Epigenetic regulation of HIF-1α in renal cancer cells involves HIF-1α/2α binding to a reverse hypoxia-response element

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene underlies the majority of sporadic clear cell renal cell carcinomas (CCRCCs) and is also responsible for the hereditary VHL cancer syndrome. VHL loss of function results in constitutive stabilization of hypoxia-inducible factors (HIF-1 alpha and HIF-2 alpha) due to insufficient proteolysis in the presence of oxygen. This activates multiple genes relevant to tumorigenesis, allowing cells to acquire further mutations and undergo malignant transformation. However, the specific role of each HIF-alpha subunit in CCRCC tumorigenesis is not yet well understood. The current paradigm supports that in the first stages of CCRCC formation the stabilization of HIF-1 alpha is dominant and this limits proliferation, but later on HIF-2 alpha increases and this induces a more aggressive cell behavior. Understanding how this transition happens is highly relevant, as it may provide novel ways to treat these cancers. Here, we show that VHL inactivation in CCRCC cells results in HIF-1 alpha/2 alpha-dependent down-regulation of HIF-1 alpha mRNA through direct binding of either subunit to a reverse hypoxia-response element in the HIF-1 alpha proximal promoter. This binding activates a series of repressive histone modification marks including histone 3 lysine 27 trimethylation (H3K27me3) to make the changes stable, and if overturned reduces CCRCC cell proliferation due to excessive HIF-1 alpha expression level. Our findings thus help understand how HIF-alpha subunits influence each other and also reinforce the idea that epigenetic mechanisms are a key step of CCRCC progression. Oncogene (2012) 31, 1065-1072; doi:10.1038/onc.2011.305; published online 15 August 2011