Nitric oxide promotes p53 nuclear retention and sensitizes neuroblastoma cells to apoptosis by ionizing radiation

Targeting focal adhesion kinase (FAK) in cancer therapy: A recent update on inhibitors and PROTAC degraders

Focal adhesion kinase (FAK) is considered as a pivotal intracellular non-receptor tyrosine kinase, and has garnered significant attention as a promising target for anticancer drug development. As of early 2024, a total of 12 drugs targeting FAK have been approved for clinical or preclinical studies worldwide, including three PROTAC degraders. In recent three years (2021-2023), significant progress has been made in designing targeted FAK anticancer agents, including the development of a novel benzenesulfofurazan type NO-releasing FAK inhibitor and the first-in-class dual-target inhibitors simultaneously targeting FAK and HDACs. Given the pivotal role of FAK in the discovery of anticancer drugs, as well as the notable advancements achieved in FAK inhibitors and PROTAC degraders in recent years, this review is underbaked to present a comprehensive overview of the function and structure of FAK. Additionally, the latest findings on the inhibitors and PROTAC degraders of FAK from the past three years, along with their optimization strategies and anticancer activities, were summarized, which might help to provide novel insights for the development of novel targeted FAK agents with promising anticancer potential and favorable pharmacological profiles.

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Design, synthesis and evaluation of nitric oxide releasing derivatives of 2,4-diaminopyrimidine as novel FAK inhibitors for intervention of metastatic triple-negative breast cancer

To search for novel medicines for intervention of triple-negative breast cancer (TNBC), a series of phenylsulfonyl furoxan-based 2,4-diaminopyrimidine derivatives (8a-t) were designed and synthesized based on blocking FAK-mediated signaling pathways through both kinase-dependent and -independent manners. The most active compound 8f not only significantly inhibited FAK kinase activity (IC₅₀ = 27.44 nM), displayed potent inhibitory effects on the proliferation (IC₅₀ = 0.126 μM), invasion and migration of MDA-MB-231 cells, superior to the most widely studied FAK inhibitor, TAE226, bearing 2,4-diaminopyrimidine, but also released high levels of NO, contributing to blockage of FAK mediated-signaling pathways by upregulating of p53 as well as suppressing the Y397 phosphorylation and its downstream effectors, including p-Akt, MMP-2, and MMP-9 via kinase-independent manner, leading to apoptosis induction and decrease of FAs and SFs in TNBC cells. Importantly, 8f inhibited the lung metastasis of TNBC in vivo. Together, 8f may serve as a promising candidate for the treatment of metastatic TNBC.

Supramolecular Nitric Oxide Depot for Hypoxic Tumor Vessel Normalization and Radiosensitization

In cancer radiotherapy, the lack of fixed DNA damage by oxygen in hypoxic microenvironment of solid tumors often leads to severe radioresistance. Nitric oxide (NO) is a potent radiosensitizer that acts in two ways. It can directly react with the radical DNA thus fixing the damage. It also normalizes the abnormal tumor vessels, thereby increasing blood perfusion and oxygen supply. To achieve these functions, the dosage and duration of NO treatment need to be carefully controlled, otherwise it will lead to the exact opposite outcomes. However, a delivery method that fulfills both requirements is still lacking. A NO depot is designed for the control of NO releasing both over quantity and duration for hypoxic tumor vessel normalization and radiosensitization. In B16-tumor-bearing mice, the depot can provide low dosage NO continuously and release large amount of NO immediately before irradiation for a short period of time. These two modes of treatment work in synergy to reverse the radioresistance of B16 tumors more efficiently than releasing at single dosage.

NO-Dependent Mechanisms of p53 Expression and Cell Death in Rat’s Dorsal Root Ganglia after Sciatic-Nerve Transection

Peripheral-nerve injury is a frequent cause of disability. Presently, no clinically effective neuroprotectors have been found. We have studied the NO-dependent expression of p53 in the neurons and glial cells of the dorsal root ganglia (DRG) of a rat’s spinal cord, as well as the role of NO in the death of these cells under the conditions of axonal stress, using sciatic-nerve axotomy as a model. It was found out that axotomy led to the nuclear–cytoplasmic redistribution of p53 in neurons, 24 h after trauma. The NO donor led to a considerable increase in the level of p53 in nuclei and, to a smaller degree, in the cytoplasm of neurons and karyoplasm of glial cells 4 and 24 h after axotomy. Application of a selective inhibitor of inducible NO-synthase (iNOS) provided the opposite effect. Introduction of the NO donor resulted in a significant increase in cell death in the injured ipsilateral DRG, 24 h and 7 days after trauma. The selective inhibitor of iNOS demonstrated a neuroprotective effect. Axotomy was shown to upregulate the iNOS in nuclei and cytoplasm of DRG cells. The NO-dependent expression of p53, which is particularly achieved through iNOS activation, is believed to be a putative signaling mechanism of neural and glial-cell death after axotomy.

Impact of intravesical instillation of a novel biological response modifier (P-MAPA) on progress of non-muscle invasive bladder cancer treatment in a rat model

This work describes the effects of immunotherapy with Protein Aggregate Magnesium-Ammonium Phospholinoleate-Palmitoleate Anhydride in the treatment of non-muscle invasive bladder cancer in an animal model. NMIBC was induced by treating female Fischer 344 rats with N-methyl-N-nitrosourea. After treatment with MNU, the rats were distributed into four experimental groups: Control (without MNU) group, MNU (cancer) group, MNU-BCG (Bacillus Calmette-Guerin) group, and MNU-P-MAPA group. P-MAPA intravesical treatment was more effective in histopathological recovery from cancer state in relation to BCG treatment. Western blot assays showed an increase in the protein levels of c-Myc, COUP-TFII, and wild-type p53 in P-MAPA-treated rats in relation to BCG-treated rats. In addition, rats treated with P-MAPA intravesical immunotherapy showed the highest BAX protein levels and the lowest proliferation/apoptotic ratio in relation to BCG-treated rats, pointing out a preponderance of apoptosis. P-MAPA intravesical treatment increased the wild-type p53 levels and enhanced c-Myc/COUP-TFII-induced apoptosis mediated by p53. These alterations were fundamental for histopathological recovery from cancer and for suppress abnormal cell proliferation. This action of P-MAPA on apoptotic pathways may represent a new strategy for treating NMIBC.

The emerging roles of nitric oxide in ferroptosis and pyroptosis of tumor cells

Tumor cells can develop resistance to cell death which is divided into necrosis and programmed cell death (PCD). PCD, including apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis. Ferroptosis and pyroptosis, two new forms of cell death, have gradually been of interest to researchers. Boosting ferroptosis and pyroptosis of tumor cells could be a potential cancer therapy. Nitric oxide (NO) is a ubiquitous, lipophilic, highly diffusible, free-radical signaling molecule that plays various roles in tumorigenesis. In addition, NO also has regulatory mechanisms through S-nitrosylation that do not depend on the classic NO/sGC/cGMP signaling. The current tumor treatment strategy for NO is to promote cell death through promoting S-nitrosylation-induced apoptosis while multiple drawbacks dampen this tumor therapy. However, numerous studies have suggested that suppression of NO is perceived to active ferroptosis and pyroptosis, which could be a better anti-tumor treatment. In this review, ferroptosis and pyroptosis are described in detail. We summarize that NO influences ferroptosis and pyroptosis and infer that S-nitrosylation mediates ferroptosis- and pyroptosis-related signaling pathways. It could be a potential cancer therapy different from NO-induced apoptosis of tumor cells. Finally, the information shows the drugs that manipulate endogenous production and exogenous delivery of NO to modulate the levels of S-nitrosylation.

Coacervate microdroplet protocell-mediated gene transfection for nitric oxide production and induction of cell apoptosis

Liquid coacervate microdroplets have been widely explored as membrane-free compartment protocells for cargo delivery in therapeutic applications. In this study, coacervate protocells were developed as gene carriers for transfection of nitric oxide synthase (NOS) and overproduction of nitric oxide (NO) for killing of cancer cells. The coacervate microdroplet protocells were formed via the liquid-liquid phase separation of oppositely charged diethylaminoethyl-dextran/polyacrylic acids. The coacervate microdroplet protocells were found to facilitate gene transfection, which was demonstrated by cell imaging of the internalized coacervate microdroplets containing plasmids of enhanced green fluorescent protein. Due to their high transfection capability, the coacervate protocells were subsequently utilized for the delivery of NOS plasmids (pNOS). The cellular internalization of pNOS-containing coacervate carriers was found to result in high NOS expression coupled with NO overproduction, which then induced cell apoptosis and decreased cell viability. The cell apoptosis is associated with NO-mediated mitochondrial damage. The enhanced gene transfection was attributed to coacervate microdroplets' unique high sequestration capability and liquid-like fluidity. Overall, the incorporation of genes in coacervate microdroplets was demonstrated as a viable and novel strategy for the development of cargo biocarriers for biomedical applications.

The Relationship of Glutathione-S-Transferase and Multi-Drug Resistance-Related Protein 1 in Nitric Oxide (NO) Transport and Storage

Nitric oxide is a diatomic gas that has traditionally been viewed, particularly in the context of chemical fields, as a toxic, pungent gas that is the product of ammonia oxidation. However, nitric oxide has been associated with many biological roles including cell signaling, macrophage cytotoxicity, and vasodilation. More recently, a model for nitric oxide trafficking has been proposed where nitric oxide is regulated in the form of dinitrosyl-dithiol-iron-complexes, which are much less toxic and have a significantly greater half-life than free nitric oxide. Our laboratory has previously examined this hypothesis in tumor cells and has demonstrated that dinitrosyl-dithiol-iron-complexes are transported and stored by multi-drug resistance-related protein 1 and glutathione-S-transferase P1. A crystal structure of a dinitrosyl-dithiol-iron complex with glutathione-S-transferase P1 has been solved that demonstrates that a tyrosine residue in glutathione-S-transferase P1 is responsible for binding dinitrosyl-dithiol-iron-complexes. Considering the roles of nitric oxide in vasodilation and many other processes, a physiological model of nitric oxide transport and storage would be valuable in understanding nitric oxide physiology and pathophysiology.

The Atr-Chek1 pathway inhibits axon regeneration in response to Piezo-dependent mechanosensation

Atr is a serine/threonine kinase, known to sense single-stranded DNA breaks and activate the DNA damage checkpoint by phosphorylating Chek1, which inhibits Cdc25, causing cell cycle arrest. This pathway has not been implicated in neuroregeneration. We show that in Drosophila sensory neurons removing Atr or Chek1, or overexpressing Cdc25 promotes regeneration, whereas Atr or Chek1 overexpression, or Cdc25 knockdown impedes regeneration. Inhibiting the Atr-associated checkpoint complex in neurons promotes regeneration and improves synapse/behavioral recovery after CNS injury. Independent of DNA damage, Atr responds to the mechanical stimulus elicited during regeneration, via the mechanosensitive ion channel Piezo and its downstream NO signaling. Sensory neuron-specific knockout of Atr in adult mice, or pharmacological inhibition of Atr-Chek1 in mammalian neurons in vitro and in flies in vivo enhances regeneration. Our findings reveal the Piezo-Atr-Chek1-Cdc25 axis as an evolutionarily conserved inhibitory mechanism for regeneration, and identify potential therapeutic targets for treating nervous system trauma.

Microarray-based Analysis of Genes, Transcription Factors, and Epigenetic Modifications in Lung Cancer Exposed to Nitric Oxide

BACKGROUND/AIM

Nitric oxide (NO) is recognized as an important biological mediator that exerts several human physiological functions. As its nature is an aqueous soluble gas that can diffuse through cells and tissues, NO can affect cell signaling, the phenotype of cancer and modify surrounding cells. The variety of effects of NO on cancer cell biology has convinced researchers to determine the defined mechanisms of these effects and how to control this mediator for a better understanding as well as for therapeutic gain.

MATERIALS AND METHODS

We used bioinformatics and pharmacological experiments to elucidate the potential regulation and underlying mechanisms of NO in non-small a lung cancer cell model.

RESULTS

Using microarrays, we identified a total of 151 NO-regulated genes (80 up-regulated genes, 71 down-regulated genes) with a strong statistically significant difference compared to untreated controls. Among these, the genes activated by a factor of more than five times were: DCBLD2, MGC24975, RAB40AL, PER3, RCN1, MRPL51, PTTG1, KLF5, NFIX. On the other hand, the expression of RBMS2, PDP2, RBAK, ORMDL2, GRPEL2, ZNF514, MTHFD2, POLR2D, RCBTB1, JOSD1, RPS27, GPR4 genes were significantly decreased by a factor of more than five times. Bioinformatics further revealed that NO exposure of lung cancer cells resulted in a change in transcription factors (TFs) and epigenetic modifications (histone modification and miRNA). Interestingly, NO treatment was shown to potentiate cancer stem cell-related genes and transcription factors Oct4, Klf4, and Myc.

CONCLUSION

Through this comprehensive approach, the present study illustrated the scheme of how NO affects molecular events in lung cancer cells.

The Role of Nitric Oxide in Cancer: Master Regulator or NOt?

Nitric oxide (NO) is a key player in both the development and suppression of tumourigenesis depending on the source and concentration of NO. In this review, we discuss the mechanisms by which NO induces DNA damage, influences the DNA damage repair response, and subsequently modulates cell cycle arrest. In some circumstances, NO induces cell cycle arrest and apoptosis protecting against tumourigenesis. NO in other scenarios can cause a delay in cell cycle progression, allowing for aberrant DNA repair that promotes the accumulation of mutations and tumour heterogeneity. Within the tumour microenvironment, low to moderate levels of NO derived from tumour and endothelial cells can activate angiogenesis and epithelial-to-mesenchymal transition, promoting an aggressive phenotype. In contrast, high levels of NO derived from inducible nitric oxide synthase (iNOS) expressing M1 and Th1 polarised macrophages and lymphocytes may exert an anti-tumour effect protecting against cancer. It is important to note that the existing evidence on immunomodulation is mainly based on murine iNOS studies which produce higher fluxes of NO than human iNOS. Finally, we discuss different strategies to target NO related pathways therapeutically. Collectively, we present a picture of NO as a master regulator of cancer development and progression.

Role of NO and S-nitrosylation in the Expression of Endothelial Adhesion Proteins That Regulate Leukocyte and Tumor Cell Adhesion

Leukocyte recruitment is one of the most important cellular responses to tissue damage. Leukocyte extravasation is exquisitely regulated by mechanisms of selective leukocyte-endothelium recognition through adhesion proteins in the endothelial cell surface that recognize specific integrins in the activated leukocytes. A similar mechanism is used by tumor cells during metastasis to extravasate and form a secondary tumor. Nitric oxide (NO) has been classically described as an anti-inflammatory molecule that inhibits leukocyte adhesion. However, the evidence available shows also a positive role of NO in leukocyte adhesion. These apparent discrepancies might be explained by the different NO concentrations reached during the inflammatory response, which are highly modulated by the expression of different nitric oxide synthases, along the inflammatory response and by changes in their subcellular locations.

TRIM72 promotes alveolar epithelial cell membrane repair and ameliorates lung fibrosis

Background

Chronic tissue injury was shown to induce progressive scarring in fibrotic diseases such as idiopathic pulmonary fibrosis (IPF), while an array of repair/regeneration and stress responses come to equilibrium to determine the outcome of injury at the organ level. In the lung, type I alveolar epithelial (ATI) cells constitute the epithelial barrier, while type II alveolar epithelial (ATII) cells play a pivotal role in regenerating the injured distal lungs. It had been demonstrated that eukaryotic cells possess repair machinery that can quickly patch the damaged plasma membrane after injury, and our previous studies discovered the membrane-mending role of Tripartite motif containing 72 (TRIM72) that expresses in a limited number of tissues including the lung. Nevertheless, the role of alveolar epithelial cell (AEC) repair in the pathogenesis of IPF has not been examined yet.

Method

In this study, we tested the specific roles of TRIM72 in the repair of ATII cells and the development of lung fibrosis. The role of membrane repair was accessed by saponin assay on isolated primary ATII cells and rat ATII cell line. The anti-fibrotic potential of TRIM72 was tested with bleomycin-treated transgenic mice.

Results

We showed that TRIM72 was upregulated following various injuries and in human IPF lungs. However, TRIM72 expression in ATII cells of the IPF lungs had aberrant subcellular localization. In vitro studies showed that TRIM72 repairs membrane injury of immortalized and primary ATIIs, leading to inhibition of stress-induced p53 activation and reduction in cell apoptosis. In vivo studies demonstrated that TRIM72 protects the integrity of the alveolar epithelial layer and reduces lung fibrosis.

Conclusion

Our results suggest that TRIM72 protects injured lungs and ameliorates fibrosis through promoting post-injury repair of AECs.

Improving tumor hypoxia and radiotherapy resistance via in situ nitric oxide release strategy

Radiation therapy remains one of the main treatments for cancer. However, conventional radiotherapy not only manifests a low radiation accumulation in the tumor site, but also displays numerous negative effects. The most serious clinical problem is the radiotherapy resistance leading to cancer deterioration. As an important gaseous signal molecule, nitric oxide (NO) has been widely studied for its role in regulating angiogenesis, improving hypoxia, and inhibiting tumor growth. However, due to the unstable characteristic, the application of NO in cancer therapy is still limited. Here, we designed a micellar system formed by a NO donor, D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS)-NO, for enabling sustained NO release to efficiently deliver NO into the tumor area. TPGS-NO could accumulate in the tumor site for extended circulation, thereby releasing NO to exert antitumor effects and enhance radiotherapy effects under low-oxygen conditions. It demonstrated the increased sensitivity of radiotherapy through enhancing tumor angiogenesis appropriately reducing tumor area hypoxia, which significantly induced tumor cell apoptosis and inhibited its repair during radiation. This work may show great potential in synergistic radiotherapy against cancer by facile NO donor administration.

Clinico-Histopathological and Immunohistochemical Study of Ruminant's Cutaneous Papillomavirus in Iraq

The papilloma viruses are constituted of double-stranded DNA and are a more common lesion in ruminant's skin in Iraq. The p53 tumor suppressor protein reveals an essential role in cell cycle control. This study intends to investigate the clinical, histopathological, and immunohistochemical features of cutaneous papilloma in ruminants in Iraq. Samples had been collected from a total of 10 animals (three cattle, three goats, and four sheep) with multiple papillomatosis lesions. The samples were processed for histopathological and immunohistochemical techniques. Clinically, the lesions appeared as multiple various sizes (0.5–11 cm), cauliflower exophytic masses on different parts of the animal's body. The histopathological features of the epidermis granular layer revealed perinuclear vacuolation (koilocytosis) accompanied by various degrees of hypergranulosis, hyperkeratosis, acanthosis, orthokeratosis, and parakeratosis. Strong positive reaction for papillomavirus antigen was seen in both epidermal basal and granular layers in the immunohistochemical investigation (IHC). Moreover, all papilloma lesions revealed an intense positive p53 reaction in cytoplasmic and perinuclear of the basal and parabasal layers. In conclusion, this study described the papillomavirus lesions in bovine, ovine, and caprine animals, which were found in different parts areas of the affected animals. All lesions show similar histopathological features with minor variations. PV antigen and p53 protein expression showed positive results in immunohistochemistry that can be used as diagnostic markers for ruminant's papilloma.

The role of myoglobin in epithelial cancers: Insights from transcriptomics

The muscle-associated respiratory protein myoglobin (MB) is expressed in multiple types of cancer, including breast and prostate tumors. In Kaplan-Meier analyses of the two tumor types, MB positivity is associated with favorable prognoses. Despite its well-characterized function in myocytes, the role of MB in cancer remains unclear. To study the impact of endogenous MB expression, small interfering RNA MB-knockdown cells were engineered using breast, prostate and colon cancer cell lines (MDA-MB468, LNCaP, DLD-1), and their transcriptomes were investigated using RNA-Seq at different oxygen levels. In MB-positive cells, increased expression of glycolytic genes was observed, which was possibly mediated by a higher activity of hypoxia-inducible factor 1α. In addition, the results of the gene set enrichment analysis suggested that MB contributed to fatty acid transport and turnover. MB-positive, wild-type-p53 LNCaP cells also exhibited increased expression of p53 target genes involved in cell cycle checkpoint control and prevention of cell migration. MB-positive cells expressing mutant p53 exhibited upregulation of genes associated with prolonged cancer cell viability and motility. Therefore, it was hypothesized that these transcriptomic differences may result from MB-mediated generation of nitric oxide or reactive oxygen species, thus employing established enzymatic activities of the globin. In summary, the transcriptome comparisons identified potential molecular functions of MB in carcinogenesis by highlighting the interaction of MB with key metabolic and regulatory processes.

Acetylation of cedrelone increases its cytotoxic activity and reverts the malignant phenotype of breast cancer cells in 3D culture

Cedrelone is a limonoid isolated from the plant Trichilia catigua (Meliaceae). Previous studies have demonstrated that cedrelone (1) has several damaging effects on triple negative breast tumor (TNBC) cell line MDA-MB-231. In this work we investigated two new derivatives of cedrelone, the acetate (1a) and the mesylate (1b), to examine whether their effects are improved in comparison to the lead molecule. Cedrelone acetate (1a) was the most cytotoxic compound on TNBC cells and was chosen for additional analyses in traditional two-dimensional (2D) monolayer cultures and three-dimensional (3D) assays. In 2D, 1a induced cell cycle arrest, apoptosis and inhibited essential steps of the metastasis process of the MDA-MB-231 cells, in vitro. Moreover, 1a was able to revert the malignant phenotype of the T4-2 cells in 3D. These effects were concomitant with the downregulation of EGFR, β1-integrin and phospho-Akt, which could have resulted in a decrease of NFκB levels and MMP9 activity. These results suggest that 1a could be used as an important model for the design of a new drug to be applied in cancer treatment and be further studied in vivo for its antitumor and antimetastatic effects.

Nitric Oxide-Mediated Enhancement and Reversal of Resistance of Anticancer Therapies

In the last decade, immune therapies against human cancers have emerged as a very effective therapeutic strategy in the treatment of various cancers, some of which are resistant to current therapies. Although the clinical responses achieved with many therapeutic strategies were significant in a subset of patients, another subset remained unresponsive initially, or became resistant to further therapies. Hence, there is a need to develop novel approaches to treat those unresponsive patients. Several investigations have been reported to explain the underlying mechanisms of immune resistance, including the anti-proliferative and anti-apoptotic pathways and, in addition, the increased expression of the transcription factor Yin-Yang 1 (YY1) and the programmed death ligand 1 (PD-L1). We have reported that YY1 leads to immune resistance through increasing HIF-1α accumulation and PD-L1 expression. These mechanisms inhibit the ability of the cytotoxic T-lymphocytes to mediate their cytotoxic functions via the inhibitory signal delivered by the PD-L1 on tumor cells to the PD-1 receptor on cytotoxic T-cells. Thus, means to override these resistance mechanisms are needed to sensitize the tumor cells to both cell killing and inhibition of tumor progression. Treatment with nitric oxide (NO) donors has been shown to sensitize many types of tumors to chemotherapy, immunotherapy, and radiotherapy. Treatment of cancer cell lines with NO donors has resulted in the inhibition of cancer cell activities via, in part, the inhibition of YY1 and PD-L1. The NO-mediated inhibition of YY1 was the result of both the inhibition of the upstream NF-κB pathway as well as the S-nitrosylation of YY1, leading to both the downregulation of YY1 expression as well as the inhibition of YY1-DNA binding activity, respectively. Also, treatment with NO donors induced the inhibition of YY1 and resulted in the inhibition of PD-L1 expression. Based on the above findings, we propose that treatment of tumor cells with the combination of NO donors, at optimal noncytotoxic doses, and anti-tumor cytotoxic effector cells or other conventional therapies will result in a synergistic anticancer activity and tumor regression.

Peptidylarginine deiminase 4 overexpression resensitizes MCF-7/ADR breast cancer cells to adriamycin via GSK3β/p53 activation

Background

Adriamycin (ADR) is widely used in the clinical chemotherapy against breast cancer. But its efficacy is strongly limited due to the acquisition of multidrug resistance (MDR). Therefore, acquisition of the resistance to ADR is still a major cause of chemotherapy failure in breast cancer patients. Peptidylarginine deiminase IV (PAD4) is reported to target non-histone proteins for citrullination, regulate their substrate activities, and thereby play critical roles in maintaining cell phenotype in breast cancer cells. However, whether PAD4 is involved in the development of MDR in breast cancer is poorly understood.

Materials and methods

We examined the expression of PAD family members, including PAD4 in ADR-resistant MCF-7 cells compared with the parental control cells by real-time PCR and Western blotting analyses. Rescue of PAD4 expression in MCF-7/ADR cells was performed to assess whether PAD4 could restore the sensitivity of MCF-7/ADR cells to ADR treatment with cell counting kit-8, flow cytometry, TUNEL, nuclear and cytoplasmic extract preparations, and immunofluorescence staining analyses.

Results

Both PAD2 and PAD4 were significantly decreased in ADR-resistant cells. However, only PAD4 overexpression can increase the sensitivity of MCF-7/ADR cells to ADR treatment and decrease MDR1 gene expression. Overexpression of PAD4 in MCF-7/ADR cells inhibited cell proliferation by inducing cell apoptosis. Under ADR treatment, overexpression of PAD4 promoted nuclear accumulation of glycogen synthase kinase-3β and p53, which further activated proapoptotic gene expression and downregulated MDR1 expression. Moreover, PAD4 activity was required for activating proapoptotic gene transcripts.

Conclusion

We demonstrate the previously unappreciated role of PAD4 in reversing ADR resistance in MCF-7/ADR cells and help establish PAD4 as a candidate biomarker of prognosis and chemotherapy target for MDR in breast cancers.

Molecular mechanism of bystander effects and related abscopal/cohort effects in cancer therapy

Cancer cells subjected to ionizing radiation may release signals which can influence nearby non-irradiated cells, termed bystander effects. The transmission of bystander effects among cancer cells involves the activation of inflammatory cytokines, death ligands, and reactive oxygen/nitrogen species. In addition to bystander effects, two other forms of non-target effects (NTEs) have been identified in radiotherapy, as one is called cohort effects and the other is called abscopal effects. Cohort effects represent the phenomenon where irradiated cells can produce signals that reduce the survival of neighboring cells within an irradiated volume. The effects suggest the importance of cellular communication under irradiation with non-uniform dose distribution. In contrast, abscopal effects describe the NTEs that typically occur in non-irradiated cells distant from an irradiated target. These effects can be mediated primarily by immune cells such as T cells. Clinical trials have shown that application of radiation along with immunotherapy may enhance abscopal effects and improve therapeutic efficacy on non-target lesions outside an irradiated field. According to NTEs, cell viability is reduced not only by direct irradiation effects, but also due to signals emitted from nearby irradiated cells. A clinical consideration of NTEs could have a revolutionary impact on current radiotherapy via the establishment of more efficient and less toxic radiobiological models for treatment planning compared to conventional models. Thus, we will review the most updated findings about these effects and outline their mechanisms and potential applications in cancer treatment with a special focus on the brain, lung, and breast cancers.

Laminin signals initiate the reciprocal loop that informs breast-specific gene expression and homeostasis by activating NO, p53 and microRNAs

How mammalian tissues maintain their architecture and tissue-specificity is poorly understood. Previously, we documented both the indispensable role of the extracellular matrix (ECM) protein, laminin-111 (LN1), in the formation of normal breast acini, and the phenotypic reversion of cancer cells to acini-like structures in 3-dimensional (3D) gels with inhibitors of oncogenic pathways. Here, we asked how laminin (LN) proteins integrate the signaling pathways necessary for morphogenesis. We report a surprising reciprocal circuitry comprising positive players: laminin-5 (LN5), nitric oxide (NO), p53, HOXD10 and three microRNAs (miRNAs) - that are involved in the formation of mammary acini in 3D. Significantly, cancer cells on either 2-dimensional (2D) or 3D and non-malignant cells on 2D plastic do not produce NO and upregulate negative players: NFκB, EIF5A2, SCA1 and MMP-9 - that disrupt the network. Introducing exogenous NO, LN5 or individual miRNAs to cancer cells reintegrates these pathways and induces phenotypic reversion in 3D. These findings uncover the essential elements of breast epithelial architecture, where the balance between positive- and negative-players leads to homeostasis.

Nitric oxide donors for prostate and bladder cancers: Current state and challenges

Nitric oxide (NO) is an endogenous molecule that plays pivotal physiological and pathophysiological roles, particularly in cancer biology. Generally, low concentrations of NO (pico- to nanomolar range) lead to tumor promotion. In contrast, high NO concentrations (micromolar range) have pro-apoptotic functions, leading to tumor suppression, and in this case, NO is involved in immune surveillance. Under oxidative stress, inducible NO synthase (iNOS) produces high NO concentrations for antineoplastic activities. Prostate and bladder cancers are the most commonly detected cancers in men, and are related to cancer death in males. This review summarizes the state of the art of NO/NO donors in combating prostate and bladder cancers, highlighting the importance of NO donors in cancer treatment, and the limitations and challenges to be overcome. In addition, the combination of NO donors with classical therapies (radio- or chemotherapy) in the treatment of prostate and bladder cancers is also presented and discussed. The combination of NO donors with conventional anticancer drugs is reported to inhibit tumor growth, since NO is able to sensitize tumor cells, enhancing the efficacy of the traditional drugs. Although important progress has been made, more studies are still necessary to definitely translate the administration of NO donors to clinical sets. The purpose of this review is to inspire new avenues in this topic.

Bacillus Calmette-Guerin improves local and systemic response to radiotherapy in invasive bladder cancer

BACKGROUND

A key factor contributing to radio-resistance in conservative invasive bladder cancer (BCa) treatment is tumor hypoxia and a strategy to overcome it is to trigger the production of nitric oxide (NO). On the other hand, ionizing radiation (IR) applied to a primary tumor can induce immunogenic cell death which may set off a cytotoxic immune response against the primary tumor and its metastasis.

PURPOSE

To study in vitro and in vivo, the role of BCG as a local sensitizer to overcome hypoxia-associated radio-resistance through the production of NO, and as an immune-stimulator to be used in combination with IR to generate a systemic response for invasive BCa treatment.

MATERIALS AND METHODS

We selected the invasive murine BCa cell line MB49-I which expresses inducible NO synthase and produces NO, cultured in vitro in 2D and 3D models, and inoculated in vivo in the subcutaneous of syngeneic mice.

RESULTS

in vitro, multicellular murine invasive spheroids mimicked in vivo central tumor necrosis. BCG pre-treatment radio-sensitized spheroids through the induction of NO production, while no effect was shown in monolayers. In vivo, not only did BCG improve the local response to IR but it also decreased the metastatic spread and promoted the development of abscopal effect/rejection of a second tumor.

CONCLUSION

Since BCG has already and successfully been used for the treatment of non-invasive BCa and it improves the response to ionizing radiation in invasive BCa, these results are translational relevant to be analyzed in patients with this pathology.

Exogenous Nitric Oxide Suppresses in Vivo X-ray-Induced Targeted and Non-Targeted Effects in Zebrafish Embryos

The present paper studied the X-ray-induced targeted effect in irradiated zebrafish embryos (Danio rerio), as well as a non-targeted effect in bystander naïve embryos partnered with irradiated embryos, and examined the influence of exogenous nitric oxide (NO) on these targeted and non-targeted effects. The exogenous NO was generated using an NO donor, S-nitroso-N-acetylpenicillamine (SNAP). The targeted and non-targeted effects, as well as the toxicity of the SNAP, were assessed using the number of apoptotic events in the zebrafish embryos at 24 h post fertilization (hpf) revealed through acridine orange (AO) staining. SNAP with concentrations of 20 and 100 µM were first confirmed to have no significant toxicity on zebrafish embryos. The targeted effect was mitigated in zebrafish embryos if they were pretreated with 100 µM SNAP prior to irradiation with an X-ray dose of 75 mGy but was not alleviated in zebrafish embryos if they were pretreated with 20 µM SNAP. On the other hand, the non-targeted effect was eliminated in the bystander naïve zebrafish embryos if they were pretreated with 20 or 100 µM SNAP prior to partnering with zebrafish embryos having been subjected to irradiation with an X-ray dose of 75 mGy. These findings revealed the importance of NO in the protection against damages induced by ionizing radiations or by radiation-induced bystander signals, and could have important impacts on development of advanced cancer treatment strategies.

NO to cancer: The complex and multifaceted role of nitric oxide and the epigenetic nitric oxide donor, RRx-001

The endogenous mediator of vasodilation, nitric oxide (NO), has been shown to be a potent radiosensitizer. However, the underlying mode of action for its role as a radiosensitizer – while not entirely understood – is believed to arise from increased tumor blood flow, effects on cellular respiration, on cell signaling, and on the production of reactive oxygen and nitrogen species (RONS), that can act as radiosensitizers in their own right. NO activity is surprisingly long-lived and more potent in comparison to oxygen. Reports of the effects of NO with radiation have often been contradictory leading to confusion about the true radiosensitizing nature of NO. Whether increasing or decreasing tumor blood flow, acting as radiosensitizer or radioprotector, the effects of NO have been controversial. Key to understanding the role of NO as a radiosensitizer is to recognize the importance of biological context. With a very short half-life and potent activity, the local effects of NO need to be carefully considered and understood when using NO as a radiosensitizer. The systemic effects of NO donors can cause extensive side effects, and also affect the local tumor microenvironment, both directly and indirectly. To minimize systemic effects and maximize effects on tumors, agents that deliver NO on demand selectively to tumors using hypoxia as a trigger may be of greater interest as radiosensitizers. Herein we discuss the multiple effects of NO and focus on the clinical molecule RRx-001, a hypoxia-activated NO donor currently being investigated as a radiosensitizer in the clinic.

•NO radiosensitizer activity is complex with variable results in clinical and non-clinical studies

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NO radiosensitizes by reaction with DNA radicals, by its metabolites and by impact on the vasculature.

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Understanding the local and context-specific activity of NO is key for radiosensitizer development

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RRx-001 induces NO production under hypoxia with promising radiosensitizing activity.

Disruptive chemicals, senescence and immortality

Carcinogenesis is thought to be a multistep process, with clonal evolution playing a central role in the process. Clonal evolution involves the repeated 'selection and succession' of rare variant cells that acquire a growth advantage over the remaining cell population through the acquisition of 'driver mutations' enabling a selective advantage in a particular micro-environment. Clonal selection is the driving force behind tumorigenesis and possesses three basic requirements: (i) effective competitive proliferation of the variant clone when compared with its neighboring cells, (ii) acquisition of an indefinite capacity for self-renewal, and (iii) establishment of sufficiently high levels of genetic and epigenetic variability to permit the emergence of rare variants. However, several questions regarding the process of clonal evolution remain. Which cellular processes initiate carcinogenesis in the first place? To what extent are environmental carcinogens responsible for the initiation of clonal evolution? What are the roles of genotoxic and non-genotoxic carcinogens in carcinogenesis? What are the underlying mechanisms responsible for chemical carcinogen-induced cellular immortality? Here, we explore the possible mechanisms of cellular immortalization, the contribution of immortalization to tumorigenesis and the mechanisms by which chemical carcinogens may contribute to these processes.

Synchronization in stress p53 network

We study transition of the temporal behaviours of p53 and MDM2 in a stress p53-MDM2-NO regulatory network induced by a bioactive molecule NO (Nitric Oxide). We further study synchronization among a group of identical stress systems arranged in a 3D array with nearest neighbour diffusive coupling. The role of NO and the effect of noise are investigated. In the single system study, we found three distinct types of temporal behaviour of p53, namely oscillation death, damped oscillation and sustained oscillation, depending on the amount of stress induced by NO, indicating how p53 responds to incoming stress. The correlation among coupled systems increases as the value of the coupling constant (ϵ) is increased (γ increases) and becomes constant after a certain value of ϵ. The permutation entropy spectra H(ϵ) for p53 and MDM2 as a function of ϵ are found to be different due to direct and indirect interaction of NO with respective proteins. We find γ versus ϵ for p53 and MDM2 to be similar in a deterministic approach but different in a stochastic approach, and the separation between γ of the respective proteins as a function of ϵ decreases as system size increases. The role of NO is found to be two-fold: stress induced by NO is prominent at small and large values of ϵ but synchrony induced by it dominates in the moderate range of ϵ. Excess stress induces apoptosis.

Glutathione S-transferase and MRP1 form an integrated system involved in the storage and transport of dinitrosyl-dithiolato iron complexes in cells

Nitrogen monoxide (NO) is vital for many essential biological processes as a messenger and effector molecule. The physiological importance of NO is the result of its high affinity for iron in the active sites of proteins such as guanylate cyclase. Indeed, NO possesses a rich coordination chemistry with iron and the formation of dinitrosyl-dithiolato iron complexes (DNICs) is well documented. In mammals, NO generated by cytotoxic activated macrophages has been reported to play a role as a cytotoxic effector against tumor cells by binding and releasing intracellular iron. Studies from our laboratory have shown that two proteins traditionally involved in drug resistance, namely multidrug-resistance protein 1 and glutathione S-transferase, play critical roles in intracellular NO transport and storage through their interaction with DNICs (R.N. Watts et al., Proc. Natl. Acad. Sci. USA 103:7670-7675, 2006; H. Lok et al., J. Biol. Chem. 287:607-618, 2012). Notably, DNICs are present at high concentrations in cells and are biologically available. These complexes have a markedly longer half-life than free NO, making them an ideal "common currency" for this messenger molecule. Considering the many critical roles NO plays in health and disease, a better understanding of its intracellular trafficking mechanisms will be vital for the development of new therapeutics.

P53-participated cellular and molecular responses to irradiation are cell differentiation-determined in murine intestinal epithelium

AIM

Cells respond differently to DNA damaging agents, which may related to cell context and differentiation status. The aim of present study was to observe the cellular and molecular responses of cells in different differentiation status to ionizing irradiation (IR).

METHODS

Crypt-villus unit of murine small intestine was adopted as a cell differentiation model. DNA damage responses (DDRs) of crypt and villus were observed 1-24 h after 12 Gy IR using gene expression microarray analysis, immunohistochemical staining, Western blotting and Electrophoretic Mobility Shift Assay.

RESULTS

Microarray analysis revealed that most differentially expressed genes were related to p53 signaling pathway in crypt 4h after IR and in both crypt and villus 24h after IR. In crypt stem cells/progenitor cells, H2AX was phosphorylated and dephosphorylated quickly, Ki67 attenuated, cell apoptosis enhanced, phosphorylated P53 increased and translocated into nuclear with the ability to bind p53-specific sequence. In upper crypt (transit amplifying cells) and crypt-villus junction, cells kept survive and proliferate as indicated by retained Ki67 expression, suppressed p53 activation, and rare apoptosis.

CONCLUSIONS

DDRs varied with cell differentiation status and cell function in small intestinal epithelium. P53 signaling pathway could be an important regulatory mechanism of DDRs.

Selective inhibitors of nuclear export for the treatment of non-Hodgkin's lymphomas

The nuclear export protein chromosome maintenance region 1, found to be elevated in non-Hodgkin's lymphomas, controls localization of critical tumor suppressor proteins. Nuclear localization of tumor suppressor proteins is necessary for their cell surveillance function. However, their nuclear exclusion by chromosome maintenance region 1 renders them ineffective making this nuclear transporter an attractive therapeutic target. We have identified selective inhibitors of nuclear export that lock tumor suppressor proteins in the cell nucleus leading to apoptosis of lymphoid but not normal cells. Our inhibitors induce tumor suppressor protein nuclear retention-dependent growth inhibition and apoptosis in a panel of non-Hodgkin's lymphoma cell lines. Western blot of nuclear protein fraction and confocal microscopy analysis demonstrated retention of major tumor suppressor proteins in the cell nucleus. Co-immunoprecipitation studies showed disruption of the tumor suppressor protein-chromosome maintenance region 1 interaction. Small inhibitor RNA knockdown of two major tumor suppressor proteins, p53 in wild-type protein-53 and protein 73 in mutant-protein-53, abrogated inhibitor activity. Oral administration of related inhibitor at 75 and 150 mg/kg resulted in 65 and 70% tumor reduction, respectively and subcutaneous injections of inhibitor (25 and 75 mg/kg) resulted in 70 and 74% suppression of non-Hodgkin's lymphoma tumor growth with no toxicity; residual tumors showed activation of the protein 73 pathway. Our study verifies chromosome maintenance region 1 as a therapeutic target in non-Hodgkin's lymphoma, indicating that this nuclear export protein warrants further clinical investigations.

Equine sarcoids: Bovine Papillomavirus type 1 transformed fibroblasts are sensitive to cisplatin and UVB induced apoptosis and show aberrant expression of p53

Bovine papillomavirus type 1 infects not only cattle but also equids and is a causative factor in the pathogenesis of commonly occurring equine sarcoid tumours. Whilst treatment of sarcoids is notoriously difficult, cisplatin has been shown to be one of the most effective treatment strategies for sarcoids. In this study we show that in equine fibroblasts, BPV-1 sensitises cells to cisplatin-induced and UVB-induced apoptosis, a known cofactor for papillomavirus associated disease, however BPV-1 transformed fibroblasts show increased clonogenic survival, which may potentially limit the therapeutic effects of repeated cisplatin treatment. Furthermore we show that BPV-1 increases p53 expression in sarcoid cell lines and p53 expression can be either nuclear or cytoplasmic. The mechanism and clinical significance of increase/abnormal p53 expression remains to be established.

Synthesis and characterization of a multi-arm poly(acrylic acid) star polymer for application in sustained delivery of cisplatin and a nitric oxide prodrug

Functionalized polymeric nanocarriers have been recognized as drug delivery platforms for delivering therapeutic concentrations of chemotherapies. Of this category, star-shaped multiarm polymers are emerging candidates for targeted delivery of anti-cancer drugs, due to their compact structure, narrow size distribution, large surface area and high water solubility. In this study, we synthesized a multi-arm poly(acrylic acid) star polymer via MADIX/RAFT polymerization and characterized it using NMR and size exclusion chromatography. The poly(acrylic acid) star polymer demonstrated excellent water solubility and extremely low viscosity, making it highly suited for targeted drug delivery. Subsequently, we selected a hydrophilic drug, cisplatin, and a hydrophobic nitric oxide-donating prodrug, O²-(2,4-dinitrophenyl) 1-[4-(2-hydroxy)ethyl]-3-methylpiperazin-1-yl]diazen-1-ium-1,2-diolate, as two model compounds to evaluate the feasibility of using poly(acrylic acid) star polymers for delivery of chemotherapeutics. After synthesizing and characterizing two poly(acrylic acid) star polymer-based nanoconjugates, poly(acrylic acid)-cisplatin (acid-Pt) and poly(acrylic acid)-nitric oxide prodrug (acid-NO), the in vitro drug release kinetics of both acid-Pt and acid-NO were determined at physiological conditions. In summary, we have designed and evaluated a polymeric nanocarrier for sustained-delivery of chemotherapies, either as a single treatment or a combination therapy regimen.

Tumor suppressor genes and ROS: complex networks of interactions

Tumor suppressor genes regulate diverse cellular activities including DNA damage repair, cell cycle arrest, mitogenic signaling, cell differentiation, migration, and programmed cell death. In this review the tumor suppressor genes p53, FoxO, retinoblastoma (RB), p21, p16, and breast cancer susceptibility genes 1 and 2 (BRCA1 and BRCA2) and their roles in oxidative stress are summarized with a focus on the links and interplay between their pathways and reactive oxygen species (ROS). The results of a number of studies have demonstrated an antioxidant role for tumor suppressor proteins, activating the expression of some well-known antioxidant genes in response to oxidative stress. On the other hand, recent studies have revealed a pro-oxidant role for p53 by which cellular ROS are increased by enhanced transcription of proapoptotic genes. A tightly regulated feedback loop between ROS and FoxO proteins, with ROS regulating FoxO activity through posttranslational modifications and protein interactions and FoxO controlling intracellular ROS levels, has been demonstrated. Furthermore, these studies have shown that FoxO transcription factors and p38 mitogen-activated protein kinases may interact with the RB pathway under stress conditions. In addition, cellular senescence studies established an unexpected role for ROS in inducing and maintaining senescence-induced tumor suppression that blocks cytokinesis to ensure senescent cells never divide again. p21 and p16 have been shown to act as tumor suppressor proteins and this function extends beyond cell cycle control and includes important roles in regulating oxidative stress. Consequently, these important interactions indicate a critical potential role for tumor suppressor genes in the cellular response against oxidative stress and emphasize links between ROS and tumor suppressor genes that might be therapeutic targets in oxidative damage-associated diseases.

Mapping of interactions between human macrophages and Staphylococcus aureus reveals an involvement of MAP kinase signaling in the host defense

Staphylococcus aureus is a dangerous opportunistic human pathogen that causes serious invasive diseases when it reaches the bloodstream. Recent studies have shown that S. aureus is highly resistant to killing by professional phagocytes and that such cells even provide a favorable environment for intracellular survival of S. aureus. Importantly, the reciprocal interactions between phagocytes and S. aureus have remained largely elusive. Here we have employed kinase profiling to define the nature and time resolution of the human THP-1 macrophage response toward S. aureus and proteomics to identify the response of S. aureus toward macrophages. The results of these studies reveal major macrophage signaling pathways triggered by S. aureus and proteomic signatures of the responses of S. aureus to macrophages. We also identify human proteins bound to S. aureus that have potential roles in bacterial killing and internalization. Most noticeably, our observations challenge the classical concept that macrophage responses are mainly mediated through Toll-like receptor 2 and NF-κB signaling and highlight the important role of the stress-activated MAP kinase signaling in orchestrating the host defense.

A calcium-insensitive attenuated nitrosative stress response contributes significantly in the radioresistance of Sf9 insect cells

Lepidopteran insects/insect cells display 50-100 times higher radioresistance than humans, and are evolutionarily closest to mammals amongst all radioresistant organisms known. Compared to mammalian cells, Lepidopteran cells (TN-368, Sf9) display more efficient antioxidant system and DNA repair and suffer considerably less radiation-induced DNA/cytogenetic damage and apoptosis. Recent studies indicate that a considerably lower radiation-induced oxidative stress may significantly reduce macromolecular damage in Lepidopteran cells. Since nitrosative stress contributes in radiation-induced cellular damage, we investigated its nature in the γ-irradiated Sf9 cells (derived from Spodoptera frugiperda; order Lepidoptera; family Noctuidae) and compared with BMG-1 human cell line having significant NOS expression. Radiation induced considerably less ROS/RNS in Sf9 cells, which remained unchanged on treatment with NOS inhibitor l-NMMA. Surprisingly, growth of Sf9 cultures or irradiation could not induce NO or its metabolites, indicating negligible basal/radiation-induced NOS activity that remained unchanged even after supplementation with arginine. Cytosolic calcium release following high-dose (1000-2000Gy at 61.1cGys(-1)) γ-irradiation or H(2)O(2) (250μM) treatment also failed to generate NO in Sf9 cells having high constitutive levels of calmodulin, whereas BMG-1 cells displayed considerable calcium-dependent NO generation even following 10Gy dose. These results strongly imply the lack of calcium-mediated NOS activity in Sf9 cells. Addition of exogenous NO from GSH-NO caused considerable increase in radiation-induced apoptosis, indicating significant contribution of constitutively attenuated nitrosative stress response into the radioresistance of Lepidopteran cells. Our study demonstrates for the first time that a calcium-insensitive, attenuated nitrosative stress response may contribute significantly in the unusual radioresistance displayed by Lepidopteran insect cells.

Phosphorylated TP63 induces transcription of RPN13, leading to NOS2 protein degradation

Head and neck squamous cell carcinoma cells exposed to cisplatin display ATM-dependent phosphorylation of the most predominant TP63 isoform (ΔNp63α), leading to its activation as a transcription factor. Here, we found that the phospho-ΔNp63α protein binds to the genomic promoter of RPN13 through the TP63-responsive element. We further found that the phospho-ΔNp63α protein associates with other transcription factors (DDIT3 (also known as CHOP), NF-Y, and NF-κB), activating RPN13 gene transcription. Furthermore, cisplatin-induced and phospho-ΔNp63α-dependent RPN13 gene transcription leads to NOS2 degradation. Finally, we show that RPN13 knockdown by siRNA essentially rescues NOS2 from cisplatin-dependent inactivation. These data provide a novel mechanism for the phospho-ΔNp63α-dependent regulation of NOS2 function in cells upon cisplatin treatment, contributing to the cell death pathway of tumor cells.

Nitration of the tumor suppressor protein p53 at tyrosine 327 promotes p53 oligomerization and activation

Previous studies demonstrate that nitric oxide (NO) promotes p53 transcriptional activity by a classical DNA damage responsive mechanism involving activation of ATM/ATR and phosphorylation of p53. These studies intentionally used high doses of NO donors to achieve the maximum DNA damage. However, lower concentrations of NO donors also stimulate rapid and unequivocal nuclear retention of p53 but apparently do not require ATM/ATR-dependent p53 phosphorylation or total p53 protein accumulation. To identify possible mechanisms for p53 activation at low NO levels, the role of Tyr nitration in p53 activation was evaluated. Low concentrations of the NO donor, DETA NONOate (<200 microM), exclusively nitrate Tyr327 within the tetramerization domain promoting p53 oligomerization, nuclear accumulation, and increased DNA-binding activity without p53 Ser15 phosphorylation. Molecular modeling indicates that nitration of one Tyr327 stabilizes the dimer by about 2.67 kcal mol(-1). Significant quantitative and qualitative differences in the patterns of p53-target gene modulation by low (50 microM), non-DNA-damaging and high (500 microM), DNA-damaging NO donor concentrations were shown. These results demonstrate a new posttranslational mechanism for modulating p53 transcriptional activity responsive to low NO concentrations and independent of DNA damage signaling.

Escape from p53-mediated tumor surveillance in neuroblastoma: switching off the p14(ARF)-MDM2-p53 axis

A primary failsafe program against unrestrained proliferation and oncogenesis is provided by the p53 tumor suppressor protein, inactivation of which is considered as a hallmark of cancer. Intriguingly, mutations of the TP53 gene are rarely encountered in neuroblastoma tumors, suggesting that alternative p53-inactivating lesions account for escape from p53 control in this childhood malignancy. Several recent studies have shed light on the mechanisms by which neuroblastoma cells circumvent the p53-driven antitumor barrier. We review here these mechanisms for evasion of p53-mediated growth control and conclude that deregulation of the p14(ARF)-MDM2-p53 axis seems to be the principal mode of p53 inactivation in neuroblastoma, opening new perspectives for targeted therapeutic intervention.

Effect of nitric oxide donor, a modulator of tumor drug resistance, on cell death and p53 protein expression

Exogenous NO donor 3,3-bis-(nitroxymethyl)oxetane (NMO) was synthesized at the Institute for Problems of Chemical Physics (Russian Academy of Sciences). This compound was shown to inhibit cell death (apoptosis and necrosis) in cyclophosphamide-sensitive and cyclophosphamide-resistant P388 murine tumor. p53 protein was expressed in both lines of tumor cells. NO donor NMO had little effect on p53 protein expression in cells of both stains. Our results suggest that the proapoptotic effect of NMO is mediated by the p53-independent molecular mechanisms.