miR-17对线粒体呼吸代谢功能的调控机制及miR-17*纳米在前列腺癌治疗中的实验研究

Aberrant microRNA (miRNA) expression has been implicated in the pathogenesis of cancer. Numerous studies have shown that elevated miR-17-92 cluster is associated with tumorigenesis, which includes the 5'-arm of six miRNA precursors. However, the function of the miRNAs produced from the 3'-arm of these precursors remains unknown. Recently, we reported that miR-17*, a complementary strand to miR-17, is able to suppress three primary mitochondrial antioxidant enzymes, such as manganese superoxide dismutase (MnSOD), glutathione peroxidase (GPX) and thioredoxin reductase (TrxR). Interestingly, Disulfiram (DSF), a dithiolcarbomate drug shown to have an anticancer effect, induces the level of mature miR-17* and cell death in prostate cancer, suggesting that miR-17* may suppress tumorigenicity of prostate cancer through inhibition of mitochondrial antioxidant enzymes. In addition, miR-17 has been shown to suppresses hypoxia-inducible factor 1-α(HiF-1α), another redox-associated protein. Therefore, we propose that miR-17and miR-17* play the important roles in regulation of cellular redox homeostasis and bioenergetics. High levels of antioxidant enzymes in aggressive prostate cancer protect the cancer cells against radiotherapy-induced reactive oxygen species (ROS). Thus, we propose to develop a miR-17* nanoparticle to enhance radiotherapeutic efficiency by specifically targeting prostate-specific membrane antigen (PSMA) highly expressed in prostate tumors.

MicroRNA介入的信使RNA翻译水平上负调节是基因调控中的一个重要环节。本课题前期研究发现了一种负链转录的miR-17* 能同时抑制三种线粒体内抗氧化酶在前列腺肿瘤细胞中的表达: 含锰超氧化物歧化酶，谷胱甘肽过氧化物酶和硫氧还原蛋白还原酶。我们还发现乙醛脱氢酶抑制剂能特异性地激活miR-17* 转录，下调三种抗氧化酶活性和抑制前列腺癌细胞体外体内增殖。因此，本课题将进一步探索miR-17和miR-17* 如何配合调节线粒体氧化还原反应平衡，以维持线粒体有氧环境下的能量代谢，以及miR-17* 如何造成细胞呼吸代谢的紊乱。由于其三种抗氧化酶在肿瘤细胞内过高表达，其抗氧化功能直接增强肿瘤细胞抵抗治疗尤其是放射性治疗的能力，本课题设计一种miR-17* 纳米且附有与前列腺特殊膜蛋白抗原特异性结合能力，使之能选择性地靶向前列腺肿瘤和抑制三种抗氧化酶的活性，以达到增效前列腺癌放射性治疗的目标。

前列腺癌放疗抵抗、恶性化骨转移是临床中突出问题。放疗过程中产生的氧化性自由基（ROS）诱导肿瘤细胞抗氧化酶应激活化是放疗抵抗的主要机理。项目前期研究发现miR-17-3p（或miR-17*）可同时下调MnSOD，Gpx和TrxR三种线粒体抗氧化酶蛋白表达，并抑制前列腺肿瘤恶性化发展。本课题设计进一步研究miR-17-3p通过下调MnSOD，Gpx和TrxR增加前列腺肿瘤细胞对放疗的敏感性和相关的细胞能量代谢途径变化的机制。研究结果表明线粒体抗氧化酶功能异常导致细胞能量代谢紊乱，是肿瘤发病和治疗耐性产生的重要驱动因子。MnSOD基因缺失导致线粒体氧化磷酸化与电子呼吸链解偶联，细胞能量代谢转向有氧糖酵解支路，启动了肿瘤发病相关的Warburg效应。相反，放射线诱导NF-kB信号通路激活抗氧化酶表达，导致放疗抵抗。恶性前列腺癌PC-3转染表达miR-17-3p抑制三种线粒体抗氧化酶在放疗中的应激活化，降低线粒体呼吸作用，有效地增敏放疗。基于病毒phi29核酸包装的3WJ-pRNA技术构建的miR-17-3p纳米可特异地靶向肿瘤细胞，增敏放疗。但因技术精度高、成本贵，大量制备尚有困难，有待后续转化研究的推进。

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