Helicobacter pylori-induced activation-induced cytidine deaminase expression and carcinogenesis

Anti-Helicobacter pylori antibody status is associated with cancer mortality: A longitudinal analysis from the Japanese DAIKO prospective cohort study

Paradoxically, patients with advanced stomach cancer who are Helicobacter pylori-positive (HP+) have a higher survival rate than those who are HP-. This finding suggests that HP infection has beneficial effects for cancer treatment. The present study examines whether HP+ individuals have a lower likelihood of death from cancer than those who are HP-. Prospective cohort data (n = 4,982 subjects enrolled in the DAIKO study between 2008-2010) were used to assess whether anti-HP antibody status was associated with cancer incidence. The median age in the primary registry was 53 years-old (range 35-69 years-old). Over the 8-year observation period there were 234 (4.7%) cancer cases in the cohort and 88 (1.8%) all-cause deaths. Urine anti-HP antibody data was available for all but one participant (n = 4,981; 99.98%). The number of HP+ and HP- individuals was 1,825 (37%) and 3,156 (63%), respectively. Anti-HP antibody distribution per birth year revealed that earlier birth year was associated with higher HP+ rates. With a birth year-matched cohort (n = 3,376), all-cancer incidence was significantly higher in HP+ individuals than those who were HP- (p = 0.00328), whereas there was no significant difference in the cancer death rate between HP+ and HP- individuals (p = 0.888). Cox regression analysis for prognostic factors revealed that the hazards ratio of HP+ was 1.59-fold (95%CI 1.17-2.26) higher than HP- in all-cancer incidence. Potential systemic effects of HP+ status may contribute to reduced likelihood of death for patients after an initial diagnosis of cancer.

Helicobacter pylori promotes gastric cancer progression through the tumor microenvironment

Gastric cancer (GC) is a leading type of cancer. Although immunotherapy has yielded important recent progress in the treatment of GC, the prognosis remains poor due to drug resistance and frequent recurrence and metastasis. There are multiple known risk factors for GC, and infection with Helicobacter pylori is one of the most significant. The mechanisms underlying the associations of H. pylori and GC remain unclear, but it is well known that infection can alter the tumor microenvironment (TME). The TME and the tumor itself constitute a complete ecosystem, and the TME plays critical roles in tumor progression, metastasis, and drug resistance. H. pylori infection can act synergistically with the TME to cause DNA damage and abnormal expression of multiple genes and activation of signaling pathways. It also modulates the host immune system in ways that enhance the proliferation and metastasis of tumor cells, promote epithelial-mesenchymal transition, inhibit apoptosis, and provide energy support for tumor growth. This review elaborates myriad ways that H. pylori infections promote the occurrence and progression of GC by influencing the TME, providing new directions for immunotherapy treatments for this important disease. KEY POINTS: • H. pylori infections cause DNA damage and affect the repair of the TME to DNA damage. • H. pylori infections regulate oncogenes or activate the oncogenic signaling pathways. • H. pylori infections modulate the immune system within the TME.

Mutagenic Activity of AID/APOBEC Deaminases in Antiviral Defense and Carcinogenesis

Proteins of the AID/APOBEC family are capable of cytidine deamination in nucleic acids forming uracil. These enzymes are involved in mRNA editing, protection against viruses, the introduction of point mutations into DNA during somatic hypermutation, and antibody isotype switching. Since these deaminases, especially AID, are potent mutagens, their expression, activity, and specificity are regulated by several intracellular mechanisms. In this review, we discuss the mechanisms of impaired expression and activation of AID/APOBEC proteins in human tumors and their role in carcinogenesis and tumor progression. Also, the diagnostic and potential therapeutic value of increased expression of AID/APOBEC in different types of tumors is analyzed. We assume that in the case of solid tumors, increased expression of endogenous deaminases can serve as a marker of response to immunotherapy since multiple point mutations in host DNA could lead to amino acid substitutions in tumor proteins and thereby increase the frequency of neoepitopes.

APOBEC3A catalyzes mutation and drives carcinogenesis in vivo

The APOBEC3 family of antiviral DNA cytosine deaminases is implicated as the second largest source of mutation in cancer. This mutational process may be a causal driver or inconsequential passenger to the overall tumor phenotype. We show that human APOBEC3A expression in murine colon and liver tissues increases tumorigenesis. All other APOBEC3 family members, including APOBEC3B, fail to promote liver tumor formation. Tumor DNA sequences from APOBEC3A-expressing animals display hallmark APOBEC signature mutations in TCA/T motifs. Bioinformatic comparisons of the observed APOBEC3A mutation signature in murine tumors, previously reported APOBEC3A and APOBEC3B mutation signatures in yeast, and reanalyzed APOBEC mutation signatures in human tumor datasets support cause-and-effect relationships for APOBEC3A-catalyzed deamination and mutagenesis in driving multiple human cancers.

Helicobacter pylori infection is associated with favorable outcome in advanced gastric cancer patients treated with S-1 adjuvant chemotherapy

BACKGROUND AND OBJECTIVES

Limited information exists regarding beneficial effects of Helicobacter pylori. To examine the effect in advanced gastric cancer, we compared survival for patients treated with surgery-only or adjuvant chemotherapy on the basis of H. pylori infection status.

METHODS

A cohort of 491 patients who underwent R0 resection for locally advanced gastric cancer between 2000 and 2009 at 12 institutions in northern Japan was included. H. pylori infection status, was assessed from paraffin-embedded formalin-fixed samples. Overall survival (OS) and disease-free survival (DFS) in surgery-only (Surgery) and adjuvant chemotherapy (S-1) groups were analyzed. A propensity score matching was employed to correct for confounding factors by indication.

RESULTS

H. pylori infection was positive in 175 patients and negative in 316 patients. H. pylori-positive patients showed significantly better survival than H. pylori-negative patients in both OS (hazard ratio [HR] 0.593, 95% confidence interval [CI] 0.417-0.843; P = 0.003]) and DFS (HR 0.679, 95%CI 0.492-0.937; P = 0.018). Propensity score matching further confirmed that S-1 was virtually only effective when tumors were H. pylori-positive.

CONCLUSIONS

The favorable outcome of H. pylori-positive patients implies that the host immune system is modulated by H. pylori enhancing the chemotherapeutic efficacy.

An overview of new biomolecular pathways in pathogen-related cancers

Cancer molecular pathways are combinations of metabolic processes deregulated in neoplastic cells. Besides pathways specific to tissues from which cancers originate, common neoplastic traits are present among most tumors. Hanahan and Weinberg have described the most critical 'hallmarks' shared by many cancer types. In recent years, cancer stem cell specific properties and pathways have also been identified. Other altered pathways are peculiar of cancer type and cancer stage, even in different cancer stem cell types. In pathogen-related tumors, the alteration of inflammatory and immunologic response along with impairment of cell cycle control represents key molecular events of tumor progression. This article summarizes the recent discoveries of new altered pathways in cancer and their importance in cancer diagnosis and tailored therapies.

TGF-β triggers HBV cccDNA degradation through AID-dependent deamination

The covalently closed circular DNA (cccDNA) of hepatitis B virus (HBV) is a viral center molecule for HBV infection and persistence. However, the cellular restriction factors of HBV cccDNA are not well understood. Here, we show that TGF-β can induce nuclear viral cccDNA degradation and hypermutation via activation-induced cytidine deaminase (AID) deamination activity in hepatocytes. This suppression by TGF-β is abrogated when AID or the activity of uracil-DNA glycosylase (UNG) is absent, which indicates that AID deamination and the UNG-mediated excision of uracil act in concert to degrade viral cccDNA. Moreover, the HBV core protein promotes the interaction between AID and viral cccDNA. Overall, our results indicate a novel molecular mechanism that allows cytokine TGF-β to restrict viral nuclear cccDNA in innate immunity, thereby suggesting a novel method for potentially eliminating cccDNA.

Molecular Pathogenesis of Helicobacter pylori-Related Gastric Cancer

Helicobacter pylori infection plays a crucial role in gastric carcinogenesis. H pylori exerts oncogenic effects on gastric mucosa through complex interaction between bacterial virulence factors and host inflammatory responses. On the other hand, gastric cancer develops via stepwise accumulation of genetic and epigenetic alterations in H pylori-infected gastric mucosa. Recent comprehensive analyses of gastric cancer genomes indicate a multistep process of genetic alterations as well as possible molecular mechanisms of gastric carcinogenesis. Both genetic processes of gastric cancer development and molecular oncogenic pathways related to H pylori infection are important to completely understand the pathogenesis of H pylori-related gastric cancer.

Effect of Helicobacter pylori Infection on the Composition of Gastric Microbiota in the Development of Gastric Cancer

BACKGROUND

Gastric cancer is one of the most common cancer types worldwide. In China, gastric cancer has become one of the major threats for public health, ranking second on incidence and third on cause of cancer death. Despite the common risk factors that promote the development of gastric cancer, the huge quantity of microorganism colonies within the gastrointestinal tract, particularly Helicobacter pylori infection, demonstrates a correlation with chronic inflammation and gastric carcinogenesis, as epidemiological studies have determined that H. pylori infection confers approximately 75% of the attributable risk for gastric cancer.

SUMMARY

The current article draws an overview on the correlation between the microbiota, inflammation and gastric tumorigenesis. H. pylori infection has been identified as the main risk factor as it triggers epithelial barrier disruption, survival signaling as well as genetic/epigenetic modulation. Apart from H. pylori, the existence of a diverse and complex composition of microbiota in the stomach has been identified, which supports a role of microbiota in the development of gastric cancer. Moreover, metagenomics studies focused on the composition and function of the microbiota have associated microbiota with gastric metabolic diseases and even tumorigenesis. Apart from the gastric microbiota, inflammation is another identified contributor to cancer development as well.

KEY MESSAGE

Though H. pylori infection and the non-H. pylori microbiota play a role in gastric cancer, the properties of gastric microbiota and mechanisms by which they participate in the genesis of gastric cancer are still not clearly depicted. Moreover, it remains to be understood how the presence of microbiota along with H. pylori infection affects the progress from gastric disease to cancer.

PRACTICAL IMPLICATIONS

This article summarized a clue of the current studies on microbiota, H. pylori infection and the progression from gastric disease to cancer.

Helicobacter pylori CagA and gastric cancer: a paradigm for hit-and-run carcinogenesis

Helicobacter pylori is a gastric bacterial pathogen that is etiologically linked to human gastric cancer. The cytotoxin-associated gene A (CagA) protein of H. pylori, which is delivered into gastric epithelial cells via bacterial type IV secretion, is an oncoprotein that can induce malignant neoplasms in mammals. Upon delivery, CagA perturbs multiple host signaling pathways by acting as an extrinsic scaffold or hub protein. On one hand, signals aberrantly raised by CagA are integrated into a direct oncogenic insult, whereas on the other hand, they engender genetic instability. Despite its decisive role in the development of gastric cancer, CagA is not required for the maintenance of a neoplastic phenotype in established cancer cells. Therefore, CagA-conducted gastric carcinogenesis progresses through a hit-and-run mechanism in which pro-oncogenic actions of CagA are successively taken over by a series of genetic and/or epigenetic alterations compiled in cancer-predisposing cells during long-standing infection with cagA-positive H. pylori.

Enhanced expression of activation-induced cytidine deaminase in human gastric mucosa infected by Helicobacter pylori and its decrease following eradication

BACKGROUND

Recent studies have shown important roles for activation-induced cytidine deaminase (AID), an intrinsic genome mutator, in H. pylori-associated gastric cancer development. Here, we evaluated the relationship between H. pylori-induced gastritis and AID expression from human biopsy specimens.

METHODS

In 109 patients with dyspeptic symptoms who had undergone endoscopy and received biopsy of the antrum, angulus, and corpus, H. pylori infection was diagnosed by serologic test, (13)C urea breath test, and histological examination. Histological scores of H. pylori, neutrophils, mononuclear cells, atrophy, and intestinal metaplasia (IM) were assessed using the updated Sydney system (USS). Immunohistochemical AID expression of the biopsy specimens was scored.

RESULTS

Sixty of 109 (55.0 %) patients were positive for H. pylori and eradication was successful in 48 patients. AID expression in H. pylori-infected mucosa was significantly higher (p < 0.01) than in non-infected mucosa. AID expression was highest in the antrum and was significantly (p < 0.01) reduced toward the proximal portion of the stomach. For USS, multivariate analysis using linear regression revealed that mononuclear cell infiltration (p < 0.01) and IM (p < 0.05) correlated independently with AID expression. After eradication of H. pylori, AID expression was significantly decreased (p < 0.01), but was still higher than that in H. pylori-negative patients in all sites of the stomach.

CONCLUSIONS

AID expression is elevated in H. pylori-positive patients and is reduced following H. pylori eradication. Moreover, AID expression is highest in the antrum and correlated with severity of chronic inflammation and IM, suggesting an important role for AID in gastric cancer development through gastritis.

Analysis of activation-induced cytidine deaminase mRNA levels in patients with chronic lymphocytic leukemia with different cytogenetic status

Activation induced cytidine deaminase (AID) enzyme, which converts cytosine into uracil and is expressed only by activated B lymphocytes, plays a role in B cells in both the mechanisms of somatic hypermutation (SHM) and class switch recombination (CSR). There are studies showing that AID can cause numerous translocations in different lymphoproliferative diseases. Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of monoclonal B cells in bone marrow and peripheral blood. The predictability and clinical status of B-CLL are difficult to determine. About 30-50% of patients have chromosomal abnormalities. AID, which is thought to create fraction segments for translocations, might also cause deletions in DNA regions of 17p13, 11q22.3, 13q14 and 13q34 that are associated with prognostic implications in patients with CLL. In this study, the AID gene expression in patients with CLL with and without deletions was investigated. When compared to healthy subjects and patients without deletions, increased levels of AID expression in patients with deletions of 17p13, 11q22.3 or 13q14 were found, but not for the 13q34 region. Our results show that AID expression may be associated with deletions in patients with CLL.

A robust, sensitive assay for genomic uracil determination by LC/MS/MS reveals lower levels than previously reported

Considerable progress has been made in understanding the origins of genomic uracil and its role in genome stability and host defense; however, the main question concerning the basal level of uracil in DNA remains disputed. Results from assays designed to quantify genomic uracil vary by almost three orders of magnitude. To address the issues leading to this inconsistency, we explored possible shortcomings with existing methods and developed a sensitive LC/MS/MS-based method for the absolute quantification of genomic 2'-deoxyuridine (dUrd). To this end, DNA was enzymatically hydrolyzed to 2'-deoxyribonucleosides and dUrd was purified in a preparative HPLC step and analyzed by LC/MS/MS. The standard curve was linear over four orders of magnitude with a quantification limit of 5 fmol dUrd. Control samples demonstrated high inter-experimental accuracy (94.3%) and precision (CV 9.7%). An alternative method that employed UNG2 to excise uracil from DNA for LC/MS/MS analysis gave similar results, but the intra-assay variability was significantly greater. We quantified genomic dUrd in Ung(+/+) and Ung(-/-) mouse embryonic fibroblasts and human lymphoblastoid cell lines carrying UNG mutations. DNA-dUrd is 5-fold higher in Ung(-/-) than in Ung(+/+) fibroblasts and 11-fold higher in UNG2 dysfunctional than in UNG2 functional lymphoblastoid cells. We report approximately 400-600 dUrd per human or murine genome in repair-proficient cells, which is lower than results using other methods and suggests that genomic uracil levels may have previously been overestimated.

Why do we need IgM memory B cells?

Immunological memory is our reservoir of ready-to-use antibodies and memory B cells. Because of immunological memory a secondary infection will be very light or not occur at all. Antibodies and cells, generated in the germinal center in response to the first encounter with antigen, are highly specific, remain in the organism virtually forever and are mostly of IgG isotype. Long lived plasma cells homing to the bone marrow ensure the constant production of protective antibodies, whereas switched memory B cells proliferate and differentiate in response to secondary challenge. IgM memory B cells represent our first-line defense against infections. They are generated by a T-cell independent mechanism probably triggered by Toll-like receptor-9. They produce natural antibodies with anti-bacterial specificity and the spleen is indispensable for their maintenance. We will review the characteristics and functions of IgM memory B cells that explain their importance in the immediate protection from pathogens. IgM memory B cells, similar to mouse B-1a B cells, may be a remnant of a primitive immune system that developed in the spleen of cartilaginous fish and persisted throughout evolution notwithstanding the sophisticated tools of the adaptive immune system.

NF-κB and STAT3 signaling pathways collaboratively link inflammation to cancer

Although links between cancer and inflammation were firstly proposed in the nineteenth century, the molecular mechanism has not yet been clearly understood. Epidemiological studies have identified chronic infections and inflammation as major risk factors for various types of cancer. NF-κB transcription factors and the signaling pathways are central coordinators in innate and adaptive immune responses. STAT3 regulates the expression of a variety of genes in response to cellular stimuli, and thus plays a key role in cell growth and apoptosis. Recently, roles of NF-κB and STAT3 in colon, gastric and liver cancers have been extensively investigated. The activation and interaction between STAT3 and NF-κB play vital roles in control of the communication between cancer cells and inflammatory cells. NF-κB and STAT3 are two major factors controlling the ability of pre-neoplastic and malignant cells to resist apoptosis-based tumor-surveillance and regulating tumor angiogenesis and invasiveness. Understanding the molecular mechanisms of NF-κB and STAT3 cooperation in cancer will offer opportunities for the design of new chemo-preventive and chemotherapeutic approaches.

Regulation of Aicda expression and AID activity

Activation-induced cytidine deaminase (AID) is expressed in a B cell differentiation stage-specific fashion and is essential for immunoglobulin (Ig) gene class switch DNA recombination (CSR) and somatic hypermutation (SHM). CSR and SHM play a central role in the maturation of antibody and autoantibody responses. AID displays a mutagenic activity by catalyzing targeted deamination of deoxycytidine (dC) residues in DNA resulting in dU:dG mismatches, which are processed into point-mutations in SHM or double-strand breaks (DSBs) in CSR. Although AID specifically targets the Ig gene loci (IgH, Igκ and Igλ), it can also home into a wide array of non-Ig genes in B-and non-B-cell backgrounds. Aberrant expression of AID is associated with multiple diseases such as allergy, inflammation, autoimmunity and cancer. In autoimmune systemic lupus erythematosus, dysregulated AID expression underpins increased CSR, SHM and autoantibody production. As a potent mutator, AID is under stringent transcriptional, post-transcriptional and post-translational regulation. AID is also regulated in its targeting and enzymatic function. In resting naïve or memory B cells, AID transcripts and protein are undetectable. These, however, are readily and significantly up-regulated in B cells induced to undergo CSR and/or SHM. Transcription factors, such as HoxC4 and NF-κB, which are up-regulated in a B cell lineage-and/or differentiation stage-specific manner, regulate the induction of AID. HoxC4 induces AID expression by directly binding to the AID gene promoter through an evolutionarily conserved 5'-ATTT-3' motif. HoxC4 is induced by the same stimuli that induce AID and CSR. It is further up-regulated by estrogen through three estrogen responsive elements in its promoter region. The targeting of AID to switch (S) regions is mediated by 14-3-3 adaptor proteins, which specifically bind to 5'-AGCT-3' repeats that are exist at high frequency in S region cores. Like HoxC4, 14-3-3 adaptors are induced by the same stimuli that induce AID. These include "primary" inducing stimuli, that is, those that play a major role in inducing AID, i.e., engagement of CD40 by CD154, engagement of Toll-like receptors (TLRs) by microbial-associated molecular patterns (MAMPs) and cross-linking of the BCR, as synergized by "secondary" inducing stimuli, that is, those that synergize for AID induction and specify CSR to different isotypes, i.e., switch-directing cytokines IL-4, TGF-β or IFN-γ. In this review, we focus on the multi-levels regulation of AID expression and activity. We also discuss the dysregulation or misexpression of AID in autoimmunity and tumorigenesis.

Gastric adenocarcinoma has a unique microRNA signature not present in esophageal adenocarcinoma

BACKGROUND

MicroRNAs (miRNAs) play critical roles in tumor development and progression. The finding that a single miRNA can regulate hundreds of genes places miRNAs at critical hubs of signaling pathways. For the current study, the authors investigated the miRNA expression profile of gastric adenocarcinomas and compared it with esophageal adenocarcinomas to better identify a unique miRNA signature of gastric adenocarcinoma.

METHODS

miRNA expression profiles were obtained using 2 different proprietary microarray platforms on primary gastric adenocarcinoma tissue samples. The cross comparison of results identified 17 up-regulated miRNAs and 12 down-regulated miRNAs that overlapped in both platforms. Quantitative real-time polymerase chain reaction was performed for independent validation of a representative set of 8 miRNAs in gastric and esophageal adenocarcinomas compared with normal gastric mucosa or esophageal mucosa, respectively.

RESULTS

The deregulation of miR-146b-5p, miR-375, miR-148a, miR-31, and miR-451 was associated significantly with gastric adenocarcinomas. Conversely, deregulation of miR-21 (up-regulation) and miR-133b (down-regulation) was detectable in both gastric and esophageal adenocarcinomas. It was noteworthy that miR-200a was significantly down-regulated in gastric adenocarcinoma samples (P = .04) but was up-regulated in esophageal adenocarcinoma samples (P = .001). In addition, the expression level of miR-146b-5p displayed a strong correlation with the tumor stage of gastric cancer.

CONCLUSIONS

Gastric adenocarcinoma displayed a unique miRNA signature that distinguished it from esophageal adenocarcinoma. This specific signature may reflect differences in the etiology and/or molecular signaling in these 2 closely related cancers. The current findings suggest important miRNA candidates that can be investigated for their biological functions and for their possible diagnostic, prognostic, and therapeutic role in gastric adenocarcinoma.

DNA methylation and cancer

Cancer has been considered a genetic disease with a wide array of well-characterized gene mutations and chromosomal abnormalities. Of late, aberrant epigenetic modifications have been elucidated in cancer, and together with genetic alterations, they have been helpful in understanding the complex traits observed in neoplasia. "Cancer Epigenetics" therefore has contributed substantially towards understanding the complexity and diversity of various cancers. However, the positioning of epigenetic events during cancer progression is still not clear, though there are some reports implicating aberrant epigenetic modifications in very early stages of cancer. Amongst the most studied aberrant epigenetic modifications are the DNA methylation differences at the promoter regions of genes affecting their expression. Hypomethylation mediated increased expression of oncogenes and hypermethylation mediated silencing of tumor suppressor genes are well known examples. This chapter also explores the correlation of DNA methylation and demethylation enzymes with cancer.

Whole-genome reconstruction and mutational signatures in gastric cancer

Background

Gastric cancer is the second highest cause of global cancer mortality. To explore the complete repertoire of somatic alterations in gastric cancer, we combined massively parallel short read and DNA paired-end tag sequencing to present the first whole-genome analysis of two gastric adenocarcinomas, one with chromosomal instability and the other with microsatellite instability.

Results

Integrative analysis and de novo assemblies revealed the architecture of a wild-type KRAS amplification, a common driver event in gastric cancer. We discovered three distinct mutational signatures in gastric cancer - against a genome-wide backdrop of oxidative and microsatellite instability-related mutational signatures, we identified the first exome-specific mutational signature. Further characterization of the impact of these signatures by combining sequencing data from 40 complete gastric cancer exomes and targeted screening of an additional 94 independent gastric tumors uncovered ACVR2A, RPL22 and LMAN1 as recurrently mutated genes in microsatellite instability-positive gastric cancer and PAPPA as a recurrently mutated gene in TP53 wild-type gastric cancer.

Conclusions

These results highlight how whole-genome cancer sequencing can uncover information relevant to tissue-specific carcinogenesis that would otherwise be missed from exome-sequencing data.

Fhit, E-cadherin, p53, and activation-induced cytidine deaminase expression in endoscopically resected early stage esophageal squamous neoplasia

BACKGROUND AND AIM

Abnormal expression of Fragile Histidine Triad (Fhit), E-cadherin and p53 is observed in esophageal squamous cell carcinoma. It has recently been reported that aberrant expression of activation-induced cytidine deaminase (AID) in gastric epithelium leads to the accumulation of nucleotide alterations in the p53 gene. However, little is known about the association between these molecular events and the clinicopathological characteristics of early stage esophageal squamous neoplasia, especially in endoscopically resected tumors.

METHODS

Esophageal squamous neoplasias (n = 49) comprising nine cases of low-grade intraepithelial neoplasia (LGIN), 22 of high-grade intraepithelial neoplasia/carcinoma in situ (HGIN/CIS) and 18 of invasive cancers, were endoscopically resected. Their expression of the tumor-related proteins: Fhit, E-cadherin, p53 and AID was assessed using immunohistochemical methods, and the relationship between protein expression and clinicopathological data was examined.

RESULTS

Reduced or absent Fhit and E-cadherin expression was detected in 22% and 0% of LGIN cases, 73% and 14% of HGIN/CIS cases, and 94% and 61% of invasive cancer cases, respectively, showing progressive increases during neoplastic progression (Fhit: P < 0.01, E-cadherin: P < 0.01). Although p53 and AID were overexpressed in these samples, no change in their expression occurred during neoplastic progression. Moreover, p53 expression was not significantly associated with AID expression.

CONCLUSIONS

These results indicate that a decrease in Fhit and E-cadherin expression could be related to the development and progression of esophageal squamous neoplasia, and that the expression of p53 was independent of aberrant AID expression in the early stage of esophageal carcinogenesis.

Bile acid-induced expression of activation-induced cytidine deaminase during the development of Barrett's oesophageal adenocarcinoma

Activation-induced cytidine deaminase (AID) induces somatic mutations in various host genes of non-lymphoid tissues, thereby contributing to carcinogenesis. We recently demonstrated that Helicobacter pylori infection and/or proinflammatory cytokine stimulation triggers aberrant AID expression in gastric epithelial cells, causing mutations in the tumour-suppressor TP53 gene. The findings of the present study provide evidence of ectopic AID expression in Barrett's oesophagus and Barrett's oesophageal adenocarcinoma, a cancer that develops under chronic inflammatory conditions. Immunoreactivity for endogenous AID was observed in 24 of 28 (85.7%) specimens of the columnar cell-lined Barrett's oesophagus and in 20 of 22 (90.9%) of Barrett's adenocarcinoma, whereas weak or no AID protein expression was detectable in normal squamous epithelial cells of the oesophagus. We validated these results by analysing tissue specimens from another cohort comprising 16 cases with Barrett's oesophagus and four cases with Barrett's adenocarcinoma. In vitro treatment of human non-neoplastic oesophageal squamous-derived cells with sodium salt deoxycholic acid induced ectopic AID expression via the nuclear factor-kappaB activation pathway. These findings suggest that aberrant AID expression occurs in a substantial proportion of Barrett's epithelium, at least in part due to bile acid stimulation. Considering the genotoxic activity of AID, our current findings suggest that aberrant AID expression might enhance the susceptibility to genetic alterations in Barrett's columnar-lined epithelial cells, leading to cancer development.

AID and partners: for better and (not) for worse

Post-rearrangement diversification of the antibody repertoire relies on a DNA editing factor, the cytidine deaminase AID. How B lymphocytes avoid generalized mutagenesis while expressing high levels of AID remained a long-standing question. Genome-wide studies of AID targeting combined to the discovery of several co-factors controlling its recruitment and its local activity shed new light on this enigma.

Role of activation-induced cytidine deaminase in inflammation-associated cancer development

Human cancer is a genetic disease resulting from the stepwise accumulation of genetic alterations in various tumor-related genes. Normal mutation rates, however, cannot account for the abundant genetic changes accumulated in tumor cells, suggesting that certain molecular mechanisms underlie such a large number of genetic alterations. Activation-induced cytidine deaminase (AID), a nucleotide-editing enzyme that triggers DNA alterations and double-strand DNA breaks in the immunoglobulin gene, has been identified in activated B lymphocytes. Recent studies revealed that AID-mediated genotoxic effects target not only immunoglobulin genes but also a variety of other genes in both B lymphocytes and non-lymphoid cells. Consistent with the finding that several transcription factors including nuclear factor-κB (NF-κB) mediate AID expression in B cells, proinflammatory cytokine stimulation of several types of gastrointestinal epithelial cells, such as gastric, colonic, hepatic, and biliary epithelium, induces aberrant AID expression through the NF-κB signaling pathway. In vivo studies revealed that constitutive AID expression promotes the tumorigenic pathway by enhancing the susceptibility to mutagenesis in a variety of epithelial organs. The activity of AID as a genome mutator provides a new avenue for studies aimed at understanding mutagenesis mechanisms during carcinogenesis.