Coleman P S
Ann N Y Acad Sci. 1986;488:451-67. doi: 10.1111/j.1749-6632.1986.tb46578.x.
We have established that a preferential export of pyruvate-generated citrate occurs from cholesterol-rich tumor mitochondria, with both isolated mitochondrial systems as well as with viable tumor tissue slices (i.e., with whole tumors cells). Furthermore, we have demonstrated that the more rapid citrate efflux kinetics (catalyzed by the tricarboxylate exchange carrier) of isolated tumor mitochondria is completely inhibited upon addition of 1,2,3-benzenetricarboxylate (BTC) and have shown that this inhibition is apparently also obtained in viable tumor tissue when the inhibitor is added to the tissue incubation. Upon BTC inhibition of tumor mitochondrial citrate export in viable tumor tissue incubations, the incorporation of [14C]pyruvate into newly synthesized cholesterol is severely inhibited as well. Among the most interesting conclusions drawn from our results, we catalog the following. The preferential export of citrate from isolated tumor mitochondria appears to be coupled, functionally, to a high linear rate of incorporation of 14C from pyruvate to cholesterol in viable tumor tissue slices, simultaneously supporting the postulate of a truncated Krebs cycle and corroborating the well-established deregulated and continuous cholesterogenesis pathway in tumors, especially hepatomas. The extent of [14C]pyruvate flux to newly generated cholesterol in either tumor or normal liver tissue is inversely related to the extent of 14CO2 production. Despite the evolution of some CO2 during cholesterogenesis, the predominant portion presumably arises via metabolic processing of pyruvate-generated citrate during Krebs cycle-linked respiration. Isolated tumor mitochondrial systems, as well as viable tumor tissue incubations, can manifest a reversal in the pattern of enhanced mitochondrial citrate efflux coupled to increased cholesterogenesis, when BTC is added to the system. This implies that BTC, a hydrophobic but negatively charged moiety at pH 7, can indeed penetrate the plasma membrane of cells. Upon entry into the cell, BTC apparently blocks the tricarboxylate carrier of tumor tissue mitochondria, thus forcing the mitochondrial citrate into Krebs cycle-linked respiration rather than permitting it to serve as the predominant provider of an increased supply of cytosolic acetyl CoA precursor required for deregulated cholesterogenesis during the development of the tumor.
我们已经证实，富含胆固醇的肿瘤线粒体存在丙酮酸生成的柠檬酸优先输出现象，这在分离的线粒体系统以及活的肿瘤组织切片（即完整的肿瘤细胞）中均有体现。此外，我们还证明，添加1,2,3-苯三甲酸（BTC）后，分离的肿瘤线粒体更快的柠檬酸流出动力学（由三羧酸交换载体催化）会被完全抑制，并且表明当将该抑制剂添加到组织培养液中时，在活的肿瘤组织中显然也会出现这种抑制作用。在活的肿瘤组织培养液中，当BTC抑制肿瘤线粒体柠檬酸输出时，[14C]丙酮酸掺入新合成胆固醇的过程也会受到严重抑制。从我们的研究结果得出的最有趣的结论如下。分离的肿瘤线粒体中柠檬酸的优先输出在功能上似乎与活的肿瘤组织切片中丙酮酸的14C快速线性掺入胆固醇的过程相关联，这同时支持了截短的三羧酸循环假说，并证实了肿瘤尤其是肝癌中已确立的胆固醇生成途径失调且持续的观点。在肿瘤或正常肝组织中，[14C]丙酮酸流向新生成胆固醇的通量程度与14CO2产生的程度呈负相关。尽管在胆固醇生成过程中有一些CO2生成，但主要部分可能是在三羧酸循环相关呼吸过程中通过丙酮酸生成的柠檬酸的代谢过程产生的。当向系统中添加BTC时，分离的肿瘤线粒体系统以及活的肿瘤组织培养液会表现出与胆固醇生成增加相关的线粒体柠檬酸流出增强模式的逆转。这意味着BTC在pH 7时是一种疏水但带负电荷的部分，确实可以穿透细胞膜。进入细胞后，BTC显然会阻断肿瘤组织线粒体的三羧酸载体，从而迫使线粒体柠檬酸进入三羧酸循环相关呼吸过程，而不是使其作为肿瘤发展过程中失调的胆固醇生成所需的胞质乙酰辅酶A前体增加供应的主要提供者。
