Nuclear ARRB1 induces pseudohypoxia and cellular metabolism reprogramming in prostate cancer [ChIP-seq]

Tumour cells sustain their high proliferation rate through metabolic reprogramming, whereby cellular metabolism shifts from oxidative phosphorylation to aerobic glycolysis, even under normal oxygen levels. HIF1A is a major regulator of this process but activation of HIF1A under normoxic conditions, termed pseudohypoxia, is not well documented. Here, using an integrative approach combining the first genome-wide mapping of chromatin binding for an endocytic adaptor, ARRB1, both in vitro and in vivo with gene expression profiling, we demonstrate that nuclear ARRB1 contributes to this metabolic shift in prostate cancer cells via regulation of Hypoxia Inducible Factor 1A (HIF1A) transcriptional activity under normoxic conditions through regulation of succinate dehydrogenase A (SDHA) and fumarate hydratase (FH) expression. ARRB1-induced pseudohypoxia may facilitate adaptation of cancer cells to growth in the harsh conditions that are frequently encountered within solid tumours. Our study is the first example of an endocytic adaptor protein regulating metabolic pathways. It implicates ARRB1 as a potential tumour promoter in prostate cancer and highlights the importance of metabolic alterations in prostate cancer. In an attempt to identify the ARRB1 cistrome in prostate cancer cells, C4-2 prostate cancer cells expressing endogenous levels of ARRB1 were used to ChIP for ARRB1, p300 (previously shown to interact with ARRB1within transcriptional complexes), RNA PolII and histone markers H3K4me1 and H4K4me3 (markers for enhancer and promoter regions, respectively). Cells were untreated and cultured in FBS supplemented with 10%FBS. In parallel, C4-2 cells stably expressing a nuclear form of ARRB1 (nucARRB1) were also used to ChIP the same complexes under the same conditions. Finally, human prostate tissue was used to ChIP for ARRB1 and histone markers.