Li X, Roife D, Kang Y, Dai B, Pratt M, Fleming J B
Department of Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Oncogene. 2016 Sep 15;35(37):4881-90. doi: 10.1038/onc.2016.20. Epub 2016 Feb 15.
Lumican, an extracellular matrix proteoglycan overexpressed by pancreatic stellate cells (PSCs) and pancreatic ductal adenocarcinoma cells (PDACs), drives the formation of a tumor-specific microenvironment. We recently showed that extracellular lumican inhibits pancreatic cancer cell growth and is associated with prolonged survival after surgery. Here we investigated the role of extracellular lumican in chemotherapy-mediated cancer therapy. Lumican secretion was increased by chemotherapeutic agents in PDAC, and especially in PSCs, and appeared to be linked to the extent of cells' response to chemotherapy-induced growth inhibition. In multiple PDAC models, including cell lines, patient-derived xenografts and lumican knockout mice, lumican significantly increased antitumor effect of chemotherapy. This effect was associated with DNA damage, apoptosis and inhibition of cell viability, glucose consumption, lactate production and vascular endothelial growth factor secretion. In PDAC cells, chemotherapeutic agents triggered autophagosome formation and increased LC3 expression through the reactive oxygen species-mediated AMP-activated kinase (AMPK) signaling pathway. Inhibition of gemcitabine-induced autophagy in cancer cells by treatment with AMPK inhibitor compound C, lysosomal inhibitor chloroquine or autophagy inhibitor 3MA enhanced gemcitabine-induced apoptosis, suggesting that autophagy is a protective cellular response to gemcitabine treatment. Importantly, lumican dramatically decreased AMPK activity, inhibiting chemotherapy-induced autophagy in both in vitro and in vivo PDAC models. Co-treatment of PDAC cells with lumican and gemcitabine increased mitochondrial damage, reactive oxygen species (ROS) production and cytochrome c release, indicating that lumican-induced disruption of mitochondrial function may be the mechanism of sensitization to gemcitabine. Together, our findings demonstrate that extracellular lumican augments cytotoxicity of chemotherapy in PDAC cells through inhibition of chemotherapeutic agent-induced autophagy.
层黏蛋白聚糖是一种细胞外基质蛋白聚糖，由胰腺星状细胞（PSC）和胰腺导管腺癌细胞（PDAC）过度表达，它驱动肿瘤特异性微环境的形成。我们最近发现，细胞外层黏蛋白聚糖可抑制胰腺癌细胞生长，并与手术后生存期延长相关。在此，我们研究了细胞外层黏蛋白聚糖在化疗介导的癌症治疗中的作用。化疗药物可增加PDAC中，尤其是PSC中层黏蛋白聚糖的分泌，且这似乎与细胞对化疗诱导的生长抑制的反应程度有关。在多种PDAC模型中，包括细胞系、患者来源的异种移植模型和层黏蛋白聚糖基因敲除小鼠，层黏蛋白聚糖显著增强了化疗的抗肿瘤效果。这种作用与DNA损伤、细胞凋亡以及细胞活力、葡萄糖消耗、乳酸生成和血管内皮生长因子分泌的抑制有关。在PDAC细胞中，化疗药物通过活性氧介导的AMP激活蛋白激酶（AMPK）信号通路触发自噬体形成并增加LC3表达。用AMPK抑制剂化合物C、溶酶体抑制剂氯喹或自噬抑制剂3MA处理癌细胞，抑制吉西他滨诱导的自噬，增强了吉西他滨诱导的细胞凋亡，表明自噬是细胞对吉西他滨治疗的一种保护性反应。重要的是，层黏蛋白聚糖显著降低AMPK活性，在体外和体内PDAC模型中均抑制化疗诱导的自噬。将层黏蛋白聚糖与吉西他滨联合处理PDAC细胞，增加了线粒体损伤、活性氧（ROS）生成和细胞色素c释放，表明层黏蛋白聚糖诱导的线粒体功能破坏可能是对吉西他滨致敏的机制。总之，我们的研究结果表明，细胞外层黏蛋白聚糖通过抑制化疗药物诱导的自噬增强了PDAC细胞中化疗的细胞毒性。
