Cloning of the hamster p16 gene 5' upstream region and its aberrant methylation patterns in pancreatic cancer

Emodin enhances the demethylation by 5-Aza-CdR of pancreatic cancer cell tumor-suppressor genes P16, RASSF1A and ppENK

5-Aza-2'-deoxycytidine (5-Aza-CdR) is currently acknowledged as a demethylation drug, and causes a certain degree of demethylation in a variety of cancer cells, including pancreatic cancer cells. Emodin, a traditional Chinese medicine (TCM), is an effective monomer extracted from rhubarb and has been reported to exhibit antitumor activity in different manners in pancreatic cancer. In the present study, we examined whether emodin caused demethylation and increased the demethylation of three tumor-suppressor genes P16, RASSF1A and ppENK with a high degree of methylation in pancreatic cancer when combined with 5-Aza-CdR. Our research showed that emodin inhibited the growth of pancreatic cancer Panc-1 cells in a dose- and time-dependent manner. Dot-blot results showed that emodin combined with 5-Aza-CdR significantly suppressed the expression of genome 5mC in PANC-1 cells. In order to verify the effect of methylation, methylation-specific PCR (MSP) and bisulfite genomic sequencing PCR (BSP) combined with TA were selected for the cloning and sequencing. Results of MSP and BSP confirmed that emodin caused faint demethylation, and 5-Aza-CdR had a certain degree of demethylation. When emodin was combined with 5-Aza-CdR, the demethylation was more significant. At the same time, fluorescent quantitative PCR and western blot analysis results confirmed that when emodin was combined with 5-Aza-CdR, the expression levels of P16, RASSF1A and ppENK were increased more significantly compared to either treatment alone. In contrast, the expression levels of DNA methyltransferase 1 (DNMT1) and DNMT3a were more significantly reduced with the combination treatment than the control or either agent alone, further proving that emodin in combination with 5-Aza-CdR enhanced the demethylation effect of 5-Aza-CdR by reducing the expression of methyltransferases. In conclusion, the present study confirmed that emodin in combination with 5-Aza-CdR enhanced the demethylation by 5-Aza-CdR of tumor-suppressor genes p16, RASSF1A and ppENK by reducing the expression of methyltransferases DNMT1 and DNMT3a.

Involvement of inflammatory factors in pancreatic carcinogenesis and preventive effects of anti-inflammatory agents

Chronic inflammation is known to be a risk for many cancers, including pancreatic cancer. Heavy alcohol drinking and cigarette smoking are major causes of pancreatitis, and epidemiological studies have shown that smoking and chronic pancreatitis are risk factors for pancreatic cancer. Meanwhile, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) are elevated in pancreatitis and pancreatic cancer tissues in humans and in animal models. Selective inhibitors of iNOS and COX-2 suppress pancreatic cancer development in a chemical carcinogenesis model of hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). In addition, hyperlipidemia, obesity, and type II diabetes are also suggested to be associated with chronic inflammation in the pancreas and involved in pancreatic cancer development. We have shown that a high-fat diet increased pancreatic cancer development in BOP-treated hamsters, along with aggravation of hyperlipidemia, severe fatty infiltration, and increased expression of adipokines and inflammatory factors in the pancreas. Of note, fatty pancreas has been observed in obese and/or diabetic cases in humans. Preventive effects of anti-hyperlipidemic/anti-diabetic agents on pancreatic cancer have also been shown in humans and animals. Taking this evidence into consideration, modulation of inflammatory factors by anti-inflammatory agents will provide useful data for prevention of pancreatic cancer.

Enhancement of carcinogenesis and fatty infiltration in the pancreas in N-nitrosobis(2-oxopropyl)amine-treated hamsters by high-fat diet

OBJECTIVES

Obesity is associated with increased pancreatic cancer risk, although the mechanisms have yet to be detailed. This study aimed to elucidate promotion of pancreatic cancer by obesity and hyperlipidemia.

METHODS

Six-week-old female Syrian golden hamsters were treated with N-nitrosobis(2-oxopropyl)amine (BOP) and after 1 week were fed a high-fat diet (HFD) or standard diet (STD) for 6 or 17 weeks.

RESULTS

Body weight and serum levels of lipids and leptin were significantly higher in the HFD than the STD group at 14 weeks of age. Pancreatic ductal adenocarcinomas developed only in the BOP + HFD group, with an incidence of 67% (P < 0.01) at 14 weeks of age. In addition, the multiplicity was 2-fold greater in the BOP + HFD group than in the BOP + STD group (P < 0.05) at 25 weeks of age. Pancreatic fatty infiltration was increased by BOP treatment and further enhanced by the HFD, correlating with progression of BOP-induced pancreatic ductal adenocarcinoma and up-regulated expression of adipocytokines and cell proliferation-related genes in the pancreas.

CONCLUSIONS

High-fat diet is shown to increase serum lipid levels and enhance fatty infiltration in the pancreas with abnormal adipocytokine production, which may accelerate and enhance pancreatic cancer.

Infrequent mutation of lysophosphatidic Acid receptor-1 gene in hamster pancreatic duct adenocarcinomas and established cell lines

To evaluate the involvement of lysophosphatidic acid receptor-1 (LPA1) gene alteration in pancreatic carcinogenesis, we investigated mutations in the LPA1 gene in hamster pancreatic duct adenocarcinomas (PDAs) and established cell lines. Female Syrian golden hamsters received 30 mg/kg of N-nitrosobis(2-oxopropyl)amine (BOP) followed by repeated exposure to an augmentation pressure regimen consisting of a choline-deficient diet combined with DL-ethionine and then L-methionine and a further administration of 20 mg/kg BOP. A total of 10 PDAs obtained 10 weeks after beginning the experiment and three cell lines established from subcutaneously transplantable PDAs in syngeneic hamsters were examined for mutations using reverse transcription-polymerase chain reaction-single strand conformation polymorphism (RT-PCR-SSCP) analysis. A mutation was detected in only one PDA (1/10, 10%) in the form of a GGA to GTA (Gly to Val) transversion at codon 355, and no mutations were detected in the three cell lines. These results suggest that the LPA1 gene mutation may play roles in a limited fraction of BOP-induced pancreatic duct carcinogenesis in hamsters.

Reduced expression of the Rassf1a gene and its aberrant DNA methylation in pancreatic duct adenocarcinomas induced by N-nitrosobis(2-oxopropyl)amine in hamsters

Alterations of the Rassf1a gene were investigated in pancreatic duct adenocarcinomas (PDAs) induced by N-nitrosobis(2-oxopropyl)amine (BOP) in hamsters. Female Syrian golden hamsters received 70 mg/kg BOP, followed by repeated exposures to an augmentation pressure regimen consisting of a choline-deficient diet combined with a sequential course of DL-ethionine, L-methionine, and 20 mg/kg BOP. A total of 15 PDAs were obtained, and total RNAs were assessed by real-time quantitative reverse transcription (RT)-polymerase chain reaction (PCR). Expression of the Rassf1a was significantly reduced in PDAs (P < 0.005) compared with normal pancreatic tissues. For analysis of methylation status, bisulfite sequencing was performed. Normal tissues were all unmethylated in the 5' upstream region of Rassf1a. In contrast, four PDAs were highly methylated, correlating with reduced expression of the Rassf1a gene. Using reverse transcription (RT)-polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis, mutations were detected in 3 out of 15 PDAs (20%). These results suggested that alterations of the Rassf1a gene may be involved in development of PDAs induced by BOP in hamsters.

Aberrant DNA methylation of the 5' upstream region of Tslc1 gene in hamster pancreatic tumors

To determine if the Tslc1 gene is involved in pancreatic carcinogenesis, the expression level of Tslc1 and the DNA methylation status of its 5' upstream region were investigated in pancreatic duct adenocarcinomas (PDAs) induced in hamsters by N-nitrosobis(2-oxopropyl)amine (BOP). Female Syrian golden hamsters received 70 mg/kg of BOP followed by repeated exposure to an augmentation pressure regimen consisting of a choline-deficient diet combined with ethionine-methionione-BOP injection. Total RNA was extracted from 11 PDAs and the level of Tslc1 expression was measured in each by real-time quantitative reverse transcription (RT)-polymerase chain reaction (PCR). The expression level of Tslc1 was significantly reduced in PDAs (p < 0.05) compared with normal pancreatic tissues. In order to assess the DNA methylation status of the 5' upstream region of Tslc1, bisulfite sequencing was performed. Although this region was unmethylated in normal pancreatic tissue, it was highly methylated in four PDAs, correlating with reduced Tslc1 expression. These results suggest that a reduction in the expression of Tslc1 due to aberrant DNA methylation might be involved in the development of PDAs induced in hamsters by BOP.

Reduced expression of the Tslc1 gene and its aberrant DNA methylation in rat lung tumors

TSLC1 gene inactivation due to promoter methylation has been reported in several human cancers. Here, we investigated the expression of the Tslc1 gene and its methylation pattern in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Six-week-old male Wistar rats were given 2000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were sacrificed at 25 weeks. Total RNA was extracted from a total of 11 lung adenocarcinomas and their Tslc1 gene expressions were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. Tslc1 expression was significantly reduced in the lung adenocarcinomas compared with three normal lung tissues (p < 0.05). Bisulfite sequence analysis of four lung adenocarcinomas and two normal lung tissues revealed that the 5' upstream region of the Tslc1 gene was highly methylated in the four lung adenocarcinomas, but unmethylated in the two normal lung tissues. These results suggest that aberrant Tslc1 gene methylation may be involved in BHP-induced development of lung adenocarcinomas in rats.

Reduced expression of the E-cadherin gene and its aberrant DNA methylation in hamster pancreatic tumors

The expression of the E-cadherin gene and its DNA methylation status in the 5' upstream region were investigated in pancreatic duct adenocarcinomas (PDAs) induced by N-nitrosobis(2-oxopropyl)amine (BOP) in hamsters. Female Syrian golden hamsters received 70mg/kg BOP, followed by repeated exposure to an augmentation pressure regimen consisting of a choline-deficient diet combined with dl-ethionine then l-methionine and a further administration of 20mg/kg BOP. A total of 15 PDAs were obtained, along with total RNA for assessment of expression by real-time quantitative reverse transcription-polymerase chain reaction. The expression of the E-cadherin was significantly reduced in PDAs (p<0.05) compared with normal pancreatic tissue. For the analysis of methylation status, bisulfite sequencing was performed with two normal pancreatic tissues and six tumors. The normal pancreatic tissue was all demethylated in this region of E-cadherin. In contrast, six PDAs were highly methylated, correlating with reduced expression of the E-cadherin. These results suggest that aberrant DNA methylation of the E-cadherin gene may play a role in the development of PDAs induced by BOP in hamsters.