摘要
采用癌症基因组图谱(TCGA)、基因型及基因表达量关联数据库(GTEX)和基因表达综合数据库(GEO)分析m6A编辑器、擦除器和阅读器相关基因的表达水平,并采用Kaplan-Meier生存曲线分析m6A阅读器IGF2BP2表达与胰腺癌患者预后的关系;采用免疫组化在胰腺癌组织及癌旁组织临床标本中验证IGF2BP2的表达水平;采用CCK-8实验、流式细胞周期检测、平板克隆形成实验、Transwell分析m6A阅读器IGF2BP2敲低后胰腺癌细胞增殖活性、细胞周期、克隆形成数目与迁移能力的变化。
TCGA-GTEX及GEO数据库分析显示,m6A阅读器基因IGF2BP2在胰腺癌组织中高表达(均P<0.05),且高表达与不良的总体生存期相关(均P<0.05)。临床标本的免疫组化结果证实m6A阅读器IGF2BP2在胰腺癌组织的表达高于癌旁组织。功能性实验结果显示,IGF2BP2基因敲减后,两株细胞的增殖能力明显减弱,且细胞周期更多停在静止期(G0~G1期),细胞克隆形成数目明显减少,细胞迁移能力明显降低(均P<0.05)。
胰腺癌是一种发病率持续上升且致命性高的消化系统肿瘤,2024年美国癌症统计数
胰岛素样生长因子2 mRNA结合蛋白(IGF2BP)家族是一类新发现的m6A阅读器蛋白,可以稳定含有m6A修饰的mRNA,并且通过K同源(KH)结构域促进翻
使用GP6244平台,从癌症基因组图谱(TCGA,https://portal.gdc.cancer.gov)中收集胰腺组织样本的转录组数据,其中胰腺癌样本178例,癌旁组织样本4例。从基因型及基因表达量关联数据库(GTEX,https://xenabrowser.net/datapages)中收集胰腺组织样本的转录组数据,正常胰腺组织样本167例。从基因表达综合数据库(GEO,https://www.ncbi.nlm.nihgov/geo)下载胰腺癌相关基因表达数据集GSE28735、GSE62452中的表达数据。
将常规保存于中南大学湘雅三医院中心实验室的BXPC3和SW1990人胰腺癌细胞株接种于含有10%胎牛血清、1%青霉素(100 U/mL)和链霉素(100 μg/mL)的DMEM培养液中,置于37 ℃、5% CO2的孵育箱中培养,每隔2~3 d传代1次。
将癌和癌旁组织切片置于玻片上,放入60 ℃恒温箱中烘烤60 min,使其固定,玻片浸泡于二甲苯中脱蜡3次,10 min/次。依次将玻片浸入100%、95%、85%、70%、50%的乙醇溶液中,每个步骤3 min,蒸馏水冲洗,完成水化;滴加3%过氧化氢溶液于组织切片上,室温孵育10 min,去除内源性过氧化物酶活性;采用磷酸盐缓冲液(PBS)轻轻洗涤3次,每次5 min,玻片置于柠檬酸钠缓冲液(pH 6.0)进行抗原修复,微波炉100 ℃,10 min;切片自然冷却至室温,采用PBS冲洗切片3次,每次5 min;采用5%牛血清白蛋白(BSA)在室温下孵育切片30 min,阻断非特异性蛋白结合位点。倾去封闭液,不洗涤,滴加兔多克隆IGF2BP2抗体(1∶300稀释),确保完全覆盖组织,4 ℃孵育过夜,确保抗体与抗原充分结合,使用PBS缓冲液轻轻洗涤切片3次,每次5 min。滴加辣根过氧化物酶标记的山羊抗兔二抗(1∶50稀释),确保覆盖整个组织,室温孵育1 h,使用PBS洗涤切片3次,每次5 min,向切片滴加DAB显色剂,于显微镜下观察,直至切片出现棕色或棕黄色,用蒸馏水轻轻冲洗10 min终止反应;将切片置于苏木精染液中染色1 min,自来水冲洗切片,浸泡10 min,使组织返蓝,按脱蜡的逆向顺序将切片依次置于70%、85%、95%和100%乙醇中脱水,每个步骤3 min;将切片置于二甲苯中透明,共2次,每次5 min;滴加中性树胶于切片上,盖上盖玻片,常温下晾干切片;于显微镜下观察癌和癌旁组织中IGF2BP2的表达情况(阳性信号表现为棕色或棕黄色颗粒),并评估癌和癌旁组织中IGF2BP2表达水平。
Lipofectamine 3000转染试剂购自美国Invitrogen公司;阴性对照小干扰RNA(si-NC),IGF2BP2小干扰RNA(si-IGF2BP2)购自吉玛基因;提取RNA试剂盒、cDNA逆转录试剂盒和RT-PCR试剂盒源于翌圣生物(中国上海,11123ES)。按照常规方法将BXPC3、SW1990细胞分别于中板培养,当细胞融合度为60%时,使用无血清的培养液洗涤细胞,并按照Lipofectamine 3000步骤依次转染si-NC(si-NC组)和si-IGF2BP2(si-IGF2BP2组),再孵育48 h后备用。
使用TRIzol试剂提取转染后si-NC组和si-IGF2BP2组细胞的总RNA,检测RNA浓度及纯度;逆转录获得cDNA,-20 ℃保存备用;采用SYBR Green试剂盒,在荧光定量PCR仪上进行实时定量PCR分析,PCR反应条件为:95 ℃预变性30 s;95 ℃变性20 s,60 ℃退火30 s,72 ℃延伸30 s,45个循环,72 ℃,延伸5 min;实验重复3次。采用
将BXPC3及SW1990细胞分别接种至6孔板,接种量为2×1
将BXPC3及SW1990细胞转染48 h后的si-NC组、si-IGF2BP2组,分别胰酶消化并接种至96孔板(5×1
将BXPC3和SW1990细胞分别以每孔1×1
使用0.25%的胰蛋白酶处理对数生长期的BXPC3和SW1990细胞转染样本,轻轻震荡制成单细胞悬浮液后,接种于6孔板上(1 000个细胞/孔),置37 ℃、5% CO2温箱培养,待克隆肉眼可见时终止培养,并丢弃培养基,4%多聚甲醛固定15 min,结晶紫染色30 min,最后计数克隆数。
将分别已转染48 h的si-NC、si-IGF2BP2的SW1990、BXPC3细胞消化,并分别将细胞密度调整为×1
分别将TCGA与GTEX数据库及GEO数据集GSE28735与GSE62452胰腺癌数据合并矩阵并去批次效应,m6A编辑器相关基因(ZC3H13、RBM15B、METTL3、RBM15、METTL14、WTAP)、擦除器相关基因(FTO、ALKBH5)、阅读器相关基因(HNRNPA2B1、YTHDF1、YTHDC1、YTHDC2、YTHDF3、IGF2BP1、IGF2BP2、IGF2BP3、RBMX、YTHDF2、HNRNPC)中有18个相关基因在TCGA-GTEX数据库(胰腺癌样本178例、正常胰腺样本171例)显示具有明显的表达差异,其中IGF2BP2在胰腺癌中呈高表达(均P<0.05);19个m6A表观遗传学修饰相关基因中有17个在GEO数据集胰腺癌样本(n=114)和正常胰腺样本(n=106)中表达,并有9个显示差异化表达,其中IGF2BP2在胰腺癌中呈高表达(均P<0.05)(图

图1 m6A相关基因差异表达分析 A:TCGA-GTEX;B:GEO
Figure 1 Differential expression analysis of m6A related genes A: TCGA-GTEX; B: GEO

图2 IGF2BP2肿瘤与正常样本差异表达分析 A:TCGA-GTEX;B:GEO
Figure 2 Differential expression analysis of IGF2BP2 in tumor and normal samples A: TCGA-GTEX; B: GEO
TCGA-GTEX、GEO数据库中Kaplan-Meier生存分析显示,m6A阅读器IGF2BP2高表达与较差的总体生存期相关(均P<0.05)(

图3 不同IGF2BP2表达水平胰腺癌患者的生存曲线 A:TCGA;B:GEO
Figure 3 Survival curves of pancreatic cancer patients with different IGF2BP2 expression levels A: TCGA; B: GEO
进一步用临床样本通过免疫组化验证其表达情况,结果与生信分析相一致的是,相较于胰腺正常组织,IGF2BP2在肿瘤样本中呈明显高表达(

图4 免疫组化检测IGF2BP2在胰腺癌组织与正常胰腺组织样本中的表达 A:正常胰腺组织结构清晰、细胞排列整齐;B:胰腺肿瘤组织结构混乱,细胞大小不一,排列混乱,整个视野被IGF2BP2染成深黄色
Figure 4 Immunohistochemical staining for IGF2BP2 expression in pancreatic cancer tissues and normal pancreatic tissue samples (magnification indicated in the images above) A: Normal pancreatic tissue with a clear structure and orderly cell arrangement; B: Pancreatic tumor tissue with a disorganized structure, irregular cell sizes, and chaotic arrangement, with the entire field stained dark yellow for IGF2BP2
为了进一步分析m6A阅读器IGF2BP2的生物学功能,选择了两种胰腺癌细胞株(SW1990及BXPC3)作为研究对象。转染效果分析显示,两株细胞进行IGF2BP2基因敲减后,si-IGF2BP2组的IGF2BP2表达在转录水平及蛋白水平均较各自si-NC组明显降低(均P<0.05)(

图5 转染效果检测 A:IGF2BP2 mRNA表达检测;B:IGF2BP2蛋白表达检测
Figure 5 Transfection efficiency detection A: IGF2BP2 mRNA expression analysis; B: IGF2BP2 protein expression analysis

图6 细胞功能学实验 A:CCK-8实验检测细胞增殖活性;B:流式细胞术检测细胞周期;C:克隆形成实验检测细胞扩增能力;D:Transwell实验检测细胞迁移能力
Figure 6 Cell functional experiments A: CCK-8 assay for cell proliferation activity; B: Flow cytometry for cell cycle analysis; C: Colony formation assay for cell expansion ability; D: Transwell assay for cell migration ability
越来越多的研究证据揭示,m6A是真核生物mRNA中最常见的转录后修饰,对于mRNA的稳定性具有重要的意
m6A阅读器包括IGF2BP1、IGF2BP2、IGF2BP3等,人类胰岛素样生长因子2(IGF2)mRNA结合蛋白家族(IMP/IGF2BP)参与了一系列的生物过程,包括发育、肿瘤生成和干细胞性
近年来,m6A阅读器IGF2BP2在多种肿瘤的发生和发展机制中受到了广泛关注,其在不同类型肿瘤中的作用机制已进行了研究。在结直肠癌中,IGF2BP2通过识别并结合m6A修饰的SOX2 mRNA,增强了SOX2 mRNA的稳定性,维持SOX2的高表达水平,从而推动了癌细胞的干性维持、侵袭和转移能力增
综上所述,m6A阅读器IGF2BP2在胰腺癌组织中呈高表达,且与胰腺癌患者不良预后密切相关,其作用机制可能与促进癌细胞生长与迁移有关,IGF2BP2有望成为胰腺癌的生物标志物及潜在治疗靶点,为胰腺癌的治疗提供新途径。
作者贡献声明
朱卫东、向伟负责实验设计实施、数据整理、统计分析、论文撰写,严安、欧峥嵘负责生信分析;朱红伟、余枭负责研究指导,论文修改。
利益冲突
所有作者均声明不存在利益冲突。
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