Terpestacin Inhibits Tumor Angiogenesis by Targeting UQCRB of Mitochondrial Complex III and Suppressing Hypoxia-induced Reactive Oxygen Species Production and Cellular Oxygen Sensing

Abstract

Cellular oxygen sensing is required for hypoxia-inducible factor-1␣ stabilization, which is important for tumor cell survival, proliferation, and angiogenesis. Here we find that terpestacin, a small molecule previously identified in a screen of microbial extracts, binds to the 13.4-kDa subunit (UQCRB) of mitochondrial Complex III, resulting in inhibition of hypoxia-induced reactive oxygen species generation. Consequently, such inhibition blocks hypoxia-inducible factor activation and tumor angiogenesis in vivo, without inhibiting mitochondrial respiration. Overexpression of UQCRB or its suppression using RNA interference demonstrates that it plays a crucial role in the oxygen sensing mechanism that regulates responses to hypoxia. These findings provide a novel molecular basis of terpestacin targeting UQCRB of Complex III in selective suppression of tumor progression.Progression of many solid tumors requires angiogenesis (1). Mitochondrial function has been linked to angiogenesis, because mitochondria are the primary sites of oxygen consumption, and angiogenesis is an oxygen concentration-sensitive process (2). Reports suggest that reactive oxygen species (ROS) 3 generation at mitochondrial Complex III is necessary and sufficient to trigger HIF-1␣ stabilization during hypoxia, and cells lacking mitochondrial DNA and electron transport activity ( cells) fail to exhibit increased ROS or up-regulation of HIF-1␣ target genes during hypoxia (3-5). Inhibitors of Complex III such as myxothiazol and stigmatellin also block mitochondrial ROS generation and inhibit the stabilization and transcriptional activity of HIF-1␣ during hypoxia. These findings suggest that the generation of ROS from mitochondrial Complex III is a critical event in the signaling of cellular hypoxia (6, 7). However, details regarding which of the components of Complex III contribute to this signaling remain to be described.Biological screening tools are useful for identifying naturally occurring small molecules capable of inducing a specific phenotype change (8, 9). We performed a large scale screen of microbial extracts in an attempt to identify small molecules that could inhibit the angiogenic response to pro-angiogenic stimuli, such as hypoxia, in endothelial cells. We identified terpestacin as a small molecule with unique bicyclo sesterterpene structure capable of inhibiting the angiogenic response at concentrations below the toxic threshold (10). Terpestacin strongly inhibits the functional response to hypoxia of human umbilical vein endothelial cells in vitro and angiogenesis within the embryonic chick chorioallantoic membrane in vivo. In addition to this anti-angiogenic activity, terpestacin has previously been reported to inhibit syncytium formation during human immunodeficiency virus infection and has been chemically synthesized (11-13). However, neither the molecular target of this compound nor the cellular mechanism of its anti-angiogenic activity has been identified.In the present study we identified the binding protein of terpestacin and...

Chronic myeloid leukemia stem cells display alterations in expression of genes involved in oxidative phosphorylation

“…The reason for this effect is not known, but it may result from transcriptional regulation and/or better adaptation to bone marrow niche conditions [15][16][17]. Overall, elevated or normal expression of the components of MRC complex I and II suggests that OXPHOS reaction and electron flow can be properly initiated, but deregulated expression of the members of MRC complex III may "derail" and/or slow down the flow of electrons causing their "leakage".…”

A Novel Ca2+/Calmodulin Antagonist HBC Inhibits Angiogenesis and Down-regulates Hypoxia-inducible Factor

“…In particular, among the HIF-1 inhibitors tested, terpestacin exhibited the greatest anti-angiogenic activity in combination with HBC. Terpestacin blocks hypoxia-induced ROS generation by targeting UQCRB of mitochondrial Complex III, thereby resulting in suppression of HIF-1 activation (44,50). It is conceivable that combined treatment of terpestacin and HBC may inhibit HIF-1␣ activity at multiple levels, including synthesis, stability, translocation, and transcriptional activity, by blocking both ROS and calcium signaling in hypoxic conditions.…”

“…We therefore evaluated whether HBC increased the anti-angiogenic activity of various anti-cancer agents known to inhibit HIF-1 by different mechanisms. For this study, we assessed the effect of combination treatment with HBC and the histone deacetylase (HDAC) inhibitor SAHA, the mTOR inhibitor rapamycin, or a new mitochondria Complex III ubiquinol-cytochrome c reductase binding protein (UQCRB) inhibitor terpestacin (42)(43)(44). To determine the anti-angiogenic activity of the inhibitors, a chemoinvasion assay was conducted using endothelial cells.…”

Cyclic stretch stimulates mitochondrial reactive oxygen species and Nox4 signaling in pulmonary artery smooth muscle cells

“…The stretch model of PPHN in vitro, together with PPHN lambs, may identify potential therapeutic targets in the prevention and/or treatment of PPHN. The continuing development of novel pharmacological inhibitors of mitochondrial complex III, such as terpestacin (24), and Nox4, such as GKT137831 (5), may prove to be beneficial in these studies.…”