Abstract 741: CpG methylation abrogates KLF2-mediated transcriptional repression of telomerase in human T cells.

Abstract Many genes in tumor cells are DNA-methylated and transcriptionally repressed. Constitutive expression of the limiting catalytic subunit of telomerase, hTERT, is one of the common signatures of tumor cells, even though its promoter is DNA-methylated. On the other hand, in normal somatic cells the promoter is unmethylated and transcription of hTERT is strictly regulated. In this study, we examined transcriptional regulation of the hTERT gene in normal and tumor cells. We identified a novel promoter element, which bound the zinc-finger transcription factor Krüpple-like factor 2 (KLF2) in normal human T Lymphocytes. The binding of KLF2 to the hTERT promoter element paralleled repression of hTERT transcription in resting normal T cells. T cell growth induced KLF2 release from the element and hTERT transcription. Forced reduction of KLF2 expression by siRNA in normal resting T cells increased the level of endogenous hTERT mRNA. The hTERT promoter is methylated in the KLF2-positive human T leukemic cell line, Kit 225, and KLF2-negative human T leukemic cell line, Jurkat. Treatment with the DNA methyltransferase inhibitor, Zebularine, reduced levels of CpG methylation in the hTERT promoter, resulting in downregulation of hTERT mRNA expression in KLF2-positive Kit 225 cells, while the Zebularine treatment did not cause any appreciable effects on hTERT expression in KLF2-negative Jurkat cells. Methylation of CpG sequences in endogenous and exogenous hTERT promoter elements inhibited the KLF2 binding to the element. Furthermore, KLF2 binding to the promoter is associated with histone H3 repressive marks, indicating KLF2-mediated epigenetic silencing of the hTERT promoter. Our results suggest that KLF2 partly controls strict transcriptional regulation of the hTERT gene through association and dissociation with the promoter in normal T cells, but in tumor cells these important interactions are prevented by DNA methylation. Citation Format: Toshifumi Hara, Manami Yoshita, Masataka Nakamura. CpG methylation abrogates KLF2-mediated transcriptional repression of telomerase in human T cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 741. doi:10.1158/1538-7445.AM2013-741