Department of Bio-system Pharmacology, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, 565-0871, Osaka, Japan.
Present address: School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangzhou, 510006, Guangdong, China.
J Exp Clin Cancer Res. 2020 Nov 30;39(1):266. doi: 10.1186/s13046-020-01762-0.
Tumor angiogenesis is regarded as a rational anti-cancer target. The efficacy and indications of anti-angiogenic therapies in clinical practice, however, are relatively limited. Therefore, there still exists a demand for revealing the distinct characteristics of tumor endothelium that is crucial for the pathological angiogenesis. L-type amino acid transporter 1 (LAT1) is well known to be highly and broadly upregulated in tumor cells to support their growth and proliferation. In this study, we aimed to establish the upregulation of LAT1 as a novel general characteristic of tumor-associated endothelial cells as well, and to explore the functional relevance in tumor angiogenesis.
Expression of LAT1 in tumor-associated endothelial cells was immunohistologically investigated in human pancreatic ductal adenocarcinoma (PDA) and xenograft- and syngeneic mouse tumor models. The effects of pharmacological and genetic ablation of endothelial LAT1 were examined in aortic ring assay, Matrigel plug assay, and mouse tumor models. The effects of LAT1 inhibitors and gene knockdown on cell proliferation, regulation of translation, as well as on the VEGF-A-dependent angiogenic processes and intracellular signaling were investigated in in vitro by using human umbilical vein endothelial cells.
LAT1 was highly expressed in vascular endothelial cells of human PDA but not in normal pancreas. Similarly, high endothelial LAT1 expression was observed in mouse tumor models. The angiogenesis in ex/in vivo assays was suppressed by abrogating the function or expression of LAT1. Tumor growth in mice was significantly impaired through the inhibition of angiogenesis by targeting endothelial LAT1. LAT1-mediated amino acid transport was fundamental to support endothelial cell proliferation and translation initiation in vitro. Furthermore, LAT1 was required for the VEGF-A-dependent migration, invasion, tube formation, and activation of mTORC1, suggesting a novel cross-talk between pro-angiogenic signaling and nutrient-sensing in endothelial cells.
These results demonstrate that the endothelial LAT1 is a novel key player in tumor angiogenesis, which regulates proliferation, translation, and pro-angiogenic VEGF-A signaling. This study furthermore indicates a new insight into the dual functioning of LAT1 in tumor progression both in tumor cells and stromal endothelium. Therapeutic inhibition of LAT1 may offer an ideal option to potentiate anti-angiogenic therapies.
肿瘤血管生成被认为是一种合理的抗癌靶点。然而，抗血管生成疗法在临床实践中的疗效和适应证相对有限。因此，仍然需要揭示对病理性血管生成至关重要的肿瘤内皮细胞的独特特征。L 型氨基酸转运蛋白 1（LAT1）在肿瘤细胞中高度广泛地上调，以支持其生长和增殖。在这项研究中，我们旨在将 LAT1 的上调确立为肿瘤相关内皮细胞的另一个新的普遍特征，并探讨其在肿瘤血管生成中的功能相关性。
在人胰腺导管腺癌（PDA）和异种移植及同基因小鼠肿瘤模型中，通过免疫组织化学方法研究肿瘤相关内皮细胞中 LAT1 的表达。在主动脉环试验、Matrigel plugs 试验和小鼠肿瘤模型中，研究了内皮细胞 LAT1 的药理和遗传消融的效果。通过使用人脐静脉内皮细胞，在体外通过 LAT1 抑制剂和基因敲低对细胞增殖、翻译调控以及 VEGF-A 依赖性血管生成过程和细胞内信号转导的影响进行了研究。
LAT1 在人 PDA 的血管内皮细胞中高度表达，但在正常胰腺中不表达。同样，在小鼠肿瘤模型中也观察到高内皮 LAT1 表达。在 ex/in vivo 试验中，通过破坏 LAT1 的功能或表达抑制血管生成。通过靶向内皮 LAT1 抑制血管生成，显著抑制小鼠肿瘤的生长。LAT1 介导的氨基酸转运是体外支持内皮细胞增殖和翻译起始的基础。此外，LAT1 对于 VEGF-A 依赖性迁移、侵袭、管状形成和 mTORC1 的激活是必需的，这表明在血管生成内皮细胞中存在一种新的促血管生成信号和营养感应之间的交叉对话。
这些结果表明，内皮细胞 LAT1 是肿瘤血管生成的一个新的关键调节因子，它调节增殖、翻译和促血管生成的 VEGF-A 信号。本研究进一步表明，LAT1 在肿瘤细胞和基质内皮细胞中的双重作用为肿瘤进展提供了新的见解。抑制 LAT1 的治疗可能是增强抗血管生成治疗的理想选择。
