NO to breast: when, why and why not?

Nitric Oxide-Scavenging, Anti-Migration Effects, and Glycosylation Changes after Hemin Treatment of Human Triple-Negative Breast Cancer Cells: A Mechanistic Study

The enhanced expression of nitric oxide (•NO) synthase predicts triple-negative breast cancer outcome and its resistance to different therapeutics. Our earlier work demonstrated the efficiency of hemin to scavenge the intra- and extracellular •NO, proposing its potency as a therapeutic agent for inhibiting cancer cell migration. In continuation, the present work evaluates the effects of •NO on the migration of MDA-MB-231 cells and how hemin modulates the accompanied cellular behavior, focusing on the corresponding expression of cellular glycoproteins, migration-associated markers, and mitochondrial functions. We demonstrated for the first time that while •NO induced cell migration, hemin contradicted that by •NO-scavenging. This was in combination with modulation of the •NO-enhanced glycosylation patterns of cellular proteins with inhibition of the expression of specific proteins involved in the epithelial-mesenchymal transition. These effects were in conjunction with changes in the mitochondrial functions related to both •NO, hemin, and its nitrosylated product. Together, these results suggest that hemin can be employed as a potential anti-migrating agent targeting •NO-scavenging and regulating the expression of migration-associated proteins.

Regulation of pleiotropic physiological roles of nitric oxide signaling

Nitric Oxide (NO) is a highly diffusible, ubiquitous signaling molecule and a free radical that is naturally synthesized by our body. The pleiotropic effects of NO in biological systems are due to its reactivity with different molecules, such as molecular oxygen (O₂), superoxide anion, DNA, lipids, and proteins. There are several contradictory findings in the literature pertaining to its role in oncology. NO is a Janus-faced molecule shown to have both tumor promoting and tumoricidal effects, which depend on its concentration, duration of exposure, and location. A high concentration is shown to have cytotoxic effects by triggering apoptosis, and at a low concentration, NO promotes angiogenesis, metastasis, and tumor progression. Upregulated NO synthesis has been implicated as a causal factor in several pathophysiological conditions including cancer. This dichotomous effect makes it highly challenging to discover its true potential in cancer biology. Understanding the mechanisms by which NO acts in different cancers helps to develop NO based therapeutic strategies for cancer treatment. This review addresses the physiological role of this molecule, with a focus on its bimodal action in various types of cancers.

Myoglobin mutant with enhanced nitrite reductase activity regulates intracellular oxidative stress in human breast cancer cells

Heme proteins play vital roles in regulating the reactive oxygen/nitrogen species (ROS/RNS) levels in cells. In this study, we overexpressed human wild-type (WT) myoglobin (Mb) and its double mutant, F43H/H64A Mb with enhanced nitrite reductase (NIR) activity, in the typical representative triple-negative breast cancer cell, MDA-MB-231 cells. The results showed that the overexpression of F43H/H64A Mb increased the level of nitric oxide (NO) and the degree of oxidative stress, and then activated Akt/MAPK mediated apoptotic cascade, whereas WT Mb showed the opposite effect. This study indicates that Mb plays an important role in maintaining the balance of the cellular redox system and could thus be a valuable target for cancer therapy.

Enhancement of BCAT2-Mediated Valine Catabolism Stimulates β-Casein Synthesis via the AMPK-mTOR Signaling Axis in Bovine Mammary Epithelial Cells

Valine, a kind of branched-chain amino acid, plays a regulatory role beyond that of a building block in milk protein synthesis. However, the underlying molecular mechanism through which valine stimulates β-casein synthesis has not been clarified. Therefore, our study aimed to evaluate the effect of valine on β-casein synthesis and shed light into the molecular mechanism using an in vitro model. Results showed that valine supplementation significantly increased β-casein synthesis in bovine mammary epithelial cells (BMECs). Meanwhile, the supplementation of valine resulted in high levels of branched-chain aminotransferase transaminase 2 (BCAT2), TCA-cycle intermediate metabolites, and ATP, AMP-activated protein kinase (AMPK) inhibition, and mammalian target of rapamycin (mTOR) activation. Furthermore, the inhibition of BCAT2 decreased the β-casein synthesis and downregulated the AMPK-mTOR pathway, with similar results observed for AMPK activation. Together, the present data indicate that valine promotes the synthesis of β-casein by affecting the AMPK-mTOR signaling axis and that BCAT2-mediated valine catabolism is the key target.

Regulation of redox signaling in HIF-1-dependent tumor angiogenesis

Angiogenesis is the process of blood vessel growth. The angiogenic switch consists of new blood vessel formation that, in carcinogenesis, can lead to the transition from a harmless cluster of dormant cells to a large tumorigenic mass with metastatic potential. Hypoxia, that is, the scarcity of oxygen, is a hallmark of solid tumors to which they adapt by activating hypoxia-inducible factor-1 (HIF-1), a transcription factor triggering de novo angiogenesis. HIF-1 and the angiogenic molecules that are expressed upon its activation are modulated by redox status. Modulations of the redox environment can influence the angiogenesis signaling at different levels, thereby impinging on the angiogenic switch. This review provides a molecular overview of the redox-sensitive steps in angiogenic signaling, the main molecular players involved, and their crosstalk with the unfolded protein response. New classes of inhibitors of these modulators which might act as antiangiogenic drugs in cancer are also discussed.

Soluble guanylate cyclase isoenzymes: The expression of α1, α2, β1, and β2 subunits in the benign and malignant breast tumors

Soluble guanylate cyclase (sGC) encompasses α and β subunits. This study examined the expression of α1, α2, β1, and β2 subunits in the malignant and benign breast tumors using the Western blot  analysis. Both benign and malignant tumors showed a significantly higher expression of the α1 subunit in comparison with normal tissues (p < 0.0001). In contrast, the expression of α2 and β2 sGC were significantly lower in these tumors than normal tissues (p < .0015 and p < .001, p < .007 and p < .0001, respectively). The expression level of α1 sGC was significantly correlated with ER + PR+ (p < .0001). A significant correlation was also detected for sGC-α1 and -α2 expression with c-erbB2-negative status (p < .01). However, the expression level of sGC was not associated with tumor stage, tumor grade, or other clinicopathological features. In conclusion, as the expression of α1 sGC is upregulated and α2 and β2 sGC are downregulated in malignant breast tumors. Variations in the expression of sGC isoenzymes may be suggested as an indicator to confirm the enzyme antitumor activity.

Elevation of soluble guanylate cyclase suppresses proliferation and survival of human breast cancer cells

Nitric oxide (NO) is an essential signaling molecule in biological systems. Soluble guanylate cyclase (sGC), composing of α1 and β1 subunit, is the receptor for NO. Using radioimmunoassay, we discovered that activation of sGC by treatment with bradykinin or sodium nitroprusside (SNP) is impaired in MCF-7 and MDA-MB-231 breast cancer cells as compared to normal breast epithelial 184A1 cells. The 184A1 cells expressed both sGC α1 and sGCβ1 mRNAs. However, levels of sGCβ1 mRNAs were relatively lower in MCF-7 cells while both mRNA of sGC subunits were absent in MDA-MB-231 cells. Treatment with DNA methyltransferase inhibitor 5-aza-2’-deoxycytidine (5-aza-dC) increased mRNA levels of both sGCα1 and sGCβ1 in MDA-MB-231 cells but only sGCβ1 mRNAs in MCF-7 cells. The 5-aza-dC treatment increased the SNP-induced cGMP production in MCF-7 and MDA-MB-231, but not in 184A1 cells. Bisulfite sequencing revealed that the promoter of sGCα1 in MDA-MB-231 cells and promoter of sGCβ1 in MCF-7 cells were methylated. Promoter hypermethylation of sGCα1 and sGCβ1 was found in 1 out of 10 breast cancer patients. Over-expression of both sGC subunits in MDA-MB-231 cells induced apoptosis and growth inhibition in vitro as well as reduced tumor incidence and tumor growth rate of MDA-MB-231 xenografts in nude mice. Elevation of sGC reduced protein abundance of Bcl-2, Bcl-xL, Cdc2, Cdc25A, Cyclin B1, Cyclin D1, Cdk6, c-Myc, and Skp2 while increased protein expression of p53. Our study demonstrated that down-regulation of sGC, partially due to promoter methylation, provides growth and survival advantage in human breast cancer cells.

Oxidative stress specifically downregulates survivin to promote breast tumour formation

Background:

Breast cancer, a heterogeneous disease has been broadly classified into oestrogen receptor positive (ER+) or oestrogen receptor negative (ER−) tumour types. Each of these tumours is dependent on specific signalling pathways for their progression. While high levels of survivin, an anti-apoptotic protein, increases aggressive behaviour in ER− breast tumours, oxidative stress (OS) promotes the progression of ER+ breast tumours. Mechanisms and molecular targets by which OS promotes tumourigenesis remain poorly understood.

Results:

DETA-NONOate, a nitric oxide (NO)-donor induces OS in breast cancer cell lines by early re-localisation and downregulation of cellular survivin. Using in vivo models of HMLE^HRAS xenografts and E2-induced breast tumours in ACI rats, we demonstrate that high OS downregulates survivin during initiation of tumourigenesis. Overexpression of survivin in HMLE^HRAS cells led to a significant delay in tumour initiation and tumour volume in nude mice. This inverse relationship between survivin and OS was also observed in ER+ human breast tumours. We also demonstrate an upregulation of NADPH oxidase-1 (NOX1) and its activating protein p67, which are novel markers of OS in E2-induced tumours in ACI rats and as well as in ER+ human breast tumours.

Conclusion:

Our data, therefore, suggest that downregulation of survivin could be an important early event by which OS initiates breast tumour formation.

Ets-1 is a transcriptional mediator of oncogenic nitric oxide signaling in estrogen receptor-negative breast cancer

Introduction

The Ets-1 transcription factor is a candidate breast cancer oncogene that regulates the expression of genes involved in tumor progression and metastasis. Ets-1 signaling has also been linked to the development of a basal-like breast cancer phenotype. We recently described a nitric oxide (NO)-induced gene signature that is associated with poor disease outcome in estrogen receptor-negative (ER-) breast cancer and contains both stem cell-like and basal-like components. Thus, we examined the role of Ets-1 in NO signaling and NO-induced phenotypes in ER- human breast cancer cells.

Methods

Promoter region analyses were performed on genes upregulated in inducible nitric oxide synthase (NOS2) high expressing tumors for Ets-binding sites. In vitro mechanisms were examined in human basal-like breast cancer cells lines. NO signaling effects were studied using either forced NOS2 expression or the use of a chemical NO-donor, diethlylenetriamine NONOate (DETANO).

Results

Promoter region analysis of genes that are up-regulated in human ER-negative breast tumors with high NOS2 expression revealed that the Ets-binding sequence is the only common promoter element present in all of these genes, indicating that Ets-1 is the key transcriptional factor down-stream of oncogenic NOS2-signaling. Accordingly, both forced NOS2 over-expression and exposure to NO-donors resulted in significant Ets-1 transcriptional activation in ER- breast cancer cells. Functional studies showed that NO activated Ets-1 transcriptional activity via a Ras/MEK/ERK signaling pathway by a mechanism that involved Ras S-nitrosylation. RNA knock-down of Ets-1 suppressed NO-induced expression of selected basal-like breast cancer markers such as P-cadherin, S100A8, IL-8 and αβ-crystallin. Additionally, Ets-1 knock-down reduced NO-mediated cellular proliferation, matrix metalloproteinase and cathepsin B activities, as well as matrigel invasion.

Conclusions

These data show that Ets-1 is a key transcriptional mediator of oncogenic NO signaling that promotes the development of an aggressive disease phenotype in ER- breast cancer in an Ets-1 and Ras-dependent manner, providing novel clues of how NOS2 expression in human breast tumors is functionally linked to poor patient survival.

Heterogeneous kinetics of the carbon monoxide association and dissociation reaction to nitrophorin 4 and 7 coincide with structural heterogeneity of the gate-loop

NO is an important signaling molecule in human tissue. However, the mechanisms by which this molecule is controlled and directed are currently little understood. Nitrophorins (NPs) comprise a group of ferriheme proteins originating from blood-sucking insects that are tailored to protect and deliver NO via coordination to and release from the heme iron. Therefore, the kinetics of the association and dissociation reactions were studied in this work using the ferroheme-CO complexes of NP4, NP4(D30N), and NP7 as isoelectronic models for the ferriheme-NO complexes. The kinetic measurements performed by nanosecond laser-flash-photolysis and stopped-flow are accompanied by resonance Raman and FT-IR spectroscopy to characterize the carbonyl species. Careful analysis of the CO rebinding kinetics reveals that in NP4 and, to a larger extent, NP7 internal gas binding cavities are located, which temporarily trap photodissociated ligands. Moreover, changes in the free energy barriers throughout the rebinding and release pathway upon increase of the pH are surprisingly small in case of NP4. Also in case of NP4, a heterogeneous kinetic trace is obtained at pH 7.5, which corresponds to the presence of two carbonyl species in the heme cavity that are seen in vibrational spectroscopy and that are due to the change of the distal heme pocket polarity. Quantification of the two species from FT-IR spectra allowed the fitting of the kinetic traces as two processes, corresponding to the previously reported open and closed conformation of the A-B and G-H loops. With the use of the A-B loop mutant NP4(D30N), it was confirmed that the kinetic heterogeneity is controlled by pH through the disruption of the H-bond between the Asp30 side chain and the Leu130 backbone carbonyl. Overall, this first study on the slow phase of the dynamics of diatomic gas molecule interaction with NPs comprises an important experimental contribution for the understanding of the dynamics involved in the binding/release processes of NO/CO in NPs.

Interplay between membrane lipid peroxidation, transglutaminase activity, and cyclooxygenase 2 expression in the tissue adjoining to breast cancer

Breast cancer, a leading cause of cancer related deaths worldwide, is one of the most common neoplasms in women. The increased generation of reactive oxygen species (ROS) in breast lesion is critically involved in the mutagenic processes that drive to breast carcinoma initiation and progression. To date, the molecular events occurring in the tissue adjoin the cancer lesion have not been elucidated. Here, we investigated the role of excess ROS generation during human breast carcinogenesis by evaluating oxidative stress biomarkers, tissue transglutaminase (t-TGase) activity, and expression levels of ubiquitin and cyclooxygenase-2 (COX-2) in the normal tissue adjoin to fibroadenoma (nFA), atypical ductal hyperplasia (nADH), and invasive ductal carcinoma (nIDC) from 45 breast cancer patients. We found that lipid peroxidation and nitric oxide production significantly increased in nIDC respect to nFA and nADH (P < 0.005) whereas the 4-hydroxy-2-nonenal (HNE) protein-adducts increased only in nADH (P < 0.005). The increased lipid damage observed in nIDC correlates with estrogen receptor exposure in IDC (R(2) = 0.89). Moreover, nIDC and invasive ductal carcinoma (IDC) showed a 10-fold higher t-TGase activity compared to nFA and nADH. Contrary, COX-2 expression levels significantly decreased nIDC and IDC respect to the nFA and nADH (P < 0.001). The analysis of the free ubiquitin expression revealed equal levels in nADH and nIDC samples whereas high molecular weight-ubiquitin conjugate increased about fivefold only in nIDC (P < 0.01 vs. nADH). These novel findings reveal an interplay between membrane lipid peroxidation, t-TGase activity, and COX-2 expression levels in the tissue adjoining to neoplastic lesion during breast cancer progression.

Soy foods and urinary isoprostanes: results from a randomized study in premenopausal women

In addition to their antiestrogenic effects, soy isoflavones may protect against cancer through alternate biological actions, for example, antioxidant properties. This randomized crossover study explored the relationship between dietary isoflavone intake through common soy foods and oxidative stress quantified by urinary isoprostane levels. Eighty-two women aged 39.2 ± 6.1 years were randomly selected to receive a high soy diet of 2 soy food servings per day and a low soy diet of <3 servings per week for 6 months each, separated by a 1-month washout period. Urine samples were collected at baseline and at the end of each dietary period. Urinary isoprostane levels were measured using enzyme-linked immunosorbent assays (ELISA) and adjusted for creatinine levels. Mixed models using log-transformed values were applied to evaluate the effect of the high soy diet. Unadjusted isoprostane excretion levels were lower during the high rather than the low soy diet, but this effect was not statistically significant (p = 0.81). After adjustment for urinary creatinine, isoprostane excretion was slightly higher during the high soy diet (p = 0.02), an observation that was confirmed in a regression analysis between urinary isoflavones and isoprostanes during the high soy diet. The original association remained significant when restricted to adherent participants, however this effect disappeared after exclusion of three extreme values. In agreement with several previous reports, these findings do not support the hypothesis that soy exerts antioxidant effects, as measured by urinary isoprostane excretions, but additional markers of oxidative stress need to be investigated in future studies.

S-nitrosylation-regulated GPCR signaling

G protein-coupled receptors (GPCRs) are the most numerous and diverse type of cell surface receptors, accounting for about 1% of the entire human genome and relaying signals from a variety of extracellular stimuli that range from lipid and peptide growth factors to ions and sensory inputs. Activated GPCRs regulate a multitude of target cell functions, including intermediary metabolism, growth and differentiation, and migration and invasion. The GPCRs contain a characteristic 7-transmembrane domain topology and their activation promotes complex formation with a variety of intracellular partner proteins, which form basis for initiation of distinct signaling networks as well as dictate fate of the receptor itself. Both termination of active GPCR signaling and removal from the plasma membrane are controlled by protein post-translational modifications of the receptor itself and its interacting partners. Phosphorylation, acylation and ubiquitination are the most studied post-translational modifications involved in GPCR signal transduction, subcellular trafficking and overall expression. Emerging evidence demonstrates that protein S-nitrosylation, the covalent attachment of a nitric oxide moiety to specified cysteine thiol groups, of GPCRs and/or their associated effectors also participates in the fine-tuning of receptor signaling and expression. This newly appreciated mode of GPCR system modification adds another set of controls to more precisely regulate the many cellular functions elicited by this large group of receptors. This article is part of a Special Issue entitled: Regulation of cellular processes by S-nitrosylation.

Estrogen-induced apoptosis of breast epithelial cells is blocked by NO/cGMP and mediated by extranuclear estrogen receptors

Estrogen action, via both nuclear and extranuclear estrogen receptors (ERs), induces a variety of cellular signals that are prosurvival or proliferative, whereas nitric oxide (NO) can inhibit apoptosis via caspase S-nitrosylation and via activation of soluble guanylyl cyclase to produce cGMP. The action of 17β-estradiol (E(2)) at ER is known to elicit NO signaling via activation of NO synthase (NOS) in many tissues. The MCF-10A nontumorigenic, mammary epithelial cell line is genetically stable and insensitive to estrogenic proliferation. In this cell line, estrogens or NOS inhibitors alone had no significant effect, whereas in combination, apoptosis was induced rapidly in the absence of serum; the presence of inducible NOS was confirmed by proteomic analysis. The application of pharmacological agents determined that apoptosis was dependent upon NO/cGMP signaling via cyclic GMP (cGMP)-dependent protein kinase and could be replicated by inhibition of the phosphatidylinositol 3 kinase/serine-threonine kinase pathway prior to addition of E(2). Apoptosis was confirmed by nuclear staining and increased caspase-3 activity in E(2) + NOS inhibitor-treated cells. Apoptosis was partially inhibited by a pure ER antagonist and replicated by agonists selective for extranuclear ER. Cells were rescued from E(2)-induced apoptosis after NOS blockade, by NO-donors and cGMP pathway agonists; preincubation with NO donors was required. The NOS and ER status of breast cancer tissues is significant in etiology, prognosis, and therapy. In this study, apoptosis of preneoplastic mammary epithelial cells was triggered by estrogens via a rapid, extranuclear ER-mediated response, after removal of an antiapoptotic NO/cGMP/cGMP-dependent protein kinase signal.