Department of Biomedical and Neuromotor Sciences, Laboratory of Biochemistry and Mitochondrial Pathophysiology, University of Bologna, via Irnerio, 48, 40126 Bologna, Italy.
Department of Biomedical and Neuromotor Sciences, Laboratory of Biochemistry and Mitochondrial Pathophysiology, University of Bologna, via Irnerio, 48, 40126 Bologna, Italy.
Biochim Biophys Acta Bioenerg. 2018 Feb;1859(2):99-109. doi: 10.1016/j.bbabio.2017.10.007. Epub 2017 Oct 31.
The physiological role of the mitochondrial ATP synthase complex is to generate ATP through oxidative phosphorylation. Indeed, the enzyme can reverse its activity and hydrolyze ATP under ischemic conditions, as shown in isolated mitochondria and in mammalian heart and liver. However, what occurs when cancer cells experience hypoxia or anoxia has not been well explored. In the present study, we investigated the bioenergetics of cancer cells under hypoxic/anoxic conditions with particular emphasis on ATP synthase, and the conditions driving it to work in reverse. In this context, we further examined the role exerted by its endogenous inhibitor factor, IF, that it is overexpressed in cancer cells. Metabolic and bioenergetic analysis of cancer cells exposed to severe hypoxia (down to 0.1% O) unexpectedly showed that Δψ is preserved independently of the presence of IF and that ATP synthase still phosphorylates ADP though at a much lower rate than in normoxia. However, when we induced an anoxia-mimicking condition by collapsing Δμ with the FCCP uncoupler, the IF-silenced clones only reversed the ATP synthase activity hydrolyzing ATP in order to reconstitute the electrochemical proton gradient. Notably, in cancer cells IF overexpression fully prevents ATP synthase hydrolytic activity activation under uncoupling conditions. Therefore, our results suggest that IF overexpression promotes cancer cells survival under temporary anoxic conditions by preserving cellular ATP despite mitochondria dysfunction.
线粒体 ATP 合酶复合物的生理作用是通过氧化磷酸化生成 ATP。事实上，该酶可以在缺血条件下逆转其活性并水解 ATP，这在分离的线粒体以及哺乳动物心脏和肝脏中都有显示。然而，当癌细胞经历缺氧或缺氧时会发生什么，尚未得到很好的探索。在本研究中，我们研究了缺氧/缺氧条件下癌细胞的生物能量学，特别强调了 ATP 合酶及其驱动其反向工作的条件。在这种情况下，我们进一步研究了其内源性抑制剂因子 IF 所发挥的作用，IF 在癌细胞中过度表达。暴露于严重缺氧（低至 0.1% O）下的癌细胞的代谢和生物能量学分析出人意料地表明，Δψ 独立于 IF 的存在而得以保留，并且 ATP 合酶仍可通过 ADP 磷酸化，但磷酸化速率远低于正常氧合时的速率。然而，当我们用 FCCP 解偶联剂使 Δμ崩溃以诱导类似缺氧的条件时，沉默 IF 的克隆仅逆转 ATP 合酶活性以水解 ATP，从而重新构成电化学质子梯度。值得注意的是，IF 过表达完全阻止了在解偶联条件下 ATP 合酶水解活性的激活。因此，我们的结果表明，IF 过表达通过在粒体功能障碍的情况下仍保持细胞内 ATP，促进了癌细胞在暂时缺氧条件下的存活。
