Combined loss of expression of O6-methylguanine-DNA methyltransferase and hMLH1 accelerates progression of hepatocellular carcinoma

Long non-coding RNA X-inactive specific transcript suppresses the progression of hepatocellular carcinoma through microRNA-221-3p-targeted regulation of O6-methylguanine-DNA methyltransferase

MicroRNA-221-3p (miR-221-3p) is an important regulator involved in the progression and prognosis of various cancers. In this study, we aimed to investigate the diagnostic and prognostic value of miR-221-3p expression along with long non-coding RNA X–inactive specific transcript (XIST), which was identified as its upstream regulator in hepatocellular carcinoma (HCC) by bioinformatics analysis, and further validated by RNA immunoprecipitation (RIP) and dual-luciferase reporter assays. Their expression was measured in tumor tissues and corresponding non-tumor tissues by quantitative real-time PCR (qRT-PCR), which revealed that XIST was weakly expressed in HCC cells and tumors, while miR-221-3p was overexpressed. Complete knockdown of XIST enhanced HCC cell proliferation and migration and inhibited apoptosis, as observed by MTT, transwell, and flow cytometry experiments, respectively. Animal studies validated that XIST knockdown induces tumor growth in vivo. In contrast, upregulation of XIST in HCC cells suppressed their proliferation and migration, stimulated apoptosis, and retarded the growth rate of tumors in vivo. These effects were partially reversed by upregulating miR-221-3p expression. Furthermore, we demonstrated that O⁶-methylguanine-DNA methyltransferase (MGMT) is a downstream target of miR-221-3p. It was weakly expressed in HCC cells and tumors and showed a negative correlation with miR-221-3p. Forced MGMT expression repressed proliferation and migration and enhanced apoptosis in HCC cells. Nevertheless, these anti-tumor effects induced by MGMT overexpression could be abolished by miR-221-3p upregulation. Collectively, our findings reveal that XIST blocks the development of HCC through miR-221-3p-targeted regulation of MGMT. This reveals a new mechanism involved in the development of HCC.

MTHFR Knockdown Assists Cell Defense against Folate Depletion Induced Chromosome Segregation and Uracil Misincorporation in DNA

Folate depletion causes chromosomal instability by increasing DNA strand breakage, uracil misincorporation, and defective repair. Folate mediated one-carbon metabolism has been suggested to play a key role in the carcinogenesis and progression of hepatocellular carcinoma (HCC) through influencing DNA integrity. Methylenetetrahydrofolate reductase (MTHFR) is the enzyme catalyzing the irreversible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate that can control folate cofactor distributions and modulate the partitioning of intracellular one-carbon moieties. The association between MTHFR polymorphisms and HCC risk is inconsistent and remains controversial in populational studies. We aimed to establish an in vitro cell model of liver origin to elucidate the interactions between MTHFR function, folate status, and chromosome stability. In the present study, we (1) examined MTHFR expression in HCC patients; (2) established cell models of liver origin with stabilized inhibition of MTHFR using small hairpin RNA delivered by a lentiviral vector, and (3) investigated the impacts of reduced MTHFR and folate status on cell cycle, methyl group homeostasis, nucleotide biosynthesis, and DNA stability, all of which are pathways involved in DNA integrity and repair and are critical in human tumorigenesis. By analyzing the TCGA/GTEx datasets available within GEPIA2, we discovered that HCC cancer patients with higher MTHFR had a worse survival rate. The shRNA of MTHFR (shMTHFR) resulted in decreased MTHFR gene expression, MTHFR protein, and enzymatic activity in human hepatoma cell HepG2. shMTHFR tended to decrease intracellular S-adenosylmethionine (SAM) contents but folate depletion similarly decreased SAM in wildtype (WT), negative control (Neg), and shMTHFR cells, indicating that in cells of liver origin, shMTHFR does not exacerbate the methyl group supply in folate depletion. shMTHFR caused cell accumulations in the G2/M, and cell population in the G2/M was inversely correlated with MTHFR gene level (r = −0.81, p < 0.0001), MTHFR protein expression (r = −0.8; p = 0.01), and MTHFR enzyme activity (r = −0.842; p = 0.005). Folate depletion resulted in G2/M cell cycle arrest in WT and Neg but not in shMTHFR cells, indicating that shMTHFR does not exacerbate folate depletion-induced G2/M cell cycle arrest. In addition, shMTHFR promoted the expression and translocation of nuclei thymidine synthetic enzyme complex SHMT1/DHFR/TYMS and assisted folate-dependent de novo nucleotide biosynthesis under folate restriction. Finally, shMTHFR promoted nuclear MLH1/p53 expression under folate deficiency and further reduced micronuclei formation and DNA uracil misincorporation under folate deficiency. In conclusion, shMTHFR in HepG2 induces cell cycle arrest in G2/M that may promote nucleotide supply and assist cell defense against folate depletion-induced chromosome segregation and uracil misincorporation in the DNA. This study provided insight into the significant impact of MTHFR function on chromosome stability of hepatic tissues. Data from the present study may shed light on the potential regulatory mechanism by which MTHFR modulates the risk for hepatic malignancies.

miR-221-3p promotes hepatocellular carcinogenesis by downregulating O6-methylguanine-DNA methyltransferase

This study aimed to investigate the influence of miR-221-3p and O⁶-methylguanine-DNA methyltransferase (MGMT) interaction in human hepatocellular carcinoma (HCC), thereby revealing a novel molecular mechanism of hepatic carcinogenesis involving miR-221-3p and MGMT.

Fluorescence qPCR and immunoblot assays were performed to determine the expression of RNA and protein in HCC tissues and cell lines. We also employed the firefly and Renilla luciferase assay to verify the target relationship between miR-221-3p and MGMT mRNA. Assessments including the MTT assay, wound-healing assay, transwell assay, colony foci formation experiment, and flow cytometric experiment were carried out to determine the viability, migration, invasion, proliferation, cell cycle progression, and apoptosis of SMMC-7721 and BEL-7404 cell lines with the modulated expression of miR-221-3p and MGMT. Compared to healthy tissues and cell line HL7702, miR-221-3p was significantly upregulated but MGMT was significantly downregulated in carcinomas and cancerous cell lines. Forced miR-221-3p overexpression was found to enhance the proliferation, migration, invasion, and clonogenicity of cell lines, but it suppressed cell apoptosis. Findings also revealed that forced miR-221-3p overexpression had little effect on cell cycle progression. After MGMT was confirmed to be atarget gene of miR-221-3p, it was found that the forced upregulation of miR-221-3p downregulated MGMT mRNA and protein levels significantly. MiR-221-3p was identified as an HCC promoting factor, and it specifically inhibited the expression of the MGMT. Besides, the upregulation of miR-221-3p had apositive influence on HCC pathogenesis by inhibiting MGMT expression.

Investigation of DNA repair-related SNPs underlying susceptibility to papillary thyroid carcinoma reveals MGMT as a novel candidate gene in Belarusian children exposed to radiation

BACKGROUND

Genetic factors may influence an individual's sensitivity to ionising radiation and therefore modify his/her risk of developing papillary thyroid carcinoma (PTC). Previously, we reported that common single nucleotide polymorphisms (SNPs) within the DNA damage recognition gene ATM contribute to PTC risk in Belarusian children exposed to fallout from the Chernobyl power plant accident. Here we explored in the same population the contribution of a panel of DNA repair-related SNPs in genes acting downstream of ATM.

METHODS

The association of 141 SNPs located in 43 DNA repair genes was examined in 75 PTC cases and 254 controls from the Gomel region in Belarus. All subjects were younger than 15 years at the time of the Chernobyl accident. Conditional logistic regressions accounting for radiation dose were performed with PLINK using the additive allelic inheritance model, and a linkage disequilibrium (LD)-based Bonferroni correction was used for correction for multiple testing.

RESULTS

The intronic SNP rs2296675 in MGMT was associated with an increased PTC risk [per minor allele odds ratio (OR) 2.54 95% CI 1.50, 4.30, P per allele = 0.0006, P corr.= 0.05], and gene-wide association testing highlighted a possible role for ERCC5 (P Gene = 0.01) and PCNA (P Gene = 0.05) in addition to MGMT (P Gene = 0.008).

CONCLUSIONS

These findings indicate that several genes acting in distinct DNA repair mechanisms contribute to PTC risk. Further investigation is needed to decipher the functional properties of the methyltransferase encoded by MGMT and to understand how alteration of such functions may lead to the development of the most common type of thyroid cancer.

Progression of O⁶-methylguanine-DNA methyltransferase and temozolomide resistance in cancer research

Temozolomide (TMZ) is an alkylating agent that is widely used in chemotherapy for cancer. A key mechanism of resistance to TMZ is the overexpression of O(6)-methylguanine-DNA methyltransferase (MGMT). MGMT specifically repairs the DNA O(6)-methylation damage induced by TMZ and irreversibly inactivates TMZ. Regulation of MGMT expression and research regarding the mechanism of TMZ resistance will help rationalize the clinical use of TMZ. In this review, we provide an overview of recent advances in the field, with particular emphasis on MGMT structure, function, expression regulation, and the association between MGMT and resistance to TMZ.

Involvement of DNA damage response pathways in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has been known as one of the most lethal human malignancies, due to the difficulty of early detection, chemoresistance, and radioresistance, and is characterized by active angiogenesis and metastasis, which account for rapid recurrence and poor survival. Its development has been closely associated with multiple risk factors, including hepatitis B and C virus infection, alcohol consumption, obesity, and diet contamination. Genetic alterations and genomic instability, probably resulted from unrepaired DNA lesions, are increasingly recognized as a common feature of human HCC. Dysregulation of DNA damage repair and signaling to cell cycle checkpoints, known as the DNA damage response (DDR), is associated with a predisposition to cancer and affects responses to DNA-damaging anticancer therapy. It has been demonstrated that various HCC-associated risk factors are able to promote DNA damages, formation of DNA adducts, and chromosomal aberrations. Hence, alterations in the DDR pathways may accumulate these lesions to trigger hepatocarcinogenesis and also to facilitate advanced HCC progression. This review collects some of the most known information about the link between HCC-associated risk factors and DDR pathways in HCC. Hopefully, the review will remind the researchers and clinicians of further characterizing and validating the roles of these DDR pathways in HCC.

Expression of DNA repair proteins MSH2, MLH1 and MGMT in human benign and malignant thyroid lesions: an immunohistochemical study

Background

DNA repair is a major defense mechanism, which contributes to the maintenance of genetic sequence, and minimizes cell death, mutation rates, replication errors, DNA damage persistence and genomic instability. Alterations in the expression levels of proteins participating in DNA repair mechanisms have been associated with several aspects of cancer biology. The present study aimed to evaluate the clinical significance of DNA repair proteins MSH2, MLH1 and MGMT in benign and malignant thyroid lesions.

Material/Methods

MSH2, MLH1 and MGMT protein expression was assessed immunohistochemically on paraffin-embedded thyroid tissues from 90 patients with benign and malignant lesions.

Results

The expression levels of MLH1 was significantly upregulated in cases with malignant compared to those with benign thyroid lesions (p=0.038). The expression levels of MGMT was significantly downregulated in malignant compared to benign thyroid lesions (p=0.001). Similar associations for both MLH1 and MGMT between cases with papillary carcinoma and hyperplastic nodules were also noted (p=0.014 and p=0.026, respectively). In the subgroup of malignant thyroid lesions, MSH2 downregulation was significantly associated with larger tumor size (p=0.031), while MLH1 upregulation was significantly associated with the presence of lymphatic and vascular invasion (p=0.006 and p=0.002, respectively).

Conclusions

Alterations in the mismatch repair proteins MSH2 and MLH1 and the direct repair protein MGMT may result from tumor development and/or progression. Further studies are recommended to draw definite conclusions on the clinical significance of DNA repair proteins in thyroid neoplasia.

Immunohistochemical expression of mismatch repair genes (hMSH2 and hMLH1) in hepatocellular carcinoma in Egypt

Egypt has the highest prevalence rate of hepatitis C virus (HCV) infection in the world. HCV contributes to the development of about 70% of hepatocellular carcinoma (HCC) cases. Understanding the molecular basis of hepatocarcinogenesis is important for planning the therapeutic regimen for HCC patients. To clarify the possible role of mismatch repair (MMR) genes in HCV-related HCC, we studied 50 HCV-related HCC specimens (28 of which were with adjacent non-cancerous cirrhotic liver tissue, ANCLT) and 30 specimens of chronic liver disease (CLD) with no evidence of HCC. All cases were examined immunohistochemically to demonstrate the protein expression of hMSH2 and hMLH1. Thirty-two (64%) and 35 (70%) of the HCC cases revealed reduced expression of hMSH2 and hMLH1, respectively. Reduced expression of both the proteins was obtained in 26 (52%) of the HCC cases. The expression of hMSH2 and hMLH1 was reduced in 53.6% and 64.3% of ANCLT cases, respectively, with no significant difference between HCC and ANCLT. All 30 specimens of CLD had preserved expression of hMSH2 and hMLH1. Multivariate analysis showed that the reduced expression of hMSH2 or hMLH1 was significantly associated with higher grades of the tumor (p = 0.002 and 0.02, respectively).The relationships of these MMR genes with other clinicopathologic factors were not significant. Reduced expression of hMSH2 and hMLH1 in both HCC and ANCLT suggests that this event occurs at early stages of HCV-related hepatocarcinogenesis. Moreover, the significant association between reduced expression of both MMR genes and poor histologic grades of the tumor claims that these proteins are involved in the process of cancer progression.

Expression of DNA repair proteins, MSH2, MLH1 and MGMT in mobile tongue squamous cell carcinoma: associations with clinicopathological parameters and patients' survival

BACKGROUND

DNA repair is a major defense mechanism, which contributes to the maintenance of genetic sequence, minimizing cell death, mutation rates, replication errors, DNA damage persistence and genomic instability. Alterations of proteins participating in DNA repair mechanisms have been associated with several aspects of cancer biology. The present study aimed to evaluate the clinical significance of DNA repair proteins, MSH2, MLH1 and MGMT in mobile tongue squamous cell carcinoma (SCC).

METHODS

MSH2, MLH1 and MGMT protein expression was assessed immunohistochemically on 49 mobile tongue SCC tissue samples and was analyzed in relation with clinicopathological characteristics, overall and disease-free patients' survival.

RESULTS

MSH2 expression was significantly associated with depth of invasion (P=0.0335), tumor shape (P=0.0396) and muscular invasion (P=0.0098). MLH1 expression was significantly associated with lymph node metastases (P=0.0484) and borderline with perineural invasion (P=0.0699). MGMT expression was significantly associated with depth of invasion (P=0.0472), tumor shape (P=0.0187), perineural invasion (P=0.0115) and lymph node metastases (P=0.0032) and borderline with vascular invasion (P=0.0755). MSH2 expression was significantly associated with disease-free patients' survival in univariate analysis (P=0.0441), being also identified as an independent prognostic factor in multivariate analysis (P=0.0451).

CONCLUSIONS

The present study supported evidence for possible implication of MSH2, MLH1 and MGMT proteins in the formation and progression of mobile tongue SCC.

O6-methylguanine DNA methyltransferase status determined by promoter methylation and immunohistochemistry in gliosarcoma and their clinical implications

O(6)-methylguanine-DNA methyltransferase (MGMT) is known as a DNA repair protein, and loss of function in MGMT is related to an increase in survival in patients with malignant gliomas treated with alkylating agents. In the present study, we determined the status of MGMT using methylation-specific polymerase chain reaction (PCR) and immunohistochemistry on paraffin-embedded specimens in 12 human gliosarcomas, and these results were then related to overall survival (OS) and response to alkylating agents. The MGMT promoter was methylated in six patients. Immunostaining of MGMT was positive in 58.3% of patients. MGMT methylation status was correlated with immunostaining results in five patients (41.7%). The median OS and progression-free survival (PFS) of the whole population were 13.4 months [95% confidence interval (CI), 12.3-14.5 months] and 8.3 months (95% CI, 7.4-9.2 months), respectively. In patients with methylated MGMT promoter, median OS was 15.0 months, compared with 11.3 months in the unmethylated group. Median PFS of gliosarcoma patients was 10.3 months for the methylated group, whereas it was 7.3 months for the unmethylated group. On multivariate analysis, patients with methylated MGMT promoter had better prognosis than patients with unmethylated MGMT promoter with respect to OS and PFS (P = 0.045 and 0.034, respectively). However, there was no statistical significance between MGMT protein expression and survival. The results show that a significant fraction of gliosarcomas have MGMT promoter methylation and protein expression, and suggest that patient survival is associated with MGMT methylation status.

Tumor suppressor and hepatocellular carcinoma

A few signaling pathways are driving the growth of hepatocellular carcinoma. Each of these pathways possesses negative regulators. These enzymes, which normally suppress unchecked cell proliferation, are circumvented in the oncogenic process, either the over-activity of oncogenes is sufficient to annihilate the activity of tumor suppressors or tumor suppressors have been rendered ineffective. The loss of several key tumor suppressors has been described in hepatocellular carcinoma. Here, we systematically review the evidence implicating tumor suppressors in the development of hepatocellular carcinoma.

Oxidative stress and cancer: have we moved forward?

'Reactive species' (RS) of various types are formed in vivo and many are powerful oxidizing agents, capable of damaging DNA and other biomolecules. Increased formation of RS can promote the development of malignancy, and the 'normal' rates of RS generation may account for the increased risk of cancer development in the aged. Indeed, knockout of various antioxidant defence enzymes raises oxidative damage levels and promotes age-related cancer development in animals. In explaining this, most attention has been paid to direct oxidative damage to DNA by certain RS, such as hydroxyl radical (OH*). However, increased levels of DNA base oxidation products such as 8OHdg (8-hydroxy-2'-deoxyguanosine) do not always lead to malignancy, although malignant tumours often show increased levels of DNA base oxidation. Hence additional actions of RS must be important, possibly their effects on p53, cell proliferation, invasiveness and metastasis. Chronic inflammation predisposes to malignancy, but the role of RS in this is likely to be complex because RS can sometimes act as anti-inflammatory agents.

A quest to understand molecular mechanisms for genetic stability

In the midst of the post-war turmoil in Japan, I fortunately followed a path to become a scientist. Sometime at an early stage of my career, I encountered the problem of the cellular response to DNA damage and had the chance to discover a DNA repair enzyme. This event greatly influenced the subsequent course of my research, and I extended my studies toward elucidating the molecular mechanisms of mutagenesis as well as of carcinogenesis. Through these studies I came to understand the importance of mechanisms for dealing with the actions of reactive oxygen species to the living systems. These recollections deal with these endeavors with emphasis on the early part of my scientific career.

DNA hypermethylation status of multiple genes in soft tissue sarcomas

The aberrant methylation of promoter CpG islands is known to be a major inactivation mechanism of tumor-related genes. To determine the clinicopathological significance of gene promoter methylation in soft tissue sarcomas, we examined the promoter methylation status of 10 tumor-related genes in 65 soft tissue sarcomas and 19 adjacent non-neoplastic tissues by methylation-specific PCR. The methylation frequencies of tumor-related genes tested in soft tissue sarcomas were 17 (26%) for RASSF1A, 11 (17%) for DAP kinase, 10 (15%) for MGMT, nine (14%) for GSTP1, eight (12%) for PTEN, six (9%) for p16 and hMLH1, five (8%) for hMSH2, two (3%) for p14, and one (2%) for RB. Promoter methylation of these genes was not recognized in non-neoplastic tissues. All those cases of soft tissue sarcoma that had MGMT methylation, with the exception of one case of malignant peripheral nerve sheath tumor, showed large tumor size (> or = 10 cm) or recurrence. Moreover, eight of 10 cases with MGMT methylation revealed high American Joint Committee on Cancer stage. Seven of 10 cases (70%) with MGMT methylation showed a loss of MGMT expression by immunohistochemistry. In addition, MGMT methylation status had a statistically significant correlation with a loss of MGMT expression (P=0.014). In conclusion, although methylation of tumor-related genes was a relatively rare event in soft tissue sarcomas, methylation was tumor-specific. Of 10 tumor-related genes, cases with MGMT methylation had a tendency to be aggressive behavior. Moreover, MGMT methylation was closely associated with a loss of MGMT expression. Although our findings need to be extending to a large series, promoter methylation of tumor-related genes is likely to have an association with the pathogenesis of soft tissue sarcomas. Furthermore, MGMT methylation may be associated with tumor aggressiveness and the inactivation of MGMT gene.

Epigenetic silencing of the MGMT gene in cancer

Silencing of the O6-methylguanine-DNA methyltransferase (MGMT) gene, a key to DNA repair, plays a critical role in the development of cancer. The gene product, functioning normally, removes a methyl group from mutagenic O6-methylguanine, which is produced by alkylating agents and can make a mismatched pair with thymine, leading to transition mutation through DNA replication. MGMT is epigenetically silenced in various human tumors. It is well known that DNA hypermethylation at the promoter CpG island plays a pivotal role in the epigenetic silencing of tumor suppressor genes. MGMT silencing, however, occurs without DNA hypermethylation in some cancer cells. Dimethylation of histone H3 lysine 9 and binding of methyl-CpG binding proteins are common and essential in MGMT-silenced cells. Silencing of MGMT has been shown to be a poor prognostic factor but a good predictive marker for chemotherapy when alkylating agents are used. In this review, we describe recent advances in understanding the silencing of MGMT and its role in carcinogenesis; epigenetic mechanisms; and clinical implications.

Killing and mutagenic actions of dacarbazine, a chemotherapeutic alkylating agent, on human and mouse cells: effects of Mgmt and Mlh1 mutations

Among various types of drugs designed for use in cancer chemotherapy, some have the potential for alkylation. After metabolic activation, these chemicals attack DNA and alkylate their bases, thereby preventing multiplication of rapidly growing tumor cells. Some of alkylated bases cause mutations, leading to untoward induction of tumors. To search for the rationale to separate lethal and mutagenic effects of alkylation drugs, we investigated actions of dacarbazine, a monofunctional triazene, on mouse and human cell lines defective in the Mgmt and/or the Mlh1 gene, the former encoding a DNA repair methyltransferase and the latter a protein involved in mismatch repair and induction of apoptosis. Mgmt-deficient cells are hypersensitive to the killing action of dacarbazine. On the other hand, cells defective in both Mgmt and Mlh1 genes are as resistant to the drug as are wild-type cells, in terms of survival, but do have many mutations after dacarbazine treatment. Thus, the killing and mutagenic actions of dacabazine can be dissociated by manipulating actions of these gene products.

Defective mismatch repair and the development of recurrent endometrial carcinoma

OBJECTIVE

To investigate whether defective DNA mismatch repair (MMR) defines a subgroup at risk for recurrence in sporadic endometrial carcinoma patients.

METHODS

Primary tumors from 44 patients with recurrent stage I endometrial carcinoma were compared after matching, with tumors of 44 patients being free of recurrence for minimal 3 years. Paraffin-embedded primary tumors (n = 88) and recurrent tumors (n = 32) were subjected to immunohistochemical analysis for hMSH2 and hMLH1 expression. Subsequently, a staining index (SI = 0-9) was calculated based on staining intensity and quantity. DNA was extracted from paraffin-embedded tissues, and promoter methylation of hMLH1 was determined by nested methylation-specific PCR (MSP). Microsatellite instability (MSI) was assessed by BAT-26 or BAT-25.

RESULTS

Low hMSH2 expression was observed in 2% of primary tumors of control patients without recurrence, 14% of primary tumors of patients with recurrence, and 0% of recurrent tumors. Low hMLH1 expression was observed in 32%, 19%, and 22%, respectively. hMLH1 gene promoter methylation was detected in 50%, 47%, and 32%, and MSI was found in 16%, 14%, and 30%, respectively. No significant differences were found between primary tumors of patients with and without recurrence with respect to hMSH2 and hMLH1 expression, hMLH1 promoter methylation, and MSI. When primary and recurrent tumors were compared, there was an increased correlation of hMLH1 methylation with low hMLH1 expression and MSI in recurrent tumors.

CONCLUSION

MSI, hMLH1 promoter methylation, and the expression of hMLH1 and hMSH2 are not predictive for the development of recurrent stage I endometrial carcinoma. In the progression of tumor, "de novo" hMLH1 methylation rarely occurs, instead there is further derailment of the MMR pathway in affected tumors.

Expression of MGMT, hMLH1 and hMSH2 and its clinopathological significance in pancreatic carcinoma tissues

AIM: To study the expression of MGMT, hMLH₁ and hMSH₂ and their clinicopathological significances in the tissues of chronic pancreatitis and pancreatic adenocarcinoma.

METHODS: The expression levels of MGMT, hMLH₁ and hMSH₂ were assayed by immunohistochemical method of avidin-biotin complex on the formalin-fixed and routinely paraffin-embedded sections of surgical resected specimen with chronic pancreatitis (n = 10) and pancreatic carcinoma (n = 51).

RESULTS: The positive rates and the scores of MGMT, hMLH₁ and hMSH₂ were significantly higher in chroinic pancreatitis than those of pancreatic carcinoma (MGMT: 100.0% vs 39.2%,3.8±0.8 vs 1.8±1.4; hMLH1: 100.0% vs 45.1%, 3.8±1.0 vs 1.7±1.6; hMSH2: 90.0% vs 50.9%, 3.5±0.9 vs 1.9±1.7). The positive rates and the scores of MGMT, hMLH₁ and hMSH₂ were significantly higher in well-differentiated adenocarcinomas than those of poorly differentiated adenocarcinomas (P < 0.05 or P < 0.01). The positive rates and the scores of MGMT, hMLH₁ and hMSH₂ were higher in metastasis-free cases than those of ones with metastasis, but no statistic difference was found (P>0.05). There was also no difference among the expression of three proteins and the other clinicopathological characteristics of pancreatic carcinoma.

CONCLUSION: The expression of MGMT, hMLH₁ or hMSH₂ may be related to the carcinogenesis and progression, and have inhibifory effects on the carcinogenesis and progression of pancreatic carcinoma.