Identification of novel colorectal tumor suppressor genes through genome-wide promoter hypermethylation analysis

Cancer initiation and progression are driven by both genetic and epigenetic changes. Although recent genome/exome sequencing efforts have significantly contributed to the thorough characterization of the genetic changes associated with the oncogenic process, further investigation is required to systematically identify the driver genes regulated by promoter hypermethylation. Using genome-wide analysis of the levels of promoter methylation (HumanMethylation27, Illumina) and the levels of mRNA expression (microarray analysis) in a panel of 30 colorectal cancer cell lines and 223 primary colorectal tumors (TCGA), we found a subset of 553 (5.6%) genes whose levels of promoter methylation showed a significant negative association with their expression. Higher overall methylation levels were associated with microsatellite instability (MSI), a CpG methylator phenotype (CIMP), faster proliferation and absence of APC mutations. Next, because genes that are epigenetically silenced could represent important drivers of the oncogenic process we investigated the role of the zinc finger transcriptional regulator ZNF238/ZBTB18, a gene silenced by promoter methylation, on the growth of colon cancer cells. Reintroduction of ZNF238 in HCT116 and HT29 colon cancer cells with low endogenous levels and promoter methylation of ZNF238, resulted in a significant reduction of cell proliferation both in vitro and in a subcutaneous xenograft NOD/SCID mouse model. Moreover, using immunohistochemical analysis with a validated antibody we found that ZNF238 is lost or reduced in the majority of the 133 primary colorectal tumors included in a tissue microarray, and that lower ZNF238 expression is associated with lymph node metastasis and shorter survival of patients with locally advanced colorectal cancer. In summary, we identified a set of 553 genes putatively silenced by promoter methylation in colorectal tumors that could significantly contribute to the oncogenic process. Moreover, as a proof of concept, we demonstrate that the epigenetically silenced gene ZNF238 has tumor suppressor activity and is associated with the survival of colorectal cancer patients. Citation Format: Sarah Bazzocco, Jose Higinio Dopeso, Águeda Martínez-Barriocanal, Estefanía Anguita, Rocio Nieto, Alex Sanchez, John M. Mariadason, Diego Arango. Identification of novel colorectal tumor suppressor genes through genome-wide promoter hypermethylation analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 840.