Hypoxia Increases Sirtuin 1 Expression in a Hypoxia-inducible Factor-dependent Manner

Abstract

Hypoxia-inducible factors (HIFs) are stress-responsive transcriptional regulators of cellular and physiological processes involved in oxygen metabolism. Although much is understood about the molecular machinery that confers HIF responsiveness to oxygen, far less is known about HIF isoform-specific mechanisms of regulation, despite the fact that HIF-1 and HIF-2 exhibit distinct biological roles. We recently determined that the stress-responsive genetic regulator sirtuin 1 (Sirt1) selectively augments HIF-2 signaling during hypoxia. However, the mechanism by which Sirt1 maintains activity during hypoxia is unknown. In this report, we demonstrate that Sirt1 gene expression increases in a HIF-dependent manner during hypoxia in Hep3B and in HT1080 cells. Impairment of HIF signaling affects Sirt1 deacetylase activity as decreased HIF-1 signaling results in the appearance of acetylated HIF-2␣, which is detected without pharmacological inhibition of Sirt1. We also find that Sirt1 augments HIF-2 mediated, but not HIF-1 mediated, transcriptional activation of the isolated Sirt1 promoter. These data in summary reveal a bidirectional link of HIF and Sirt1 signaling during hypoxia.The ability to sense and respond to changes in oxygen content, conserved in almost all eukaryotic organisms, is conferred at the cellular level and is dictated by changes in gene expression, including by de novo transcriptional events (1). Members of the hypoxia-inducible factor (HIF) 2 family of transcription factors are key regulators of genes whose expression is altered during hypoxia. HIFs, obligate heterodimeric protein complexes, are composed of an oxygen-labile ␣-subunit and a shared, oxygen-stable ␤-subunit also referred to as ARNT (2). Whereas invertebrates contain a single HIF-␣ member, mammals contain three HIF-␣ genes: HIF-1␣, HIF-2␣ (also called endothelial PAS domain protein 1 (EPAS1)) (3-5), and HIF-3␣. HIF-␣ proteins have similar domain structures with conserved sequence identity in some regions, particularly for HIF-1␣ and HIF-2␣. The N termini of HIF-␣ and HIF-␤ proteins contain the highly conserved basic helix-loop-helix and Per/ARNT/Sim (PAS) domains involved in DNA binding and protein-protein interactions, respectively. The PAS domain may also contribute to HIF target gene specificity and may serve as a target for small molecules that disrupt specific HIF complexes (6, 7).The levels of HIF-␣ subunits increase during hypoxia due to impaired modifications of two proline residues (8, 9) situated within the oxygen-dependent degradation domain (10), part of a larger domain known as the N-terminal activation domain (NTAD) located in the midportion of HIF-␣ proteins. These two proline residues are otherwise selectively hydroxylated under normoxic conditions by oxygen-dependent prolyl hydroxylases (8, 9, 11) and subsequently target the HIF-␣ proteins for proteasomal degradation by the von Hippel-Lindau (VHL) ubiquitin-protein ligase complex (12-16).A second oxygen-dependent hydroxylation by asparaginyl hydroxylases (17, 18) targets an ...

SIRT1 and AMPK Mediate Hypoxia-Induced Resistance of Non–Small Cell Lung Cancers to Cisplatin and Doxorubicin

“…Indeed, the hypoxic regulation of SIRT1 expression remains as a conflicting phenomenon. Chen and colleagues demonstrated that SIRT1 in Hep3B and HT1080 cell-lines is induced under hypoxia at the transcriptional level by both HIF-1a and HIF-2a (37). In contrast, Zhang and colleagues showed that the SIRT1 transcription in fibroblasts is noticeably repressed under hypoxia in a CtBP-dependent fashion (21).…”

Oxygen Consumption and Usage During Physical Exercise: The Balance Between Oxidative Stress and ROS-Dependent Adaptive Signaling

“…NAD-dependent lysine deacetylases, sirtuins, control various cellular processes, including chromatin structure by the deacetylation of lysine residues of histones (271,396), apoptosis and cell survival, by the interaction with p53 and FOXO transcription factors (233,354,444), mitochondrial biogenesis via deacetylation of PGC1a (252), lipid metabolism by the interaction with SREBP-1c among other proteins (291,352,390), insulin homeostasis (98,205), DNA repair (171,224,231), inflammation by modulating the activity of NF-jB (344,439), and oxygen sensing by deacetylating hypoxia-inducible factor-1a (HIF-1a) and HIF2a (66,82,210) among other mechanisms. Sirtuin-mediated deacetylation of these transcription factors would readily effect the expression of pro-and antioxidant genes, such as PUMA, NOXA, PIG3, GADD45, Nrf2, and Mn-SOD, and stress-activated protein kinases etc., which can readily regulate redox signaling.…”

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