Abstract 821: DNA hypermethylation of IRX4 is a frequent event that may confer growth advantage to pancreatic cancer cells

Abstract

Abstract Epigenetic gene silencing by aberrant DNA methylation is one of the important mechanisms leading to the loss of key cellular pathways in tumorigenesis. Methyl-CpG targeted transcriptional activation (MeTA) reactivates hypermethylation-mediated silenced genes in a different way from DNA demethylating agents. Previous study using microarray coupled with MeTA (MeTA-array) identified seven commonly hypermethylation-mediated silenced genes in pancreatic cancer cell lines. In this study, IRX4 (Iroquois homeobox 4) was focused on because IRX4 was located at chromosome 5p15.33 where one of pancreatic cancer susceptibility loci has been identified through genome-wide association study (GWAS). IRX4 has also been identified as a candidate tumor suppressor gene in prostate cancer. IRX4 was greatly downregulated in all of the analyzed 12 pancreatic cancer cell lines by promoter hypermethylation. In addition, IRX4 promoter region was found to be frequently and specifically hypermethylated in primary resected pancreatic cancers (15/22: 68%); corresponding normal pancreatic tissues were unmethylated. To examine whether IRX4 has the growth inhibitory effect on pancreatic cancer cell lines, colony formation assay using PK-1 and PK-9 cell lines has been performed; compared with empty vector-transfected cells, IRX4 expression vector-transfected cells formed significantly reduced number of colonies. Furthermore, tetracycline-inducible IRX4 expressing vector system was constructed and a pancreatic cancer cell line PK-1 was analyzed for further functional investigation; induction of IRX4 suppressed cell growth in PK-1. Our results suggest that DNA methylation-mediated silencing of IRX4 is a frequent event that may confer growth advantage to pancreatic cancer cells and MeTA may be a powerful tool to search critical hypermethylated genes in tumorigenesis. Citation Format: Kanchan Chakma, Zhaodi Gu, Fuyuhiko Motoi, Michiaki Unno, Akira Horii, Shinichi Fukushige. DNA hypermethylation of IRX4 is a frequent event that may confer growth advantage to pancreatic cancer cells [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 821.