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在45例结直肠癌中有28例FHIT蛋白表达显著减少或缺失, 即阴性表达率为62.2%, 5例表达减弱, 12例表达阳性, 且阳性表达者染色强度较正常黏膜高; 其中结直肠癌Dukes A, B和C期FHIT蛋白表达阴性比例分别为6/11, 5/12和17/22. 结直肠癌FHIT蛋白阴性表达率显著高于正常对照组(62.2% vs 4.4%, x2 = 25.33, P<0.01), 具有显著性差异. FHIT蛋白在未伴淋巴转移的Dukes A+B期和已伴淋巴转移的C期中表达有显著性差异(47.8% vs 77.3%, x2 = 4.28, P<0.05).
2.2 FHIT蛋白在结直肠腺瘤中的表达
在36例结直肠腺瘤中有7例FHIT蛋白表达显著减少或缺失, 即阴性表达率为19.4%, 4例表达减弱, 25例表达阳性; 其中结直肠腺瘤伴轻度、中度和重度不典型增生FHIT蛋白表达阴性比例分别为2/16, 1/7和4/13. FHIT蛋白阴性表达率在结直肠腺瘤与结直肠癌间存在显著性差异(19.4% vs 62.2%, x2 = 14.19, P<0.01).FHIT蛋白阴性表达在结直肠腺瘤伴轻度不典型增生和中+重度不典型增生中表达无显著差异(12.5% vs 25.0%, x2 = 0.84, P>0.25), 与正常对照组比较亦无显著性差异(19.4% vs 4.4%, x2 = 3.51, P>0.05).
3 讨论
FHIT基因定位于染色体3p14.2, 其cDNA全长为1 095 bp, 共有10个外显子, 其中5-9为编码外显子, 跨越t (3; 8)易位断裂点和极脆性区域FRA3B. FHIT存在于大多数正常组织中, 国外发现多种肿瘤组织中FHIT蛋白表达频繁降低或丢失, 并发现与FHIT基因转录和缺失有关, 提示该基因为肿瘤候选抑制基因, 该蛋白有肿瘤抑制性和很强的诱导细胞凋亡能力. Capuzzi et al[17]对55例胃腺癌的研究表明, 49%的病例FHIT蛋白完全丢失, FHIT蛋白缺失与Lauren分类、肿瘤浸润、核分级无关, 而与分期、分级、生存期相关, 分期越晚、分级越高, FHIT丢失率越大, FHIT表达阴性患者存活时间明显低于FHIT表达阳性患者. Ho et al[18]对48例早期肺非小细胞癌(NSCLC)的研究显示, 58.3%存在FHIT表达缺失, 说明FHIT变化在支气管上皮细胞生长中起重要作用.
我们研究证实结直肠癌中存在FHIT蛋白表达显著减少或缺失, 其阴性表达率为62.2%, 略高于国外研究结果, Hao et al[16]采用免疫组化检测结肠癌和中重度不典型增生腺瘤中FHIT蛋白表达, 发现FHIT蛋白阴性表达率分别为44%和17%. 赵坡 et al[19]采用类似方法检测60例结肠癌中FHIT蛋白表达, 发现55%结肠癌FHIT蛋白表达显著减少或缺失, 说明FHIT低表达在结肠癌发生、发展中具有重要作用.我们研究中癌组织FHIT蛋白低表达在Dukes分期组中的分布差异具有显著性, 提示FHIT蛋白表达减少与转移状况具有一定的相关关系, 与Kuwai et al[20]的研究结果相一致. Mori et al[21]采用RT-PCR方法对62例结肠癌研究中, 发现结肠癌异常FHIT转录本的检出率为50%. Luceri et al[22]在56例结直肠癌中发现29例(55.18%)存在FHIT基因高频率的缺失、异常转录, 提示FHIT基因主要通过缺失和/或异常转录参与肿瘤的发病机制.
目前有关FHIT与结直肠腺瘤的关系尚有争议, 我们研究发现结直肠腺瘤FHIT阴性表达率为19.4%, 与Hao et al[16]的研究结果一致, 但低于Morikawa et al[23]的研究结果, 在他的研究中, 47%结直肠腺瘤存在FHIT异常表达, 且与不典型增生程度有关. Saitoh et al[24]检测211例腺瘤(其中22.7%为扁平凹陷型腺瘤)FHIT蛋白表达情况, 发现扁平凹陷型腺瘤FHIT蛋白表达明显强于同样大小的隆起型腺瘤, FHIT在腺瘤中的表达异常, 有待于进一步探讨.
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