Autophagy in cancer associated fibroblasts promotes tumor cell survival Role of hypoxia, HIF1 induction and NFκB activation in the tumor stromal microenvironment
Autophagy in cancer associated fibroblasts promotes tumor cell survival Role of hypoxia, HIF1 induction and NFκB activation in the tumor stromal microenvironment
复制标题
DOI：
10.4161/cc.9.17.12928
复制
发表时间：
2010-09-01
期刊：
影响因子：
4.3
通讯作者：
Sotgia, Federica
中科院分区：
文献类型：
--
作者：
Martinez-Outschoorn, Ubaldo E.;Trimmer, Casey;Sotgia, Federica
最近，利用共培养系统，我们证明了MCF7上皮性癌细胞在邻近的肿瘤相关成纤维细胞中诱导氧化应激，导致基质小窝蛋白-1(CaV-1)的自噬/溶酶体降解。然而，这一过程背后的详细信号机制(S)在很大程度上仍不清楚。在这里，我们表明，低氧足以诱导基质成纤维细胞中Cav-1的自噬降解，这一过程可被溶酶体抑制剂氯喹阻断。在低氧诱导Cav-1降解的同时，我们看到一些成熟的自噬/有丝分裂吞噬标记上调，即LC3、ATG16L、BNIP3、BNIP3L、HIF-1α和NF-kappa B。此外，HIF-1α的药理激活驱动Cav-1的降解，而HIF-1的药理失活阻止Cav-1的下调。同样，另一种自噬诱导剂--核因子kappa B的药理失活也能阻止Cav-1的降解。此外，用谷胱甘肽合成酶的抑制剂，即BSO处理，通过耗尽还原的谷胱甘肽库来诱导氧化应激，足以诱导Cav-1的自噬降解。因此，氧化应激诱导成纤维细胞中HIF1和核因子kappaB的激活似乎推动了Cav-1的自噬降解。为了直接支持这一假设，我们发现MCF7癌细胞通过旁分泌机制激活邻近癌症相关成纤维细胞中由HIF-1α和NF-kappa B驱动的荧光素酶报告。与这些发现一致的是，使用siRNA方法在间质成纤维细胞中急性敲除Cav-1确实足以诱导自噬，同时上调溶酶体和有丝分裂吞噬标记。基质Cav-1的缺失和基质自噬的诱导是如何影响癌细胞存活的？有趣的是，我们发现基质成纤维细胞中Cav-1的缺失可以保护邻近的癌细胞免受细胞凋亡的影响。因此，自噬的癌症相关成纤维细胞除了为癌细胞代谢提供可循环的营养物质外，还在防止邻近的上皮性癌细胞死亡方面发挥了保护作用。我们证明了癌症相关的成纤维细胞上调了邻近的上皮性癌细胞中TIGAR的表达，从而产生了对凋亡和自噬的抵抗。最后，Cav-1(-/-)缺失小鼠的乳房脂肪垫在体内表现出类似低氧的反应，并上调了自噬标志物，如LC3和BNIP3L。综上所述，我们的研究结果为“癌症代谢的自噬肿瘤间质模型”提供了直接支持，并解释了癌症患者间质Cav-1缺失的特殊预后价值。因此，基质成纤维细胞Cav-1的缺失是肿瘤微环境中慢性缺氧、氧化应激和自噬的生物标志物，与其预测乳腺癌早期肿瘤复发、淋巴结转移和他莫昔芬耐药的能力一致。我们的结果提示，缺乏间质Cav-1的癌症患者应该受益于HIF抑制剂、核因子kappa B抑制剂、抗氧化治疗以及自噬/溶酶体抑制剂。这些互补的靶向治疗可以单独或联合使用，以防止肿瘤间质间自噬的发生，这会导致“致命的”肿瘤微环境。
Recently, using a co-culture system, we demonstrated that MCF7 epithelial cancer cells induce oxidative stress in adjacent cancer-associated fibroblasts, resulting in the autophagic/lysosomal degradation of stromal caveolin-1 (Cav-1). However, the detailed signaling mechanism(s) underlying this process remain largely unknown. Here, we show that hypoxia is sufficient to induce the autophagic degradation of Cav-1 in stromal fibroblasts, which is blocked by the lysosomal inhibitor chloroquine. Concomitant with the hypoxia-induced degradation of Cav-1, we see the upregulation of a number of well-established autophagy/mitophagy markers, namely LC3, ATG16L, BNIP3, BNIP3L, HIF-1 alpha and NF kappa B. In addition, pharmacological activation of HIF-1 alpha drives Cav-1 degradation, while pharmacological inactivation of HIF-1 prevents the downregulation of Cav-1. Similarly, pharmacological inactivation of NF kappa B-another inducer of autophagy-prevents Cav-1 degradation. Moreover, treatment with an inhibitor of glutathione synthase, namely BSO, which induces oxidative stress via depletion of the reduced glutathione pool, is sufficient to induce the autophagic degradation of Cav-1. Thus, it appears that oxidative stress mediated induction of HIF1- and NF kappa B-activation in fibroblasts drives the autophagic degradation of Cav-1. In direct support of this hypothesis, we show that MCF7 cancer cells activate HIF-1 alpha- and NF kappa B-driven luciferase reporters in adjacent cancer-associated fibroblasts, via a paracrine mechanism. Consistent with these findings, acute knock-down of Cav-1 in stromal fibroblasts, using an siRNA approach, is indeed sufficient to induce autophagy, with the upregulation of both lysosomal and mitophagy markers. How does the loss of stromal Cav-1 and the induction of stromal autophagy affect cancer cell survival? Interestingly, we show that a loss of Cav-1 in stromal fibroblasts protects adjacent cancer cells against apoptotic cell death. Thus, autophagic cancer-associated fibroblasts, in addition to providing recycled nutrients for cancer cell metabolism, also play a protective role in preventing the death of adjacent epithelial cancer cells. We demonstrate that cancer-associated fibroblasts upregulate the expression of TIGAR in adjacent epithelial cancer cells, thereby conferring resistance to apoptosis and autophagy. Finally, the mammary fat pads derived from Cav-1 (-/-) null mice show a hypoxia-like response in vivo, with the upregulation of autophagy markers, such as LC3 and BNIP3L. Taken together, our results provide direct support for the "Autophagic Tumor Stroma Model of Cancer Metabolism", and explain the exceptional prognostic value of a loss of stromal Cav-1 in cancer patients. Thus, a loss of stromal fibroblast Cav-1 is a biomarker for chronic hypoxia, oxidative stress and autophagy in the tumor microenvironment, consistent with its ability to predict early tumor recurrence, lymph node metastasis and tamoxifen-resistance in human breast cancers. Our results imply that cancer patients lacking stromal Cav-1 should benefit from HIF-inhibitors, NF kappa B-inhibitors, anti-oxidant therapies, as well as autophagy/lysosomal inhibitors. These complementary targeted therapies could be administered either individually or in combination, to prevent the onset of autophagy in the tumor stromal compartment, which results in a "lethal" tumor microenvironment.