Aberrant Activation-induced Cytidine Deaminase Research Articles

Aberrant Activation-Induced Cytidine Deaminase Gene Expression Links BCR/ABL1-Negative Classical Myeloproliferative Neoplasms

Aberrant Activation-Induced Cytidine Deaminase Gene Expression Links BCR/ABL1-Negative Classical Myeloproliferative Neoplasms

Unravelling the Sequential Interplay of Mutational Mechanisms during Clonal Evolution in Relapsed Pediatric Acute Lymphoblastic Leukemia.

Pediatric acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy and is characterized by clonal heterogeneity. Genomic mutations can increase proliferative potential of leukemic cells and cause treatment resistance. However, mechanisms driving mutagenesis and clonal diversification in ALL are not fully understood. In this proof of principle study, we performed whole genome sequencing of two cases with multiple relapses in order to investigate whether groups of mutations separated in time show distinct mutational signatures. Based on mutation allele frequencies at diagnosis and subsequent relapses, we clustered mutations into groups and performed cluster-specific mutational profile analysis and de novo signature extraction. In patient 1, who experienced two relapses, the analysis unraveled a continuous interplay of aberrant activation induced cytidine deaminase (AID)/apolipoprotein B editing complex (APOBEC) activity. The associated signatures SBS2 and SBS13 were present already at diagnosis, and although emerging mutations were lost in later relapses, the process remained active throughout disease evolution. Patient 2 had three relapses. We identified episodic mutational processes at diagnosis and first relapse leading to mutations resembling ultraviolet light-driven DNA damage, and thiopurine-associated damage at first relapse. In conclusion, our data shows that investigation of mutational processes in clusters separated in time may aid in understanding the mutational mechanisms and discovery of underlying causes.

Exposure to 1,2-Dichloropropane Upregulates the Expression of Activation-Induced Cytidine Deaminase (AID) in Human Cholangiocytes Co-Cultured With Macrophages.

1,2-dichloropropane (1,2-DCP) was reclassified recently by IARC as a Group 1 carcinogen based on epidemiological studies on an outbreak of cholangiocarcinoma in offset-printing workers exposed to 1,2-DCP in Japan. However, the underlying mechanism of 1,2-DCP-induced cholangiocarcinoma remains obscure. A previous whole-genome mutation analysis of cholangiocarcinoma of 4 cases exposed to 1,2-DCP suggested the involvement of activation-induced cytidine deaminase (AID), based on specific signatures of mutation patterns. The objective of the present study is to determine whether exposure to 1,2-DCP induces expression of AID in human cholangiocytes. Human MMNK-1 cholangiocytes, differentiated THP-1 macrophages, and co-cultures of MMNK-1/THP-1 cells were exposed to 1,2-DCP at different concentrations and time intervals. The mRNA expression levels of AID and related genes were quantified by real-time PCR. Protein expression was measured by immunostaining. Alkaline Comet assay was performed to examine DNA damage. The results showed that 1,2-DCP alone did not change AID expression in MMNK-1 cholangiocytes. 1,2-DCP significantly increased pro-inflammatory cytokine TNF-α expression in THP-1 macrophages. TNF-α treatment upregulated expression of AID, NF-κB, and IκB in MMNK-1 cholangiocytes. SN50, a NF-κB inhibitor, significantly downregulated TNF-α-induced AID expression, suggesting the involvement of NF-κB pathway in TNF-α-induced AID expression. Exposure to 1,2-DCP significantly increased AID expression in MMNK-1 cholangiocytes co-cultured with THP-1 macrophages. Comet assay showed that 1,2-DCP-induced DNA damage in MMNK-1 cholangiocytes, as indicated by increased tail DNA% and tail moment, was enhanced when co-cultured with macrophages. The results suggest that inflammatory response of macrophages and consequent aberrant AID expression or DNA damage in the cholangiocytes underlie the mechanism of 1,2-DCP-induced cholangiocarcinoma in humans.

Whole-genome sequencing of chronic lymphocytic leukaemia reveals distinct differences in the mutational landscape between IgHVmut and IgHVunmut subgroups

Chronic lymphocytic leukaemia (CLL) consists of two biologically and clinically distinct subtypes defined by the abundance of somatic hypermutation (SHM) affecting the Ig variable heavy-chain locus (IgHV). The molecular mechanisms underlying these subtypes are incompletely understood. Here, we present a comprehensive whole-genome sequencing analysis of somatically acquired genetic events from 46 CLL patients, including a systematic comparison of coding and non-coding single-nucleotide variants, copy number variants and structural variants, regions of kataegis and mutation signatures between IgHVmut and IgHVunmut subtypes. We demonstrate that one-quarter of non-coding mutations in regions of kataegis outside the Ig loci are located in genes relevant to CLL. We show that non-coding mutations in ATM may negatively impact on ATM expression and find non-coding and regulatory region mutations in TCL1A, and in IgHVunmut CLL in IKZF3, SAMHD1,PAX5 and BIRC3. Finally, we show that IgHVunmut CLL is dominated by coding mutations in driver genes and an aging signature, whereas IgHVmut CLL has a high incidence of promoter and enhancer mutations caused by aberrant activation-induced cytidine deaminase activity. Taken together, our data support the hypothesis that differences in clinical outcome and biological characteristics between the two subgroups might reflect differences in mutation distribution, incidence and distinct underlying mutagenic mechanisms.

Frequent aberrant p53 and Fhit expression in endoscopically resected superficial hypopharyngeal cancer and esophageal cancer.

In the last decade, the incidence rate of detection rate of superficial head, neck and esophageal squamous cell carcinomas has increased with the development of endoscopic imaging techniques. These cancers are thought to arise independently subsequent to tissue exposure to a common carcinogen e.g. alcohol or tobacco. This phenomenon has been termed field cancerization. To determine the molecular background of the development of hypopharyngeal squamous cell carcinomas (HPSCCs) and double esophageal squamous cell carcinomas (DESCCs), the present study immunohistochemically assessed tumor-related protein expression [p53, Fhit (fragile histidine triad), E-cadherin and activation-induced cytidine deaminase (AID)], and subsequently determined the correlation between protein expression and clinicopathological data. Tumor specimens of 9 HPSCCs and 9 DESCCs were endoscopically obtained from 8 patients with HPSCC. The 9 DESCCs, including 5 synchronous and 4 metachronous lesions, were all obtained from four patients with HPSCC. The overexpression of p53 and loss of Fhit expression was immunohistochemically detected in 8 (88.9%) and 8 (88.9%) of the 9 HPSCCs and in 8 (88.9%) and 8 (88.9%) of the 9 DESCCs, respectively, which demonstrated the high frequency of such expression. Additionally, 7 out of 9 HPSCCs, and 7 out of 9 DESCCs demonstrated aberrant expression of p53 and Fhit. The rate of aberrant AID and E-cadherin expression was 67 and 44% in HPSCCs and 44 and 44% in DESCC, respectively. These results suggested that aberrant p53 and Fhit expression was involved in the development of HPSCC and their DESCC, and that their expression may be used for the prediction of DESCC development in patients with HPSCC, thereby acting as a biomarker of field cancerization.

Higher Expression of Activation-induced Cytidine Deaminase Is Significantly Associated with Merkel Cell Polyomavirus-negative Merkel Cell Carcinomas

Merkel cell carcinomas (MCCs), clinically aggressive neuroendocrine skin cancers, are divided into Merkel cell polyomavirus (MCPyV)-positive and -negative tumors, which show different clinicopathological features and may develop through different mechanisms of carcinogenesis. Aberrant expression of activation-induced cytidine deaminase (AID) as a genomic modulator was demonstrated through pathogen-related NF-κB signal in Helicobacter pylori-associated gastric cancer, adult T cell leukemia/lymphoma (HTLV-1), hepatoma (HCV), and Burkitt lymphoma (EBV). To elucidate the relation of aberrant AID expression in MCPyV-positive and -negative MCCs, we evaluated immunohistochemical expressions of AID and AID-regulating factors between 24 MCPyV-positive and 17 MCPyV-negative MCCs. AID expression was significantly higher in MCPyV-negative MCCs than MCPyV-positive ones (P = 0.026), although expression of NF-κB p65 (phospho S536) (AID-enhancer) was significantly higher in MCPyV-positive MCCs than MCPyV-negative ones (P = 0.034). Expressions of PAX5 and c-Myb were not significantly different between these subgroups. Expressions of AID and AID-regulating factors were not correlated to prognosis of MCC patients. Our findings suggest that although pathogen-induced AID expression through upregulation of NF-κB may be relevant to carcinogenesis of MCPyV-positive MCCs, the significantly higher aberrant AID expression in MCPyV-negative MCCs is consistent with the fact that MCPyV-negative MCCs have an extremely higher mutation burden than MCPyV-positive ones.

Aberrant activation-induced cytidine deaminase expression in Philadelphia chromosome-positive B-cell acute lymphoblastic leukemia

Activation-induced cytidine deaminase (AID) is expressed in germinal center B cells and plays a critical role in somatic hypermutation and class-switch recombination of immunoglobulin genes. Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) carries a poor prognosis and is specifically treated with tyrosine kinase inhibitors. Interestingly, AID has been shown to be aberrantly expressed and functional in Ph+ ALL and is thought to contribute to genetic instability. We hypothesized that AID might be detectable in routinely processed bone marrow biopsies by immunohistochemistry (IHC) and assist in identifying Ph+ ALL. We found that AID was expressed in 26 (70%) of 37 cases of Ph+ ALL but only 1 (2.9%) of 38 cases of Ph- ALL cases. There was a significant difference in AID expression between these 2 ALL groups (P < .001, Fisher exact test). The expression of AID was confirmed by RT-PCR (reverse-transcriptase polymerase chain reaction) and correlated with IHC scoring. AID protein is expressed in a large proportion of Ph+ ALL cases at levels detectable by IHC in clinical samples and might be useful to rapidly identify cases likely to have a BCR/ABL1 fusion.

AID, p53 and MLH1 expression in early gastric neoplasms and the correlation with the background mucosa.

A number of tumor-associated genes have been associated with gastric cancer development. The present study evaluated differences in tumor-associated protein expression and phenotype among early gastric neoplasms, and correlated these data with those of the background mucosa. The expression of activation-induced cytidine deaminase (AID), p53 and MLH1 in 151 early gastric neoplasms [22 gastric adenomas, 92 intramucosal carcinomas (MCs), and 37 submucosal carcinomas (SMCs)] was examined immunohistochemically and compared with that of the corresponding background mucosal condition. The cellular phenotypes of the neoplasms and the corresponding background intestinal metaplasia were also determined. Aberrant AID, p53 and MLH1 expression was detected in 36.4, 0 and 0% of the adenomas, in 35.9, 32.6 and 16.3% of the MCs, and in 56.8, 62.2 and 21.6% of the SMCs, respectively. The frequency of aberrant AID and p53 expression in the SMCs was significantly increased compared with that in the MCs (AID, P<0.05; p53, P<0.01). Aberrant AID expression was significantly associated with p53 overexpression in the SMCs (P<0.01), but not in the adenomas or MCs. In addition, AID expression was associated with the severity of mononuclear cell activity in the non-cancerous mucosa adjacent to the tumor (P<0.05), particularly in the SMC cases. The percentage of MCs (34.8%) and SMCs (24.3%) that were of the gastric phenotype was higher compared with the percentage of adenomas (18.2%). These results indicated that p53 and MLH1 expression and a gastric phenotype may be important for carcinogenesis, and that chronic inflammation and AID and p53 expression are associated with submucosal progression.

The involvement of Streptococcus anginosus infection and the aberrant activation-induced cytidine deaminase (AID) expression in human oral squamous cell carcinoma

The involvement of Streptococcus anginosus infection and the aberrant activation-induced cytidine deaminase (AID) expression in human oral squamous cell carcinoma

Overexpression of Activation-Induced Cytidine Deaminase in MTX- and Age-Related Epstein-Barr Virus-Associated B-Cell Lymphoproliferative Disorders of the Head and Neck.

Recent research has shown that activation-induced cytidine deaminase (AID) triggers somatic hypermutation and recombination, in turn contributing to lymphomagenesis. Such aberrant AID expression is seen in B-cell leukemia/lymphomas, including Burkitt lymphoma which is associated with c-myc translocation. Moreover, Epstein-Barr virus (EBV) latent membrane protein-1 (LMP-1) increases genomic instability through early growth transcription response-1 (Egr-1) mediated upregulation of AID in B-cell lymphoma. However, few clinicopathological studies have focused on AID expression in lymphoproliferative disorders (LPDs). Therefore, we conducted an immunohistochemical study to investigate the relationship between AID and LMP-1 expression in LPDs (MTX-/Age-related EBV-associated), including diffuse large B-cell lymphomas (DLBCLs). More intense AID expression was detected in LPDs (89.5%) than in DLBCLs (20.0%), and the expression of LMP-1 and EBER was more intense in LPDs (68.4% and 94.7%) than in DLBCLs (10.0% and 20.0%). Furthermore, stronger Egr-1 expression was found in MTX/Age-EBV-LPDs (83.3%) than in DLBCLs (30.0%). AID expression was significantly constitutively overexpressed in LPDs as compared with DLBCLs. These results suggest that increased AID expression in LPDs may be one of the processes involved in lymphomagenesis, thereby further increasing the survival of genetically destabilized B-cells. AID expression may be a useful indicator for differentiation between LPDs and DLBCLs.

Abstract 5350: Aberrant activation-induced cytidine deaminase (AID) expression is induced in the process of hepatitis C virus-associated hepatocarcinogenesis

Abstract Activation-induced cytidine deaminase (AID) is a DNA mutator enzyme, which is encoded by Aicda gene. Under physiological condition, AID is essential for somatic hypermutation of immunogloburin genes in activated B lymphocytes and involved in immune diversity. Previous in vitro studies demonstrated that in cultured adult hepatocytes, both the response to chronic inflammation and hepatitis C virus (HCV) infection itself triggers aberrant AID upregulation, and due to the mutagenic activity of AID, nucleotide alterations gradually accumulate in tumor-related genes. In this study, we aimed to obtain a direct evidence of AID expression induced by HCV infection in vivo using human and mice subjects. Immunostaining of human clinical specimen revealed endogenous AID expression was detectable in both the hepatocellular carcinoma (HCC) and the non-tumorous inflamed liver tissues in patients with chronic HCV infection while no AID expression was detected in normal liver tissues without HCV infection. In mice, as endogenous AID expression level of liver is not sufficient to detect by immustaining, we utilized the transgenic mouse (Aicda-cre transgenic mouse), which was generated by inserting the coding sequence of Cre recombinase into the locus of the Aicda gene, crossing with a genetically-marked reporter mouse (Rosa-tdRFP mouse). In this Aicda-cre/Rosa-tdRFP mouse model, AID-expressing cells can be detected as RFP-positive. We injected HCV core antigen-inserted plasmid to the liver of Aicda-cre/Rosa-tdRFP mice by “hydrodynamic tail vein injection” procedure. 14days after injection, RFP-positive hepatocytes were detected in the HCV antibody-labelled liver cells whereas no RFP-positive cells were found in control mice with physiological saline injection, indicating HCV core antigen induced aberrant AID expression in hepatocytes. Next, to examine the effect of constitutive AID expression in hepatic-lineage cells, we established a transplantation model of hepatic progenitor cells derived from AID Tg mice. We enriched hepatic progenitor cells from the E13.5 fetal liver of AID Tg mice and transplanted those cells into recipient mice. HCC developed in 7 of 11 (63.6%) recipient mice receiving enriched hepatic progenitor cells from AID Tg mice. On the other hand, no tumor was found in recipient mice transplanted with hepatic progenitor cells derived from wild-type mice (control). In addition, whole exome sequencing of tumor cells clarified the landscape of the accumulated genetic alterations during tumorigenesis and detected a large number of somatic mutations in each tumor tissue originating from the transplanted hepatic progenitor cells of AID Tg mice. These results suggested aberrant AID production induced by HCV infection could contribute to hepatocarcinogenesis via the accumulation of genetic alterations by its mutagenic activity. Citation Format: Soo Ki Kim, Hiroyuki Marusawa, Tsutomu Chiba. Aberrant activation-induced cytidine deaminase (AID) expression is induced in the process of hepatitis C virus-associated hepatocarcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5350. doi:10.1158/1538-7445.AM2014-5350

Activation-induced cytidine deaminase auto-activates and triggers aberrant gene expression

DNA methylation is a well-characterized epigenetic landmark involved in transcriptional regulation; however, mechanisms underlying its regulation remain poorly characterized. Recent studies demonstrate that activation-induced cytidine deaminase (AID) is involved in active DNA demethylation. AID is aberrantly expressed in inflammation-associated cancers and generates point mutations; however, cellular disorders attributed to its demethylation function are largely unexplored. Here we demonstrate that ectopic AID expression perturbs tumor-related gene expression. AID (with Gadd45) activated a methylated paired box gene 5 (Pax5) reporter construct, and induced expression and association of endogenous Pax5 with the AID promoter, suggesting that aberrant AID expression triggers an auto-activation circuit to consolidate self-expression.

Role of Activation-Induced Cytidine Deaminase in the Development of Oral Squamous Cell Carcinoma

PurposeIn humans, activation-induced cytidine deaminase (AID) expression results due to inflammation and this deaminase activity is also involved in carcinogenesis. The aim of this study is to investigate the correlation between AID expression and the clinical classification of oral cancer tissues.Experimental DesignThe current study investigated the correlation between AID expression and the clinical classification of oral cancer tissues from 27 patients who underwent surgical resection using immunohistochemistry. Specific AID expression and its induction by cytokine stimulation were investigated in cultured HSC oral cancer cell lines by reverse transcriptase PCR.ResultsAID expression was detected in 10 of 27 specimens (37.0%). AID expression was more frequently detected in early-stage cancer, especially in early stage T, than in late-stage cancer (T1/T2 vs. T3/4; P = 0.0493, N0 vs. N1/2/3; P = 0.0793). HSC-2, a nonmetastatic oral cancer cell line, abundantly expressed endogenous AID, whereas no such expression was observed in HSC-3, a metastatic oral cancer cell line. Moreover, AID expression was substantially induced in HSC-2 cells by stimulation of an inflammation-related cytokine, TNF-α.ConclusionsAberrant AID expression in the oral epithelium would contribute to the initiation of oral squamous cell carcinoma. Avoiding persistent AID inducible condition such as frequent cleaning of oral cavity would play an important role for the prevention of developing oral cancer.

Attenuating homologous recombination stimulates an AID-induced antileukemic effect

Activation-induced cytidine deaminase (AID) is critical in normal B cells to initiate somatic hypermutation and immunoglobulin class switch recombination. Accumulating evidence suggests that AID is also prooncogenic, inducing cancer-promoting mutations or chromosome rearrangements. In this context, we find that AID is expressed in >40% of primary human chronic lymphocytic leukemia (CLL) cases, consistent with other reports. Using a combination of human B lymphoid leukemia cells and mouse models, we now show that AID expression can be harnessed for antileukemic effect, after inhibition of the RAD51 homologous recombination (HR) factor with 4,4'-diisothiocyanatostilbene-2-2'-disulfonic acid (DIDS). As a proof of principle, we show that DIDS treatment inhibits repair of AID-initiated DNA breaks, induces apoptosis, and promotes cytotoxicity preferentially in AID-expressing human CLL. This reveals a novel antineoplastic role of AID that can be triggered by inhibition of HR, suggesting a potential new paradigm to treat AID-expressing tumors. Given the growing list of tumor types with aberrant AID expression, this novel therapeutic approach has potential to impact a significant patient population.

Activation-induced cytidine deaminase (AID): single activity – pleiotropic effect

Activation-induced cytidine deaminase (AID) plays an essential role in the generation of a highly competent reper- toire of antibodies by participating in class switch recombination (CSR) and somatic hypermutation (SHM). After B cell stimulation by antigens, AID initiates SHM and CSR by deamination of cytidine to uridine in the variable and constant regions of Ig genes. An adverse effect of AID's ability to directly modify genome sequences is its mutagenic potential. AID has been shown to occasionally target non-Ig genes and its abnormal expression is strongly associated with tumorigenesis. Aberrant AID expression can also be triggered by some oncogenic patho- gens, such as Helicobacter pylori and several viruses. The latest reports show that also under physiological con- ditions AID might act beyond the immune system. Data exist suggesting that AID can play a role in the process of active genome demethylation - the heart of epigenetic gene activation and reprogramming. Moreover, it has been shown that abnormal genome demethylation mediated by AID might be associated with human colon can- cers. The potential role of AID in the active demethylation process is still controversial, but the hypothesis that aberrant AID expression may cause cancerogenesis by changing genome methylation patterns appears highly attractive. As a unique human enzyme able to induce both genetic and epigenetic alterations under physiological and pathological conditions, AID could be a promising and versatile drug target. In this review we present the current state of knowledge on this topic and the controversies surrounding the pleiotropic effect of AID function.

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

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. 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. 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. 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.

Activation-induced cytidine deaminase (AID) linking immunity, chronic inflammation, and cancer

Activation-induced cytidine deaminase (AID) is critically involved in class switch recombination and somatic hypermutation of Ig loci resulting in diversification of antibodies repertoire and production of high-affinity antibodies and as such represents a physiological tool to introduce DNA alterations. These processes take place within germinal centers of secondary lymphoid organs. Under physiological conditions, AID is expressed predominantly in activated B lymphocytes. Because of the mutagenic and recombinogenic potential of AID, its expression and activity is tightly regulated on different levels to minimize the risk of unwanted DNA damage. However, chronic inflammation and, probably, combination of other not-yet-identified factors are able to create a microenvironment sufficient for triggering an aberrant AID expression in B cells and, importantly, in non-B-cell background. Under these circumstances, AID may target also non-Ig genes, including cancer-related genes as oncogenes, tumor suppressor genes, and genomic stability genes, and modulate both genetic and epigenetic information. Despite ongoing progress, the complete understanding of fundamental aspects is still lacking as (1) what are the crucial factors triggering an aberrant AID expression/activity including the impact of Th2-driven inflammation and (2) to what extent may aberrant AID in human non-B cells lead to abnormal cell state associated with an increased rate of genomic alterations as point mutations, small insertions or deletions, and/or recurrent chromosomal translocations during solid tumor development and progression.

Expression of AID, P53, and Mlh1 proteins in endoscopically resected differentiated-type early gastric cancer.

To analyze the expression of the tumor-related proteins in differentiated-type early gastric carcinoma (DEGC) samples. Tumor specimens were obtained from 102 patients (75 males and 27 females) who had received an endoscopic tumor resection at Tottori University Hospital between 2007 and 2009. Ninety-one cancer samples corresponded to noninvasive or intramucosal carcinoma according to the Vienna classification system, and 11 samples were submucosal invasive carcinomas. All of the EGCs were histologically differentiated carcinomas. All patients were classified as having Helicobacter pylori (H. pylori) infections by endoscopic atrophic changes or by testing seropositive for H. pylori IgG. All of the samples were histopathologically classified as either tubular or papillary adenocarcinoma according to their structure. The immunohistochemical staining was performed in a blinded manner with respect to the clinical information. Two independent observers evaluated protein expression. All data were statistically analyzed then. The rates of aberrant activation-induced cytidine deaminase (AID) expression and P53 overexpression were both 34.3% in DEGCs. The expression of Mlh1 was lost in 18.6% of DEGCs. Aberrant AID expression was not significantly associated with P53 overexpression in DEGCs. However, AID expression was associated with the severity of mononuclear cell activity in the non-cancerous mucosa adjacent to the tumor (P = 0.064). The rate of P53 expression was significantly greater in flat or depressed tumors than in elevated tumors. The frequency of Mlh1 loss was significantly increased in distal tumors, elevated gross-type tumors, papillary histological-type tumors, and tumors with a severe degree of endoscopic atrophic gastritis (P < 0.05). Aberrant AID expression, P53 overexpression, and the loss of Mlh1 were all associated with clinicopathological features and gastric mucosal alterations in DEGCs. The aberrant expression of AID protein may partly contribute to the induction of nuclear P53 expression.

Molecular mechanism of colitis-associated colorectal carcinogenesis

The development of colorectal cancer caused by chronic inflammatory bowel disease (IBD) is the representative example of inflammation-associated carcinogenesis. The mechanism underlying the development of colorectal cancers through chronic inflammation, however, is not known. Activation-induced cytidine deaminase (AID) was originally identified as an inducer of somatic hypermutation in the immunoglobulin gene. We recently demonstrated that the mutagenic activity of AID expression links colonic inflammation to the development of colitis associated colorectal cancers. Immunohistochemistry revealed enhanced expression of endogenous AID protein not only in the inflamed colonic mucosa of ulcerative colitis patients, but also in tumor lesions of colitis-associated colorectal cancers. Pro-inflammatory cytokine TNF-α and/or T helper cell-2-driven cytokines IL-4 and IL-13 induced strong aberrant expression of AID in human colonic epithelial cells. In vivo, aberrant AID expression in the inflamed colon is associated with the accumulation of somatic mutations in tumor suppressor Trp53 gene, and AID deficiency resulted in a reduced incidence of colitis-associated colon cancers. These findings suggested that pro-inflammatory cytokine-mediated aberrant expression of AID in colonic epithelial cells plays a role as a genotoxic factor that enhances genetic instability during chronic colonic inflammation, leading to colitis-associated colorectal cancer development.

Activation-induced cytidine deaminase mRNA expression in oral squamous cell carcinoma-derived cell lines is upregulated by inflammatory cytokines

Activation-induced cytidine deaminase (AID) induces cytosine deamination to generate somatic hypermutation and class switch recombnation in immunoglobulin genes. AID expression is upregulated by inflammatory cytokines such as interferon-γ and tumor necrosis factor (TNF)-α, which in turn induce p53 mutations in inflammatory or cancer cells. In this study, the effects of growth factors, cytokines or sodium butyrate on AID mRNA expression were examined in human OSCC-derived cells using real-time RT-PCR. Expression of AID mRNA was detected in OSCC cells and the expression was increased by EGF, TNF-a, or sodium butyrate. These results suggest that aberrant AID expression may play an important role in the dysplasia-carcinoma sequence in the oral cavity.