微小RNA-205在肿瘤化学治疗耐药中的作用和机制

李　龙　黄洪章

中山大学光华口腔医学院•附属口腔医院口腔颌面外科广东省口腔医学重点实验室 广州 510055

微小RNA-205在肿瘤化学治疗耐药中的作用和机制

李龙黄洪章

中山大学光华口腔医学院•附属口腔医院口腔颌面外科广东省口腔医学重点实验室 广州 510055

肿瘤对化学治疗药物的耐药常导致化学治疗失败，肿瘤耐药是临床治疗的一大难题。肿瘤的化学治疗耐药涉及多基因多信号转导通路的复杂调控过程，其机制迄今不明。微小RNA（miRNA）是由一类长18～25碱基组成的内源性非编码单链小RNA分子，在调节多种细胞生物学过程中起着重要的作用。miRNA的异常表达与肿瘤的发生进展、迁移及化学治疗耐药存在密切的关系，而miRNA-205（miR-205）在肿瘤化学治疗耐药中起重要的调控作用，但其具体机制尚不清楚。本文就miR-205及其在肿瘤化学治疗耐药中的作用和机制等研究进展作一综述。

微小RNA-205； 肿瘤； 化学治疗耐药

化学治疗是肿瘤治疗的重要手段之一，但肿瘤细胞对化学药物产生的耐药现象极易导致治疗失败。化学治疗耐药是多因素作用的结果，机制尚不清楚，其影响因素包括肿瘤组织内血压及血流量调节功能异常导致的化学治疗药物吸收不足而有效药物质量浓度降低[1-2]，细胞内外环境改变导致细胞对药物吸附能力降低[3-4]，从而降低细胞对药物的吸收或增加药物的排出与失活[5-6]，DNA损伤修复[7]，对程序性细胞死亡途径的干扰进而抑制程序性细胞死亡[8]，相关信号转导通路激活介导化学治疗耐药等等。诸多研究[9-10]证实，微小RNA（microRNA，miRNA）的表达水平与肿瘤发生发展以及化学治疗耐药间存在着密切的联系。miRNA的多态性常常导致miRNA对靶基因的调控作用削弱或增强，影响肿瘤细胞对药物的吸收和代谢等功能。此外，miRNA异常表达可改变肿瘤细胞与药物作用靶点的结合[11]并异常调控细胞增殖、程序性细胞死亡[12]等基本生物学过程，在肿瘤细胞对抗化学治疗药物方面起重要作用[13]。miRNA-250（miR-205）异常表达与多肿瘤的化学治疗耐药相关。如在胆管癌肿瘤细胞系中，miR-205过表达可提高胆管癌细胞对吉西他滨药物的敏感性[14]，而在非小细胞肺癌细胞系中，miR-205过表达反而提高非小细胞肺癌细胞对顺铂的耐药性[15]。Vera等[16]通过对多黑色素瘤细胞遗传特征的检测发现，miR-205异常表达也与化学治疗耐药性密切相关；因此以miR-205作为新的切入点，深入了解化学治疗耐药的分子机制可为肿瘤化学治疗开辟新的途径。

1　miR-205

miR-205是高度保守的小RNA分子，位于染色体1q32.2位置，其前体miR-205位于LOC642587基因的第二内含子和第三外显子连接处，常以与miR-200家族结合的表达形式发挥作用[17]，与不同的物种存在着同源性。人种属来源的miR-205是基于小鼠和鲀科动物其序列高度保守性利用计算机扫描技术预测[18]获得的，后来在斑马鱼和人[19]种属中进一步确认。miR-205在组织和细胞表达上具有一定特异性。miR-205主要在上皮表达，尤其是在鳞状上皮表达具有高度特异性[20]。例如在斑马鱼中，miR-205的主要在上皮表达[21]；在小鼠中，表达于舌、角膜上皮和脚掌表皮等上皮部位[22]。miR-205参与了多种细胞生命活动，其表达水平不同可以影响细胞的增殖和分化等生物学功能[23]。在上皮组织细胞形态发生[24]和上皮功能维持过程中起较重要作用[25]。此外，miR-205通过抑制低密度脂蛋白受体相关蛋白1或血管内皮生长因子-A的表达来抑制肿瘤细胞的侵袭，或通过结合特定抑癌基因抑制肿瘤细胞的增殖分化[26-28]。miR-205在不同的肿瘤中表达水平不一，miR-205在前列腺癌、乳腺癌和食管癌中的表达呈明显下调，而在肾癌、膀胱癌和卵巢癌]细胞中表达上调[20,25,29-30]。

2　miR-205在肿瘤化学治疗耐药中的作用

miR-205在肿瘤化学治疗的耐药过程中起着重要作用，其相关作用机制尚不清楚。Puhr等[31]在构建前列腺癌多西他赛耐药细胞株过程中发现：肿瘤细胞在药物筛选过程中出现上皮间质转化（epithelial-mesenchymal transition，EMT），在多西他赛处理的肿瘤细胞系或取自多西他赛药物化学治疗患者的组织标本中，内皮钙黏着蛋白（endothelial-cadherin，E-cad）的表达水平明显降低，同时miR-205的表达水平也相应降低；在耐药细胞系中，E-cad的表达缺失可导致miR-205和miR-200c表达下调，反过来上调miR-205和miR-200c也可导致E-cad的表达上调；因此，miR-205很可能参与调控EMT而在肿瘤细胞耐药产生中发挥作用。Okamoto等[15]利用基因芯片技术对两个胆管癌细胞系（HuH28和HuCCT1）进行筛选发现，miR-205在相对耐药的肿瘤细胞系中表达下调，上调miR-205表达水平后可明显提高胆管癌细胞对吉西他滨的敏感性。

在前列腺癌肿瘤细胞中，miR-205通过介导抗B细胞淋巴瘤/白血病基因（B cell lymphoma/ leukmia，BCL）2L2程序性细胞死亡基因在前列腺癌肿瘤细胞耐药中发挥作用；在前列腺癌中，miR-205表达下调可抑制化学治疗诱导的程序性细胞死亡水平，进一步提高肿瘤细胞对药物的耐药性；miR-205通过与靶基因BCL2L2的3'非编码区（untranslated region，UTR）部分序列结合，下调BCL-w表达水平后miR-205表达上调，而miR-205过表达后却又进一步促进肿瘤细胞对药物的敏感性[32]。在非小细胞肺癌中，miR-205可负调控同源性第10号染色体缺失的磷酸酶和张力蛋白同源基因（phosphatase and tensin homology deleted on chromosome ten，PTEN），miR-205与PTEN的3' UTR位点结合，上调miR-205的表达水平后，可促进非小细胞肺癌肿瘤细胞的生长、迁移和侵袭，增强肿瘤细胞的耐药性；而miR-205敲除后，可抑制以上细胞生命活动，明显提高PTEN的表达水平，而上调PTEN表达水平可抑制miR-205在肿瘤细胞中的表达[33]。

miR-205可靶向调控P73，与E2F1和DNp73等形成复杂调控网络。体内外研究[16,34]显示：上调miR-205表达水平后可促进肿瘤细胞的程序性死亡并抑制瘤体的生长；敲除miR-205后，BCL2和相关转运蛋白表达水平也相应上调，进而促进肿瘤细胞的耐药作用。此外，miR-205还可通过调控细胞的自噬过程增强肿瘤细胞对化学治疗药物的解毒作用，进而提高肿瘤细胞对化学治疗药物的耐药性[35]。

3　miR-205在肿瘤化学治疗中耐药的机制

miR-205在肿瘤化学治疗耐药研究领域日趋成为热点，但其在肿瘤中的生物学特性及作用尚不清楚。研究[36]显示，无论是临床组织标本还是肿瘤细胞系，miR-205在鳞状细胞癌中的表达水平均较其他肿瘤要高。在口腔鳞状细胞癌中，miR-205在肿瘤鳞状上皮的表达具有高度特异性，且与肿瘤的转移与否有密切关系；miR-205的表达率在具有转移性的恶性肿瘤组织标本中较高，而在良性组织标本中几乎无表达，在健康组织上皮或基质中并未见明显表达[37]。研究[38-39]显示，miR-205的激活与DNA低甲基化水平有关，与肿瘤迁移无明显关系，与肿瘤干细胞形成密切相关。在健康组织癌变过程中，miR-205通过抑制EMT来维持上皮细胞的干性，从而促进肿瘤细胞侵袭迁移[40]。

Kim等[41]通过检测口腔癌上皮细胞生物学功能发现：miR-205在口腔癌上皮细胞系中具有抑癌作用，其表达水平低于其他口腔健康的角化细胞；此外，上调miR-205表达水平后，miR-205通过激活半胱氨酸天冬酰胺特异蛋白酶（cysteinyl aspartale specific protease，caspase）-3/7等程序性细胞死亡蛋白酶，促进上皮程序性细胞死亡和提高口腔癌上皮细胞的细胞毒性；上调miR-205表达水平后，可以直接与白细胞介素-24启动子一道诱导抑癌基因的表达，进而发挥抑癌作用。Kim等[42]还发现，miR-205与轴抑制基因（axis inhibitor，Axin）2的3'UTR（64～92）位点结合抑制Axin2基因表达，进一步调控程序性细胞死亡过程和细胞毒性，而程序性细胞死亡和细胞毒性作用与肿瘤细胞的耐药性密切相关。

研究[43]显示，miR-205表达与EMT间存在着一定的关系，miR-205表达的降低会导致E-cad、神经钙黏素和纤连接蛋白表达下降，而EMT又常与肿瘤细胞耐药相关。上调miR-205表达水平可以有效地逆转肿瘤细胞EMT表型和抑制肿瘤细胞的侵袭迁移，进一步提高肿瘤细胞对化学治疗药物的敏感性[44]。本课题组在前期研究中发现，miR-205在顺铂耐药细胞株中表达下调，下调miR-205表达水平后可提高耐药细胞对顺铂药物的敏感性。

4　小结

miR-205在肿瘤化学治疗耐药的研究尚处起步阶段，其具体的耐药机制尚待进一步阐明。但越来越多的研究表明，miR-205可与多个基因靶向结合调控肿瘤细胞的各种生命活动，在参与肿瘤化学治疗耐药过程中发挥重要作用。研究[45]显示，miR-205在鳞状上皮的表达具有高度特异性，且在口腔癌中的表达水平较其他肿瘤组织高，在调控口腔癌肿瘤细胞增殖和程序性细胞死亡过程中起关键作用。miR-205在肿瘤化学治疗耐药中的研究价值不可估量，以miR-205为作用靶点，通过逆转miR-205的表达水平可以有效地提高肿瘤细胞的化学治疗敏感性。利用基因组学的方法分析患者的miRNA和mRNA表达谱，构建以miR-205为药物作用靶标的新型化学治疗药物及个性化用药，将为克服肿瘤化学治疗耐药开辟新的途径。

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（本文采编 王晴）

Role of microRNA-205 on chemoresistance and its mechanism in tumor

Li Long, Huang Hongzhang.
(Dept. of Oral and Maxillofacial Surgery, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University; Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510055, China)

This study was supported by the National Natural Science Foundation of China(81272949).

Resistance to chemotherapeutic drugs is a difficult problem that often leads to the failure of chemotherapy in tumor clinical treatment. Chemoresistance mechanism involves the complex and unclear regulation of multiple genes and signaling pathways. MicroRNA(miRNA) are endogenous, small non-coding, single-strand RNA molecules that are 18-25 nucleotides in length. They play a crucial role in regulating various cellular biological processes. Accumulated studies show that aberrant expression of miRNA is associated with progression, migration, and chemotherapy resistance in various cancers. Recently, an increasing number of studies reveal that miRNA-250(miR-205) participates in regulating chemotherapy resistance in cancers. However, the role of miR-205 in chemoresistance is still unclear. This paper reviews the relationship between miR-205 and chemotherapy resistance in tumors.

microRNA-205； tumor； chemoresistance

Q 786

A [doi] 10.7518/gjkq.2016.06.025

2016-02-11；

2016-07-04

国家自然科学基金（81272949）

李龙，主治医师，博士，Email：k369_ll@126.com

黄洪章，教授，博士，Email：huanghongzhang@tom.com