PM_2.5-induced down-regulation of Dnmt1 activates expression of Foxp3 in BEAS2B cells

  Objective  To explore the molecular mechanism of the expression of forkhead box P3 (Foxp3) activated by particulate matter ≤ 2.5 μm in aerodynamic diameter (PM_2.5) in human bronchial epithelial (BEAS2B) cells.

  Methods  The BEAS2B cells were treated with 300 μg/ml PM_2.5 dissolved in phosphate buffered saline (PBS) for 48 hours and the BEAS2B cells treated only with PBS were taken as the control. After being treated with PM_2.5 for 24 hours, the cells were also treated with 5.0 μM 5-azacytidine (5-AzaC) – a DNA methyltransferase inhibitor or 0.2 μM trichostatin A (TSA) – a histone deacetylase inhibitor, and the BEAS2B cells treated only with PM_2.5 were taken as the control. The expression of Foxp3, homeobox A1 (HOXA1) and homeobox A2 (HOXA2) were detected with reverse transcription real-time PCR (RT-PCR) assay. The expression of DNA methyltransferases (Dnmts)-related protein was determined with Western blot and the DNA methylation level was measured with methylation-specific PCR (MSP-PCR).

  Results  Compared to those in the control group, the expression of Foxp3 and DNA methyltransferase 3a (Dnmt3a) in BEAS2B cells treated with PM_2.5 were increased by 1.15 and 1.51 folds (both P < 0.05); while the expression of DNA methyltransferase 1 (Dnmt1) and DNA methyltransferase 3b (Dnmt3b) were decreased by 0.51 and 0.38 fold (both P < 0.05), respectively. Moreover, after the cells being treated with 5-AzaC or TSA, the expression of Foxp3 was increased by 1.61 or 1.20 folds (both P < 0.05), with the significantly down-regulated expressions of hypomethylation of Foxp3 promoter and the Dnmt1 protein (both P < 0.05).

  Conclusion  The expression of Foxp3 may be activated by PM_2.5 through inhibiting the expression of Dnmt1.