Heme oxygenase-1 in tumors: is it a false friend?

Effect of Arsenic Exposure on NRF2-KEAP1 Pathway and Epigenetic Modification

Arsenic (As) is a known toxic element and carcinogen. Transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2) controls cellular adaptation to oxidants and electrophiles by inducing antioxidant genes in response to redox stress. To explore associations between As level and NRF2-regulated cytoprotective genes expression, an observational study was conducted in a population of 61 occupationally exposed men with median (Me) age 50 years (interquartile range (IQR) 42-54) and in a control group of 52 men aged 40 (IQR 31-51.5) without occupational exposure. NRF2, KEAP1, GSTP1, HMOX1, NQO1, PRDX1, and TXNRD1 transcript levels were determined by means of quantitative real-time PCR along with the gene expression, methylation of NRF2 and KEAP1, as well as global DNA methylation were assessed. The median urine As tot. level in the exposed and control group was found to be 21.8 μg/g creat. (IQR 15.5-39.8 μg/g creat.) and 3.8 μg/g creat. (IQR 2.5-9.3) (p < 0.001). Global DNA methylation was significantly higher in occupationally exposed workers than in controls (Me 14.1 (IQR 9.5-18.1) vs Me 8.5 (IQR 5.9-12.6) p < 0.0001). NRF2 mRNA level was positively correlated with expression of all investigated NRF2-target genes in both groups (0.37 > R < 0.76, all p values < 0.0001). The multivariate linear regression adjusting for global methylation showed that As(III) level was significantly associated with expression of TXNRD1, GSTP1, HMOX1, and PRDX1. The results of this study indicate that arsenic occupational exposure is positively associated with global DNA methylation. The findings provide evidence for rather inactivation of NRF2-KEAP1 pathway in response to chronic arsenic exposure.

Itaconic acid mediates crosstalk between macrophage metabolism and peritoneal tumors

Control of cellular metabolism is critical for efficient cell function, although little is known about the interplay between cell subset–specific metabolites in situ, especially in the tumor setting. Here, we determined how a macrophage-specific (Mϕ-specific) metabolite, itaconic acid, can regulate tumor progression in the peritoneum. We show that peritoneal tumors (B16 melanoma or ID8 ovarian carcinoma) elicited a fatty acid oxidation–mediated increase in oxidative phosphorylation (OXPHOS) and glycolysis in peritoneal tissue–resident macrophages (pResMϕ). Unbiased metabolomics identified itaconic acid, the product of immune-responsive gene 1–mediated (Irg1-mediated) catabolism of mitochondrial cis-aconitate, among the most highly upregulated metabolites in pResMϕ of tumor-bearing mice. Administration of lentivirally encoded Irg1 shRNA significantly reduced peritoneal tumors. This resulted in reductions in OXPHOS and OXPHOS-driven production of ROS in pResMϕ and ROS-mediated MAPK activation in tumor cells. Our findings demonstrate that tumors profoundly alter pResMϕ metabolism, leading to the production of itaconic acid, which potentiates tumor growth. Monocytes isolated from ovarian carcinoma patients’ ascites fluid expressed significantly elevated levels of IRG1. Therefore, IRG1 in pResMϕ represents a potential therapeutic target for peritoneal tumors.

Flutamide Induces Hepatic Cell Death and Mitochondrial Dysfunction via Inhibition of Nrf2-Mediated Heme Oxygenase-1

Flutamide is a widely used nonsteroidal antiandrogen for prostate cancer therapy, but its clinical application is restricted by the concurrent liver injury. Increasing evidence suggests that flutamide-induced liver injury is associated with oxidative stress, though the precise mechanism is poorly understood. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master transcription factor regulating endogenous antioxidants including heme oxygenase-1 (HO-1). This study was designed to delineate the role of Nrf2/HO-1 in flutamide-induced hepatic cell injury. Our results showed that flutamide concentration dependently induced cytotoxicity, hydrogen peroxide accumulation, and mitochondrial dysfunction as indicated by mitochondrial membrane potential loss and ATP depletion. The protein expression of Nrf2 and HO-1 was induced by flutamide at 12.5 μM but was downregulated by higher concentrations of flutamide. Silencing either Nrf2 or HO-1 was found to aggravate flutamide-induced hydrogen peroxide accumulation and mitochondrial dysfunction as well as inhibition of the Nrf2 pathway. Moreover, preinduction of HO-1 by Copp significantly attenuated flutamide-induced oxidative stress and mitochondrial dysfunction, while inhibition of HO-1 by Snpp aggravated these deleterious effects. These findings suggest that flutamide-induced hepatic cell death and mitochondrial dysfunction is assoicated with inhibition of Nrf2-mediated HO-1. Pharmacologic intervention of Nrf2/HO-1 may provide a promising therapeutic approach in flutamide-induced liver injury.

Heme Oxygenase Inhibition Sensitizes Neuroblastoma Cells to Carfilzomib

Neuroblastoma (NB) is an embryonic malignancy affecting the physiological development of adrenal medulla and paravertebral sympathetic ganglia in early infancy. Proteasome inhibitors (PIs) (i.e., carfilzomib (CFZ)) may represent a possible pharmacological treatment for solid tumors including NB. In the present study, we tested the effect of a novel non-competitive inhibitor of heme oxygenase-1 (HO-1), LS1/71, as a possible adjuvant therapy for the efficacy of CFZ in neuroblastoma cells. Our results showed that CFZ increased both HO-1 gene expression (about 18-fold) and HO activity (about 8-fold), following activation of the ER stress pathway. The involvement of HO-1 in CFZ-mediated cytotoxicity was further confirmed by the protective effect of pharmacological induction of HO-1, significantly attenuating cytotoxicity. In addition, HO-1 selective inhibition by a specific siRNA increased the cytotoxic effect following CFZ treatment in NB whereas SnMP, a competitive pharmacological inhibitor of HO, showed no changes in cytotoxicity. Our data suggest that treatment with CFZ produces ER stress in NB without activation of CHOP-mediated apoptosis, whereas co-treatment with CFZ and LS1/71 led to apoptosis activation and CHOP expression induction. In conclusion, our study showed that treatment with the non-competitive inhibitor of HO-1, LS1 / 71, increased cytotoxicity mediated by CFZ, triggering apoptosis following ER stress activation. These results suggest that PIs may represent a possible pharmacological treatment for solid tumors and that HO-1 inhibition may represent a possible strategy to overcome chemoresistance and increase the efficacy of chemotherapic regimens.

Near-infrared light-controlled systems for gene transcription regulation, protein targeting and spectral multiplexing

Near-infrared (NIR, 740-780 nm) optogenetic systems are well-suited to spectral multiplexing with blue-light-controlled tools. Here, we present two protocols, one for regulation of gene transcription and another for control of protein localization, that use a NIR-responsive bacterial phytochrome BphP1-QPAS1 optogenetic pair. In the first protocol, cells are transfected with the optogenetic constructs for independently controlling gene transcription by NIR (BphP1-QPAS1) and blue (LightOn) light. The NIR and blue-light-controlled gene transcription systems show minimal spectral crosstalk and induce a 35- to 40-fold increase in reporter gene expression. In the second protocol, the BphP1-QPAS1 pair is combined with a light-oxygen-voltage-sensing (LOV) domain-based construct into a single optogenetic tool, termed iRIS. This dual-light-controllable protein localization tool allows tridirectional protein translocation among the cytoplasm, nucleus and plasma membrane. Both procedures can be performed within 3-5 d. Use of NIR light-controlled optogenetic systems should advance basic and biomedical research.

4-Hydroxyestradiol induces mammary epithelial cell transformation through Nrf2-mediated heme oxygenase-1 overexpression

Estrogen (17β-estradiol, E₂) undergoes oxidative metabolism by CYP1B1 to form 4-hydroxyestradiol (4-OHE₂), a putative carcinogenic metabolite of estrogen. Our previous study showed that 4-OHE₂-induced production of reactive oxygen species contributed to neoplastic transformation of human breast epithelial (MCF-10A) cells. In this study, 4-OHE₂, but not E₂, increased the expression of heme oxygenase-1 (HO-1), a sensor and regulator of oxidative stress, in MCF-10A cells. Silencing the HO-1 gene in MCF-10A cells suppressed 4-OHE₂-induced cell proliferation and transformation. In addition, subcutaneous administration of 4-OHE₂ markedly enhanced the growth of the MDA-MB-231 human breast cancer xenografts, which was retarded by zinc protoporphyrin, a pharmacological inhibitor of HO-1. 4-OHE₂-induced HO-1 expression was mediated by NF-E2-related factor 2 (Nrf2). We speculate that an electrophilic quinone formed as a consequence of oxidation of 4-OHE₂ binds directly to Kelch-like ECH-associated protein 1 (Keap1), an inhibitory protein that sequesters Nrf2 in the cytoplasm. This will diminish association between Nrf2 and Keap1. 4-OHE₂ failed to interrupt the interaction between Keap1 and Nrf2 and to induce HO-1 expression in Keap1-C273S or C288S mutant cells. Lano-LC-ESI-MS/MS analysis in MCF-10A-Keap1-WT cells which were treated with 4-OHE₂ revealed that the peptide fragment containing Cys288 gained a molecular mass of 287.15 Da, equivalent to the addition of a single molecule of 4-OHE₂-derived ortho-quinones.

The macrophage heme-heme oxygenase-1 system and its role in inflammation

Heme oxygenase (HO)-1, the inducible isoform of the heme-degrading enzyme HO, plays a critical role in inflammation and iron homeostasis. Regulatory functions of HO-1 are mediated via the catalytic breakdown of heme, which is an iron-containing tetrapyrrole complex with potential pro-oxidant and pro-inflammatory effects. In addition, the HO reaction produces the antioxidant and anti-inflammatory compounds carbon monoxide (CO) and biliverdin, subsequently converted into bilirubin, along with iron, which is reutilized for erythropoiesis. HO-1 is up-regulated by a plethora of stimuli and injuries in most cell types and tissues and provides salutary effects by restoring physiological homeostasis. Notably, HO-1 exhibits critical immuno-modulatory functions in macrophages, which are a major cell population of the mononuclear phagocyte system. Macrophages play key roles as sentinels and regulators of the immune system and HO-1 in these cells appears to be of critical importance for driving resolution of inflammatory responses. In this review, the complex functions and regulatory mechanisms of HO-1 in macrophages will be high-lighted. A particular focus will be the intricate interactions of HO-1 with its substrate heme, which play a contradictory role in distinct physiological and pathophysiological settings. The therapeutic potential of targeted modulation of the macrophage heme-HO-1 system will be discussed in the context of inflammatory disorders.

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.

Iron overload impact on P-ATPases

Iron is a chemical element that is active in the fundamental physiological processes for human life, but its burden can be toxic to the body, mainly because of the stimulation of membrane lipid peroxidation. For this reason, the action of iron on many ATPases has been studied, especially on P-ATPases, such as the Na⁺,K⁺-ATPase and the Ca²⁺-ATPase. On the Fe²⁺-ATPase activity, the free iron acts as an activator, decreasing the intracellular Fe²⁺ and playing a protection role for the cell. On the Ca²⁺-ATPase activity, the iron overload decreases the enzyme activity, raising the cytoplasmic Ca²⁺ and decreasing the sarco/endoplasmic reticulum and the Golgi apparatus Ca²⁺ concentrations, which could promote an enzyme oxidation, nitration, and fragmentation. However, the iron overload effect on the Na⁺,K⁺-ATPase may change according to the tissue expressions. On the renal cells, as well as on the brain and the heart, iron promotes an enzyme inactivation, whereas its effect on the erythrocytes seems to be the opposite, directly stimulating the ATPase activity, or stimulating it by signaling pathways involving ROS and PKC. Modulations in the ATPase activity may impair the ionic transportation, which is essential for cell viability maintenance, inducing irreversible damage to the cell homeostasis. Here, we will discuss about the iron overload effect on the P-ATPases, such as the Na⁺,K⁺-ATPase, the Ca²⁺-ATPase, and the Fe²⁺-ATPase.

Association between (GT)n Repeats in Heme Oxygenase-1 Gene Promoter and 3-Year Survival of Patients with Acute Leukemia: a Controlled, Cross-Sectional Study

Background: Acute leukemia is a common pediatric cancer. Novel strategies for treatment of acute leukemia have been developed, but treatment resistance is remained as the most problematic issue. It is hypothesized that the HO-1 gene up-regulation is responsible for tumor resistance to chemotherapy or radiotherapy-induced apoptosis. The levels of HO-1 expression are related to (GT)_n microsatellite polymorphisms in the location of its promoter. This study designed to compare allelic frequencies of (GT)_n microsatellite polymorphisms in HO-1 gene between acute leukemia patients and healthy controls. Indeed, 3-year disease-free survival was also evaluated. Methods: Sixty-three patients with acute leukemia and seventy healthy infants were included in this study. We used the medical records of patients to collect information about survival after chemotherapy. The number of GT repeats in HO-1 promoter was determined by an ABI 3100 sequencer. Results: The HO-1 GT repeats ranged from 14 to 34 with peaks at 27 repeats in both cases and controls. Children with longer alleles ((GT)_n ≥ 27) had enhanced 3-year survival rate after treatment with chemotherapy or radiotherapy (P<0.05). Conclusion: Although no significant differences were observed between leukemia patients and controls regarding allelic frequency, we found elevated frequency of "LL" genotype in leukemia patients with good prognosis and 3-year surveillance. Radiotherapy and chemotherapy might elevate the expression levels of HO-1 with subsequent increased resistance of leukemia patients to therapy.

Low heme oxygenase-1 expression promotes gastric cancer cell apoptosis, inhibits proliferation and invasion, and correlates with increased overall survival in gastric cancer patients

Heme oxygenase-1 (HO-1) plays a key role in anti-oxidation, anti-apoptosis, and anti-proliferation in various types of cancers. However, the relationship between HO-1 expression and gastric cancer development remains largely unknown. In this study, the protein expression of HO-1 in human gastric cancer was measured by immunohistochemistry on paraffin sections of 89 paired gastric carcinoma tissues and adjacent non-cancer tissues. The correlation of HO-1 expression with 5-year overall survival rate was estimated. The effects of decreased HO-1 expression by two strands of small interfered RNAs (siRNAs) on cell apoptosis, proliferation, and invasion of gastric cancer cell lines were examined by flow cytometry, the MTT assay, and the cell migration assay, respectively. High expression of HO-1 was detected in 11.2% (10/89) of gastric carcinoma tissues, compared with 1.1% (1/89) in matched adjacent normal tissues, and correlated with a decreased survival rate in gastric cancer patients. There were no significant correlations between HO-1 expression and clinical characteristics. Downregulation of HO-1 expression using two strands of siRNAs promoted apoptosis and inhibited the proliferation and invasion of two gastric cancer cell lines, SGC7901 and MKN-28 cells. This study demonstrated that HO-1 plays a vital role in the development of gastric cancer and may serve as a therapeutic target of this type of cancer.

New Ultrasound Techniques Promise Further Advances in AKI and CKD

AKI and CKD are important clinical problems because they affect many patients and the associated diagnostic and treatment paradigms are imperfect. Ultrasound is a cost-effective, noninvasive, and simple imaging modality that offers a multitude of means to improve the diagnosis, monitoring, and treatment of both AKI and CKD, especially considering recent advances in this technique. Ultrasound alone can attenuate AKI and prevent CKD by stimulating the splenic cholinergic anti-inflammatory pathway. Additionally, microbubble contrast agents are improving the sensitivity and specificity of ultrasound for diagnosing kidney disease, especially when these agents are conjugated to ligand-specific mAbs or peptides, which make the dynamic assessment of disease progression and response to treatment possible. More recently, drug-loaded microbubbles have been developed and the load release by ultrasound exposure has been shown to be a highly specific treatment modality, making the potential applications of ultrasound even more promising. This review focuses on the multiple strategies for using ultrasound with and without microbubble technology for enhancing our understanding of the pathophysiology of AKI and CKD.

Antagonism of proteasome inhibitor-induced heme oxygenase-1 expression by PINK1 mutation

PTEN-induced putative kinase 1 (PINK1) is an integral protein in the mitochondrial membrane and maintains mitochondrial fidelity. Pathogenic mutations in PINK1 have been identified as a cause of early-onset autosomal recessive familial Parkinson’s disease (PD). The ubiquitin proteasome pathway is associated with neurodegenerative diseases. In this study, we investigated whether mutations of PINK1 affects the cellular stress response following proteasome inhibition. Administration of MG132, a peptide aldehyde proteasome inhibitor, significantly increased the expression of heme oxygenase-1 (HO-1) in rat dopaminergic neurons in the substantia nigra and in the SH-SY5Y neuronal cell line. The induction of HO-1 expression by proteasome inhibition was reduced in PINK1 G309D mutant cells. MG132 increased the levels of HO-1 through the Akt, p38, and Nrf2 signaling pathways. Compared with the cells expressing WT-PINK1, the phosphorylation of Akt and p38 was lower in those cells expressing the PINK1 G309D mutant, which resulted in the inhibition of the nuclear translocation of Nrf2. Furthermore, MG132-induced neuronal death was enhanced by the PINK1 G309D mutation. In this study, we demonstrated that the G309D mutation impairs the neuroprotective function of PINK1 following proteasome inhibition, which may be related to the pathogenesis of PD.

Heme Oxygenase Database (HemeOxDB) and QSAR Analysis of Isoform 1 Inhibitors

Due to increasing interest in the field of heme oxygenases (HOs), we built a ligand database called HemeOxDB that includes the entire set of known HO-1 and HO-2 inhibitors, resulting in more than 400 compounds. The HemeOxDB is available online at http://www.researchdsf.unict.it/hemeoxdb/, and having a robust search engine allows end users to build complex queries, sort tabulated results, and generate color-coded two- and three-dimensional graphs. This database will grow to be a tool for the design of potent and selective HO-1 or HO-2 inhibitors. We were also interested in virtually searching for alternative inhibitors, and, for the first time in the field of HOs, a quantitative structure-activity relationship (QSAR) model was built using half-maximal inhibitory concentration (IC₅₀ ) values of the whole set of known HO-1 inhibitors, taken from the HemeOxDB and employing the Monte Carlo technique. The statistical quality suggested that the model is robust and possesses desirable predictive potential. The screening of US Food and Drug Administration (FDA)-approved drugs, external to our dataset, suggested new predicted inhibitors, opening the way for replacing imidazole groups. The HemeOxDB and the QSAR model reported herein may help in prospectively identifying or repurposing new drugs with optimal structural attributes for HO enzyme inhibition.

MiR-1254 suppresses HO-1 expression through seed region-dependent silencing and non-seed interaction with TFAP2A transcript to attenuate NSCLC growth

MicroRNAs (miRNAs) are a class of small non-coding RNAs, which direct post-transcriptional gene silencing (PTGS) and function in a vast range of biological events including cancer development. Most miRNAs pair to the target sites through seed region near the 5’ end, leading to mRNA cleavage and/or translation repression. Here, we demonstrated a miRNA-induced dual regulation of heme oxygenase-1 (HO-1) via seed region and non-seed region, consequently inhibited tumor growth of NSCLC. We identified miR-1254 as a negative regulator inhibiting HO-1 translation by directly targeting HO-1 3’UTR via its seed region, and suppressing HO-1 transcription via non-seed region-dependent inhibition of transcriptional factor AP-2 alpha (TFAP2A), a transcriptional activator of HO-1. MiR-1254 induced cell apoptosis and cell cycle arrest in human non-small cell lung carcinoma (NSCLC) cells by inhibiting the expression of HO-1, consequently suppressed NSCLC cell growth. Consistently with the in vitro studies, mouse xenograft studies validated that miR-1254 suppressed NSCLC tumor growth in vivo. Moreover, we found that HO-1 expression was inversely correlated with miR-1254 level in human NSCLC tumor samples and cell lines. Overall, these findings identify the dual inhibition of HO-1 by miR-1254 as a novel functional mechanism of miRNA, which results in a more effective inhibition of oncogenic mRNA, and leads to a tumor suppressive effect.

It is generally accepted that miRNAs bind to 3`UTR of target mRNAs and direct post-transcriptional gene silencing (PTGS) via its seed sequence. Here we report a new dual regulatory mechanism of miRNA. We described that miR-1254 repressed HO-1 at post-transcriptional level by directly targeting HO-1 3’UTR via its seed sequence and also inhibited HO-1 transcription by suppressing the transcriptional factor AP-2 alpha (TFAP2A) via its non-seed sequence. MiR-1254 induced cell apoptosis and cell cycle arrest in human non-small cell lung carcinoma (NSCLC) cells by inhibiting the expression of HO-1, consequently suppressed NSCLC cell growth. Moreover, in vivo mouse xenograft studies also supported the inhibitory effect of miR-1254 on NSCLC growth. These findings identify the dual regulation of miR-1254 on HO-1 as a novel functional mechanism of miRNA, which results in a more effective inhibition on the oncogenic mRNA, and leads to a suppressive effect on NSCLC growth, thus significantly advance our understanding of miRNA-directed gene regulation.

HMOX-1 inhibits TGF-β-induced epithelial-mesenchymal transition in the MCF-7 breast cancer cell line

Epithelial‑mesenchymal transition (EMT) is a key mechanism underlying metastatic breast cancer. Reactive oxygen species (ROS) play an important role in EMT. Heme oxygenase‑1 (HMOX‑1) can reduce oxidative stress. However, the effect of HMOX‑1 on the EMT process in breast cancer cells is unknown. We treated the MCF‑7 breast cancer cell line with the HMOX‑1 inducer hemin and observed that hemin induced HMOX‑1 expression and inhibited migration, invasion and ROS generation in transforming growth factor‑β (TGF‑β)‑treated MCF‑7 cells using quantitative RT‑qPCR, western blotting, wound‑healing and cell invasion assays as well as fluorescent probe DCFDA. Hemin inhibited TGF‑β‑induced EMT in the MCF‑7 cells, whereas HMOX‑1 siRNA attenuated the suppressive effect of hemin as determined by the expression and cellular distribution of selected EMT markers. In summary, our results revealed that hemin treatment increased HMOX‑1 expression and inhibited TGF‑β‑induced EMT in MCF‑7 cells.

How to Increase Brightness of Near-Infrared Fluorescent Proteins in Mammalian Cells

Numerous near-infrared (NIR) fluorescent proteins (FPs) were recently engineered from bacterial photoreceptors but lack of their systematic comparison makes researcher's choice rather difficult. Here we evaluated side-by-side several modern NIR FPs, such as blue-shifted smURFP and miRFP670, and red-shifted mIFP and miRFP703. We found that among all NIR FPs, miRFP670 had the highest fluorescence intensity in various mammalian cells. For instance, in common HeLa cells miRFP703, mIFP, and smURFP were 2-, 9-, and 53-fold dimmer than miRFP670. Either co-expression of heme oxygenase or incubation of cells with heme precursor weakly affected NIR fluorescence, however, in the latter case elevated cellular autofluorescence. Exogenously added chromophore substantially increased smURFP brightness but only slightly enhanced brightness of other NIR FPs. mIFP showed intermediate, while monomeric miRFP670 and miRFP703 exhibited high binding efficiency of endogenous biliverdin chromophore. This feature makes them easy to use as GFP-like proteins for spectral multiplexing with FPs of visible range.

Reprint of: Heme oxygenase 1 affects granulopoiesis in mice through control of myelocyte proliferation

Heme oxygenase-1 (HO-1) is stress-inducible, cytoprotective enzyme degrading heme to carbon monoxide (CO), biliverdin and Fe²⁺. We showed that HO-1 knock-out mice (HO-1^-/-) have a twofold higher level of granulocytes than wild type (WT) mice, despite decreased concentration of granulocyte colony-stimulating factor (G-CSF) in the blood and reduced surface expression of G-CSF receptor on the hematopoietic precursors. This suggests the effect of HO-1 on granulopoiesis. Here we aimed to determine the stage of granulopoiesis regulated by HO-1. The earliest stages of hematopoiesis were not biased toward myeloid differentiation in HO-1^-/- mice. Within committed granulocytic compartment, in WT mice, HO-1 was up-regulated starting from myelocyte stage. This was concomitant with up-regulation of miR-155, which targets Bach1, the HO-1 repressor. In HO-1^-/- mice granulopoiesis was accelerated between myelocyte and metamyelocyte stage. There was a higher fraction of proliferating myelocytes, with increased nuclear expression of pro-proliferative C/EBPβ (CCAAT/enhancer binding protein beta) protein, especially its active LAP (liver-enriched activator proteins) isoform. Also our mathematical model confirmed shortening the myelocyte cyclic-time and prolonged mitotic expansion in absence of HO-1. It seems that changes in C/EBPβ expression and activity in HO-1^-/- myelocytes can be associated with reduced level of its direct repressor miR-155 or with decreased concentration of CO, known to reduce nuclear translocation of C/EBPs. Mature HO-1^-/- granulocytes were functionally competent as determined by oxidative burst capacity. In conclusion, HO-1 influences granulopoiesis through regulation of myelocyte proliferation. It is accompanied by changes in expression of transcriptionally active C/EBPβ protein. As HO-1 expression vary in human and is up-regulated in response to chemotherapy, it can potentially influence chemotherapy-induced neutropenia.

HO-1 Induction in Cancer Progression: A Matter of Cell Adaptation

The upregulation of heme oxygenase-1 (HO-1) is one of the most important mechanisms of cell adaptation to stress. Indeed, the redox sensitive transcription factor Nrf2 is the pivotal regulator of HO-1 induction. Through the antioxidant, antiapoptotic, and antinflammatory properties of its metabolic products, HO-1 plays a key role in healthy cells in maintaining redox homeostasis and in preventing carcinogenesis. Nevertheless, several lines of evidence have highlighted the role of HO-1 in cancer progression and its expression correlates with tumor growth, aggressiveness, metastatic and angiogenetic potential, resistance to therapy, tumor escape, and poor prognosis, even though a tumor- and tissue-specific activity has been observed. In this review, we summarize the current literature regarding the pro-tumorigenic role of HO-1 dependent tumor progression as a promising target in anticancer strategy.

Acute HIV-1 infection is associated with increased plasma levels of heme oxygenase-1 and presence of heme oxygenase-1-specific regulatory T cells

OBJECTIVE

Heme oxygenase-1 (HO-1) is an inducible stress response protein with potent anti-inflammatory activity and recent data suggest a potentially beneficial role in HIV pathogenesis. We investigated the impact of HO-1 and a novel subset of HO-1-specific CD8 regulatory T cells on virus-specific T-cell immunity in HIV-1-infected individuals.

METHODS

HO-1 protein levels were quantified in plasma from individuals at different stages of HIV-1 disease and longitudinally following primary HIV infection. HO-1-specific CD8 T cells were investigated by flow cytometry using human leukocyte antigen (HLA) class I pentamers. Flow-sorted HO-1-specific CD8 T cells were cultured and tested for suppressive activity on HIV-1-specific cytotoxic T-cell clones clones. HO-1 gene expression was determined in sorted peripheral blood mononuclear cell (PBMC) subsets from individuals with acute HIV-1 infection.

RESULTS

HO-1 plasma levels were significantly increased in HIV-1 infection, with the highest levels in individuals with acute HIV-1 infection, and gradually declined over time. The frequency of CD8 T cells specific for HO-1 was elevated in study participants with primary HIV-1 infection and flow-sorted HO-1-specific CD8 T cells were capable of suppressing HIV-1-specific lysis of cytotoxic T-cell clones clones. HO-1 gene expression was upregulated in multiple immune cell subsets during acute HIV-1 infection and HO-1 overexpression modulated anti-HIV immunity in vitro.

CONCLUSION

Our data suggest that HO-1 is induced during acute HIV-1 infection, likely mediating anti-inflammatory effects and driving expansion of HO-1-specific CD8 regulatory T cells capable of suppressing HIV-1-specific immune responses in vitro. The investigation of HO-1 and the novel CD8 regulatory cell type described here provide further insight into immune regulation in HIV-1 infection and may hold potential for future immunotherapeutic intervention.

Thermosensitive micellar hydrogel for enhanced anticancer therapy through redox modulation mediated combinational effects

Illustration of the design and action pathway of the PECT/DOX micelle and PECT/ZnPP micelle in situ formed thermosensitive micellar hydrogel.

Heme oxygenase-1 in the forefront of a multi-molecular network that governs cell-cell contacts and filopodia-induced zippering in prostate cancer

Prostate cancer (PCa) cells display abnormal expression of cytoskeletal proteins resulting in an augmented capacity to resist chemotherapy and colonize distant organs. We have previously shown that heme oxygenase 1 (HO-1) is implicated in cell morphology regulation in PCa. Here, through a multi 'omics' approach we define the HO-1 interactome in PCa, identifying HO-1 molecular partners associated with the integrity of the cellular cytoskeleton. The bioinformatics screening for these cytoskeletal-related partners reveal that they are highly misregulated in prostate adenocarcinoma compared with normal prostate tissue. Under HO-1 induction, PCa cells present reduced frequency in migration events, trajectory and cell velocity and, a significant higher proportion of filopodia-like protrusions favoring zippering among neighboring cells. Moreover forced expression of HO-1 was also capable of altering cell protrusions in transwell co-culture systems of PCa cells with MC3T3 cells (pre-osteoblastic cell line). Accordingly, these effects were reversed under siHO. Transcriptomics profiling evidenced significant modulation of key markers related to cell adhesion and cell–cell communication under HO-1 induction. The integration from our omics-based research provides a four molecular pathway foundation (ANXA2/HMGA1/POU3F1; NFRSF13/GSN; TMOD3/RAI14/VWF; and PLAT/PLAU) behind HO-1 regulation of tumor cytoskeletal cell compartments. The complementary proteomics and transcriptomics approaches presented here promise to move us closer to unravel the molecular framework underpinning HO-1 involvement in the modulation of cytoskeleton pathways, pushing toward a less aggressive phenotype in PCa.

Inhibition of heme oxygenase-1 enhances the chemosensitivity of laryngeal squamous cell cancer Hep-2 cells to cisplatin

It has been previously reported that cisplatin is a well-known anticancer drug being used against a wide range of malignancies including head and neck, ovarian and non-small cell lung carcinoma, and demonstrated its anticancer activity by reacting with DNA or changing cell structure, immune response, reactive oxygen species level (ROS). In this research we proved that cisplatin induced cell injuries and heme oxygenase-1 (HO-1) expression in laryngeal squamous cell cancer Hep-2 cells through ROS generation. The induction of HO-1 clearly protected Hep-2 cells from cisplatin-induced cell death and ROS reaction, and the inhibitor of HO-1 enhanced the cell death and ROS generation induced by cisplatin. Furthermore, the HO-1 expression induced by cisplatin was strongly inhibited by the knockdown of nuclear factor-erythroid-2-related factor-2 (Nrf-2), and the oxidative damages induced by cisplatin were significantly enhanced. Therefore, it may be concluded that the inhibition of HO-1 or the knockdown of Nrf-2 significantly enhanced cisplatin's anticancer effects on Hep-2 cells. In clinic, with the overexpression of HO-1 in laryngeal squamous cancer tissues, the combination of cisplatin with the inhibitor of HO-1 or Nrf-2 siRNA may act as a new method to the treatment of laryngeal squamous cancer.

The Ratio of Hmox1/Nrf2 mRNA Level in the Tumor Tissue Is a Predictor of Distant Metastasis in Colorectal Cancer

Heme oxygenase 1 (Hmox1) plays an important role in the growth and spread of tumor, and its expression is regulated positively by Nrf2 [nuclear factor (erythroid-derived 2)-like 2; NFE2L2] and negatively by kelch-like ECH-associated protein 1 (Keap1) and by BTB and CNC homology 1 (Bach1). Both Hmox1 and Nrf2 contribute to distant metastasis of cancer. The mRNA levels of Hmox1, Nrf2, Keap1, and Bach1 in the tumor and normal tissues of 84 subjects with colorectal cancer (CRC) were determined by real-time polymerase chain reaction. The tumor had lower Hmox1 but higher Bach1 mRNA levels than the normal tissue. The correlations of Hmox1 with components of the Nrf2 pathway were not significant in the tumor tissue of CRC subjects with distant metastasis. The ratio of Hmox1/Nrf2 mRNA level (by percentage) in the tumor tissue was lower in the subjects with distant metastasis (97.4% (84.4–111.1%)) than in those without (101.0% (92.7–136.5%)) and was a predictor for distant metastasis in CRC (odds ratio: 0.83; 95% confidence interval: 0.68–0.97) along with serum carcinoembryonic antigen (1.0027, 1.006–1.064). The mRNA level of Hmox1 in the tumor tissue of CRC is not correlated with that of the Nrf2 pathway molecules, and its ratio to the Nrf2 level may be useful for suggesting distant metastasis in CRC.

Enhancement of DEN-induced liver tumorigenesis in heme oxygenase-1 G143H mutant transgenic mice

Heme oxygenase (HO) is the rate-limiting enzyme in heme metabolism. HO-1 exhibits anti-oxidative and anti-inflammatory function via the actions of its metabolite, respectively. A growing body of evidence demonstrates that HO-1 is implicated in the pathogenesis and progression of several types of cancer. However, whether HO-1 takes part in healthy-premalignant-malignant transformation is still undefined. In this study, we took advantage of transgenic mice which over-expressed HO-1 dominant negative mutant (HO-1 G143H) and observed its susceptibility to DEN-induced hepatocarcinogenesis. Our results indicate that HO-1 G143H mutant accelerates the progression of tumorigenesis and tumor growth. The mechanism is closely related to enhancement of ROS production which induce more hepatocytes death and secretion of inflammatory cytokines, proliferation of surviving hepatocytes. Our result provides the direct evidence that HO-1 plays an important protective role in liver carcinogenesis. Alternatively, we suggest the possible explanation on effect of HO-1 promoter polymorphism which involved in tumorigenesis.

Heme oxygenase 1 affects granulopoiesis in mice through control of myelocyte proliferation

Heme oxygenase-1 (HO-1) is stress-inducible, cytoprotective enzyme degrading heme to carbon monoxide (CO), biliverdin and Fe²⁺. We showed that HO-1 knock-out mice (HO-1^-/-) have a twofold higher level of granulocytes than wild type (WT) mice, despite decreased concentration of granulocyte colony-stimulating factor (G-CSF) in the blood and reduced surface expression of G-CSF receptor on the hematopoietic precursors. This suggests the effect of HO-1 on granulopoiesis. Here we aimed to determine the stage of granulopoiesis regulated by HO-1. The earliest stages of hematopoiesis were not biased toward myeloid differentiation in HO-1^-/- mice. Within committed granulocytic compartment, in WT mice, HO-1 was up-regulated starting from myelocyte stage. This was concomitant with up-regulation of miR-155, which targets Bach1, the HO-1 repressor. In HO-1^-/- mice granulopoiesis was accelerated between myelocyte and metamyelocyte stage. There was a higher fraction of proliferating myelocytes, with increased nuclear expression of pro-proliferative C/EBPβ (CCAAT/enhancer binding protein beta) protein, especially its active LAP (liver-enriched activator proteins) isoform. Also our mathematical model confirmed shortening the myelocyte cyclic-time and prolonged mitotic expansion in absence of HO-1. It seems that changes in C/EBPβ expression and activity in HO-1^-/- myelocytes can be associated with reduced level of its direct repressor miR-155 or with decreased concentration of CO, known to reduce nuclear translocation of C/EBPs. Mature HO-1^-/- granulocytes were functionally competent as determined by oxidative burst capacity. In conclusion, HO-1 influences granulopoiesis through regulation of myelocyte proliferation. It is accompanied by changes in expression of transcriptionally active C/EBPβ protein. As HO-1 expression vary in human and is up-regulated in response to chemotherapy, it can potentially influence chemotherapy-induced neutropenia.

Heme oxygenase-1 in macrophages controls prostate cancer progression

Innate immune cells strongly influence cancer growth and progression via multiple mechanisms including regulation of epithelial to mesenchymal transition (EMT). In this study, we investigated whether expression of the metabolic gene, heme oxygenase-1 (HO-1) in tumor microenvironment imparts significant effects on prostate cancer progression.

We showed that HO-1 is expressed in MARCO-positive macrophages in prostate cancer (PCa) xenografts and human prostate cancers. We demonstrated that macrophage specific (LyzM-Cre) conditional deletion of HO-1 suppressed growth of PC3 xenografts in vivo and delayed progression of prostate intraepithelial neoplasia (PIN) in TRAMP mice. However, initiation and progression of cancer xenografts in the presence of macrophages lacking HO-1 resulted in loss of E-cadherin, a known marker of poor prognosis as well as EMT. Application of CO, a product of HO-1 catalysis, increased levels of E-cadherin in the adherens junctions between cancer cells. We further showed that HO-1-driven expression of E-cadherin in cancer cells cultured in the presence of macrophages is dependent on mitochondrial activity of cancer cells.

In summary, these data suggest that HO-1-derived CO from tumor-associated macrophages influences, in part, E-cadherin expression and thus tumor initiation and progression.

Heme oxygenase-1 retards hepatocellular carcinoma progression through the microRNA pathway

Heme metabolism system is involved in microRNA (miRNA) biogenesis. The complicated interplay between heme oxygenase-1 (HO-1) and miRNA has been observed in various tissues and diseases, including human malignancy. In the present study, our data showed that stable HO-1 overexpression in hepatocellular carcinoma (HCC) cells downregulated several oncomiRs. The most stably downregulated are miR-30d and miR-107. Iron, one of HO-1 catalytic products, was an important mediator in this regulation. Cell function analysis demonstrated that HO-1 inhibited the proliferation and metastasis of HepG2 cells, whereas miR-30d/miR-107 improved the proliferative and migratory ability of HepG2 cells. The beneficial effect of HO-1 in HCC inhibition could be reversed by upregulating miR-30d and miR-107. Akt and ERK pathways may be involved in the regulation of HO-1/miR-30d/miR-107 in HCC. These data indicate that HO-1 significantly suppresses HCC progression by regulating the miR-30d/miR-107 level, suggesting miR-30d/miR-107 regulation as a new molecular mechanism of HO-1 anticancer effect.

Withaferin A suppresses the growth of myelodysplasia and leukemia cell lines by inhibiting cell cycle progression

Treatment outcomes for acute myeloid leukemia and myelodysplastic syndromes (MDS) remain unsatisfactory despite progress in various types of chemotherapy and hematopoietic stem cell transplantation. Therefore, there is a need for the development of new treatment options. We investigated the growth‐suppressive effects of withaferin A (WA), a natural plant steroidal lactone, on myelodysplasia and leukemia cell lines. WA exhibited growth‐suppressive effects on the cell lines, MDS‐L, HL‐60, THP‐1, Jurkat and Ramos, and induction of cell cycle arrest at G2/M phase at relatively low doses. Evaluation by annexin V/PI also confirmed the induction of partial apoptosis. Gene expression profiling and subsequent gene set enrichment analysis revealed increased expression of heme oxygenase‐1 (HMOX1). HMOX1 is known to induce autophagy during anticancer chemotherapy and is considered to be involved in the treatment resistance. Our study indicated increased HMOX1 protein levels and simultaneous increases in the autophagy‐related protein LC3A/B in MDS‐L cells treated with WA, suggesting increased autophagy. Combined use of WA with chloroquine, an autophagy inhibitor, enhanced early apoptosis and growth suppression. Together with the knowledge that WA had no apparent suppressive effect on the growth of human normal bone marrow CD34‐positive cells in the short‐term culture, this drug may have a potential for a novel therapeutic approach to the treatment of leukemia or MDS.

Identification of cyclins A1, E1 and vimentin as downstream targets of heme oxygenase-1 in vascular endothelial growth factor-mediated angiogenesis

Angiogenesis is an essential physiological process and an important factor in disease pathogenesis. However, its exploitation as a clinical target has achieved limited success and novel molecular targets are required. Although heme oxygenase-1 (HO-1) acts downstream of vascular endothelial growth factor (VEGF) to modulate angiogenesis, knowledge of the mechanisms involved remains limited. We set out identify novel HO-1 targets involved in angiogenesis. HO-1 depletion attenuated VEGF-induced human endothelial cell (EC) proliferation and tube formation. The latter response suggested a role for HO-1 in EC migration, and indeed HO-1 siRNA negatively affected directional migration of EC towards VEGF; a phenotype reversed by HO-1 over-expression. EC from Hmox1(-/-) mice behaved similarly. Microarray analysis of HO-1-depleted and control EC exposed to VEGF identified cyclins A1 and E1 as HO-1 targets. Migrating HO-1-deficient EC showed increased p27, reduced cyclin A1 and attenuated cyclin-dependent kinase 2 activity. In vivo, cyclin A1 siRNA inhibited VEGF-driven angiogenesis, a response reversed by Ad-HO-1. Proteomics identified structural protein vimentin as an additional VEGF-HO-1 target. HO-1 depletion inhibited VEGF-induced calpain activity and vimentin cleavage, while vimentin silencing attenuated HO-1-driven proliferation. Thus, vimentin and cyclins A1 and E1 represent VEGF-activated HO-1-dependent targets important for VEGF-driven angiogenesis.

Redox Homeostasis and Cellular Antioxidant Systems: Crucial Players in Cancer Growth and Therapy

Reactive oxygen species (ROS) and their products are components of cell signaling pathways and play important roles in cellular physiology and pathophysiology. Under physiological conditions, cells control ROS levels by the use of scavenging systems such as superoxide dismutases, peroxiredoxins, and glutathione that balance ROS generation and elimination. Under oxidative stress conditions, excessive ROS can damage cellular proteins, lipids, and DNA, leading to cell damage that may contribute to carcinogenesis. Several studies have shown that cancer cells display an adaptive response to oxidative stress by increasing expression of antioxidant enzymes and molecules. As a double-edged sword, ROS influence signaling pathways determining beneficial or detrimental outcomes in cancer therapy. In this review, we address the role of redox homeostasis in cancer growth and therapy and examine the current literature regarding the redox regulatory systems that become upregulated in cancer and their role in promoting tumor progression and resistance to chemotherapy.

Heme oxygenase-1 promotes tumor progression and metastasis of colorectal carcinoma cells by inhibiting antitumor immunity

Heme oxygenase-1 (HO-1) is upregulated in colorectal carcinoma (CRC) cells. However, the role of HO-1 in the metastatic potential of CRC remains to be elucidated. In this study, we investigated the potential of HO-1 to control the antitumor immunity of CRC. Intercellular adhesion molecule-1 (ICAM-1) plays an important role in the immune surveillance system. Hemin-induced HO-1 expression suppressed the expression of ICAM-1 in human CRC cells. HO-1 regulated ICAM-1 expression via tristetraprolin, an mRNA-binding protein, at the posttranscriptional level in CRC cells. The upregulated HO-1 expression in CRC cells markedly decreased the adhesion of peripheral blood mononuclear lymphocytes (PBMLs) to CRC cells and PBML-mediated cytotoxicity against CRC cells. Production of CXCL10, an effector T cell-recruiting chemokine, was significantly reduced by the increased HO-1 expression. The expression of the CXCL10 receptor, CXCR3, decreased significantly in PBMLs that adhered to CRC cells. HO-1 expression correlated negatively, although nonsignificantly, with ICAM-1 and CXCL10 expression in xenograft tumors. Taken together, our data suggest that HO-1 expression is functionally linked to the mediation of tumor progression and metastasis of CRC cells by inhibiting antitumor immunity.

Overexpression of heme oxygenase-1 induced by constitutively activated NF-κB as a potential therapeutic target for activated B-cell-like diffuse large B-cell lymphoma

There is an urgent requirement for a new therapeutic target for activated B-cell-like lymphoma (ABC-DLBCL), which is known to have dismal outcome and constitutive activation of NF-κB. Heme oxygenase-1 (HO-1) can inhibit apoptosis and promote proliferation in many cancers. To our knowledge, no studies have been performed on the correlation between HO-1 and DLBCL. In this study, immunohistochemical analysis of 31 tumor tissues from DLBCL patients [20 of ABC subtype and 11 of germinal center B-cell-like (GCB) subtype] and 11 normal lymph nodes revealed that HO-1 overexpression was characteristic of ABC-DLBCL. In addition, HO-1 mRNA expression levels were consistent with the immunohistochemistry results. High levels of HO-1 expression were significantly correlated with the involvement of more than 1 extranodal site (p=0.025), with a high positivity rate of Ki-67 (p<0.01). Similar to its anti-apoptotic role in other malignancies, HO-1 upregulation suppressed apoptosis of the ABC-DLBCL cell line OCI-ly10, whereas its downregulation sensitized the tumor cells to chemotherapeutic drugs. Further study demonstrated that the HO-1 overexpression was mediated by constitutively activated NF-κB which together played an anti-apoptotic role in ABC-DLBCL. Combination of the NF-κB inhibitor Bay11‑7082 and the lentivirus vector Lenti-siHO-1 significantly decreased HO-1 protein expression and increased apoptosis in OCI-ly10 cells. However, in GCB-DLBCL cells with low levels of NF-κB expression, the TNF-α-mediated activation of NF-κB leading to HO-1 upregulation rescued the cells from apoptosis caused by HO-1 silencing. These results indicated that HO-1 can be a potential target for the treatment of ABC-DLBCL.

Hawthorn Fruit Extract Elevates Expression of Nrf2/HO-1 and Improves Lipid Profiles in Ovariectomized Rats

The purpose of this study was to investigate the effects of hawthorn (Crataegus pinnatifida Bunge) extract on the lipid profiles and antioxidant properties in ovariectomized (OVX) rats. After ovariectomy, the rats were randomly divided into four groups: the non-OVX control (Sham), the OVX-control (OVX), the OVX + 100 mg/kg b.w. of hawthorn extract (OL), and the OVX + 200 mg/kg b.w. of hawthorn extract (OH). The final body weights of the OVX group were significantly increased, but the increment was significantly decreased in hawthorn groups (p < 0.05). The serum total and low-density lipoprotein (LDL) cholesterol levels were significantly elevated in the OVX group, whereas the hawthorn groups showed a significant decrease in these levels (p < 0.05). The hepatic triglyceride (TG) and malondialdehyde (MDA) levels were significantly reduced in the hawthorn groups compared with the OVX group (p < 0.05). The mRNA expression of nuclear factor erythroid 2–related factor (Nrf2), heme oxygenase-1 (HO-1), and glutathione peroxidase (GPx) were significantly decreased in the OVX group, whereas the hawthorn groups exhibited a significant increase in expression (p < 0.05). The protein expressions of Nrf2, HO-1, and GPx were lower in the OVX group than the Sham group (p < 0.05). The oral administration of hawthorn extract reversed the suppression of protein levels. These results suggest that hawthorn extract could have protective effects in OVX rats by improving lipid profiles, decreasing oxidative stress, and improving the antioxidant defense system.

Diverse prognostic value of the GTn promoter polymorphism in squamous cell and adeno carcinoma of the oesophagus

The basal transcription of heme oxygenase-1 (HO-1) regulation is dependent upon a GT repeat germ line polymorphism (GTn) in the promoter of the HO-1 gene. We determined the prognostic value of HO-1 promoter polymorphism on the natural postoperative course of complete resected oesophageal cancer. Genomic DNA from 297 patients was amplified by polymerase chain reaction and sequenced. The results were correlated with clinicopathological parameters, disseminated tumour cells in bone marrow (DTC) and clinical outcome. Depending on short allele with <25 and long allele with ≥25, GTn repeats three genotypes (SS, SL and LL) were defined. A diverse role of GTn was evident in squamous cell carcinoma (SCC) and adenocarcinoma (AC). In SCC, the SS genotype presented less advanced tumours with lower rate DTC in bone marrow and relapse compared with L-allele carriers. In contrast, AC patients with the SS genotype displayed a complete opposing tumour characteristic. The disease-free (DFS) and overall survival (OS) in SCC patients was markedly reduced in LL genotypes (p < 0.001). In AC contrarily the SS genotype patients displayed the worst DFS and OS (p < 0.001). GTn is a strong prognostic factor with diverse prognostic value for recurrence and survival in AC and SCC.

Triterpenoid saponin flaccidoside II from Anemone flaccida triggers apoptosis of NF1-associated malignant peripheral nerve sheath tumors via the MAPK-HO-1 pathway

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue neoplasms that are extremely rare and are frequently associated with neurofibromatosis type 1 patients. MPNSTs are typically fatal, and there is no effective treatment so far. In our previous study, we showed that flaccidoside II, one of the triterpenoid saponins isolated from Anemone flaccida Fr. Schmidt, has antitumor potential by inducing apoptosis. In the present study, we found that flaccidoside II inhibits proliferation and facilitates apoptosis in MPNST cell lines ST88-14 and S462. Furthermore, this study provides a mechanism by which the downregulation of heme oxygenase-1 via extracellular signal-regulated kinase-1/2 and p38 mitogen-activated protein kinase pathways is involved in the apoptotic role of flaccidoside II. This study suggested the potential of flaccidoside II as a novel pharmacotherapeutic approach for MPNSTs.

Role of Nrf2, HO-1 and GSH in Neuroblastoma Cell Resistance to Bortezomib

The activation of Nrf2 has been demonstrated to play a crucial role in cancer cell resistance to different anticancer therapies. The inhibition of proteasome activity has been proposed as a chemosensitizing therapy but the activation of Nrf2 could reduce its efficacy. Using the highly chemoresistant neuroblastoma cells HTLA-230, here we show that the strong reduction in proteasome activity, obtained by using low concentration of bortezomib (BTZ, 2.5 nM), fails in reducing cell viability. BTZ treatment favours the binding of Nrf2 to the ARE sequences in the promoter regions of target genes such as heme oxygenase 1 (HO-1), the modulatory subunit of γ-glutamylcysteine ligase (GCLM) and the transporter for cysteine (x-CT), enabling their transcription. GSH level is also increased after BTZ treatment. The up-regulation of Nrf2 target genes is responsible for cell resistance since HO-1 silencing and GSH depletion synergistically decrease BTZ-treated cell viability. Moreover, cell exposure to all-trans-Retinoic acid (ATRA, 3 μM) reduces the binding of Nrf2 to the ARE sequences, decreases HO-1 induction and lowers GSH level increasing the efficacy of bortezomib. These data suggest the role of Nrf2, HO-1 and GSH as molecular targets to improve the efficacy of low doses of bortezomib in the treatment of malignant neuroblastoma.

Potential scenarios leading to ovarian cancer arising from endometriosis

OBJECTIVES

The aim of this review was to highlight recent advances in our understanding of the pathogenesis of malignant transformation of endometriosis.

METHODS

This study reviewed the English-language literature concerning basic science studies of the potential promotion of carcinogenesis.

RESULTS

Repeated episodes of hemorrhage occur in endometriosis at the onset of menstruation. Extracellular hemoglobin, heme, and iron derivatives in endometriosis cause DNA damage and mutations, which create increased cellular susceptibility to oxidant-mediated cell killing. Excess DNA damage and mutations are linked to cell death, but not carcinogenesis. In response to an oxidative and inflammatory microenvironment, endometriotic cells and macrophages secrete antioxidants that control excess oxidative stress in the surrounding environment. Exposure of endometriotic cells to a sublethal level of oxidative stress may lead to carcinogenesis. Macrophages also secrete immunosuppressive factors that lead to promotion of malignant transformation.

DISCUSSION

At least two potential scenarios could result in ovarian cancer arising from endometriosis. The first step: extracellular hemoglobin, heme, and iron cause cellular oxidative damage by promoting reactive oxygen species formation, which results in DNA damage and mutations (ovarian cancer initiation from endometriosis). The second step: cancer progression may be associated with persistent antioxidant production favoring a protumoral microenvironment.

Cross-talk between two antioxidants, thioredoxin reductase and heme oxygenase-1, and therapeutic implications for multiple myeloma

Multiple myeloma (MM) is characterized by an accumulation of abnormal clonal plasma cells in the bone marrow. Despite recent advancements in anti-myeloma therapies, MM remains an incurable disease. Antioxidant molecules are upregulated in many cancers, correlating with tumor proliferation, survival, and chemoresistance and therefore, have been suggested as potential therapeutic targets. This study investigated the cross-talk between two antioxidant molecules, thioredoxin reductase (TrxR) and heme oxygenase-1 (HO-1), and their therapeutic implications in MM. We found that although auranofin, a TrxR inhibitor, significantly inhibited TrxR activity by more than 50% at lower concentrations, myeloma cell proliferation was only inhibited at higher concentrations of auranofin. Inhibition of TrxR using lower auranofin concentrations induced HO-1 protein expression in myeloma cells. Using a sub-lethal concentration of auranofin to inhibit TrxR activity in conjunction with HO-1 inhibition significantly decreased myeloma cell growth and induced apoptosis. TrxR was shown to regulate HO-1 via the Nrf2 signaling pathway in a ROS-dependent manner. Increased HO-1 mRNA levels were observed in bortezomib-resistant myeloma cells compared to parent cells and HO-1 inhibition restored the sensitivity to bortezomib in bortezomib-resistant myeloma cells. These findings indicate that concurrent inhibition of HO-1 with either a TrxR inhibitor or with bortezomib would improve therapeutic outcomes in MM patients. Hence, our findings further support the need to target multiple antioxidant systems alone or in combination with other therapeutics to improve therapeutic outcomes in MM patients.

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TrxR inhibition induces HO-1 expression in myeloma cells.

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Inhibiting TrxR and HO-1 together induces myeloma cell apoptosis.

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HO-1 serves as a secondary anti-apoptotic mechanism in TrxR-inhibited myeloma cells.

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HO-1 inhibition overcomes bortezomib resistance in myeloma cells.

Haem oxygenase 1 expression is associated with prognosis in cholangiocarcinoma patients and with drug sensitivity in xenografted mice

OBJECTIVE

Haem oxygenase-1 (HO-1) plays important roles in cytoprotection and tumour growth. Cholangiocarcinoma (CCA) is a deadly malignancy with very poor prognosis. The role of HO-1 in tumour progression in CCA up to now has been relatively unexplored, thus, its possible therapeutic implications in CCA have been investigated here.

MATERIALS AND METHODS

HO-1 expression in tumour tissues from 50 CCA patients was determined by immunohistochemical analysis and its association with survival time was evaluated using the Kaplan-Meier method. Its role in CCA cells in vitro was evaluated by transwell and wound healing assays and suppression of HO-1 expression by siRNA. Effects of HO-1 inhibition on gemicitabine (GEM)-mediated tumour suppression was evaluated in nude mice xenografted with CCA cells.

RESULTS

HO-1 expression was inversely associated with median overall survival time. Hazard ratio of patients with high HO-1 expression was 2.42 (95% CI: 1.16-5.08) with reference to low expression and HO-1 knock-down expression inhibited transwell cell migration. Suppression of HO-1 by Zn-protoporphyrin (ZnPP) enhanced cytotoxicity to GEM in CCA cells, validated in CCA xenografts. Treatment with GEM and ZnPP almost completely arrested tumour growth, whereas treatment with only a single reagent, retarded it. Tumour inhibition was associated with reduction in expression of Ki-67 and microvascular density, and enhanced p53 and p21 immunohistochemical staining.

CONCLUSION

High HO-1 expression was associated with poor prognosis of CCA. Synergistic role of HO-1 inhibition in chemotherapy of CCA is a promising insight for treatment of this tumour and warrants further investigation.

Targeting of heme oxygenase-1 as a novel immune regulator of neuroblastoma

Heme oxygenase (HO)-1 catalyzes the degradation of cytotoxic heme into biliverdin and blocks antitumor immune responses, thus protecting cancer against host defense. Whether this scenario also applies to neuroblastoma (NB), the most common extracranial solid childhood tumor, is not known. Here, we demonstrate for the first time a prognostic relevance of HO-1 expression in samples from NB patients and show that targeting of HO-1 prevents both cancer resistance against cellular stress and immune escape in the syngeneic NXS2 A/J mouse model of NB. High HO-1 RNA expression in NB tissues emerged as unfavorable prognostic marker, in particular for patients older than 18 months as indicated by univariate as well as multivariate survival probability analyses including disease stage and MYCN status. On the basis of this observation we aimed to target HO-1 by systemic as well as tumor-specific zinc protoporphyrin-mediated HO-1 suppression in a syngeneic immunocompetent NB mouse model. This resulted in 50% reduction of primary tumor growth and a suppression of spontaneous liver metastases. Importantly, HO-1 inhibition abrogated immune cell paralysis affecting CD4 and CD8 T-effector cells. This in turn reverted HO-1-dependent immune escape mechanisms in NB by increasing NB apoptosis and improved DC maturation. In summary, HO-1 emerges as a novel immune regulator in NB and emerges as a promising target for the development of therapeutic approaches.

The Nrf2/HO-1 Axis in Cancer Cell Growth and Chemoresistance

The transcription factor, nuclear factor erythroid 2 p45-related factor 2 (Nrf2), acts as a sensor of oxidative or electrophilic stresses and plays a pivotal role in redox homeostasis. Oxidative or electrophilic agents cause a conformational change in the Nrf2 inhibitory protein Keap1 inducing the nuclear translocation of the transcription factor which, through its binding to the antioxidant/electrophilic response element (ARE/EpRE), regulates the expression of antioxidant and detoxifying genes such as heme oxygenase 1 (HO-1). Nrf2 and HO-1 are frequently upregulated in different types of tumours and correlate with tumour progression, aggressiveness, resistance to therapy, and poor prognosis. This review focuses on the Nrf2/HO-1 stress response mechanism as a promising target for anticancer treatment which is able to overcome resistance to therapies.

A knockdown with smoke model reveals FHIT as a repressor of Heme oxygenase 1

Fragile histidine triad (FHIT) gene deletions are among the earliest and most frequent events in carcinogenesis, particularly in carcinogen-exposed tissues. Though FHIT has been established as an authentic tumor suppressor, the mechanism underlying tumor suppression remains opaque. Most experiments designed to clarify FHIT function have analyzed the consequence of re-expressing FHIT in FHIT-negative cells. However, carcinogenesis occurs in cells that transition from FHIT-positive to FHIT-negative. To better understand cancer development, we induced FHIT loss in human bronchial epithelial cells with RNA interference. Because FHIT is a demonstrated target of carcinogens in cigarette smoke, we combined FHIT silencing with cigarette smoke extract (CSE) exposure and measured gene expression consequences by RNA microarray. The data indicate that FHIT loss enhances the expression of a set of oxidative stress response genes after exposure to CSE, including the cytoprotective enzyme heme oxygenase 1 (HMOX1) at the RNA and protein levels. Data are consistent with a mechanism in which Fhit protein is required for accumulation of the transcriptional repressor of HMOX1, Bach1 protein. We posit that by allowing superinduction of oxidative stress response genes, loss of FHIT creates a survival advantage that promotes carcinogenesis.

Heme oxygenase-1 is a predictive biomarker for therapeutic targeting of advanced clear cell renal cell carcinoma treated with sorafenib or sunitinib

Background

We analyzed the expression of heme oxygenase-1 (HO-1) in patients undergoing radical nephrectomy for advanced clear cell renal cell carcinoma (CC-RCC) and evaluated the effects of the targeted therapies treated with sorafenib and sunitinib.

Methods

Expression of HO-1 in cancer tissue from 66 patients was measured by immunohis-tochemical staining. The patients received either oral sorafenib (n=40) or oral sunitinib (n=26) within 4 weeks after nephrectomy and were followed up long term to determine the tumor response and prognosis.

Results

Our current study revealed a high HO-1 expression level in 57.6% (38/66) of patients and a low HO-1 expression level in 42.4% (28/66) of patients with CC-RCC. The study also revealed that patients with high HO-1 expression did not have a higher objective response rate (2.6% versus 53.6%, P<0.01), clinical benefit rate (47.4% versus 92.9%, P<0.01), longer progression-free survival (4.4 versus 42 months, P=0.022), or overall survival (χ²=4.775, P=0.029) than patients with low HO-1 expression. In the low HO-1 level group, a higher tumor response rate and a longer survival time was achieved in patients who received sorafenib or sunitinib. Multivariate analysis showed that HO-1 expression was an independent prognostic factor for tumor response and overall survival.

Conclusion

High expression of HO-1 was associated with a lower tumor response rate and a shorter overall survival time when compared with low expression of HO-1. Overall, HO-1 expression might be a useful biomarker for predicting the response to sunitinib and sorafenib for patients with metastatic CC-RCC.