一种潜在的骨肉瘤治疗靶向—TWEAK/Fn14 信号通路
2013-08-15综述俞光荣审校
于 涛(综述),俞光荣(审校)
同济大学附属同济医院骨科,上海 200065
骨肉瘤是骨骼系统最常见的原发性恶性肿瘤,好发于中、青年,在中国的发病率占到原发恶性骨肿瘤的44%[1],近三分之一的患者会发生肺转移[2]。随着各种新辅助化疗方法的广泛实施,术前术后化疗的综合治疗已使骨肉瘤患者的5年生存率从单纯截肢的15%~20%提高到60%~70%[3],但仍有30%~40%的患者最终仍因各种原因死亡。故骨肉瘤恶性程度高,预后差,目前针对本病尚无有效、彻底的治疗方法。给患者及家属带来极大的痛苦,给社会造成一定的经济负担。
1 骨肉瘤的分子生物学治疗现状
随着分子生物学技术的广泛开展和应用,发现很多致病因子参与骨肉瘤的发生,也为对该病的治疗提供了一条新的有可行性的治疗策略。参与骨肉瘤发生的细胞因子很多,其中包括CD44、选择素、钙粘附素、转化生长因子、骨形态发生蛋白(BMP)、血小板衍生生长因子(PDGF)、基质金属蛋白(MMP)等[4]。参与骨肉瘤发生相关的基因有MDM2、p53、p16、CDK4、PTEN、HER2 等[5]。
基因治疗是将人正常基因或有治疗作用的基因(靶基因)通过载体导入人体靶细胞,以纠正基因缺陷或发挥治疗作用。达到治疗疾病目的的一种生物医学高科技疗法。骨肉瘤基因治疗的载体包括病毒载体和非病毒载体两大类。目前针对骨肉瘤开展了抗肿瘤血管生成、促进肿瘤细胞凋亡及免疫基因治疗等多种研究。骨肉瘤的基因治疗研究已取得一定进展,但很多基因治疗缺乏特异性靶向。如何开发更多对骨肉瘤治疗有效的基因,更好地实现基因调控,提高载体靶向性和转染效率、实现基因联合治疗等还有待进一步深入研究。
2 TWEAK/Fn14 信号通路与骨肉瘤的关系
随着信号通路研究的开展和深入,各种信号通路在骨肉瘤发生发展中的作用也越来越受到关注。其在骨肉瘤的发病和治疗方面都有重要意义。
Wnt[6-11]、Notch[12-14]、Hedgehog[15-16]、PI3/AKT[17-19]、RAS[20-22]、NF-kappa B[18,23-24]等信号转导通路均被证实在骨肉瘤的发病过程中发挥着一定作用。近年来,TWEAK/Fn14 通路在肿瘤发生发展中的作用逐渐受到关注,即与成纤维细胞因子诱导14(Fn14)绑定的大鼠肿瘤坏死因子样细胞凋亡弱诱导因子(TWEAK)通路。
2.1 TWEAK/Fn14 信号通路简介
TWEAK 是一种分泌性蛋白质,是肿瘤坏死因子超家族(TNFSF)的新成员,最早于1997年由Chicheportiche 报道[25]。其结构高度保守,在人和鼠TWEAK 的受体结合区有93%的氨基酸同源性[26]。人类TWEAK 基因位于染色体17p13.1 上,编码产物为Ⅱ型跨膜蛋白,由249个氨基酸组成,其N 端包含疏水键,允许其N 端插入细胞膜,C 端胞外区域包含其受体结合位点。TWEAK 合成初是一种膜结合蛋白,很快被转变具有生物学特性的小的可溶性片段。成纤维细胞因子诱导14 (fibroblast growth factor-inducible14,Fn14)为TWEAK 的受体。人类Fn14 基因位于染色体16p13.3 上,编码产物为129个氨基酸组成的Ⅰ型跨膜蛋白。人和鼠的Fn14 的全部序列有90%的同源性,并且人的TWEAK 能和鼠的Fn14 结合,鼠的TWEAK 也可与人的Fn14 结合[27]。Fn14 本身不具有蛋白激酶活性,是通过接头分子(adaptor molecules)将其与下游信号传导分子联系起来。有实验证实,TNFR 相关因子家族(TRAF)是联系Fnl4和下游信号传导通路的一组重要接头分子。当可溶性TWEAK 作用于Fnl4 阳性细胞株后,可通过TRAF 活化核转录因子(NF-KB)、胞外信号调节激酶(ERK)、p38 丝裂原活化蛋白激酶(p38MAPK)和c-Jun 氨基末端激酶(JNK)信号传导通路[28]。
2.2 TWEAK/Fn14 信号通路的生物学作用
2.2.1 TWEAK/Fn14 信号通路的正常生物学作用
TWEAK和它的受体成纤维细胞因子诱导14(Fn14)相互作用可调节多种细胞内反应,其在多种不同组织中构成性的表达。这些反应包括血管发生作用的兴奋、促炎性反应因子的诱导、细胞迁移、增生和凋亡的调控等[29-32]。此外,TWEAK 还可以靶向作用于软骨细胞、成骨细胞和滑膜成纤维细胞。有实验证明RANTES(激活调节正常T 细胞表达和分泌因子)产物和RANKL(破骨细胞分化因子)表达在MC3T3- E1 细胞中被TEEAK/Fn14 通路上调。所以TWEAK 可能是可以调节成骨细胞功能的一种新型细胞因子[33]。TWEAK/Fn14 通路可激活RAW 细胞(小鼠单核巨噬细胞)和人HT-29 结肠腺癌细胞中的NF-kappa B,c-Jun N-terminal 酶信号级联反应,表明TWEAK 可介导RAW264.7 单核巨噬细胞系向多核的功能性破骨细胞分化[34]。另外,重组的可溶解TWEAK 浓聚物可诱导内皮细胞核主动脉平滑肌细胞增生,降低培养物对血清和生长因子的需要量,说明TWEAK 在血管形成过程中起到重要作用[35]。另有研究表明,TWEAK 是内皮细胞存活的有效诱导物,并能在Fn14 的协同下诱导内皮细胞增生和迁移,诱导毛细血管腔形态发生[36]。TWEAK 亦可增强内皮细胞中FGA-2和VEGF-A 的有丝分裂能力[37]。TWEAK 可抑制骨形态发生蛋白(BMP)-2 诱导的成骨细胞分化标记表达,如通过促细胞分裂激活蛋白酶(MAPK)通路调节的碱性磷酸酶。此外,在MC3T3 细胞中,TWEAK 通过MAPK 细胞外信号调节激酶通路正调节RANKL(NF- kappaB 受体活化配体)表达。所有这些作用于小鼠成骨细胞系MC3T3- E1 细胞的效应可被Fn14-Fc(TWEAK 抑制蛋白)嵌合体抑制。
2.2.2 TWEAK/Fn14 信号通路在肿瘤中的生物学作用
TWEAK 分布于多种人肿瘤细胞株。在各种肿瘤组织标本中可检测出TWEAK 的表达。有研究表明,人神经胶质瘤、肺癌、直肠癌、肝癌、卵巢癌、宫颈癌、前列腺癌、乳腺癌、肾脏肿瘤、脑部肿瘤中均检测到TWEAK 的mRNA 或蛋白表达[38-44]。TWEAK 及其受体Fn14 信号通路可诱导肿瘤细胞凋亡[45],促进肿瘤细胞增殖[40-41],提高肿瘤细胞侵袭力[46],诱导肿瘤血管的形成[41],促炎性反应并藉此通过炎性介质的调控促进肿瘤播散和转移[47]。
3 总结与展望
肿瘤内新生血管是影响骨肉瘤侵袭及转移的重要因素,TWEAK/Fn14 不仅可以诱导肿瘤血管形成,还可以诱导肿瘤细胞凋亡、增殖,增强肿瘤侵袭力、播散和转移,其很有可能在骨肉瘤组织中具有特殊甚至是特异的作用和意义,并且在骨肉瘤的发生发展中发挥重要作用,成为一种潜在的肿瘤治疗的新型分子靶向[48]。研究TWEAK/Fn14 在骨肉瘤中的表达,可进一步明确骨肉瘤发生的分子生物学机制,且有可能为提供一种全新的潜在的有效的分子靶向治疗策略提供理论依据。
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