Thymoquinone Selectively Kills Hypoxic Renal Cancer Cells by Suppressing HIF-1α-Mediated Glycolysis

Abstract

Several reports have shown that thymoquinone (TQ) effectively attenuates angiogenesis in cancer cells, resulting in suppression of tumor growth. However, it is not yet clear whether TQ reduces hypoxia-inducible factor-1α (HIF-1α) expression in hypoxic cancer cells. Here, we found that TQ was a novel HIF-1α inhibitor through hypoxia response element (HRE)-luciferase assay-based large screening by using 502 natural compounds containing chemical library. TQ reduced HIF-1α protein levels in renal cancer cells; however, it did not affect the HIF-1α protein levels in the presence of proteasome inhibitor, MG132, indicating that the reduction effects of TQ on HIF-1α protein are mediated via the ubiquitination-proteasome dependent pathway. TQ boosted HIF-1α protein degradation, and the mechanism was revealed by inhibiting interaction between HSP90 and HIF-1α. TQ suppressed downstream genes of HIF-1α, indicating negative impact of TQ on HIF-1α transcriptional activities. In addition, TQ altered glucose, lactate, and ATP levels, leading to anaerobic metabolic disturbance. TQ induced apoptosis in hypoxic cancer cells as determined by crystal violet staining and flow cytometry for annexin V-stained cells. Taken together, we suggested that TQ is a potential anticancer agent targeting HIF-1α.

The role of ubiquitination and deubiquitination in cancer metabolism

“…Following phosphorylation by GSK3β, HIF-1α ubiquitination via FBXW7 is increased, which promotes proteolysis of HIF-1α and inhibits tumor growth [136]. Anticancer drug glyceollins and thymoquinone can inhibit tumor growth by elevating ubiquitination and degradation of HIF-1α [137,138]. E3 ligase FBX11 can reduce the mRNA stability rather than protein stability of HIF-1α [139].…”

<p>CircPVT1 Promoted the Progression of Breast Cancer by Regulating MiR-29a-3p-Mediated AGR2-HIF-1α Pathway</p>

“…Those genes are widely involved in energy metabolism, angiogenesis, apoptosis, and other genes whose protein products increase oxygen delivery or facilitate metabolic adaptation to hypoxia. [41][42][43] Hence, we believed that AGR2 could affect the apoptotic proteins expression via modulating HIF-1α.…”

PSF functions as a repressor of hypoxia-induced angiogenesis by promoting mitochondrial function

“…As the main producer of ROS in hypoxic cells, mitochondria determine the fate of cells under hypoxic conditions [21]. Our previous studies focused on the metabolic reprogramming in ocular diseases and found that the promotes ATP generation by enhancing anaerobic glycolysis [25][26][27]. For instance, HIF-1α induces cellular ROS production, inhibits mitochondrial respiration and electron transfer chain activity, while inducing glucose transporters, glycolytic enzymes, and apoptotic protein BNIP3 gene transcription, which increases the flow from glucose to lactic acid [28][29][30].…”

“…The role of HIF-1α in metabolic pathways can further help elucidate the effects of PSF on the bioenergetics pattern in HRMECs. Previous studies have reported that enhanced and stabilized HIF-1α regulates mitochondrial dynamics in hypoxia-induced pulmonary vascular remodeling and promotes ATP generation by enhancing anaerobic glycolysis [ 25 – 27 ]. For instance, HIF-1α induces cellular ROS production, inhibits mitochondrial respiration and electron transfer chain activity, while inducing glucose transporters, glycolytic enzymes, and apoptotic protein BNIP3 gene transcription, which increases the flow from glucose to lactic acid [ 28 – 30 ].…”