOX state and protein folding, specifically in cardiomyocytes under normal-healthy conditions and during disease states associated with morbidity and mortality in humans.

Doxorubicin acts via mitochondrial ROS to stimulate catabolism in C2C12 myotubes

Doxorubicin, a commonly prescribed chemotherapeutic agent, causes skeletal muscle wasting in cancer patients undergoing treatment and increases mitochondrial reactive oxygen species (ROS) production. ROS stimulate protein degradation in muscle by activating proteolytic systems that include caspase-3 and the ubiquitin-proteasome pathway. We hypothesized that doxorubicin causes skeletal muscle catabolism through ROS, causing upregulation of E3 ubiquitin ligases and caspase-3. We tested this hypothesis by exposing differentiated C2C12 myotubes to doxorubicin (0.2 μM). Doxorubicin decreased myotube width 48 h following exposure, along with a 40-50% reduction in myosin and sarcomeric actin. Cytosolic oxidant activity was elevated in myotubes 2 h following doxorubicin exposure. This increase in oxidants was followed by an increase in the E3 ubiquitin ligase atrogin-1/muscle atrophy F-box (MAFbx) and caspase-3. Treating myotubes with SS31 (opposes mitochondrial ROS) inhibited expression of ROS-sensitive atrogin-1/MAFbx and protected against doxorubicin-stimulated catabolism. These findings suggest doxorubicin acts via mitochondrial ROS to stimulate myotube atrophy.

The role of the proteasome in heart disease

Intensive investigations into the pathophysiological significance of the proteasome in the heart did not start until the beginning of the past decade but exciting progress has been made and summarized here as two fronts. First, strong evidence continues to emerge to support a novel hypothesis that proteasome functional insufficiency represents a common pathological phenomenon in a large subset of heart disease, compromises protein quality control in heart muscle cells, and thereby acts as a major pathogenic factor promoting the progression of the subset of heart disease to congestive heart failure. This front is represented by the studies on the ubiquitin-proteasome system (UPS) in cardiac proteinopathy, which have taken advantage of a transgenic mouse model expressing a fluorescence reporter for UPS proteolytic function. Second, pharmacological inhibition of the proteasome has been explored experimentally as a potential therapeutic strategy to intervene on some forms of heart disease, such as pressure-overload cardiac hypertrophy, viral myocarditis, and myocardial ischemic injury. Not only between the two fronts but also within each one, a multitude of inconsistencies and controversies remain to be explained and clarified. At present, the controversy perhaps reflects the sophistication of cardiac proteasomes in terms of the composition, assembly, and regulation, as well as the intricacy and diversity of heart disease in terms of its etiology and pathogenesis. A definitive role of altered proteasome function in the development of various forms of heart disease remains to be established. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!

Perturbation of cullin deneddylation via conditional Csn8 ablation impairs the ubiquitin-proteasome system and causes cardiomyocyte necrosis and dilated cardiomyopathy in mice

RATIONALE

Ubiquitin-proteasome system (UPS) dysfunction has been implicated in cardiac pathogenesis. Understanding how cardiac UPS function is regulated will facilitate delineating the pathophysiological significance of UPS dysfunction and developing new therapeutic strategies. The COP9 (constitutive photomorphogenesis mutant 9) signalosome (CSN) may regulate the UPS, but this has not been tested in a critical vertebrate organ. Moreover, the role of CSN in a postmitotic organ and the impact of cardiomyocyte-restricted UPS dysfunction on the heart have not been reported.

OBJECTIVE

We sought to determine the role of CSN-mediated deneddylation in UPS function and postnatal cardiac development and function.

METHODS AND RESULTS

Cardiomyocyte-restricted Csn8 gene knockout (CR-Csn8KO) in mice was achieved using a Cre-LoxP system. CR-Csn8KO impaired CSN holocomplex formation and cullin deneddylation and resulted in decreases in F-box proteins. Probing with a surrogate misfolded protein revealed severe impairment of UPS function in CR-Csn8KO hearts. Consequently, CR-Csn8KO mice developed cardiac hypertrophy, which rapidly progressed to heart failure and premature death. Massive cardiomyocyte necrosis rather than apoptosis appears to be the primary cause of the heart failure. This is because (1) massive necrotic cell death and increased infiltration of leukocytes were observed before increased apoptosis; (2) increased apoptosis was not detectable until overt heart failure was observed; and (3) cardiac overexpression of Bcl2 failed to ameliorate CR-Csn8KO mouse premature death.

CONCLUSIONS

Csn8/CSN plays an essential role in cullin deneddylation, UPS-mediated degradation of a subset of proteins, and the survival of cardiomyocytes and, therefore, is indispensable in postnatal development and function of the heart. Cardiomyocyte-restricted UPS malfunction can cause heart failure.

Phylogenetic origin of LI-cadherin revealed by protein and gene structure analysis

The intestine specific LI-cadherin differs in its overall structure from classical and desmosomal cadherins by the presence of seven instead of five cadherin repeats and a short cytoplasmic domain. Despite the low sequence similarity, a comparative protein structure analysis revealed that LI-cadherin may have originated from a five-repeat predecessor cadherin by a duplication of the first two aminoterminal repeats. To test this hypothesis, we cloned the murine LI-cadherin gene and compared its structure to that of other cadherins. The intron-exon organization, including the intron positions and phases, is perfectly conserved between repeats 3-7 of LI-cadherin and 1-5 of classical cadherins. Moreover, the genomic structure of the repeats 1-2 and 3-4 is identical for LI-cadherin and highly similar to that of the repeats 1-2 of classical cadherins. These findings strengthen our assumption that LI-cadherin originated from an ancestral cadherin with five domains by a partial gene duplication event.