1、解螺旋陪伴医生科研成长 1 DNADNA 损伤分泌程序损伤分泌程序 本综述由解螺旋学员 曾洋扬 负责修订(2018 年 10 月)肿瘤的发生和发展是一个复杂的、动态的过程。肿瘤微环境(tumor microenvironment,TME)参与了肿瘤细胞的发生、发展、转移等过程,癌细胞与微环境的相互作用为肿瘤进展和转移提供合适的环境。肿瘤微环境由细胞(如巨噬细胞,树突细胞,T 细胞,内皮细胞和成纤维细胞等)、细胞外基质(ECM),蛋白酶,和细胞因子等构成1。在实体瘤中,营造适于肿瘤存活的微环境是肿瘤发生、发展的第一步,其在免疫调节中具有关键作用,比如血管内皮生长因子(VEGF)和炎性趋化因子不仅
2、是主要的促血管生成因子,也是免疫调节剂,其增加血管生成并导致免疫抑制2,3。除此之外,肿瘤和基质来源的细胞外囊泡(extracellular vesicles,EV;也称为如外泌体、微泡)参与癌细胞的传播,促进癌症进展和转移,可诱导类似于病毒感染诱导的干扰素应答,参与癌细胞对放射或化学疗法的抗性4。TME 是一个动态交互系统,细胞衰老和急性组织损伤,包括基因毒性癌症治疗,都会引起 TME 变化5。解螺旋 多种细胞机制功能障碍将导致染色体不稳定性(Chromosomal instability,CIN),包括染色体分离、损伤反应缺陷、细胞周期检查点功能紊乱、端粒功能障碍等。染色体不稳定在癌症及其
3、微环境中的多方面作用,包括促进炎症信号传导,比如非整倍性诱导的衰老细胞和衰老相关分泌表型可以影响肿瘤微环境以促进肿瘤进展6,7。遗传突变和 DNA 双链断裂(DNA double-strand breaks,DSBs)等 DNA 损伤现象会破坏基因组的稳定性,为了对抗各种基因毒性和防止基因组不稳定性,细胞进化出 DNA 损伤应答(DNA Damage Response;DDR)。DDR 涉及复杂的基因网络,介导 DNA 修复,引起细胞周期延迟,长期阻滞细胞生长(衰老)和受损细胞凋亡8,9。DDR 一方面通过关键 DDR 蛋白(ATM、ATR、DNA-PKcs)及 DNA 修复基因等引起 DNA
4、 修复,另一方面通过 Chk1/2-P53-P21 等信号通路激活凋亡、自噬等死亡程序10-12。DDR 除了影响细胞自主组分,影响受损细胞本身外,还能够通过细胞非自治程序,促进细胞因子的分泌,与其他细胞相互作用,例如招募基质细胞、免疫细胞等,影响放化疗后在肿瘤微环境中幸存下来的肿瘤细胞13-15。基因毒性癌症治疗剂诱导肿瘤细胞中的 DNA 损伤,其可导致细胞死亡或衰老,但也在良性细胞如包含组织基质的肿瘤相关成纤维细胞中发挥基因毒性应激。解螺旋 在激活的肿瘤微环境中,DNA 损伤性的基因治疗方法(主要为放疗和化疗)会产生脱靶作解螺旋陪伴医生科研成长 2 用(off-target effects
5、),对于肿瘤的迁移、侵袭、转移潜力等造成了一定的影响。研究表明,DDR 是肿瘤微环境激活的重要媒介。受损细胞的分泌表型首先在细胞衰老中报道,细胞衰老是一种永久性生长停滞状态,一种肿瘤抑制机制,但同时也可诱导肿瘤微环境改变促进肿瘤发生16,17。持久性 DDR 触发衰老细胞分泌生长因子、蛋白酶和炎性细胞因子等,称为衰老相关的分泌表型(senescence-associated secretory phenotype,SASP),而持续性 DDR而非瞬时 DDR 细胞因子分泌增加也提示分泌的增加与衰老有关18。2012 年,Yu Sun 等在 Clin Cancer Res 上首次报道了 DNA
6、损伤应答可以在生物体内引发一种特别的细胞分泌表型,即 DNA 损伤分泌程序(DNA Damage Secretory Program,DDSP)19。DDSP 程序的组成复杂,包括白细胞介素(IL)-6 和 IL-8 等促炎细胞因子,血管生成生长因子以及表皮生长因子受体(EGFR)的激动剂在内的上皮有丝分裂原等。一方面 DDSP 组分通过免疫清除增强受损细胞的清除,血管生成和上皮细胞和间质细胞的迁移和增殖加速修复,但另一方面在恶性肿瘤中,DDSP 可以抑制细胞凋亡,促进血管生成、上皮-间质转化及肿瘤细胞增殖,从而增强对癌症治疗的抗性。解螺旋 炎症免疫反应是活体组织对损伤因子所起的防御反应。活性
7、氧(reactive oxygen species,ROS)和 DNA 损伤引起炎症级联反应,进而介导 DNA 氧化损伤和降低 DNA 修复能力,反过来又能诱导二级和并发炎症20,21。DNA 损伤之后,mTOR 被磷酸化,传递 DDR 信号,与 IKK复合物相互作用,通过 IL-1/IRAK1 和 mTOR/Raptor 轴激活 JNK/p38,PI3K/Akt 和 NF-B通路22。促炎细胞因子(如 IL-6、IL-8),可改变蛋白酶的细胞外基质,神经因子前体,血管生长因子和包括表皮生长因子受体(EGFR)激动剂在内的上皮细胞有丝分裂原等23,24。这些因子在肿瘤微环境中可以传递组织损伤的
8、信号,一方面通过免疫清除及时消除受损细胞,另一方面,通过诱导血管新生或促进细胞发生 EMT(上皮间质转化),促进肿瘤的增殖25和迁移23,24,良性静止期肿瘤细胞由于基因毒性会诱发 DDSP 产生耐药性,使肿瘤细胞获得对于化疗或放疗的耐受性26,对预后产生不良效果。抑制 DDSP 和炎症免疫过程可能是一个潜在的治疗靶点27。解螺旋 参考文献参考文献 1.DuFort CC,DelGiorno KE,Hingorani SR.Mounting Pressure in the Microenvironment:Fluids,Solids,and Cells in Pancreatic Ductal
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