Benzo[a]pyrene exposure affects colorectal cancer susceptibility by regulating ERβ-mediated LINC02977 transcription

Abstract

Environmental pollutants known as polycyclic aromatic hydrocarbons (PAHs) are produced through the incomplete combustion of organic material. While PAHs have been investigated as genotoxicants, they can also operate through nongenotoxic pathways in estrogen-dependent malignancies, such as breast, cervical and ovarian cancer. However, whether PAHs induce colorectal cancer (CRC) risk through estrogenic effects is still illusive. Here, we systematically investigated the abnormal expression and activation of estrogen receptor beta (ERβ) regulated by PAHs in CRC as well as the underlying mechanisms of ERβ-mediated CRC risk. Based on the 300 plasma samples from CRC patients and healthy controls detected by GC-MS/MS, we found that the plasma concentrations of benzo[a]pyrene (BaP) were significantly higher in CRC cases than in healthy controls, with significant estrogenic effects. Moreover, histone deacetylase 2 (HDAC2)-induced deacetylation of the promoter decreases ERβ expression, which is associated with poor overall survival and advanced tumor stage. The study also revealed that BaP and estradiol (E₂) had different carcinogenic effects, with BaP promoting cell proliferation and inhibiting apoptosis, while E₂ had the opposite effects. Additionally, this study mapped ERβ genomic binding regions by performing ChIP-seq and ATAC-seq and identified genetic variants of rs1411680 and its high linkage disequilibrium SNP rs6477937, which were significantly associated with CRC risk through meta-analysis of two independent Chinese population genome-wide association studies comprising 2,248 cases and 3,173 controls and then validation in a large-scale European population. By integrating data from functional genomics, we validated the regulatory effect of rs6477937 as an ERβ binding-disrupting SNP that mediated allele-specific expression of LINC02977 in a long-range chromosomal interaction manner, which was found to be highly expressed in CRC tissues. Overall, this study suggests that the different active effects on ERβ by PAHs and endogenous E₂ may play a crucial role in the development and progression of CRC and highlights the potential of targeting ERβ and its downstream targets for CRC prevention and treatment.

Keywords: Benzo[a]pyrene; Colorectal cancer; Estrogen receptor beta; Genetic variants; Polycyclic aromatic hydrocarbons.