DNA damage in inflammation-related carcinogenesis and cancer stem cells

Abstract

Infection and chronic inflammation have been recognized as important factors for carcinogenesis. Under inflammatory conditions, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from inflammatory and epithelial cells and result in oxidative and nitrative DNA damage, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine. The DNA damage can cause mutations and has been implicated in the initiation and/or promotion of inflammation-mediated carcinogenesis. It has been estimated that various infectious agents are carcinogenic to humans (IARC group 1), including parasites (Schistosoma haematobium (SH) and Opisthorchis viverrini (OV)), viruses (hepatitis C virus (HCV), human papillomavirus (HPV), and Epstein-Barr virus (EBV)), and bacterium Helicobacter pylori (HP). SH, OV, HCV, HPV, EBV, and HP are important risk factors for bladder cancer, cholangiocarcinoma, hepatocellular carcinoma, cervical cancer, nasopharyngeal carcinoma, and gastric cancer, respectively. We demonstrated that 8-nitroguanine was strongly formed via inducible nitric oxide synthase (iNOS) expression at these cancer sites of patients. Moreover, 8-nitroguanine was formed in Oct3/4-positive stem cells in SH-associated bladder cancer tissues and in Oct3/4- and CD133-positive stem cells in OV-associated cholangiocarcinoma tissues. Therefore, it is considered that oxidative and nitrative DNA damage in stem cells may play a key role in inflammation-related carcinogenesis.

Figure 1

The formation of 8-nitroguanine (red) and the expression of Oct3/4 (green) were assessed by double immunofluorescence staining [10]. In the merged image, co-localization of 8-nitroguanine and Oct3/4 is indicated in yellow. Original magnification in all pictures is 200x (SH: Schistosoma haematobium). Formalin-fixed and paraffin-embedded biopsy and surgical specimens were obtained from normal subjects and patients with SH-induced cystitis and bladder cancer. Normal tissues and urinary bladder cancer tissues without SH infection were obtained from a commercial urinary bladder tissue array (Biomax.us, USA). Normal tissues with cystitis were excluded. SH-egg antigens in sera were detected by Sandwich ELISA assay [75]. This study was performed in accordance with the Ethical Guidelines for Epidemiological Research enacted by the Japanese government. Deparaffinized and antigen-retrieved sections were incubated first with 5% skim milk, and then with a rabbit polyclonal anti-8-nitroguanine antibody (2 μg/mL, prepared as described previously [11]) and mouse monoclonal anti-Oct3/4 antibody (2 μg/mL, Santa Cruz Biotechnology, CA, USA) overnight at room temperature. The sections were then incubated for 3 h with Alexa 594-labeled goat antibody against rabbit IgG and Alexa 488-labeled goat antibody against mouse IgG (each 1 : 400, Molecular Probes, Eugene, OR, USA).

Figure 2

Postulated mechanism for generating cancer stem cells by inflammation.