DNMT3a Epigenetic Program Regulates the HIF-2alpha Oxygen Sensing Machinery

Abstract

Epigenetic regulation of gene expression by DNA methylation plays a central role in the maintenance of cellular homeostasis. Here we present evidence implicating the DNA methylation program in the regulation of hypoxia-inducible factor (HIF) oxygen-sensing machinery. We show that DNA methyltransferase 3a (DNMT3a) methylates and silences the HIF-2alpha gene (EPAS1) in normal cells. Epigenetic silencing of EPAS1 prevents activation of the HIF-2alpha gene program associated with hypoxic cell growth, thereby limiting the proliferative capacity of cells under low oxygen tension. Naturally occurring defects in DNMT3a, observed in primary tumours and malignant cells, cause the unscheduled activation of EPAS1 in early dysplastic foci. This enables incipient cancer cells to exploit the HIF-2alpha pathway in the hypoxic tumour microenvironment, which is necessary for the formation of cellular masses larger than the oxygen diffusion limit. Reintroduction of DNMT3a in DNMT3a-defective cells restores EPAS1 epigenetic silencing, prevents hypoxic cell growth, and suppresses tumour growth in vivo. In addition, restoring HIF-2alpha expression in DNMT3a-reintroduced cancer cells restores full tumorigenic potential, including the capacity to traverse the hypoxic barrier. These data support a tumour-suppressive role for DNMT3a as an epigenetic regulator of the HIF-2alpha oxygen-sensing pathway and the cellular response to hypoxia.