Mass spectrometric identification of a phorbol diester 12-O-hexadecanoylphorbol-13-acetate, an Epstein-Barr virus-activating substance, in the soil collected from under Sapium sebiferum

Formation of 8-nitroguanine, a nitrative DNA lesion, in inflammation-related carcinogenesis and its significance

Chronic infection and inflammation contribute to a substantial part of environmental carcinogenesis. Recently, it has been estimated that chronic inflammation accounts for approximately 25% of cancer cases. Various infectious diseases and physical, chemical, and immunological factors participate in inflammation-related carcinogenesis. Under inflammatory conditions, reactive oxygen and nitrogen species, which are generated from inflammatory and epithelial cells, may play an important role in carcinogenesis by causing DNA damage. 8-Nitroguanine is a mutagenic DNA lesion formed during chronic inflammation. In an earlier publication, our group reported the results of an immunohistochemical analysis of animals infected with the liver fluke Opisthorchis viverrini and demonstrated for the first time that 8-nitroguanine was formed at the sites of carcinogenesis. This DNA lesion was found to accumulate in the carcinogenic process in clinical specimens of cancer-prone inflammatory diseases caused by various pathogens, including human papillomavirus and Epstein-Barr virus. Moreover, strong 8-nitroguanine formation in tumor tissues was closely associated with a poor prognosis. On the basis of these findings, 8-nitroguanine could be a potential biomarker to evaluate the risk of inflammation-related carcinogenesis and the prognosis of cancer patients. In this review, the significance of 8-nitroguanine formation in inflammation-related carcinogenesis and tumor progression will be discussed.

Formation of 8-nitroguanine, a nitrative DNA lesion, in inflammation-related carcinogenesis and its significance

Chronic infection and inflammation contribute to a substantial part of environmental carcinogenesis. Recently, it has been estimated that chronic inflammation accounts for approximately 25% of cancer cases. Various infectious diseases and physical, chemical, and immunological factors participate in inflammation-related carcinogenesis. Under inflammatory conditions, reactive oxygen and nitrogen species, which are generated from inflammatory and epithelial cells, may play an important role in carcinogenesis by causing DNA damage. 8-Nitroguanine is a mutagenic DNA lesion formed during chronic inflammation. In an earlier publication, our group reported the results of an immunohistochemical analysis of animals infected with the liver fluke Opisthorchis viverrini and demonstrated for the first time that 8-nitroguanine was formed at the sites of carcinogenesis. This DNA lesion was found to accumulate in the carcinogenic process in clinical specimens of cancer-prone inflammatory diseases caused by various pathogens, including human papillomavirus and Epstein-Barr virus. Moreover, strong 8-nitroguanine formation in tumor tissues was closely associated with a poor prognosis. On the basis of these findings, 8-nitroguanine could be a potential biomarker to evaluate the risk of inflammation-related carcinogenesis and the prognosis of cancer patients. In this review, the significance of 8-nitroguanine formation in inflammation-related carcinogenesis and tumor progression will be discussed.

Reactive nitrogen species-dependent DNA damage in EBV-associated nasopharyngeal carcinoma: the relation to STAT3 activation and EGFR expression

Nasopharyngeal carcinoma (NPC) is strongly associated with Epstein-Barr virus (EBV) infection. Recently, reactive nitrogen and oxygen species are considered to participate in inflammation-related carcinogenesis through DNA damage. In our study, we obtained biopsy and surgical specimens of nasopharyngeal tissues from NPC patients in southern China, and performed double immunofluorescent staining to examine the formation of 8-nitroguanine, a nitrative DNA lesion and 8-oxo-7,8-dihydro-2'-deoxyguanosine, an oxidative DNA lesion, in these specimens. Strong DNA lesions were observed in cancer cells and inflammatory cells in stroma of NPC patients. Intensive immunoreactivity of iNOS was detected in the cytoplasm of 8-nitroguanine-positive cancer cells. DNA lesions and iNOS expression were also observed in epithelial cells of EBV-positive patients with chronic nasopharyngitis, although their intensities were significantly weaker than those in NPC patients. In EBV-negative subjects, no or little DNA lesions and iNOS expression were observed. EGFR and phosphorylated STAT3 were strongly expressed in cancer cells of NPC patients, but NF-kappaB was not expressed, suggesting that STAT3-dependent mechanism is important for NPC carcinogenesis. IL-6 was expressed mainly in inflammatory cells of nasopharyngeal tissues of EBV-infected patients. EBV-encoded RNAs (EBERs) and latent membrane protein 1 (LMP1) were detected in cancer cells from all EBV-infected patients. In vitro cell system, nuclear accumulation of EGFR was observed in LMP1-expressing cells, and IL-6 induced phosphorylated STAT3 and iNOS. These data suggest that nuclear accumulation of EGFR and STAT3 activation by IL-6 play the key role in iNOS expression and resultant DNA damage, leading to EBV-mediated NPC.

Epstein-Barr virus and cancer

EBV was the first human virus to be directly implicated in carcinogenesis. It infects >90% of the world's population. Although most humans coexist with the virus without serious sequelae, a small proportion will develop tumors. Normal host populations can have vastly different susceptibility to EBV-related tumors as demonstrated by geographical and immunological variations in the prevalence of these cancers. EBV has been implicated in the pathogenesis of Burkitt's lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised individuals. The presence of this virus has also been associated with epithelial malignancies arising in the gastric region and the breast, although some of this work remains in dispute. EBV uses its viral proteins, the actions of which mimic several growth factors, transcription factors, and antiapoptotic factors, to usurp control of the cellular pathways that regulate diverse homeostatic cellular functions. Recent advances in antiviral therapeutics, application of monoclonal antibodies, and generation of EBV-specific CTLs are beginning to show promise in the treatment of EBV-related disorders.