Correlations among PPARγ, DNMT1, and DNMT3B Expression Levels and Pancreatic Cancer

Abstract

Emerging evidence indicates that peroxisome proliferator-activated receptor γ (PPARγ) and DNA methyltransferases (DNMTs) play a role in carcinogenesis. In this study we aimed to evaluate the expression of PPARγ, DNMT1, and DNMT3B and their correlation with clinical-pathological features in patients with pancreatic cancer (PC), and to define the effect of PPARγ activation on DNMTs expression in PC cell lines. qRT-PCR analysis showed that DNMT3B expression was downregulated in tumors compared to normal tissues (P = 0.03), whereas PPARγ and DNMT1 levels did not show significant alterations in PC patients. Expression levels between PPARγ and DNMT1 and between DNMT1 and DNMT3B were highly correlated (P = 0.008 and P = 0.05 resp.). DNMT3B overexpression in tumor tissue was positively correlated with both lymph nodes spreading (P = 0.046) and resection margin status (P = 0.04), and a borderline association with perineural invasion (P = 0.06) was found. Furthermore, high levels of DNMT3B expression were significantly associated with a lower mortality in the whole population (HR = 0.485; 95%CI = 0.262-0.895, P = 0.02) and in the subgroup of patients without perineural invasion (HR = 0.314; 95%CI = 0.130-0.758; P = 0.01), while such association was not observed in patients with tumor invasion into perineural structures (P = 0.70). In conclusion, in vitro and in vivo PPARγ and DNMTs appear interrelated in PC, and this interaction might influence cell phenotype and disease behavior.

Figure 1

PPARγ, DNMT1, and DNMT3b mRNA expression levels in tissues from 30 patients with pancreatic ductal Adenocarcinoma (PDAC). Each blot indicates the relative expression of genes in tumour compared to normal tissue, after normalization to the endogenous GAPDH. Values greater than 1 indicate gene overexpression in inflamed tissue. For each gene, the median expression levels observed in patients group were indicated by the horizontal black bars. Relative expression values are reported in log scale (y-axis).

Figure 2

Association of DNMT3b expression levels with perineural invasion (IP) in patients with pancreatic ductal adenocarcinoma (PDAC). Patients were stratified according to IP status (No versus Yes). Each box highlights median, interquartile range (Q1–Q3) and lower and upper adjacent values (vertical bars) for each subjects group. The upper and lower boundaries of the boxes define the quartiles, 75% and 25% percentiles, respectively, and the black bar represents the median value. Relative expression values are reported in log scale (y-axis).

Figure 3

Association of DNMT3b expression levels with resection margins in patients with pancreatic ductal adenocarcinoma (PDAC). Patients were stratified according to resection margin status (R0 versus R1). Each box highlights median, interquartile range (Q1–Q3) and lower and upper adjacent values (vertical bars) for each subjects group. The upper and lower boundaries of the boxes define the quartiles, 75% and 25% percentiles, respectively, and the black bar represents the median value. Relative expression values are reported in log scale (y-axis).

Figure 4

Figure 5

Quantitative real-time PCR. mRNA relative expression levels of PPARγ, DNMT1, and 3B in four different pancreatic cancer cell lines.

Figure 6

Quantitative real-time PCR. mRNA relative expression levels of DNMT1 and 3B in BxPC3 and CFPAC pancreatic cancer cell lines upon treatment with rosiglitazone at the indicated concentrations and time points.

Figure 7

Quantitative real-time PCR. mRNA relative expression levels of DNMT1 and 3B in PANC1 and MiaPaca pancreatic cancer cell lines upon treatment with rosiglitazone at the indicated concentrations and time points.