Differential transcriptional regulation of hypoxia-inducible factor-1α by arsenite under normoxia and hypoxia: involvement of Nrf2.
Arsenite (As(III)) is widely distributed in nature and can be found in water, food, and air. There is significant evidence that exposure to As(III) is associated with human cancers originated from liver, lung, skin, bladder, kidney, and prostate. Hypoxia plays a role in tumor growth and aggressiveness; adaptation to it is, at least to a large extent, mediated by hypoxia-inducible factor-1α (HIF-1α). In the current study, we investigated As(III) effects on HIF-1α under normoxia and hypoxia in the hepatoma cell line HepG2. We found that As(III) increased HIF-1α protein levels under normoxia while the hypoxia-mediated induction of HIF1α was reduced. Thereby, the As(III) effects on HIF-1α were dependent on both, transcriptional regulation via the transcription factor Nrf2 mediated by NOX4, PI3K/Akt, and ERK1/2 as well as by modulation of HIF-1α protein stability. In line, the different effects of As(III) via participation of HIF-1α and Nrf2 were also seen in tube formation assays with endothelial cells where knockdown of Nrf2 and HIF-1α abolished As(III) effects. Overall, the present study shows that As(III) is a potent inducer of HIF-1α under normoxia but not under hypoxia which may explain, in part, its carcinogenic as well as anti-carcinogenic actions.


KEY MESSAGE
As(III) increased HIF-1α under normoxia but reduced its hypoxia-dependent induction. The As(III) effects on HIF-1α were dependent on ROS, NOX4, PI3K/Akt, and ERK1/2. The As(III) effects under normoxia involved transcriptional regulation via Nrf2. Knockdown of Nrf2 and HIF-1α abolished As(III) effects in tube formation assays. The data may partially explain As(III)'s carcinogenic and anti-carcinogenic actions.
['Al Taleb|Zukaa|Z|', 'Petry|Andreas|A|', 'Chi|Tabughang Franklin|TF|', 'Mennerich|Daniela|D|', 'Görlach|Agnes|A|', 'Dimova|Elitsa Y|EY|', 'Kietzmann|Thomas|T|0000-0003-0242-8636']
D000818:Animals D000970:Antineoplastic Agents D018053:Arsenites D002273:Carcinogens D015687:Cell Hypoxia D002460:Cell Line D002478:Cells, Cultured D048049:Extracellular Signal-Regulated MAP Kinases D005347:Fibroblasts D005786:Gene Expression Regulation D051547:Heme Oxygenase-1 D056945:Hep G2 Cells D006801:Humans D051795:Hypoxia-Inducible Factor 1, alpha Subunit D051379:Mice D000074663:NADPH Oxidase 4 D019255:NADPH Oxidases D051267:NF-E2-Related Factor 2 D019869:Phosphatidylinositol 3-Kinases D017395:Plasminogen Activator Inhibitor 1 D051057:Proto-Oncogene Proteins c-akt D017382:Reactive Oxygen Species
Arsenite As(III) Hypoxia-inducible factor 1 (HIF-1α) Mitogen-activated protein kinase (MAPK) NADPH enzyme oxidase 4 (NOX4) Reactive oxygen species (ROS)