Cancer Physiology, Moffitt Cancer Center, 12902 USF Magnolia Dr, Tampa, FL, 33612, USA.
Graduate School, University of South Florida, 4202 E Fowler Ave, Tampa, FL, 33620, USA.
BMC Biol. 2022 Jul 15;20(1):163. doi: 10.1186/s12915-022-01340-0.
Aggressive cancers commonly ferment glucose to lactic acid at high rates, even in the presence of oxygen. This is known as aerobic glycolysis, or the "Warburg Effect." It is widely assumed that this is a consequence of the upregulation of glycolytic enzymes. Oncogenic drivers can increase the expression of most proteins in the glycolytic pathway, including the terminal step of exporting H equivalents from the cytoplasm. Proton exporters maintain an alkaline cytoplasmic pH, which can enhance all glycolytic enzyme activities, even in the absence of oncogene-related expression changes. Based on this observation, we hypothesized that increased uptake and fermentative metabolism of glucose could be driven by the expulsion of H equivalents from the cell.
To test this hypothesis, we stably transfected lowly glycolytic MCF-7, U2-OS, and glycolytic HEK293 cells to express proton-exporting systems: either PMA1 (plasma membrane ATPase 1, a yeast H-ATPase) or CA-IX (carbonic anhydrase 9). The expression of either exporter in vitro enhanced aerobic glycolysis as measured by glucose consumption, lactate production, and extracellular acidification rate. This resulted in an increased intracellular pH, and metabolomic analyses indicated that this was associated with an increased flux of all glycolytic enzymes upstream of pyruvate kinase. These cells also demonstrated increased migratory and invasive phenotypes in vitro, and these were recapitulated in vivo by more aggressive behavior, whereby the acid-producing cells formed higher-grade tumors with higher rates of metastases. Neutralizing tumor acidity with oral buffers reduced the metastatic burden.
Therefore, cancer cells which increase export of H equivalents subsequently increase intracellular alkalization, even without oncogenic driver mutations, and this is sufficient to alter cancer metabolism towards an upregulation of aerobic glycolysis, a Warburg phenotype. Overall, we have shown that the traditional understanding of cancer cells favoring glycolysis and the subsequent extracellular acidification is not always linear. Cells which can, independent of metabolism, acidify through proton exporter activity can sufficiently drive their metabolism towards glycolysis providing an important fitness advantage for survival.
侵袭性癌症通常以高速度将葡萄糖发酵为乳酸，即使在有氧气的情况下也是如此。这被称为有氧糖酵解，或“Warburg 效应”。人们普遍认为，这是糖酵解酶上调的结果。致癌驱动因素可以增加糖酵解途径中大多数蛋白质的表达，包括从细胞质中输出 H 当量的末端步骤。质子外排泵维持细胞质的碱性 pH 值，即使在没有与致癌基因相关的表达变化的情况下，也可以增强所有糖酵解酶的活性。基于这一观察结果，我们假设葡萄糖的摄取和发酵代谢的增加可能是由细胞内 H 当量的排出驱动的。
为了验证这一假设，我们稳定转染低糖酵解 MCF-7、U2-OS 和糖酵解 HEK293 细胞，表达质子外排系统：PMA1（质膜 ATP 酶 1，一种酵母 H-ATP 酶）或 CA-IX（碳酸酐酶 9）。体外表达任何一种外排泵都能增强有氧糖酵解，表现为葡萄糖消耗、乳酸生成和细胞外酸化率增加。这导致细胞内 pH 值升高，代谢组学分析表明，这与丙酮酸激酶上游所有糖酵解酶的通量增加有关。这些细胞在体外也表现出更强的迁移和侵袭表型，在体内通过更具侵袭性的行为得到再现，即产酸细胞形成具有更高转移率的高级别肿瘤。用口服缓冲剂中和肿瘤酸度可降低转移负担。
因此，即使没有致癌驱动突变，增加 H 当量外排的癌细胞随后会增加细胞内碱化，这足以改变癌症代谢，使有氧糖酵解上调，出现 Warburg 表型。总的来说，我们已经表明，传统上认为癌细胞有利于糖酵解，随后导致细胞外酸化的观点并不总是线性的。独立于代谢，通过质子外排泵活性酸化的细胞可以充分将其代谢推向糖酵解，为生存提供重要的适应性优势。
