TET2 Inhibits PD-L1 Gene Expression in Breast Cancer Cells through Histone Deacetylation

Abstract

Activation of PD-1/PD-L1 checkpoint is a critical step for the immune evasion of malignant tumors including breast cancer. However, the epigenetic mechanism underlying the aberrant expression of PD-L1 in breast cancer cells remains poorly understood. To investigate the role of TET2 in the regulation of PD-L1 gene expression, quantitative reverse transcription PCR (RT-qPCR), Western blotting, chromatin immunoprecipitation (ChIP) assay and MeDIP/hMeDIP-qPCR were performed on MCF7 and MDA-MB-231 human breast cancer cells. Here, we reported that TET2 depletion upregulated PD-L1 gene expression in MCF7 cells. Conversely, ectopic expression of TET2 inhibited PD-L1 gene expression in MDA-MB-231 cells. Mechanistically, TET2 protein recruits histone deacetylases (HDACs) to PD-L1 gene promoter and orchestrates a repressive chromatin structure to suppress PD-L1 gene transcription, which is likely independent of DNA demethylation. Consistently, treatment with HDAC inhibitors upregulated PD-L1 gene expression in wild-type (WT) but not TET2 KO MCF7 cells. Furthermore, analysis of the CCLE and TCGA data showed a negative correlation between TET2 and PD-L1 expression in breast cancer. Taken together, our results identify a new epigenetic regulatory mechanism of PD-L1 gene transcription, linking the catalytic activity-independent role of TET2 to the anti-tumor immunity in breast cancer.

Clinical Significance of TET2 in Female Cancers

“…In vitro studies on breast cancer have reported that TET2 knockout upregulates the expression of programmed death-ligand 1 (PD-L1) in MCF7 cells. However, ectopic TET2 expression inhibits the gene expression of PD-L1 in MDA-MB-231 cells (Shen et al, 2021). Furthermore, KDM2A knockout significantly increases TET2 expression in various breast cancer cell lines.…”

“…In recent years, the role of TET2 in the occurrence and development of solid tumors has been gradually revealed. Decreased TET2 expression has been reported in solid malignant tumors, such as thyroid (Jia et al, 2020), gastric (Deng et al, 2016;He et al, 2018), colorectal (Huang et al, 2016;Ma et al, 2018;Zhang et al, 2019), ovarian (Zhang et al, 2015), breast (Yang et al, 2015;Chen et al, 2017;Shen et al, 2021), and prostate cancers (Nickerson et al, 2017). In vitro studies have demonstrated decreased TET2 expression is associated with solid tumor development.…”

Current insight into the regulation of PD-L1 in cancer

“…NRF2 is a crucial transcription factor for antioxidant and detoxification enzymes that protect cells from damage caused by oxidative stress [ 53 ]. This protein decreases the expression of miR-1, leading to the elevation of PD-L1 in HCC patients treated with sorafenib [ 22 ].…”

“…Recently, histone modification, particularly histone acetylation, has also been implicated in the transcriptional regulation of PD-L1. TET2, a ten-eleven translocation (TET) family member, recruits histone deacetylases (HDAC1/2) to deacetylate the histone modification H3K27ac on the PD-L1 promoter and consequently restraining PD-L1 transcription in BC [ 53 ]. HDAC3 overexpression suppressed PD-L1 and inhibited CD3 + T cell proliferation [ 65 ].…”

Dysregulated TET Family Genes and Aberrant 5mC Oxidation in Breast Cancer: Causes and Consequences

“…As one of the IFN-gamma induced genes, PD-L1 was also enhanced by TET2. Conversely, our recent work revealed that TET2 represses the expression of the PD-L1 gene in breast cancer either in the presence or absence of IFN-gamma treatment [ 74 ]. Mechanistically, we found that TET2-mediated PD-L1 repression was independent of DNA methylation, instead of the recruitment of HDAC1/2 by TET2 to the promoter of PD-L1 gene.…”