Nitric oxide induces early viral transcription coincident with increased DNA damage and mutation rates in human papillomavirus-infected cells

Association of epidermal growth factor receptor mutations with human papillomavirus 16/18 E6 oncoprotein expression in non-small cell lung cancer

BACKGROUND

Lung cancers in women, in nonsmokers, and in patients with adenocarcinoma from Asia have more prevalent mutations in the epidermal growth factor receptor (EGFR) gene than their counterparts. However, the etiology of EGFR mutations in this population remains unclear. The authors hypothesized that the human papillomavirus (HPV) type 16/18 (HPV16/18) E6 oncoprotein may contribute to EGFR mutations in Taiwanese patients with lung cancer.

METHODS

One hundred fifty-one tumors from patients with lung cancer were enrolled to determine HPV16/18 E6 and EGFR mutations using immunohistochemistry and direct sequencing, respectively. Levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in lung tumors and cells were evaluated using immunohistochemistry and liquid chromatography-mass spectrometry/mass spectrometry. An supF mutagenesis assay was used to determine H2 O2 -induced mutation rates of lung cancer cells with or without E6 expression.

RESULTS

Patients with E6-positive tumors had a greater frequency of EGFR mutations than those with E6-negative tumors (41% vs 20%; P = .006). Levels of 8-oxo-dG were correlated with EGFR mutations (36% vs 16%; P = .012). Two stable clones of E6-overexpressing H157 and CL-3 cells were established for the supF mutagenesis assay. The data indicated that the cells with high E6 overexpression had higher H2 O2 -induced SupF gene mutation rates compared with the cells that expressed lower levels of E6 and compared with vector control cells.

CONCLUSIONS

HPV16/18 E6 may contribute in part to EGFR mutations in lung cancer, at least in the Taiwanese population.

Nitric oxide and cancer: a review

Nitric oxide (NO), is a ubiquitous, water soluble, free radical gas, which plays key role in various physiological as well as pathological processes. Over past decades, NO has emerged as a molecule of interest in carcinogenesis and tumor growth progression. However, there is considerable controversy and confusion in understanding its role in cancer biology. It is said to have both tumoricidal as well as tumor promoting effects which depend on its timing, location, and concentration. NO has been suggested to modulate different cancer-related events including angiogenesis, apoptosis, cell cycle, invasion, and metastasis. On the other hand, it is also emerging as a potential anti-oncogenic agent. Strategies for manipulating in vivo production and exogenous delivery of this molecule for therapeutic gain are being investigated. However, further validation and experimental/clinical trials are required for development of novel strategies based on NO for cancer treatment and prevention. This review discusses the range of actions of NO in cancer by performing an online MEDLINE search using relevant search terms and a review of the literature. Various mechanisms by which NO acts in different cancers such as breast, cervical, gastric,colorectal, and head and neck cancers are addressed. It also offers an insight into the dichotomous nature of NO and discusses its novel therapeutic applications for cancer prevention and treatment.

Epigenetic field defects in progression to cancer

A field defect is a field of pre-malignant tissue in which a new cancer is likely to arise. Field defects often appear to be histologically normal under the microscope. Recent research indicates that cells within a field defect characteristically have an increased frequency of epigenetic alterations and these may be fundamentally important as underlying factors in progression to cancer. However, understanding of epigenetic field defects is at an early stage, and the work of Katsurano et al published this year, is a key contribution to this field. One question examined by Katsurano et al was how early could the formation of an epigenetic field defect be detected in a mouse colitis model of tumorigenesis. They highlighted a number of measurable epigenetic alterations, detected very early in normal appearing tissue undergoing histologically invisible tumorigenesis. They also documented the increasing presence of the epigenetic alterations at successive times during progression to cancer. In this commentary, we offer a perspective on the changes they observed within a broader sequence of epigenetic events that occur in progression to cancer. In particular, we highlight the likely central role of epigenetic deficiencies in DNA repair gene expression that arise during progression to cancer.

Nitric oxide-dependent downregulation of BRCA1 expression promotes genetic instability

Elevated levels of nitric oxide (NO) and reactive nitrogen species (RNS) may link inflammation to the initiation, promotion, and progression of cancer. Traditionally, this link has been thought to be mediated by the effects of NO/RNS in generating DNA damage. However, this damage also stimulates DNA repair responses with subsequent blocks to cell proliferation and apoptosis, thereby preventing accumulation of NO/RNS-generated mutations. In addressing this conundrum, I describe here an alternative mechanism for understanding mutagenesis by NO/RNS. Moderate NO/RNS concentrations stimulated mutagenesis not directly by generating DNA damage but indirectly by modifying the activities of DNA repair and genome stability factors without affecting cell proliferation. NO/RNS at concentrations physiologically relevant to inflammation stimulated PP2A activity, leading to dephosphorylation of RBL2, its accumulation in the nucleus, and formation of RBL2/E2F4 complexes. RBL2/E2F4 formation in turn led to a shift in BRCA1 promoter occupancy from complexes containing activator E2F1 to complexes containing repressor E2F4, downregulating BRCA1 expression. By inhibiting BRCA1 expression, NO/RNS thereby reduces the ability of cells to repair DNA double-strand breaks through homologous recombination repair, increasing the involvement of error-prone nonhomologous end joining (NHEJ). In summary, NO/RNS stimulates genetic instability by inhibiting BRCA1 expression and shifting DNA repair from high fidelity to error-prone mechanisms.

Nitric oxide-mediated regulation of β-amyloid clearance via alterations of MMP-9/TIMP-1

Fibrillar amyloid plaques are largely composed of amyloid-beta (Aβ) peptides that are metabolized into products, including Aβ1-16, by proteases including matrix metalloproteinase 9 (MMP-9). The balance between production and degradation of Aβ proteins is critical to amyloid accumulation and resulting disease. Regulation of MMP-9 and its endogenous inhibitor tissue inhibitor of metalloproteinase (TIMP)-1 by nitric oxide (NO) has been shown. We hypothesize that nitric oxide synthase (NOS2) protects against Alzheimer's disease pathology by increasing amyloid clearance through NO regulation of MMP-9/TIMP-1 balance. We show NO-mediated increased MMP-9/TIMP-1 ratios enhanced the degradation of fibrillar Aβ in vitro, which was abolished when silenced for MMP-9 protein translation. The in vivo relationship between MMP-9, NO and Aβ degradation was examined by comparing an Alzheimer's disease mouse model that expresses NOS2 with a model lacking NOS2. To quantitate MMP-9 mediated changes, we generated an antibody recognizing the Aβ1-16 fragment, and used mass spectrometry multi-reaction monitoring assay for detection of immunoprecipitated Aβ1-16 peptides. Aβ1-16 levels decreased in brain lysates lacking NOS2 when compared with strains that express human amyloid precursor protein on the NOS2 background. TIMP-1 increased in the APPSwDI/NOS2(-/-) mice with decreased MMP activity and increased amyloid burden, thereby supporting roles for NO in the regulation of MMP/TIMP balance and plaque clearance.

Increased production of nitric oxide correlates with tumor growth in Algerian patients with nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is thought to arise because of chronic inflammation. The correlation between nitric oxide (NO) production, a biomarker of inflammation and NPC development remains unexplored. To investigate this question, we performed a profile analysis on plasma collected from untreated, treated, remissive, cured and relapsing patients. Nitrites were measured to assess NO activity. We observed that increased nitrites concentrations in untreated and relapsing patients associated with tumor development. Moreover, nitrites levels were similar in remissive, cured and healthy individuals. Altogether, our results suggest that NO might be an interesting blood biomarker to monitor tumor growth in NPC patients.

Regulation of inflammatory pathways in cancer and infectious disease of the cervix

Cervical cancer is one of the leading gynaecological malignancies worldwide. It is an infectious disease of the cervix, associated with human papillomavirus infection (HPV), infection with bacterial agents such as Chlamydia trachomatis and Neisseria gonorrhoea as well as human immunodeficiency virus (HIV). Furthermore, it is an AIDS-defining disease with an accelerated mortality in HIV-infected women with cervical cancer. With the introduction of robust vaccination strategies against HPV in the developed world, it is anticipated that the incidence of cervical cancer will decrease in the coming years. However, vaccination has limited benefit for women already infected with high-risk HPV, and alternative therapeutic intervention strategies are needed for these women. Many pathological disorders, including cervical cancer, are characterised by the exacerbated activation and maintenance of inflammatory pathways which are considered to be regulated by infectious agents. In cervical cancer, hyperactivation of these inflammatory pathways and regulation of immune infiltrate into tissues can potentially play a role not only in tumorigenesis but also in HIV infection. In this paper we will discuss the contribution of inflammatory pathways to cervical cancer progression and HIV infection and the role of HIV in cervical cancer progression.

Human papillomavirus, smoking, and head and neck cancer

AIMS

Smoking and human papillomavirus (HPV) are both distinct risk factors for head and neck cancer, but the nature of interaction between these 2 risk factors in the development of head and neck cancer remains unclear. The purpose of this review is to determine the potential effect of smoking in causation of HPV-related head and neck carcinoma.

METHOD

A literature search was carried out using the keywords human papillomavirus, head and neck cancer, smoking, tobacco, and cervical cancer. The English-language articles, references, and other relevant studies evaluating the association of smoking, HPV, and risk of head and neck cancer were collected and analyzed.

CONCLUSION

Overall, our review points to smoking tobacco posing an additional risk for development of head and neck cancer in the presence of HPV infection. This is consistent with available laboratory data that show evidence of biological plausibility for interaction between smoking and progression of HPV infection to carcinogenesis. It is therefore important that cessation of smoking is promoted in smokers with HPV infection.

Cigarette smoke condensate-induced oxidative DNA damage and its removal in human cervical cancer cells

Exposure to cigarette smoke is well documented to increase oxidative stress and could account for higher risk of cervical cancer in smokers. Cervical pre-cancerous lesions that are initiated by human papillomavirus (HPV) infection generally regress in the absence of known risk factors such as smoking. 8-oxodeoxyguanosine (8-oxodG) is a highly mutagenic oxidative DNA lesion that is formed by the oxidation of deoxyguanosine. In the present study, we examined: a) the effect of cigarette smoke condensate (CSC) on 8-oxodG formation in and its removal from HPV-transfected (ECT1/E6 E7), HPV-positive (CaSki) and HPV-negative (C33A) human cervical cancer cells, and b) the cell cycle progression and apoptosis in CSC-treated ECT1/E6 E7 cells. CSC induced 8-oxodG in a dose- (p=0.03) and time (p=0.002)-dependent fashion in ECT1/E6 E7 cells as determined by flow cytometry. A 2.4-fold higher level of 8-oxodG was observed in HPV-positive compared with HPV-negative cells. However, 8-oxodG lesions were almost completely removed 72 h post-exposure in all cell lines as determined by ImageStream analysis. This observation correlates with the 2- and 5-fold increase in the p53 levels in ECT1/E6 E7 and CaSki cells with no significant change in C33A cells. We conclude that: a) cigarette smoke constituents induce oxidative stress with higher burden in HPV-positive cervical cancer cells and b) the significant increase observed in p53 levels in wild-type cervical cells (ECT1/E6 E7 and CaSki) may be attributed to the p53-dependent DNA repair pathway while a p53-independent pathway in C33A cells cannot be ruled out.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

HPV-DNA integration and carcinogenesis: putative roles for inflammation and oxidative stress

HPV-DNA integration into cellular chromatin is usually a necessary event in the pathogenesis of HPV-related cancer; however, the mechanism of integration has not been clearly defined. Breaks must be created in both the host DNA and in the circular viral episome for integration to occur, and studies have shown that viral integration is indeed increased by the induction of DNA double strand breaks. Inflammation generates reactive oxygen species, which in turn have the potential to create such DNA strand breaks. It is plausible that these breaks enable a greater frequency of HPV-DNA integration, and in this way contribute to carcinogenesis. Consistent with this idea, co-infections with certain sexually transmitted diseases cause cervical inflammation, and have also been identified as cofactors in the progression to cervical cancer. This article examines the idea that inflammation facilitates HPV-DNA integration into cellular chromatin through the generation of reactive oxygen species, thereby contributing to carcinogenesis.

Genomic instability and cancer: lessons learned from human papillomaviruses

High-risk HPV E6 and E7 oncoproteins cooperate to subvert critical host cell cycle checkpoint control mechanisms in order to promote viral genome replication. This results not only in aberrant proliferation but also in host cellular changes that can promote genomic instability. The HPV-16 E7 oncoprotein was found to induce centrosome abnormalities thereby disrupting mitotic fidelity and increasing the risk for chromosome missegregation and aneuploidy. In addition, expression of the high-risk HPV E7 oncoprotein stimulates DNA replication stress as a potential source of DNA breakage and structural chromosomal instability. Proliferation of genomically unstable cells is sustained by several mechanisms including the accelerated degradation of claspin by HPV-16 E7 and the degradation of p53 by the high-risk HPV E6 oncoprotein. These results highlight the oncogenic potential of aberrant proliferation and opens new avenues for prevention of malignant progression, not only in HPV-associated cervical cancer but also in non-virally associated malignancies with disrupted cell cycle checkpoint control mechanisms.

Cervical nitric oxide release and persistence of high-risk human papillomavirus in women

Nitric oxide may serve as one cofactor for human papillomavirus (HPV)-induced development of cervical cancer. Therefore, we first assessed the levels of cervical fluid nitric oxide metabolite (NOx) in 283 women with and without high-risk (hr) HPV. The NOx level in women with hr HPV (48.4 μmol/L [95% CI: 39.4-56.6], n = 199) was higher (p < 0.001) than that in women without hr HPV (24.6 μmol/L [95% CI: 19.1-38.7], n = 84). Second, we evaluated if cervical fluid NOx levels could predict the persistence of hr HPV. Therefore, we followed up 113 women with detectable hr HPV without any treatment for 12 mo and repeated hr HPV test. High-risk HPV persisted in 72 women (64%) and disappeared in 41 women (36%). The median basal levels of NOx were higher (p = 0.02) in women with persistent hr HPV (56.9 μmol/L [95% CI: 48.7-81.0]) compared to those with eradicated hr HPV (37.7 μmol/L [95% CI: 27.0-58.0]). The NOx level higher than the 75th percentile (>87.0 μmol/L) predicted hr HPV persistence (OR = 4.1 [95% CI: 1.3-13.1]). This cutoff level of NOx showed 33% sensitivity and 90% specificity in predicting the persistence of hr HPV, but it failed to predict cytological progression or regression in 12 mo. In conclusion, high cervical fluid NOx appears to be connected to the persistence of hr HPV, but the low predictive capacity of NOx prevents its clinical use at this phase.

Increased NOS2 predicts poor survival in estrogen receptor-negative breast cancer patients

Inducible nitric oxide synthase (NOS2) is involved in wound healing, angiogenesis, and carcinogenesis. NOS2 upregulation and increased nitric oxide (NO) production affect the redox state of cells and can induce protein, lipid, and DNA modifications. To investigate whether NOS2 levels influence survival of breast cancer patients, we examined NOS2 expression and its association with tumor markers and survival in 248 breast tumors. In multivariable survival analysis, increased NOS2 predicted inferior survival in women with estrogen receptor α-negative (ER-negative) tumors. Microdissected tumor epithelium from ER-negative tumors with high NOS2 had increased IL-8 and a gene expression signature characteristic of basal-like breast cancer with poor prognosis. In cell culture, NO only induced selected signature genes in ER-negative breast cancer cells. ER transgene expression in ER-negative cells inhibited NO-induced upregulation of the stem cell marker CD44 and other proteins encoded by signature genes, but not of IL-8. Exposure to NO also enhanced cell motility and invasion of ER-negative cells. Last, pathway analysis linked the tumor NOS2 gene signature to c-Myc activation. Thus, NOS2 is associated with a basal-like transcription pattern and poor survival of ER-negative patients.

The role of inflammation in HPV carcinogenesis

The role of inflammation in human papillomavirus (HPV) infection and disease is complex since it involves responses capable of preventing initial infections, clearing those ongoing as well as promoting persistence and progression of associated lesions. Avoiding the immune response has been considered a key aspect of HPV persistence which is the main factor leading to HPV-related neoplasia. HPVs have evolved different ways of targeting immune signaling pathways. Moreover, host inflammatory response may promote lesion progression and affect tumor fate by diverse mechanisms including the direct participation of inflammatory cells. In this review, we discuss the interplay between HPV oncogenic proteins and an array of inflammatory responses that ultimately may lead to cancer.

Nitric oxide: perspectives and emerging studies of a well known cytotoxin

The free radical nitric oxide (NO^•) is known to play a dual role in human physiology and pathophysiology. At low levels, NO^• can protect cells; however, at higher levels, NO^• is a known cytotoxin, having been implicated in tumor angiogenesis and progression. While the majority of research devoted to understanding the role of NO^• in cancer has to date been tissue-specific, we herein review underlying commonalities of NO^• which may well exist among tumors arising from a variety of different sites. We also discuss the role of NO^• in human physiology and pathophysiology, including the very important relationship between NO^• and the glutathione-transferases, a class of protective enzymes involved in cellular protection. The emerging role of NO^• in three main areas of epigenetics—DNA methylation, microRNAs, and histone modifications—is then discussed. Finally, we describe the recent development of a model cell line system in which human tumor cell lines were adapted to high NO^• (HNO) levels. We anticipate that these HNO cell lines will serve as a useful tool in the ongoing efforts to better understand the role of NO^• in cancer.

Activated CD4+ T cells enhance radiation effect through the cooperation of interferon-gamma and TNF-alpha

Background

Approaches that enhance radiation effect may lead to improved clinical outcome and decrease toxicity. Here we investigated whether activated CD4+ T cells (aCD4) can serve as an effective radiosensitizer.

Methods

CD4+ T cells were activated with anti-CD3 and anti-CD28 mAbs. Hela cells were presensitized with aCD4 or conditioned supernatant (aCD4S) or recombinant cytokines for 2 days, followed γ-irradiation. The treated cells were cultured for an additional 2 to 5 days for cell proliferation, cell cycle, and western blot assays. For confirmation, other cancer cell lines were also used.

Results

Presensitization of tumor cells with aCD4 greatly increased tumor cell growth inhibition. Soluble factors secreted from activated CD4⁺ T cells were primarily responsible for the observed effect. IFN-γ seemed to play a major role. TNF-α, though inactive by itself, significantly augmented the radiosensitizing activity of IFN-γ. aCD4S, but not IFN-γ or IFN-γ/TNF-α combination, was found to enhance the γ-irradiation-induced G2/M phase arrest. Bax expression was highly upregulated in Hela cells presensitized with aCD4S followed by γ-irradiation. The radio-sensitizing activity of aCD4 is not uniquely observed with Hela cell line, but also seen with other cancer cell lines of various histology.

Conclusions

Our findings suggest possible molecular and cellular mechanisms that may help explain the radio-sensitization effect of activated lymphocytes, and may provide an improved strategy in the treatment of cancer with radiotherapy.

Inducible heat shock protein 70 enhances HPV31 viral genome replication and virion production during the differentiation-dependent life cycle in human keratinocytes

Increasing data indicate heat shock proteins (HSPs) including inducible HSP70 (HSP70i) are involved in the replicative cycles of various viruses including adenoviruses (Ads), polyomaviruses (PyVs), and some RNA viruses. Cell-free system studies implicate HSP70i in human papillomavirus type 11 (HPV11) genome replication with E1 and E2 proteins, and there is evidence that HSP70 is involved in capsid assembly and disassembly for PyVs and HPVs. HSP70 expression is increased in HPV16 E6/E7 gene transduced human primary keratinocytes, and frequently detected in early stage uterine cervical cancer at levels in conjunction with lesion severity. In this study we carry out analyses in the natural host epithelial tissues to assess the role of inducible HSP70 (HSP70i) in the HPV infectious life cycle. For these studies we used the organotypic (raft) culture system to recapitulate the full viral life cycle of the high-risk HPV31. Upon heat shock of HPV31-infected organotypic tissues, we find high and sustained expression of HSP70i coincident with enhanced HPV genome replication and virion production. Whereas there is no clear effect on L1 expression levels, we find HSP70i and L1 interact and HSP70i colocalizes with and enhances the nuclear localization of L1 in differentiated cells. Ad-mediated gene transfer was used to study the effects of HSP70i in naturally HPV-infected differentiating tissues and showed results similar to those in heat shocked rafts. These results indicate that increased HSP70i augments late activities in the viral life cycle. We conclude that HSP70i contributes directly to HPV replicative viral activities and the production of infectious virions.