Background: Sufficient epidemiologic evidence shows an etiologic link between polycyclic aromatic hydrocarbons (PAH) exposure and lung cancer risk. While the genetic modifications have been found in PAH-exposed population, it is unclear whether gene-specific methylation involves in the process of PAH-associated biologic consequence.
Methods: Sixty-nine PAH-exposed workers and 59 control subjects were recruited. Using bisulfite sequencing, we examined the methylation status of p16(INK4α) promoter in peripheral blood lymphocytes (PBL) from PAH-exposed workers and in benzo(a)pyrene (BaP)-transformed human bronchial epithelial (HBE) cells. The relationships between p16(INK4α) methylation and the level of urinary 1-hydroxypyrene (1-OHP) or the frequency of cytokinesis block micronucleus (CBMN) were analyzed.
Results: Compared with the control group, PAH-exposed workers exhibited higher levels of urinary 1-OHP (10.62 vs. 2.52 μg/L), p16(INK4α) methylation (7.95% vs. 1.14% for 22 "hot" CpG sites), and CBMN (7.28% vs. 2.92%) in PBLs. p16(INK4α) hypermethylation in PAH-exposed workers exhibited CpG site specificity. Among the 35 CpG sites we analyzed, 22 were significantly hypermethylated. These 22 hypermethylated CpG sites were positively correlated to levels of urinary 1-OHP and CBMN in PBLs. Moreover, the hypermethylation and suppression of p16 expression was also found in BaP-transformed HBER cells.
Conclusion: PAH exposure induced CpG site-specific hypermethylation of p16(INK4α) gene. The degree of p16(INK4α) methylation was associated with the levels of DNA damage and internal exposure.
Impact: p16(INK4α) hypermethylation might be an essential biomarker for the exposure to PAHs and for early diagnosis of cancer.