Hulikova Alzbeta, Black Nicholas, Hsia Lin-Ting, Wilding Jennifer, Bodmer Walter F, Swietach Pawel
Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom;
Cancer and Immunogenetics Laboratory, Weatherall Institute of Molecular Medicine, Department of Oncology, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
Proc Natl Acad Sci U S A. 2016 Sep 6;113(36):E5344-53. doi: 10.1073/pnas.1610954113. Epub 2016 Aug 19.
Proliferation and invasion of cancer cells require favorable pH, yet potentially toxic quantities of acid are produced metabolically. Membrane-bound transporters extrude acid from cancer cells, but little is known about the mechanisms that handle acid once it is released into the poorly perfused extracellular space. Here, we studied acid handling by myofibroblasts (colon cancer-derived Hs675.T, intestinal InMyoFib, embryonic colon-derived CCD-112-CoN), skin fibroblasts (NHDF-Ad), and colorectal cancer (CRC) cells (HCT116, HT29) grown in monoculture or coculture. Expression of the acid-loading transporter anion exchanger 2 (AE2) (SLC4A2 product) was detected in myofibroblasts and fibroblasts, but not in CRC cells. Compared with CRC cells, Hs675.T and InMyoFib myofibroblasts had very high capacity to absorb extracellular acid. Acid uptake into CCD-112-CoN and NHDF-Ad cells was slower and comparable to levels in CRC cells, but increased alongside SLC4A2 expression under stimulation with transforming growth factor β1 (TGFβ1), a cytokine involved in cancer-stroma interplay. Myofibroblasts and fibroblasts are connected by gap junctions formed by proteins such as connexin-43, which allows the absorbed acid load to be transmitted across the stromal syncytium. To match the stimulatory effect on acid uptake, cell-to-cell coupling in NHDF-Ad and CCD-112-CoN cells was strengthened with TGFβ1. In contrast, acid transmission was absent between CRC cells, even after treatment with TGFβ1. Thus, stromal cells have the necessary molecular apparatus for assembling an acid-venting route that can improve the flow of metabolic acid through tumors. Importantly, the activities of stromal AE2 and connexin-43 do not place an energetic burden on cancer cells, allowing resources to be diverted for other activities.
癌细胞的增殖和侵袭需要适宜的pH值，但代谢过程中会产生潜在有毒数量的酸。膜结合转运蛋白将酸排出癌细胞，但对于酸一旦释放到灌注不良的细胞外空间后如何处理的机制却知之甚少。在这里，我们研究了在单培养或共培养条件下生长的肌成纤维细胞（结肠癌来源的Hs675.T、肠道肌成纤维细胞InMyoFib、胚胎结肠来源的CCD-112-CoN）、皮肤成纤维细胞（NHDF-Ad）和结肠直肠癌（CRC）细胞（HCT116、HT29）对酸的处理情况。在肌成纤维细胞和成纤维细胞中检测到酸加载转运体阴离子交换蛋白2（AE2）（SLC4A2产物）的表达，但在CRC细胞中未检测到。与CRC细胞相比，Hs675.T和InMyoFib肌成纤维细胞吸收细胞外酸的能力非常高。酸进入CCD-112-CoN和NHDF-Ad细胞的速度较慢，与CRC细胞中的水平相当，但在转化生长因子β1（TGFβ1，一种参与癌症-基质相互作用的细胞因子）刺激下，随着SLC4A2表达的增加而增加。肌成纤维细胞和成纤维细胞通过连接蛋白-43等蛋白质形成的间隙连接相连，这使得吸收的酸负荷能够跨基质合体传递。为了匹配对酸摄取的刺激作用，用TGFβ1增强了NHDF-Ad和CCD-112-CoN细胞之间的细胞间偶联。相比之下，即使在用TGFβ1处理后，CRC细胞之间也不存在酸传递。因此，基质细胞拥有组装酸排出途径所需的分子机制，可以改善代谢酸在肿瘤中的流动。重要的是，基质AE2和连接蛋白-43的活性不会给癌细胞带来能量负担，从而使资源能够转向其他活动。
