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A RASSF1A-HIF1α loop drives Warburg effect in...

June 2019

Nat Commun. 2019 May 13;10(1):2130. doi: 10.1038/s41467-019-10044-z

A RASSF1A-HIF1α loop drives Warburg effect in cancer and pulmonary hypertension

Dabral S, Muecke C, Valasarajan C, Schmoranzer M, Wietelmann A, Semenza GL, Meister M, Muley T, Seeger-Nukpezah T, Samakovlis C, Weissmann N, Grimminger F, Seeger W, Savai R, Pullamsetti SS

Hypoxia, defined as a reduction in the amount of oxygen available to a cell, tissue, or organism, is a fundamental and life-threatening biological phenomenon. Hypoxia signaling mediated via hypoxia inducible factor-1 (HIF-1α) plays a major role in non-malignant and malignant hyperproliferative diseases. Pulmonary hypertension (PH), a hypoxia-driven vascular disease, is characterized by hyperproliferative vascular cells and a glycolytic switch similar to the Warburg effect in cancer. Ras association domain family 1A (RASSF1A) is a scaffold protein that acts as a tumor suppressor. Although majorly studied in the field of malignancies, studies on its potential role in primary cells under different physiological cues such as hypoxia are unexplored.Here, we identify a molecular mechanism, where RASSF1A acts a crucial regulator of HIF-1α signaling. Upon hypoxia, RASSF1A protein is initially stabilized by NOX-1- and protein kinase C- dependent phosphorylation, and is subsequently transcriptionally upregulated by HIF-1α. Vice-versa, RASSF1A directly interacts with HIF-1α, blocks its prolyl-hydroxylation and proteasomal degradation, leading to its nuclear entry and transactivation of HIF-1 target genes (pyruvate dehydrogenase kinase 1 [PDK1], hexokinase 2 [HK2], and lactate dehydrogenase [LDHA]). This hitherto unknown feed-forward loop between RASSF1A and HIF-1α promotes the glycolytic shift. We find that this mechanism operates in experimental hypoxia-induced PH, which is blocked in RASSF1A knockout mice, in human primary PH vascular cells, and in a subset of human lung cancer cells. The underlying molecular mechanisms unveiled here (Fig. 1) provide future targets for therapeutic intervention, to be exploited for improved therapy of these diseases.

Fig. 1: Schematic depicture of RASFF1A mediated HIF regulation. Under normoxia, HIF1α is hydroxlyated at proline residues by PHDs, ubiquitinated, followed by proteasomal degradation. Under hypoxia, RASSF1A is phosphorylated by ROS activated PKCα, leading to increased stability. Increased RASSF1A binds to HIF1α, preventing its binding to PHD2 and prolyl hydroxylation, increased nuclear translocation and subsequent transcriptional activity. This in turn leads to increased expression of glycolytic genes (PDK1, HK2, LDHA) and RASSF1A itself, giving rise to a feed forward loop and increased proliferation and glycolysis, manifesting in pulmonary hypertension and lung cancer pathogenesis. RASSF1A: Ras association domain family 1A, pVHL: von Hippel-Lindau tumor suppressor protein, PHD2/3: prolyl hydroxylase 2/3, HIF1α: hypoxia-inducible factor 1 alpha, HIF1β: hypoxia-inducible factor 1 beta, HRE: hypoxia-response elements, Ub: ubiquitin, OH: hydroxylation, Pro: proline, NADPH: nicotinamide adenine dinucleotide phosphate hydrogen, ROS: reactive oxygen species, NOX1: NADPH oxidase 1, NADP: nicotinamide adenine dinucleotide phosphate, PKCα: protein kinase C alpha, P: phosphorylation, HK2: hexokinase 2, PDK1: pyruvate dehydrogenase kinase, isozyme 1, LDHA: lactate dehydrogenase A