Heme oxygenase-1 promotes survival of renal cancer cells through modulation of apoptosis- and autophagy-regulating molecules

Molecular mechanism of ferroptosis and its application in the treatment of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is a common malignant tumor of the urinary tract, the incidence of which is continuously increasing and affects human health worldwide. Despite advances in existing treatments, treatment outcomes still need to be improved due to higher rates of postoperative recurrence, chemotherapy resistance, etc.; thus, there is an urgent need for innovative therapeutic approaches. Ferroptosis is a recently found type of regulated cell death that is characterized primarily by the buildup of lipid peroxidation products and fatal reactive oxygen species created by iron metabolism, which plays a crucial role in tumor progression and therapy.With the molecular mechanisms associated with ferroptosis being increasingly studied and refined, triggering ferroptosis by regulators that target ferroptosis and ccRCC may be the key to developing potential therapeutic strategies for ccRCC. Therefore, ferroptosis is expected to be a new breakthrough in treating ccRCC. This paper examines the mechanism of ferroptosis, the regulatory mechanism of ferroptosis in ccRCC, and the potential application of ferroptosis in combination with other therapies for the treatment of ccRCC. The goal is to offer novel perspectives for the research and clinical application of ferroptosis in the treatment of ccRCC.

HO-1-Mediated Autophagic Restoration Protects Lens Epithelial Cells Against Oxidative Stress and Cellular Senescence

Purpose

Oxidative stress and cellular senescence are risk factors for age-related cataract. Heme oxygenase 1 (HO-1) is a critical antioxidant enzyme and related to autophagy. Here, we investigate the crosstalk among HO-1, oxidative stress, and cellular senescence in mouse lens epithelial cells (LECs).

Methods

The gene expression of HO-1, p21, LC3, and p62 was measured in human samples. The protective properties of HO-1 were examined in hydrogen peroxide (H2O2)-damaged LECs. Autophagic flux was examined by Western blot and mRFP-GFP-LC3 assay. Western blotting and lysotracker staining were used to analyze lysosomal function. Flow cytometry was used to detect intracellular reactive oxygen species and analyze cell cycle. Senescence-associated β-galactosidase assay was used to determine cellular senescence. The crosstalk between HO-1 and transcription factor EB (TFEB) was further observed in TFEB-knockdown cells. The TFEB binding site in the promoter region of Hmox1 was predicted by the Jasper website and was confirmed by chromatin immunoprecipitation assay.

Results

HO-1 gene expression decreased in LECs of patients with age-related nuclear cataract, whereas mRNA expression levels of p21, LC3, and p62 increased. Upon H2O2-induced oxidative stress, LECs showed the characteristics of autophagic flux blockade, lysosomal dysfunction, and premature senescence. Interestingly, HO-1 significantly restored the impaired autophagic flux and lysosomal function and delayed cellular senescence. TFEB gene silencing greatly reduced the HO-1-mediated autophagic restoration, leading to a failure to prevent LECs from oxidative stress and premature senescence.

Conclusions

We demonstrated HO-1 effects on restoring autophagic flux and delaying cellular senescence under oxidative stress in LECs, which are dependent on TFEB.

A novel combination therapy with Cabozantinib and Honokiol effectively inhibits c-Met-Nrf2-induced renal tumor growth through increased oxidative stress

Receptor tyrosine kinase (RTK), c-Met, is overexpressed and hyper active in renal cell carcinoma (RCC). Most of the therapeutic agents mediate cancer cell death through increased oxidative stress. Induction of c-Met in renal cancer cells promotes the activation of redox-sensitive transcription factor Nrf2 and cytoprotective heme oxygenase-1 (HO-1), which can mediate therapeutic resistance against oxidative stress. c-Met/RTK inhibitor, Cabozantinib, has been approved for the treatment of advanced RCC. However, acquired drug resistance is a major hurdle in the clinical use of cabozantinib. Honokiol, a naturally occurring phenolic compound, has a great potential to downregulate c-Met-induced pathways. In this study, we found that a novel combination treatment with cabozantinib + Honokiol inhibits the growth of renal cancer cells in a synergistic manner through increased production of reactive oxygen species (ROS); and it significantly facilitates apoptosis-and autophagy-mediated cancer cell death. Activation of c-Met can induce Rubicon (a negative regulator of autophagy) and p62 (an autophagy adaptor protein), which can stabilize Nrf2. By utilizing OncoDB online database, we found a positive correlation among c-Met, Rubicon, p62 and Nrf2 in renal cancer. Interestingly, the combination treatment significantly downregulated Rubicon, p62 and Nrf2 in RCC cells. In a tumor xenograft model, this combination treatment markedly inhibited renal tumor growth in vivo; and it is associated with decreased expression of Rubicon, p62, HO-1 and vessel density in the tumor tissues. Together, cabozantinib + Honokiol combination can significantly inhibit c-Met-induced and Nrf2-mediated anti-oxidant pathway in renal cancer cells to promote increased oxidative stress and tumor cell death.

Cytoprotective Role of Heme Oxygenase-1 in Cancer Chemoresistance: Focus on Antioxidant, Antiapoptotic, and Pro-Autophagy Properties

Chemoresistance remains the foremost challenge in cancer therapy. Targeting reactive oxygen species (ROS) manipulation is a promising strategy in cancer treatment since tumor cells present high levels of intracellular ROS, which makes them more vulnerable to further ROS elevation than normal cells. Nevertheless, dynamic redox evolution and adaptation of tumor cells are capable of counteracting therapy-induced oxidative stress, which leads to chemoresistance. Hence, exploring the cytoprotective mechanisms of tumor cells is urgently needed to overcome chemoresistance. Heme oxygenase-1 (HO-1), a rate-limiting enzyme of heme degradation, acts as a crucial antioxidant defense and cytoprotective molecule in response to cellular stress. Recently, emerging evidence indicated that ROS detoxification and oxidative stress tolerance owing to the antioxidant function of HO-1 contribute to chemoresistance in various cancers. Enhanced HO-1 expression or enzymatic activity was revealed to promote apoptosis resistance and activate protective autophagy, which also involved in the development of chemoresistance. Moreover, inhibition of HO-1 in multiple cancers was identified to reversing chemoresistance or improving chemosensitivity. Here, we summarize the most recent advances regarding the antioxidant, antiapoptotic, and pro-autophagy properties of HO-1 in mediating chemoresistance, highlighting HO-1 as a novel target for overcoming chemoresistance and improving the prognosis of cancer patients.

Modulation of Nrf2/HO-1 by Natural Compounds in Lung Cancer

Oxidative stresses (OSs) are considered a pivotal factor in creating various pathophysiological conditions. Cells have been able to move forward by modulating numerous signaling pathways to moderate the defects of these stresses during their evolution. The company of Kelch-like ECH-associated protein 1 (Keap1) as a molecular sensing element of the oxidative and electrophilic stress and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) as a master transcriptional regulator of the antioxidant response makes a master cytoprotective antioxidant pathway known as the Keap1/Nrf2 pathway. This pathway is considered a dual-edged sword with beneficial features for both normal and cancer cells by regulating the gene expression of the array of endogenous antioxidant enzymes. Heme oxygenase-1 (HO-1), a critical enzyme in toxic heme removal, is one of the clear state indicators for the duality of this pathway. Therefore, Nrf2/HO-1 axis targeting is known as a novel strategy for cancer treatment. In this review, the molecular mechanism of action of natural antioxidants on lung cancer cells has been investigated by relying on the Nrf2/HO-1 axis.

The dual role and mutual dependence of heme/HO-1/Bach1 axis in the carcinogenic and anti-carcinogenic intersection

INTRODUCTION

In physiological concentrations, heme is nontoxic to the cell and is essential for cell survival and proliferation. Increasing intracellular heme concentrations beyond normal levels, however, will lead to carcinogenesis and facilitate the survival of tumor cells. Simultaneously, heme in an abnormally high quantity is also a potent inducer of tumor cell death, contributing to its ability to generate oxidative stress on the cells by boosting oxidative phosphorylation and suppressing tumors through ferroptosis. During tumorigenesis and progression, therefore, heme works as a double-edged sword. Heme oxygenase 1 (HO-1) is the rate-limiting enzyme in heme catabolism, which converts heme into physiologically active catabolites of carbon monoxide (CO), biliverdin, and ferrous iron (Fe²⁺). HO-1 maintains redox equilibrium in healthy cells and functions as a carcinogenesis inhibitor. It is widely recognized that HO-1 is involved in the adaptive response to cellular stress and the anti-inflammation effect. Notably, its expression level in cancer cells corresponds with tumor growth, aggressiveness, metastasis, and angiogenesis. Besides, heme-binding transcription factor BTB and CNC homology 1 (Bach1) play a critical regulatory role in heme homeostasis, oxidative stress and senescence, cell cycle, angiogenesis, immune cell differentiation, and autoimmune disorders. Moreover, it was found that Bach1 influences cancer cells' metabolism and metastatic capacity. Bach1 controls heme level by adjusting HO-1 expression, establishing a negative feedback loop.

MATERIALS AND METHODS

Herein, the authors review recent studies on heme, HO-1, and Bach1 in cancer. Specifically, they cover the following areas: (1) the carcinogenic and anticarcinogenic aspects of heme; (2) the carcinogenic and anticarcinogenic aspects of HO-1; (3) the carcinogenic and anticarcinogenic aspects of Bach1; (4) the interactions of the heme/HO-1/Bach1 axis involved in tumor progression.

CONCLUSION

This review summarized the literature about the dual role of the heme/HO-1/Bach1 axis and their mutual dependence in the carcinogenesis and anti-carcinogenesis intersection.

Antitumor Effect of Zinc Acetate in Hepatocellular Carcinoma Cell Lines via the Induction of Apoptosis

We aimed to verify antitumor effects of zinc acetate on hepatocellular carcinoma (HCC) in vitro. Five HCC cell lines (HepG2, Hep3B, Huh7, HLE and Alex) were used to evaluate the antitumor effects of zinc acetate. Cell viability was determined by the Cell Counting Kit-8 assay. The cell-cycle alteration was evaluated by a flow cytometric analysis and the detection of cell cycle-related proteins. Apoptosis was determined based on the caspase-cleaved cytokeratin 18 (cCK18) levels. The microRNAs (miRNAs) related to an antitumor effect of zinc acetate were identified using microarrays. Zinc acetate significantly inhibited the proliferation of HCC cells in a dose-dependent manner. The treatment with zinc acetate resulted in significantly increased cCK18 levels in the supernatant and enhanced the expression of heme oxygenase-1 (HO-1) in HCC cells. The flow cytometric analysis revealed an increase of HCC cells in the S and G₂/M phases by the administration of zinc acetate, and the expressions of Cdk2 and cyclin E were increased. The miRNA expression profile of the HCC cells treated with zinc acetate was extremely different from that of the untreated HCC cells. These results suggest that the zinc acetate supplementation induces the apoptosis of HCC cells, but does not affect the cell cycle progression. Upregulation of HO-1 and the alteration of miRNAs' profile may be involved in antitumor effects of zinc acetate in HCC cells.

Non-canonical vs. Canonical Functions of Heme Oxygenase-1 in Cancer

Heme oxygenase-1 (HO-1) is a critical stress-responsive enzyme that has antioxidant and anti-inflammatory functions. HO-1 catalyzes heme degradation, which gives rise to the formation of carbon monoxide (CO), biliverdin, and iron. The upregulation of HO-1 under pathological conditions associated with cellular stress represents an important cytoprotective defense mechanism by virtue of the anti-oxidant properties of the bilirubin and the anti-inflammatory effect of the CO produced. The same mechanism is hijacked by premalignant and cancerous cells. In recent years, however, there has been accumulating evidence supporting that the upregulation of HO-1 promotes cancer progression, independently of its catalytic activity. Such non-canonical functions of HO-1 are associated with its interaction with other proteins, particularly transcription factors. HO-1 also undergoes post-translational modifications that influence its stability, functional activity, cellular translocation, etc. HO-1 is normally present in the endoplasmic reticulum, but distinct subcellular localizations, especially in the nucleus, are observed in multiple cancers. The nuclear HO-1 modulates the activation of various transcription factors, which does not appear to be mediated by carbon monoxide and iron. This commentary summarizes the non-canonical functions of HO-1 in the context of cancer growth and progression and underlying regulatory mechanisms.

Non-canonical vs. Canonical Functions of Heme Oxygenase-1 in Cancer

Heme oxygenase-1 (HO-1) is a critical stress-responsive enzyme that has antioxidant and anti-inflammatory functions. HO-1 catalyzes heme degradation, which gives rise to the formation of carbon monoxide (CO), biliverdin, and iron. The upregulation of HO-1 under pathological conditions associated with cellular stress represents an important cytoprotective defense mechanism by virtue of the anti-oxidant properties of the bilirubin and the anti-inflammatory effect of the CO produced. The same mechanism is hijacked by premalignant and cancerous cells. In recent years, however, there has been accumulating evidence supporting that the upregulation of HO-1 promotes cancer progression, independently of its catalytic activity. Such non-canonical functions of HO-1 are associated with its interaction with other proteins, particularly transcription factors. HO-1 also undergoes post-translational modifications that influence its stability, functional activity, cellular translocation, etc. HO-1 is normally present in the endoplasmic reticulum, but distinct subcellular localizations, especially in the nucleus, are observed in multiple cancers. The nuclear HO-1 modulates the activation of various transcription factors, which does not appear to be mediated by carbon monoxide and iron. This commentary summarizes the non-canonical functions of HO-1 in the context of cancer growth and progression and underlying regulatory mechanisms.

Autophagy as a Vital Therapy Target for Renal Cell Carcinoma

Autophagy is a process that degrades and recycles superfluous organelles or damaged cellular contents. It has been found to have dual functions in renal cell carcinoma (RCC). Many autophagy-related proteins are regarded as prognostic markers of RCC. Researchers have attempted to explore synthetic and phytochemical drugs for RCC therapy that target autophagy. In this review, we highlight the importance of autophagy in RCC and potential treatments related to autophagy.

Oxidized Lipoproteins Promote Resistance to Cancer Immunotherapy Independent of Patient Obesity

Antitumor immunity is impaired in obese mice. Mechanistic insight into this observation remains sparse and whether it is recapitulated in patients with cancer is unclear because clinical studies have produced conflicting and controversial findings. We addressed this by analyzing data from patients with a diverse array of cancer types. We found that survival after immunotherapy was not accurately predicted by body mass index or serum leptin concentrations. However, oxidized low-density lipoprotein (ox-LDL) in serum was identified as a suppressor of T-cell function and a driver of tumor cytoprotection mediated by heme oxygenase-1 (HO-1). Analysis of a human melanoma gene expression database showed a clear association between higher HMOX1 (HO-1) expression and reduced progression-free survival. Our in vivo experiments using mouse models of both melanoma and breast cancer revealed HO-1 as a mechanism of resistance to anti-PD1 immunotherapy but also exposed HO-1 as a vulnerability that could be exploited therapeutically using a small-molecule inhibitor. In conclusion, our clinical data have implicated serum ox-LDL as a mediator of therapeutic resistance in patients with cancer, operating as a double-edged sword that both suppressed T-cell immunity and simultaneously induced HO-1-mediated tumor cell protection. Our studies also highlight the therapeutic potential of targeting HO-1 during immunotherapy, encouraging further translational development of this combination approach.See article by Kuehm et al., p. 227.

Importance of Heme Oxygenase-1 in Gastrointestinal Cancers: Functions, Inductions, Regulations, and Signaling

INTRODUCTION : Colorectal cancer (CRC) is one of the important gastrointestinal tract tumors. Heme is mainly absorbed in the colon and induces nitrosamine formation, genotoxicity,  and oxidative stress, and increases the risk of CRC.

MATERIALS AND METHODS

Information was collected from articles on Scopus, Google Scholar, and PubMed.

RESULTS

Heme can irritate intestinal epithelial cells and increases the proliferation of colonic mucosa. Heme can be considered as a carcinogenic agent for CRC induction. In typical situations, Heme Oxygenase-1 (HO-1) is expressed at low concentration in the gastrointestinal tract, but its expression is elevated during lesion and inflammation. Based on the multiple reports, the impact of HO-1 on tumor growth is related to the cancer cell type. Increased HO-1 levels were also indicated in different human and animal malignancies, possibly through its contribution to tumor cell growth, metastasis, expression of angiogenic factors, and resistance to chemotherapy. Recent studies noted that HO-1 can act as an immunomodulator that suppresses immune cell maturation, activation, and infiltration. It also inhibits apoptosis through CO production that leads to p53 suppression. The upregulation of HO-1 significantly increases the endurance of colon cancer cell lines. Therefore, it is supposed that HO-1 inhibitors could become a novel antitumor agent. Lactobacillus rhamnosus and its metabolites can activate Nrf2 and improves anti-oxidant levels along with upregulation of its objective genes like HO-1, and downregulation of NF-κB which reduce phosphorylated TNF-α, IL-1β, and PAI-1.

CONCLUSION

The precise mechanism accountable for the anti-inflammatory features of HO-1 is not completely understood; nevertheless, the CO signaling function associated with the antioxidant property shown by bilirubin possibly will play an act in the improvement of inflammation.

A novel hemocompatible core@shell nanosystem for selective targeting and apoptosis induction in cancer cells

Synthesis, characterization and evaluation of transferrin-decorated mesoporous silica-coated silver nanoparticles as a novel hemocompatible core@shell nanosystem for selective targeting and apoptosis induction in cancer cells.

Copper-imidazo[1,2-a]pyridines induce intrinsic apoptosis and modulate the expression of mutated p53, haem-oxygenase-1 and apoptotic inhibitory proteins in HT-29 colorectal cancer cells

Metastatic colorectal cancer responds poorly to treatment and is a leading cause of cancer related deaths. Worldwide, chemotherapy of metastatic colorectal cancer remains plagued by poor efficacy, development of resistance and serious adverse effects. Copper-imidazo[1,2-a]pyridines were previously shown by our group to be selectively active against several cancer cell lines, with three complexes, JD46(27), JD47(29), and JD88(21), showing IC₅₀ values between 0.8 and 1.8 μM against HT-29 cells. Here, we report that treatment with the copper complexes resulted in fragmented nuclei suggestive of apoptotic cell death, which was confirmed by increased annexin V binding and caspase-3/7 activity. The copper complexes caused a loss of mitochondrial membrane potential and increased caspase-9 activity. The absence of caspase-8 activity indicated activation of the intrinsic pathway. Proteomic analysis revealed that copper-imidazo[1,2-a]pyridines decreased the expression of phosphorylated forms of p53 [phospho-p53(S15), phospho-p53(S46) and phospho-p53(S392)]. The expression of inhibitor of apoptosis proteins, XIAP, cIAP1, livin, and the antiapoptotic proteins, Bcl-2 and Bcl-x, was decreased. HO/HMOX/HSP32, expression was notably increased, which suggested the accumulation of reactive oxygen species. Increased expression of TRAIL-R2/DR5 death receptor indicated the possible dual activation of both the extrinsic and intrinsic apoptotic pathways; however, caspase-8 activation could not be demonstrated. In conclusion, the copper-imidazo[1,2-a]pyridines were effective inducers of apoptotic cell death at low micromolar concentrations and changed the expression levels of proteins important for cell survival and cell death. These copper complexes may be useful tools to better understand the complexity of signalling networks in cancer cell death in response to cell stress.

Nrf2-Heme oxygenase-1 modulates autophagy and inhibits apoptosis triggered by elevated glucose levels in renal tubule cells

Background

Autophagy is a highly balanced process in which lysosomes remove aged and damaged organelles and cellular proteins. Autophagy is essential to maintain homeostasis in the kidneys.

Methods

Using human renal tubule cells HK-2, we assessed the impact of high glucose (HG) on autophagy. We also evaluated the capability of sulforaphane (SFN) to protect the HK-2 cells from HG-induced apoptosis by modulating autophagy.

Results

SFN modulated autophagy and decreased apoptosis in the HK-2 cells that were cultured in 250 mM glucose medium for two days. The reactive oxygen species (ROS) levels increased, as expected, in the cells cultured in the 250 mM glucose medium. However, the SFN decreased the ROS levels in the HK-2 cells. The overexpression of heme oxygenase-1 (HO-1) by SFN decreased the expression of LC3 and beclin-1. LC3 and beclin-1 were involved in the downregulation of caspase-3 that was observed in the HG-induced cells.

Conclusion

The activation of nuclear factor E2-related factor 2 (Nrf2)–HO–1 inhibited ROS expression and subsequently attenuated autophagy and cell apoptosis after HG injury was decreased. HG injury led to the activation of autophagy and HO-1 in order to combat oxidative stress and protect against cell apoptosis. Therefore, HO-1 activation can prevent ROS development and oxidative stress during HG injury, which considerably decreases autophagy and apoptosis.

Lysosomal Destabilizing Drug Siramesine and the Dual Tyrosine Kinase Inhibitor Lapatinib Induce a Synergistic Ferroptosis through Reduced Heme Oxygenase-1 (HO-1) Levels

Ferroptosis is an iron-dependent type of cell death distinct from apoptosis or necrosis characterized by accumulation of reactive oxygen species. The combination of siramesine, a lysosomotropic agent, and lapatinib, a dual tyrosine kinase inhibitor (TKI), synergistically induced cell death in breast cancer cells mediated by ferroptosis. In this study, we showed that this combination of siramesine and lapatinib induces synergistic cell death in glioma cell line U87 and lung adenocarcinoma cell line A549. This cell death was characterized by the increase in iron content, reactive oxygen species (ROS) production, and lipid peroxidation accumulation after 24 hours of treatment. Moreover, iron chelator DFO and ferrostatin-1, a ferroptosis inhibitor, significantly reduced cell death. The mechanism underlying the activation of the ferroptotic pathway involves lysosomal permeabilization and increase in reactive iron levels in these cells. In addition, the downregulation of heme oxygenase-1 (HO-1) protein occurred. Overexpression of HO-1 resulted in reduction of ROS and lipid peroxidation production and cell death. Furthermore, knocking down of HO-1 combined with siramesine treatment resulted in increased cell death. Finally, we found that the inhibition of the proteasome system rescued HO-1 expression levels. Our results suggest that the induction of ferroptosis by combining a lysosomotropic agent and a tyrosine kinase inhibitor is mediated by iron release from lysosomes and HO-1 degradation by the proteasome system.

Deletion of HO-1 blocks development of B lymphocytes in mice

B lymphocytes, a key cluster of cells composing the immune system, can protect against abnormal biological factors. Heme oxygenase-1 (HO-1) plays important roles in cell proliferation and immune regulation, but its effects on the development and growth of B lymphocytes are still unknown. Herein, the count of B lymphocytes in HO-1 gene knockout (HO-1^+/-) mice was significantly lower than that of the HO-1 gene wild-type (HO-1^WT) mice. Meanwhile, the cell count of HO-1^+/- mice did not recover after irradiation for one week, due to the G0/G1 phase arrest of Pro-B cells and the augmented apoptosis of Pre-B cells. Up-regulation of HO-1 by lentivirus attenuated the Pro-B cell cycle arrest and Pre-B cell apoptosis. To understand the molecular mechanism by which HO-1 knockout blocked B lymphocyte development, protein-to-protein interaction network and Western blot were used. The PI3K/AKT signaling pathway mediated the regulatory effects of HO-1 on B lymphocytes. In conclusion, HO-1 is a crucial transcriptional repressor for B cell development.

Overexpression of heme oxygenase-1 in microenvironment mediates vincristine resistance of B-cell acute lymphoblastic leukemia by promoting vascular endothelial growth factor secretion

Chemoresistance often causes treatment failure of B-cell acute lymphoblastic leukemia (B-ALL). However, the mechanism remains unclear at present. Herein, overexpression of heme oxygenase-1 (HO-1) was found in the bone marrow stromal cells (BMSCs) from B-ALL patients developing resistance to vincristine (VCR), a chemotherapeutic agent. Two B-ALL cell lines Super B15 and CCRF-SB were cocultured with BMSCs transfected with lentivirus to regulate the expression of HO-1. Silencing HO-1 expression in BMSCs increased the apoptotic rates of B-ALL cell lines induced by VCR, whereas upregulating HO-1 expression reduced the rate. Cell cycle can be arrested in the G2/M phase by VCR. In contrast, B-ALL cells were arrested in the G0/G1 phase due to HO-1 overexpression in BMSCs, which avoided damage from the G2/M phase. Vascular endothelial growth factor (VEGF) in BMSCs, as a key factor in the microenvironment-associated chemoresistance, was also positively coexpressed with HO-1. VEGF secretion was markedly increased in BMSCs with HO-1 upregulation but decreased in BMSCs with HO-1 silencing. B-ALL cell lines became resistant to VCR when cultured with VEGF recombinant protein, so VEGF secretion induced by HO-1 expression may promote the VCR resistance of B-ALL cells. As to the molecular mechanism, the PI3K/AKT pathway mediated regulation of VEGF by HO-1. In conclusion, this study clarifies a mechanism by which B-ALL is induced to resist VCR through HO-1 overexpression in BMSCs, and provides a novel strategy for overcoming VCR resistance in clinical practice.

Heme Oxygenase-1 Inhibition Sensitizes Human Prostate Cancer Cells towards Glucose Deprivation and Metformin-Mediated Cell Death

High levels of heme oxygenase (HO)-1 have been frequently reported in different human cancers, playing a major role in drug resistance and regulation of cancer cell redox homeostasis. Metformin (MET), a drug widely used for type 2 diabetes, has recently gained interest for treating several cancers. Recent studies indicated that the anti-proliferative effects of metformin in cancer cells are highly dependent on glucose concentration. The present work was directed to determine whether use of a specific inhibitor of HO-1 activity, alone or in combination with metformin, affected metastatic prostate cancer cell viability under different concentrations of glucose. MTT assay and the xCELLigence system were used to evaluate cell viability and cell proliferation in DU145 human prostate cancer cells. Cell apoptosis and reactive oxygen species were analyzed by flow cytometry. The activity of HO-1 was inhibited using a selective imidazole-based inhibitor; genes associated with antioxidant systems and cell death were evaluated by qRT-PCR. Our study demonstrates that metformin suppressed prostate cancer growth in vitro and increased oxidative stress. Disrupting the antioxidant HO-1 activity, especially under low glucose concentration, could be an attractive approach to potentiate metformin antineoplastic effects and could provide a biochemical basis for developing HO-1-targeting drugs against solid tumors.

Inhibition of Heme Oxygenase-1 enhances hyperthermia-induced autophagy and antiviral effect

Hyperthermia has been clinically utilized as an adjuvant therapy in the treatment of cervical carcinoma. However, thermotolerance induced by heme oxygenase-1 (HO-1), a stress-inducible cytoprotective protein, limits the efficacy of hyperthermic therapy, for which the exact mechanism remains unknown. In the present study, we found that heat treatment induced HO-1 expression and decreased copy number of HPV16 in cervical cancer cells and tissues from cervical cancer and precursor lesions. Knockdown of HO-1 stimulated autophagy accompanied by downregulation of X-linked inhibitor of apoptosis protein. Furthermore, silencing of HO-1 led to cell intolerance to hyperthermia, as manifested by inhibition of cell viability and induction of autophagic apoptosis. Moreover, HO-1 modulated hyperthermia-induced, autophagy-dependent antiviral effect. Thus, the findings indicate that blockade of HO-1 enhances hyperthermia-induced autophagy, an event resulting in apoptosis of cervical cancer cells through an antiviral mechanism. These observations imply the potential clinical utility of hyperthermia in combination with HO-1 inhibition in the treatment of cervical cancer.

A Dual Role of Heme Oxygenase-1 in Cancer Cells

Heme oxygenase (HO)-1 is known to metabolize heme into biliverdin/bilirubin, carbon monoxide, and ferrous iron, and it has been suggested to demonstrate cytoprotective effects against various stress-related conditions. HO-1 is commonly regarded as a survival molecule, exerting an important role in cancer progression and its inhibition is considered beneficial in a number of cancers. However, increasing studies have shown a dark side of HO-1, in which HO-1 acts as a critical mediator in ferroptosis induction and plays a causative factor for the progression of several diseases. Ferroptosis is a newly identified iron- and lipid peroxidation-dependent cell death. The critical role of HO-1 in heme metabolism makes it an important candidate to mediate protective or detrimental effects via ferroptosis induction. This review summarizes the current understanding on the regulatory mechanisms of HO-1 in ferroptosis. The amount of cellular iron and reactive oxygen species (ROS) is the determinative momentum for the role of HO-1, in which excessive cellular iron and ROS tend to enforce HO-1 from a protective role to a perpetrator. Despite the dark side that is related to cell death, there is a prospective application of HO-1 to mediate ferroptosis for cancer therapy as a chemotherapeutic strategy against tumors.

Dual Imaging-Guided Oxidative-Photothermal Combination Anticancer Therapeutics

Heme oxygenase-1 (HO-1) is a stress-response protein with potent cytoprotective and antioxidant activity, and its expression in cancer cells is enhanced in response to chemotherapy and radiotherapy. HO-1 is known to serve as a shield to protect cancer cells from anticancer therapy and attenuate apoptotic signals. It can be therefore reasoned that inhibition of HO-1 reduces the antioxidant level, making cancer cells more sensitive to photothermal heating. In this work, we developed dual imaging-guided oxidative-photothermal combination nanotherapeutics (OPCN) consisting of amphiphilic polymers conjugated with zinc protoporphyrin as a HO-1 inhibitor and fluorescent IR820 as a photothermal agent. A combination of OPCN and near-infrared (NIR) laser irradiation markedly increased the temperature and exerted significant toxicity through induction of apoptosis. In a mouse model of xenografts, tumors were identified by the strong fluorescence and photoacoustic signals. OPCN combined with NIR laser irradiation resulted in effective and complete thermal ablation of tumors without discernable side effects and tumor recurrence. We believe that OPCN hold tremendous translational potential for dual imaging-guided oxidative-photothermal combination anticancer therapy.

Sorafenib and docosahexaenoic acid act in synergy to suppress cancer cell viability: a role of heme oxygenase 1

Background

Docosahexaenoic acid (DHA) is a long chain n-3 polyunsaturated fatty acid that has anticancer activity. Heme oxygenase 1 (HO-1) is a potential therapeutic target due to its cytoprotective activity in cancer cells. We recently reported that DHA induces HO-1 gene transcription in human cancer cells by augmenting the degradation of Bach1 protein, which functions as a negative regulator of HO-1. Since the degradation of Bach1 protein relies on protein phosphorylation, we hypothesized that DHA-induced HO-1 gene transcription could be attenuated by kinase inhibitors, resulting in an enhanced cytotoxicity. Sorafenib, a tyrosine kinase inhibitor, was first applied to test our hypothesis.

Methods

Human cancer cell lines and a xenograft nude mouse model were applied to test our hypothesis. Gene expression was analyzed by western blot analysis and reporter gene assay. Cell viability was analyzed using a colorimetric assay. Isobologram was applied to analyze drug action.

Results

Pretreatment of cancer cells with Sorafenib significantly attenuated DHA-induced degradation of Bach1 protein. Consequently, DHA-induced HO-1 gene transcription was reversed by Sorafenib as evidenced by western blot and reporter gene analysis. Sorafenib acted synergistically with DHA to suppress cancer cell viability in various human cancer cell lines and suppressed tumor xenograft growth in mice fed a fish oil enriched diet (high n-3/DHA), as compared to mice fed a corn oil (high n-6) diet. Screening of the NCI-Oncology Drug Set IV identified a group of anticancer compounds, including Sorafenib, which enhanced DHA’s cytotoxicity, as well as a set of compounds that attenuated DHA’s cytotoxicity.

Conclusions

We demonstrate that sorafenib attenuates DHA-induced HO-1 expression and acts in synergy with DHA to suppress cancer cell viability and tumor growth. Considering the known health benefits of DHA and the clinical effectiveness of Sorafenib, their combination is an attractive therapeutic strategy against cancer.

Cytotoxic activity and molecular targets of atractylodin in cholangiocarcinoma cells

Objectives

To evaluate the cytotoxic activity of atractylodin and its potential effects on heme oxygenase (HO)-1 production, STAT1/3 phosporylation and major NF-κB protein expression in the cholangiocarcinoma-associated cell line CL-6.

Methods

Standard MTT assay was used for accessing antiproliferative activity on CL-6 cells. Normal human embryonic fibroblast (OUMS) cell was taken as control cell line. Colony formation and wound healing assay were conducted to access the effects of atractylodin on cell proliferation and directional migration activity of CL-6 cells. Western blot was used for evaluating levels of protein expression and phosphorylation.

Key findings

Atractylodin exhibited selective cytotoxicity towards CL-6 as compared with OUMS with IC50 of 216.8 (212.4-233.8) and 351.2 (345.7-359.5) μm [median (range)], respectively. Exposure to the compound dose-dependently inhibited colony formation ability and decreased wound closure potential of CL-6 cells. Atractylodin treatment suppressed HO-1 production in CL-6 cells. It dose-dependently inhibited STAT1/3 protein phosphorylation and moderately inhibited NF-κB (p50), NF-κB (p52), and NF-κB (p65) protein expression in both dose- and time-dependent manner.

Conclusions

Atractylodin exerts significant cytotoxic activity against CL-6 cells which may be linked to its suppressive effect on HO-1 production, STAT1/3 phosphorylation and expression of key NF-κB proteins.

The Antitumor Mechanism of Paeonol on CXCL4/CXCR3-B Signals in Breast Cancer Through Induction of Tumor Cell Apoptosis

BACKGROUND

Paeonol, a phenolic component from the root bark of Paeonia moutan, has been identified to possess antitumor effects. However, the effect of paeonol and the mechanism of CXCL4/CXCR3-B signals in paeonol-induced breast cancer cell remain unknown.

MATERIALS AND METHODS

After MDA-MB-231 cells were pretreated with paeonol or DMSO, the proliferation activity was detected by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), Hoechst, Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and Annexin-V/propidium iodide staining flow cytometry. Western blot and immunohistochemistry of human breast cancer and noncancerous tissues were performed to determine the molecular alteration of CXCL4/CXCR3-B signals.

RESULTS

Compared with the control, paeonol-treated breast cancer cells had low proliferation activity and high apoptotic index, indicating that paeonol induces breast cancer cell apoptosis. Western blot and immunohistochemistry showed that paeonol increased CXCR3-B signal, downregulated CXCL4, heme oxygenase (HO-1) with a corresponding increased BACH1, and decreased nuclear factor E2-related factor 2 (Nrf2).

CONCLUSIONS

Thus, CXCL4/CXCR3-B may be involved in the mechanism of apoptosis induced by paeonol in breast cancer cells by regulating the expression of BACH1 and Nrf2 to downregulating HO-1 and promote apoptosis. Therefore, the authors suggest paeonol has a significant growth inhibitory effect on breast cancer cells, which may be related to the induction of apoptosis.

A review on heme oxygenase-1 induction: is it a necessary evil

Heme oxygenase-1 (HO-1) is considered to be the main protein in diseases arising as a result of oxidative and inflammatory insults. Tremendous research has been carried out on HO-1 since years, pertaining its cytoprotective effect against oxidative injury and other cellular stresses. HO-1, by regulating intracellular levels of pro-oxidant heme, or by other benefits of its by-products such as carbon monoxide (CO) and biliverdin (BV) had become an important candidate protein to be up-regulated to combat diverse stressful events. Although the beneficial effects of HO-1 induction have been reported in a number of cells and tissues, a growing body of evidence indicates that this increased HO-1 expression may lead to the progression of several diseases such as neurodegeneration, carcinogenesis. But it is not clear, what accounts for the increased expression of HO-1 in cells and tissues. The observed friendly role of HO-1 in a wide range of stress conditions since times is now doubtful. Therefore, more studies are needed to elucidate the exact role of HO-1 in various stressful events. Being more concise, elucidating the effect of HO-1 up-regulation on critical genes involved in particular diseases such as cancer will help to a larger extent to comprehend the exact role of HO-1. This review will assist in understanding the dual role (protective and detrimental) of HO-1 and the signaling pathway involved and will help in unraveling the doubtful role of HO-1 induction.

Heme oxygenase inhibition in cancers: possible tools and targets

Heme oxygenase-1 (HO-1, encoded by HMOX1) through degradation of pro-oxidant heme into carbon monoxide (CO), ferrous ions (Fe²⁺) and biliverdin, exhibits cytoprotective, anti-apoptotic and anti-inflammatory properties. All of these potentially beneficial functions of HO-1 may play an important role in tumors’ development and progression. Moreover, HO-1 is very often upregulated in tumors in comparison to healthy tissues, and its expression is further induced upon chemo-, radio- and photodynamic therapy, what results in decreased effectiveness of the treatment. Consequently, HO-1 can be proposed as a therapeutic target for anticancer treatment in many types of tumors. Nonetheless, possibilities of specific inhibition of HO-1 are strongly limited. Metalloporphyrins are widely used in in vitro studies, however, they are unselective and may exert serious side effects including an increase in HMOX1 mRNA level. On the other hand, detailed information about pharmacokinetics and biodistribution of imidazole-dioxolane derivatives, other potential inhibitors, is lacking. The genetic inhibition of HO-1 by RNA interference (RNAi) or CRISPR/Cas9 approaches provides the possibility to specifically target HO-1; however, the potential therapeutic application of those methods are distant at best. In summary, HO-1 inhibition might be the valuable anticancer approach, however, the ideal strategy for HO-1 targeting requires further studies.

Adipocyte-activated oxidative and ER stress pathways promote tumor survival in bone via upregulation of Heme Oxygenase 1 and Survivin

Metastatic tumor cells engage the local tumor microenvironment and activate specific pro-survival mechanisms to thrive and progress in the harsh bone marrow niche. Here we show that the major contributors to the survival of carcinoma cells that have colonized the bone marrow are the adipocyte-induced oxidative stress and ER stress pathways. We demonstrate that upon exposure to adipocyte-rich environments in vitro or in vivo, bone-trophic prostate and breast tumor cells upregulate the oxidative stress enzyme, HO-1. We also show that HO-1 levels are significantly increased in human metastatic prostate cancer tissues and that stable HO-1 overexpression in tumor cells promotes growth and invasiveness. Co-incident with the adipocyte-induced expression of HO-1, there is an upregulation of ER chaperone BIP and splicing of XBP1, indicating adipocyte-driven unfolded protein response, a process that we show to be sensitive to antioxidant treatment. Importantly, we also demonstrate that triggering of the oxidative stress and ER stress responses, or HO-1 induction by adipocyte exposure result in the activation of pro-survival pathways, involving survivin. Collectively, our findings reveal a new link between HO-1 and survivin expression in tumor cells, and provide a new insight into potentially targetable survival pathways in bone-metastatic disease.

Growth inhibitory effect of β-eudesmol on cholangiocarcinoma cells and its potential suppressive effect on heme oxygenase-1 production, STAT1/3 activation, and NF-κB downregulation

Cholangiocarcinoma (CCA) is a progressively fatal form of cancer originating from the malignant transformation of hepatic biliary cholangiocytes. The present study reports for the first time in vitro growth inhibitory activities of β-eudesmol, the bioactive sesquiterpenoid present in the rhizome of Atractylodes lancea (Thunb) DC., with respect to its underlying potential effects on heme oxygenase-1 (HO-1) production, STAT1/3 phosphorylation, and NF-κB protein expression in human CCA cell line CL-6. The cytotoxic effect of β-eudesmol on CL-6 cells was evaluated by MTT assay using normal human embryonic fibroblast (OUMS) as a control cell line. Results indicated that β-eudesmol exhibited selective cytotoxicity towards CL-6 compared to OUMS with mean (±SD) IC₅₀ (concentration that inhibits cell growth by 50%) values of 166.75 ± 3.69 and 240.01 ± 16.54 μmol/L, respectively. In addition, it also significantly suppressed colony forming and wound healing ability of CL-6 cells in a concentration-dependent manner. Western blot analysis indicated that β-eudesmol treatment resulted in significant suppression of HO-1 production in CL-6 cells. Its inhibitory effects on the phosphorylation of STAT1/3 proteins and expression of NF-κB (p65 and p50) proteins were concentration-dependent. Taken together, these results suggest that β-eudesmol exerts significant growth inhibitory activity on CL-6 cells that may be linked to its inhibitory effect on the production of HO-1, phosphorylation of STAT1/3, and expression of major NF-κB proteins.

Silencing heme oxygenase-1 increases the sensitivity of ABC-DLBCL cells to histone deacetylase inhibitor in vitro and in vivo

Heme oxygenase-1 (HO-1) can promote tumor growth and reinforce the resistance of diffuse large B-cell lymphoma (DLBCL) cells to chemotherapeutic drug vincristine. We herein found that HO-1 protein expression was higher in high-risk DLBCL patients than in low-risk ones. Silencing HO-1 gene expression resisted vorinostat-induced apoptosis and arrested cell cycle in the G0/G1 phase of LY-10 cells. Western blot, co-immunoprecipitation and chromatin immunoprecipitation assays confirmed that the possible mechanisms may be increased cleaved caspase-3 protein expression, decreased phospho-histone deacetylase 3 protein expression, and activated histone acetylation of P27^Kip1 promoter. Moreover, silencing HO-1 gene expression enhanced vorinostat-induced tumor cell apoptosis, prolonged survival time and promoted P27^Kip1 protein expression in a xenograft mouse model.

In conclusion, HO-1 is a potential therapeutic target of DLBCL. The findings provide a valuable preclinical evidence for sensitizing DLBCL patients with poor prognosis to histone deacetylase inhibitors.

Honokiol inhibits c-Met-HO-1 tumor-promoting pathway and its cross-talk with calcineurin inhibitor-mediated renal cancer growth

Honokiol (HNK) is a small molecule with potent anti-inflammatory and anti-tumorigenic properties; yet the molecular targets of HNK are not well studied. Hyperactivation of the receptor tyrosine kinase c-Met and overexpression of the cytoprotective enzyme heme oxygenase-1 (HO-1) play a critical role in the growth and progression of renal cell carcinoma (RCC). Interestingly, the calcineurin inhibitor (CNI) cyclosporine A (CsA), an immunosuppressant used to prevent allograft rejection, can also increase the risk of RCC in transplant patients. We studied the potential role of c-Met signaling axis on CNI-induced renal tumor growth and tested the anti-tumor efficacy of HNK. Importantly, CNI treatment promoted c-Met induction and enhanced c-Met-induced Ras activation. We found that HNK treatment effectively down-regulated both c-Met phosphorylation and Ras activation in renal cancer cells. It inhibited the expression of both c-Met- and CNI-induced HO-1, and promoted cancer cell apoptosis. In vivo, HNK markedly inhibited CNI-induced renal tumor growth; and it decreased the expression of phospho-c-Met and HO-1 and reduced blood vessel density in tumor tissues. Our results suggest a novel mechanism(s) by which HNK exerts its anti-tumor activity through the inhibition of c-Met-Ras-HO-1 axis; and it can have significant therapeutic potential to prevent post-transplantation cancer in immunosuppressed patients.

Heme Oxygenase 1 as a Therapeutic Target in Acute Kidney Injury

A common clinical condition, acute kidney injury (AKI) significantly influences morbidity and mortality, particularly in critically ill patients. The pathophysiology of AKI is complex and involves multiple pathways, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Recent evidence suggests that a single insult to the kidney significantly enhances the propensity to develop chronic kidney disease. Therefore, the generation of effective therapies against AKI is timely. In this context, the cytoprotective effects of heme oxygenase 1 (HO-1) in animal models of AKI are well documented. HO-1 modulates oxidative stress, autophagy, and inflammation and regulates the progression of cell cycle via direct and indirect mechanisms. These beneficial effects of HO-1 induction during AKI are mediated in part by the by-products of the HO reaction (iron, carbon monoxide, and bile pigments). This review highlights recent advances in the molecular mechanisms of HO-1-mediated cytoprotection and discusses the translational potential of HO-1 induction in AKI.

Network Pharmacological Screening of Herbal Monomers that Regulate Apoptosis-Associated Genes in Acute Pancreatitis

OBJECTIVES

In this study, we screened for differentially expressed genes in acute pancreatitis and the herbal monomers that regulate these genes.

METHODS

Gene expression profile data were downloaded from the Gene Expression Omnibus database (GSE3644). We used the Human Protein Reference Database to determine the protein-protein interaction network and CFinder software (Department of Biological Physics of Eötvös University, Budapest, Hungary) to identify several functional modules. Then, we used Database for Annotation, Visualization and Integrated Discovery software (Frederick, Md) to perform a gene ontology-biological process functional enrichment analysis. Based on a database of herbal monomers and a literature search, we constructed a gene-herbal monomer regulatory network using Cytoscape software (San Diego, Calif), and we analyzed the relationships between apoptosis, genes, and herbal monomers.

RESULTS

A total of 1745 differentially expressed genes were identified. Nine modules were identified, and the main function of module 3 was closely related to apoptosis. Within module 3, we selected 13 genes that were closely related to apoptosis for further analysis. In the gene-herbal monomer regulatory network, 18 herbal monomers that regulate multiple target genes were selected as the focus of this study.

CONCLUSIONS

These herbal monomers regulate multiple target genes to induce apoptosis and may potentially be used as new drugs for acute pancreatitis treatment in the future.

Pathological significance and prognostic implications of heme oxygenase 1 expression in non-muscle-invasive bladder cancer: Correlation with cell proliferation, angiogenesis, lymphangiogenesis and expression of VEGFs and COX-2

Heme oxygenase 1 (HO-1) is a stress-response protein and its expression is associated with malignant potential and poor prognosis in several types of cancer. The present study investigated the association between HO-1 expression levels and the pathological features, clinical outcomes and other associated factors in patients with non-muscle-invasive bladder cancer (NMIBC). HO-1 expression was evaluated using immunohistochemistry in 147 formalin-fixed tissue specimens. The proliferation index, microvessel density, lymph vessel density and expression of cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF)-A, -C, and -D were also investigated. Correlations among variables were analyzed by multivariate analysis. Survival was assessed using Kaplan-Meier survival curves and multivariate statistics. HO-1 expression levels in high-grade and pT1 tumors were significantly higher compared with low-grade and pTa tumors, and were correlated with the proliferation index (P<0.001), lymph vessel density (P=0.021) and COX-2 expression levels (P=0.003). The proliferation index and COX-2 expression levels were also identified as independent contributing factors in multivariate models. Kaplan-Meier survival curves associated HO-1 expression with a poor prognosis in metastasis-free (P=0.047) and cause-specific survival (P=0.017), but not with urinary tract recurrence (P=0.231). Furthermore, HO-1 expression was identified by multivariate analysis to be a significant predictor for cause-specific survival (hazard ratio, 4.08; 95% confidence interval, 1.06-15.66; P=0.004). HO-1 has an important role in the malignant aggressiveness of NMIBC and its expression is associated with cause-specific survival. HO-1-associated activities are regulated by cancer cell proliferation, lymphangiogenesis and COX-2. The results suggest that HO-1 may be a potential therapeutic target and a useful predictive prognostic factor in patients with NMIBC.

Cadmium-induced heme-oxygenase-1 expression plays dual roles in autophagy and apoptosis and is regulated by both PKC-δ and PKB/Akt activation in NRK52E kidney cells

Heme oxygenase-1 (HO-1) protects cells against cadmium (Cd)-induced oxidative stress. However, the mechanism underlying this protection is not well understood. In this study, we elucidated the role of HO-1 in Cd-induced cytotoxicity. Exposure of NRK52E cells to Cd induced protein kinase B (PKB)/Akt, protein kinase C (PKC)-δ, and glycogen synthase kinase (GSK) 3αb phosphorylation, and eukaryotic initiation factor (eIF) 2α dephosphorylation. Pharmacological inhibition of Akt resulted in HO-1 suppression and eIF2α activation, which partially suppressed CHOP and PARP-1 cleavage, but promoted autophagy and decreased cell viability. Pharmacological inactivation of PKC-δ markedly suppressed Cd-induced phospho-serine (p-Ser) GSK3αβ, and HO-1, and partially inhibited PARP-1 cleavage, but massively induced autophagy and decreased cell viability. Pharmacological upregulation of p-Ser GSK3αβ enhanced Cd-induced HO-1, CHOP, and PARP-1 cleavage, but decreased autophagy. Genetic deficiency of GSK3β suppressed HO-1 and PARP-1 cleavage and increased autophagy. Genetic suppression of HO-1 reduced Cd-induced PARP-1 cleavage, but increased LC3-II. Cd exposure led to accumulation of p-PKC-δ, p-Ser GSK3αβ, and HO-1 in the nucleus and particulate fractions, suggesting that they have dual functions in response to Cd. N-acetylcysteine treatment suppressed Cd-induced activation of PKC-δ and Akt. These results indicate that HO-1 induced by Cd exposure is regulated by PKC-δ, p-Ser GSK3αβ, and PKB/Akt, which restrain autophagic cell death, but mildly induce apoptosis in NRK52E cells. Together, the results suggest that HO-1 expression in response to Cd maintains cellular homeostasis during oxidative stress.

Ursodeoxycholic acid and 4-phenylbutyrate prevent endoplasmic reticulum stress-induced podocyte apoptosis in diabetic nephropathy

Endoplasmic reticulum (ER) stress, resulting from the accumulation of misfolded and/or unfolded proteins in ER membranes, is involved in the pathogenesis of diabetic nephropathy (DN). The aim of this study was to investigate the role of ER stress inhibitors ursodeoxycholic acid (UDCA) and 4-phenylbutyrate (4-PBA) in the treatment of DN in db/db mice. Findings have revealed that diabetic db/db mice were more hyperglycemic than their non-diabetic controls, and exhibited a marked increase in body weight, water intake, urine volume, fasting plasma glucose, systolic blood pressure, glucose and insulin tolerance. UDCA (40 mg/kg/day) or 4-PBA (100 mg/kg/day) treatment for 12 weeks resulted in an improvement in these biochemical and physical parameters. Moreover, UDCA or 4-PBA intervention markedly decreased urinary albuminuria and attenuated mesangial expansion in diabetic db/db mice, compared with db/db mice treated with vehicle. These beneficial effects of UDCA or 4-PBA on DN were associated with the inhibition of ER stress, as evidenced by the decreased expression of BiP, phospho-IRE1α, phospho-eIF2α, CHOP, ATF-6 and spliced X-box binding protein-1 in vitro and in vivo. UDCA or 4-PBA prevented hyperglycemia-induced or high glucose (HG)-induced apoptosis in podocytes in vivo and in vitro via the inhibition of caspase-3 and caspase-12 activation. Autophagy deficiency was also seen in glomeruli in diabetic mice and HG-incubated podocytes, exhibiting decreased expression of LC3B and Beclin-1, which could be restored by UDCA or 4-PBA treatment. Taken together, our results have revealed an important role of ER stress in the development of DN, and UDCA or 4-PBA treatment may be a potential novel therapeutic approach for the treatment of DN.

Autophagy and Tubular Cell Death in the Kidney

Many common renal insults such as ischemia and toxic injury primarily target the tubular epithelial cells, especially the highly metabolically active proximal tubular segment. Tubular epithelial cells are particularly dependent on autophagy to maintain homeostasis and respond to stressors. The pattern of autophagy in the kidney has a unique spatial and chronologic signature. Recent evidence has shown that there is complex cross-talk between autophagy and various cell death pathways. This review specifically discusses the interplay between autophagy and cell death in the renal tubular epithelia. It is imperative to review this topic because recent discoveries have improved our mechanistic understanding of the autophagic process and have highlighted its broad clinical applications, making autophagy a major target for drug development.

CYLD-mediated signaling and diseases

The conserved cylindromatosis (CYLD) codes for a deubiquitinating enzyme and is a crucial regulator of diverse cellular processes such as immune responses, inflammation, death, and proliferation. It directly regulates multiple key signaling cascades, such as the Nuclear Factor kappa B [NFkB] and the Mitogen-Activated Protein Kinase (MAPK) pathways, by its catalytic activity on polyubiquitinated key intermediates. Several lines of emerging evidence have linked CYLD to the pathogenesis of various maladies, including cancer, poor infection control, lung fibrosis, neural development, and now cardiovascular dysfunction. While CYLD-mediated signaling is cell type and stimuli specific, the activity of CYLD is tightly controlled by phosphorylation and other regulators such as Snail. This review explores a broad selection of current and past literature regarding CYLD's expression, function and regulation with emerging reports on its role in cardiovascular disease.

HO-1/CO system in tumor growth, angiogenesis and metabolism - Targeting HO-1 as an anti-tumor therapy

Heme oxygenase-1 (HO-1, hmox-1) catalyzes the rate-limiting step in the heme degradation processes. Out of three by-products of HO-1 activity, biliverdin, iron ions and carbon monoxide (CO), the latter was mostly shown to mediate many beneficial HO-1 effects, including protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. Mounting evidence suggests that HO-1/CO systemmay be of special benefit in protection inmany pathological conditions, like atherosclerosis or myocardial infarction. By contrast, the augmented expression of HO-1 in tumor tissues may have detrimental effect as HO-1 accelerates the formation of tumor neovasculature and provides the selective advantage for tumor cells to overcome the increased oxidative stress during tumorigenesis and during treatment. The inhibition of HO-1 has been proposed as an anti-cancer therapy, however, because of non-specific effects of known HO-1 inhibitors, the discovery of ideal drug lowering HO-1 expression/activity is still an open question. Importantly, in several types of cancer HO-1/CO system exerts opposite activities, making the possible treatment more complicated. All together indicates the complex role for HO-1/CO in various in vitro and in vivo conditions.

Knockdown of heme oxygenase-1 promotes apoptosis and autophagy and enhances the cytotoxicity of doxorubicin in breast cancer cells

Heme oxygenase-1 (HMOX-1) is a microsomal enzyme that exerts anti-apoptotic and cytoprotective effects. In the present study, HMOX-1 was demonstrated to be overexpressed and able to be induced by doxorubicin in breast cancer cell lines. Knockdown of HMOX-1 using short interfering (si)RNA enhanced the cytotoxicity of doxorubicin in MDA-MB-231 and BT549 cells. Knockdown of HMOX-1 downregulated B cell lymphoma (Bcl)-2 and Bcl-extra large expression, and significantly enhanced doxorubicin-induced apoptosis in MDA-MB-231 and BT549 cells. Additionally, knockdown of HMOX-1 upregulated light chain 3B expression and markedly increased the accumulation of autophagic vacuoles in MDA-MB-231 and BT549 cells treated with doxorubicin. These results indicated that HMOX-1 may be involved in conferring the chemoresistance of breast cancer cells, by preventing apoptosis and autophagy. Therefore, HMOX-1 may represent a potential therapeutic target for enhancing the cytotoxicity and efficacy of doxorubicin during the treatment of breast cancer.

Src/STAT3-dependent heme oxygenase-1 induction mediates chemoresistance of breast cancer cells to doxorubicin by promoting autophagy

Chemotherapeutic resistance in breast cancer, whether acquired or intrinsic, remains a major clinical obstacle. Thus, increasing tumor cell sensitivity to chemotherapeutic agents will be helpful in improving the clinical management of breast cancer. In the present study, we found an induction of HO-1 expression in doxorubicin (DOX)-treated MDA-MB-231 human breast adenocarcinoma cells, which showed insensitivity to DOX treatment. Knockdown HO-1 expression dramatically upregulated the incidence of MDA-MB-231 cell death under DOX treatment, indicating that HO-1 functions as a critical contributor to drug resistance in MDA-MB-231 cells. We further observed that DOX exposure induced a cytoprotective autophagic flux in MDA-MB-231 cells, which was dependent on HO-1 induction. Moreover, upregulation of HO-1 expression required the activation of both signal transducer and activator of transcription (STAT)3 and its upstream regulator, protein kinase Src. Abrogating Src/STAT3 pathway activation attenuated HO-1 and autophagy induction, thus increasing the chemosensitivity of MDA-MB-231 cells. Therefore, we conclude that Src/STAT3-dependent HO-1 induction protects MDA-MB-231 breast cancer cells from DOX-induced death through promoting autophagy. In the following study, we further demonstrated the contribution of Src/STAT3/HO-1/autophagy pathway activation to DOX resistance in another breast cancer cell line, MDA-MB-468, which bears a similar phenotype to MDA-MB-231 cells. Therefore, activation of Src/STAT3/HO-1/autophagy signaling pathway might play a general role in protecting certain subtypes of breast cancer cells from DOX-induced cytotoxicity. Targeting this signaling event may provide a potential approach for overcoming DOX resistance in breast cancer therapeutics.

Kaposi Sarcoma Herpesvirus Induces HO-1 during De Novo Infection of Endothelial Cells via Viral miRNA-Dependent and -Independent Mechanisms

Kaposi sarcoma (KS) herpesvirus (KSHV) infection of endothelial cells (EC) is associated with strong induction of heme oxygenase-1 (HO-1), a stress-inducible host gene that encodes the rate-limiting enzyme responsible for heme catabolism. KS is an angioproliferative tumor characterized by the proliferation of KSHV-infected spindle cells, and HO-1 is highly expressed in such cells. HO-1 converts the pro-oxidant, proinflammatory heme molecule into metabolites with antioxidant, anti-inflammatory, and proliferative activities. Previously published work has shown that KSHV-infected EC in vitro proliferate in response to free heme in a HO-1-dependent manner, thus implicating virus-enhanced HO-1 activity in KS tumorigenesis. The present study investigated the molecular mechanisms underlying KSHV induction of HO-1 in lymphatic EC (LEC), which are the likely spindle cell precursors. In a time course analysis of KSHV-infected cells, HO-1 expression displays biphasic kinetics characterized by an early transient induction that is followed by a more sustained upregulation coincident with the establishment of viral latency. A viral microRNA miR-K12-11 deletion mutant of KSHV was found to be defective for induction of HO-1 during latency. A potential mechanism for this phenotype was provided by BACH1, a cellular HO-1 transcriptional repressor targeted by miR-K12-11. In fact, in KSHV-infected LEC, the BACH1 message level is reduced, BACH1 subcellular localization is altered, and miR-K12-11 mediates the inverse regulation of HO-1 and BACH1 during viral latency. Interestingly, the data indicate that neither miR-K12-11 nor de novo KSHV gene expression is required for the burst of HO-1 expression observed at early times postinfection, which suggests that additional virion components promote this phenotype.

While the mechanisms underlying KSHV induction of HO-1 remain unknown, the cellular mechanisms that regulate HO-1 expression have been extensively investigated in the context of basal and pathophysiological states. The detoxifying action of HO-1 is critical for the protection of cells exposed to high heme levels. KS spindle cells are erythrophagocytic and contain erythrocyte ghosts. Erythrocyte degeneration leads to the localized release of heme, creating oxidative stress that may be further exacerbated by environmental or other cofactors. Our previous work showed that KSHV-infected cells proliferate in response to heme and that this occurs in a HO-1-dependent manner. We therefore hypothesize that KSHV induction of HO-1 contributes to KS tumor development via heme metabolism and propose that HO-1 be evaluated as a therapeutic target for KS. Our present work, which aimed to understand the mechanisms whereby KSHV induces HO-1, will be important for the design and implementation of such a strategy.

ATF4-dependent induction of heme oxygenase 1 prevents anoikis and promotes metastasis

The integrated stress response (ISR) is a critical mediator of cancer cell survival, and targeting the ISR inhibits tumor progression. Here, we have shown that activating transcription factor 4 (ATF4), a master transcriptional effector of the ISR, protects transformed cells against anoikis - a specialized form of apoptosis - following matrix detachment and also contributes to tumor metastatic properties. Upon loss of attachment, ATF4 activated a coordinated program of cytoprotective autophagy and antioxidant responses, including induced expression of the major antioxidant enzyme heme oxygenase 1 (HO-1). HO-1 upregulation was the result of simultaneous activation of ATF4 and the transcription factor NRF2, which converged on the HO1 promoter. Increased levels of HO-1 ameliorated oxidative stress and cell death. ATF4-deficient human fibrosarcoma cells were unable to colonize the lungs in a murine model, and reconstitution of ATF4 or HO-1 expression in ATF4-deficient cells blocked anoikis and rescued tumor lung colonization. HO-1 expression was higher in human primary and metastatic tumors compared with noncancerous tissue. Moreover, HO-1 expression correlated with reduced overall survival of patients with lung adenocarcinoma and glioblastoma. These results establish HO-1 as a mediator of ATF4-dependent anoikis resistance and tumor metastasis and suggest ATF4 and HO-1 as potential targets for therapeutic intervention in solid tumors.

Heme oxygenase-1 enhances autophagy in podocytes as a protective mechanism against high glucose-induced apoptosis

Injury and loss of podocytes play vital roles in diabetic nephropathy progression. Emerging evidence suggests autophagy, which is induced by multiple stressors including hyperglycemia, plays a protective role. Meanwhile, heme oxygenase-1 (HO-1) possesses powerful anti-apoptotic properties. Therefore, we investigated the impact of autophagy on podocyte apoptosis under diabetic conditions and its association with HO-1. Mouse podocytes were cultured in vitro; apoptosis was detected by flow cytometry. Transmission electron microscopy and biochemical autophagic flux assays were used to measure the autophagy markers microtubule-associated protein 1 light chain 3-II (LC3-II) and beclin-1. LC3-II and beclin-1 expression peaked 12-24h after exposing podocytes to high glucose. Inhibition of autophagy with 3-methyladenine or Beclin-1 siRNAs or Atg 5 siRNAs sensitized cells to apoptosis, suggesting autophagy is a survival mechanism. HO-1 inactivation inhibited autophagy, which aggravated podocyte injury in vitro. Hemin-induced autophagy also protected podocytes from hyperglycemia in vitro and was abrogated by HO-1 siRNA. Adenosine monophosphate-activated protein kinase phosphorylation was higher in hemin-treated and lower in HO-1 siRNA-treated podocytes. Suppression of AMPK activity reversed HO-1-mediated Beclin-1 upregulation and autophagy, indicating HO-1-mediated autophagy is AMPK dependent. These findings suggest HO-1 induction and regulation of autophagy are potential therapeutic targets for diabetic nephropathy.