NPRL2基因与奥沙利铂治疗结直肠癌的研究进展

付伟然 刘艾芸 杜雅菊

哈尔滨医科大学附属第二医院消化内科(150001)

NPRL2基因与奥沙利铂治疗结直肠癌的研究进展

付伟然 刘艾芸 杜雅菊*

哈尔滨医科大学附属第二医院消化内科(150001)

结直肠癌(CRC)是全球三大恶性肿瘤之一，具有高发病率和高死亡率。研究发现，NPRL2基因与CRC发生、发展关系密切，CRC患者NPRL2基因表达显著降低。奥沙利铂是第三代铂类抗肿瘤药物，已广泛应用于胃肠道肿瘤化疗，可提高CRC患者生存率，但部分患者存在耐药。NPRL2基因可增加奥沙利铂治疗CRC的敏感性，是CRC潜在的治疗靶点。本文就NPRL2基因与奥沙利铂治疗CRC的研究进展作一综述。

结直肠肿瘤； NPRL2基因； 奥沙利铂； 治疗

结直肠癌(colorectal cancer, CRC)是最常见的消化道恶性肿瘤之一，其发病率居全球癌症第三位，死亡率居第二位，每年新发确诊患者约120万例[1]。随着人们生活水平的提高和饮食习惯的改变，我国CRC发病率逐年增高，并已成为死亡率位居第三的恶性肿瘤[2-3]。手术切除和全身化疗是CRC的主要治疗方式，但因CRC起病隐匿，多数患者确诊时已处于疾病晚期，丧失了外科手术切除病变组织的机会，因此以化疗为主的综合治疗是晚期CRC的主要治疗方案。化疗可提高CRC患者生存率，目前常用药物包括奥沙利铂(oxaliplatin)、5-氟尿嘧啶(5-fluorouracil)和伊立替康等(irinotecan)。肿瘤化疗相关不良反应较多，临床表现和作用机制极为复杂。长期化疗患者易出现复发，复发后肿瘤恶性程度更高，且存在耐药现象，长期治疗效果不佳，其生存率通常不足6个月。肿瘤对化疗药物耐药的可能机制包括药物吸收减少、药物外排增加、解毒系统激活、DNA修复激活、肿瘤细胞上皮-间质转化(EMT)或药物诱导的细胞凋亡减弱等[4-5]。CRC相关基因的检测可能有助于开展针对性治疗，建立个体化治疗方案，进而减少耐药和不良反应的发生，改善CRC患者的预后[6-9]。本文就NPRL2(nitrogen permease regulator-like 2)基因与奥沙利铂治疗CRC的研究进展作一综述。

一、NPRL2基因结构和生物学功能

1. NPRL2基因结构：NPRL2是一种抑癌基因，又称肿瘤抑制候选基因4(tumor suppressor candidate 4, TUSC4)，位于人染色体3p21.3区域，该区域的基因组表达异常或功能失调已被证实与多种肿瘤发生、发展有关，其机制可能与NPRL2基因启动子纯合子缺失、微卫星不稳定性以及基因突变有关[10]。NPRL2基因由11个外显子和10个内含子组成，可利用多个起始密码子和终止密码子通过不同剪接方式编码成多种剪接异构体。NPRL2基因编码的NPRL2蛋白由380个氨基酸组成，在人体多种组织和器官中均有表达。此外，NPRL2基因在生物物种间具有高度保守性。

2. 生物学功能：NPRL2在人体多种正常组织(如心脏、肝脏、肾脏、脑和胰腺等)中均有显著表达[11]，而在肿瘤(如肺癌、肾癌、肝癌、乳腺癌、鼻咽癌和卵巢癌等)中表达明显减少，其具体机制尚未明确[12-13]。NPRL2基因可干扰多种肿瘤细胞生长，与肿瘤发生、发展和预后相关[10,14]。NPRL2基因可通过参与DNA错配修复、调控细胞周期信号转导、诱导细胞凋亡、抑制细胞增殖等途径发挥抑癌作用[10-11,15]，并可增加抗癌药物敏感性，促进肿瘤细胞凋亡[16]。Ueda等[17]利用携带NPRL2基因的腺病毒对肺癌裸鼠进行瘤内注射，发现癌细胞增殖和肿瘤转移均受到明显抑制，并证实NPRL2是预测肺癌和其他类型癌症中顺铂治疗敏感性的潜在标记物，可作为分子靶向药物来增加顺铂治疗的敏感性。Wang等[18]通过基因失活检测(GIT)发现小细胞肺癌细胞株U2020和肾癌细胞株KRC/Y染色体3p21.3区域存在多个抑癌基因，其中NPRL2基因在体内、外均被证实具有较强抑制肿瘤细胞增殖的作用。Senchenko等[19]发现NPRL2基因在原发性非小细胞肺癌中表达减少。NPRL2基因与顺铂联合治疗肺癌时，可通过激活DNA损伤检查点通路，使细胞周期阻滞在G2/M期并诱导凋亡，有效克服肿瘤细胞对顺铂的耐药性[20]。Otani等[13]发现肝癌患者NPRL2 mRNA表达异常，是影响患者预后的独立危险因素。Tang等[21]通过将NPRL2基因转染至肾透明细胞癌细胞株786-0中，发现NPRL2可有效调节细胞周期检查点，使肾癌细胞周期阻滞在G0/G1期，从而抑制肿瘤细胞增殖，诱导肿瘤细胞凋亡。Liu等[22]发现NPRL2表达与CRC发生、发展密切相关，外周血NPRL2 mRNA水平可作为早期腺瘤和CRC筛查的潜在标记物。

NPRL2基因失活导致相关抑癌基因表达异常，进而诱导肿瘤发生，该过程可能的发生机制如下：①DNA复制的错配修复系统异常引起DNA复制保真度降低以及基因组不稳定(如微卫星不稳定性)，进而导致NPRL2基因发生突变失活，促进肿瘤进展[23-24]。②NPRL2基因可抑制3-磷酸肌醇依赖性蛋白激酶1(PDK1)激活。PDK1是细胞增殖及其信号转导的关键调节因子，与NPRL2基因结合后导致PDK1下游信号分子Akt和核糖体蛋白S6K失活，进而抑制细胞增殖。NPRL2基因失活可引起PDK1异常激活，增强PDK1下游细胞增殖信号转导，从而导致肿瘤发生[25]。③NPRL2基因可提高Chk1和Chk2激酶活性。Chk1和Chk2是细胞周期检查点激酶，可阻滞细胞周期，在乳腺癌、前列腺癌、肺癌和食管癌中异常表达[26-27]。NPRL2基因失活可下调Chk1和Chk2激酶活性，引起DNA损伤修复系统异常，从而抑制肿瘤细胞凋亡，导致细胞周期紊乱，促进肿瘤发生[26]。

二、奥沙利铂的临床应用

奥沙利铂是一类含有1, 2-二氨环己烷基团的DNA损伤类化疗药物，是继顺铂之后的第三代铂类抗癌药，目前已广泛应用于临床，并具有较好疗效[28]。DNA损伤类药物是一类重要的化疗药物，可通过诱导DNA损伤来抑制肿瘤细胞生长并诱导凋亡，但易导致肿瘤细胞产生耐药性[29]。奥沙利铂在静止期细胞中的反应最为活跃，其以DNA为作用靶点，与DNA链上的G共价结合形成配位金属盐络合物，从而破坏DNA结构和功能，促进肿瘤细胞凋亡。奥沙利铂对晚期肿瘤的疗效和安全性均较好[30-31]，已广泛应用于晚期恶性肿瘤治疗，但由于肿瘤细胞DNA损伤修复蛋白表达上调，肿瘤细胞DNA损伤修复能力增强，导致肿瘤细胞对DNA损伤类化疗药物(如奥沙利铂等)耐药性产生[32-34]。化疗患者常出现癌症复发和耐药，故奥沙利铂长期疗效不佳。因此，提高药物敏感性以避免耐药情况出现是提高奥沙利铂化疗效果的关键。

三、NPRL2可增加奥沙利铂治疗CRC的敏感性

NPRL2可有效抑制肿瘤细胞活性，通过参与DNA错配修复、调控细胞周期信号转导以及诱导细胞凋亡等方式发挥抑癌作用[10-11]。肿瘤细胞NPRL2过度表达可抑制细胞增殖并诱导细胞凋亡，从而提高奥沙利铂对CRC的敏感性。研究[35]表明，转染NPRL2的人结肠癌细胞株HCT116中奥沙利铂的半数抑菌浓度显著低于正常细胞，且NPRL2对奥沙利铂敏感性的促进作用具有时间依赖性。

1. NPRL2通过抑制细胞生长增加奥沙利铂对结肠癌细胞的敏感性：NPRL2基因转染结肠癌细胞后，使肿瘤细胞周期阻滞于G1期，从而导致S期结肠癌细胞减少。与未转染NPRL2的肿瘤细胞相比，奥沙利铂显著抑制转染NPRL2的结肠癌细胞生长。

2. NPRL2通过促进细胞凋亡增加奥沙利铂对结肠癌细胞的敏感性：CD24是一类以糖基磷脂酰肌醇(GPI)锚定于细胞表面的糖蛋白[36]，是存在于活化内皮细胞和血小板上的黏附素受体，可促进肿瘤淋巴结转移[37]，胃癌组织CD24高表达与肿瘤淋巴结转移的相关性已被证实[38]。NPRL2过表达可导致CD24+结肠癌细胞比例下调，与奥沙利铂联合用于治疗时，可明显促进结肠癌细胞凋亡。NPRL2过表达和奥沙利铂联合诱导的结肠癌细胞凋亡较两者单独作用更为明显[35]。

3. NPRL2通过抑制PI3K/Akt/mTOR信号通路增加奥沙利铂对结肠癌细胞的敏感性：PI3K/Akt/mTOR信号通路在消化道肿瘤中过度活化，是CRC发生、发展的核心环节[39]，在肿瘤细胞增殖、凋亡、血管生成和肿瘤转移中发挥重要作用，是潜在的多分子治疗靶点[40-41]。外界刺激因子(如生长因子等)与细胞膜表面受体结合后，可激活PI3K并磷酸化Akt，Akt活化后可激活下游靶蛋白mTOR，mTOR与受体结合后进一步激活蛋白激酶p70S6K和蛋白翻译调控因子4E-BP1，从而促进细胞增殖。NPRL2可通过下调PI3K/Akt/mTOR信号通路活化水平，使肿瘤细胞周期阻滞于G1期，抑制肿瘤细胞增殖，进而提高奥沙利铂的治疗敏感性[42]。此外，对于NPRL2基因高表达的结肠癌细胞，奥沙利铂可通过上调细胞凋亡蛋白酶caspase-3和caspase-9表达，促进结肠癌细胞凋亡。

四、结语

综上所述，NPRL2基因与CRC发生、发展密切相关。目前研究已证实NPRL2可通过抑制肿瘤细胞增殖、促进肿瘤细胞凋亡、调节PI3K/Akt/mTOR信号通路活化等途径来增加奥沙利铂的治疗敏感性，逆转肿瘤细胞对奥沙利铂的耐药性。NPRL2与奥沙利铂联用的治疗方案可在分子水平为肿瘤的基因治疗提供新思路，有望成为CRC治疗的新手段。但NPRL2基因增加奥沙利铂敏感性的具体作用机制仍有待进一步研究来证实。

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AdvancesinStudyonNPRL2GeneandOxaliplatininTreatmentofColorectalCancer

FUWeiran,LIUAiyun,DUYaju.

DepartmentofGastroenterology,the2ndAffiliatedHospitalofHarbinMedicalUniversity,Harbin(150001)

DU Yaju, Email: duyaju1964@163.com

Colorectal cancer (CRC) is one of the three major malignant tumors in the world with high morbidity and mortality. It is found that NPRL2 gene is closely related to the occurrence and development of CRC, and the expression of NPRL2 gene in CRC patients is significantly reduced. Oxaliplatin is the third generation of platinum anticancer drugs, and has been widely used in the chemotherapy of gastrointestinal tumors. Oxaliplatin can improve the survival rate of CRC patients, but some patients have drug resistance. NPRL2 gene can increase the sensitivity of oxaliplatin in the treatment of CRC, and is a potential target for treatment of CRC. This article reviewed the advances in study on NPRL2 gene and oxaliplatin in the treatment of CRC.

Colorectal Neoplasms; NPRL2 Gene; Oxaliplatin; Therapy

10.3969/j.issn.1008-7125.2017.12.012

*本文通信作者，Email: duyaju1964@163.com

(2017-05-17收稿；2017-06-11修回)