散发性结直肠癌22号染色体等位基因杂合缺失

Loss of heterozygosity of chromosome 22 in sporadic colorectal carcinoma

目的 抑癌基因的杂合缺失是结直肠癌形成的关键步骤之一 ,一个等位基因已经异常的抑癌基因杂合缺失 (LOH)可导致肿瘤的形成。本实验研究结直肠癌 2 2号染色体杂合缺失情况并探讨其意义。方法 对 83例结直肠癌肿瘤患者与正常组织抽提的DNA用 6对荧光标记的微卫星标记引物行PCR反应。产物在ABIPrism 377自动荧光测序仪进行电泳 ,以GeneScan3.1和Genotyper 2 .1软件进行基因分型。LOH与临床病理参数之间的关系比较采用 χ2 检验。结果 2 2号染色体平均杂合缺失率为 2 7.2 7% ,D2 2S2 80至D2 2S2 74 (2 2 q12 .2 -q13.33)区域表现出很高的杂合缺失率 ,以D2 2S2 80(2 2q12 .2 - q12 .3)和D2 2S2 74 (2 2 q13.32 -q13.33)两个位点最高 ,分别为 35 .0 9%和 34.0 4 %。在D2 2S2 74位点直肠癌的杂合缺失率为 5 0 % (9/ 18) ,高于近端结肠癌的 12 % (2 / 17) ,差异有显著性 (P =0 .0 18)。远端结肠癌的杂合缺失率为 4 2 % (5 / 12 ) ,较近端结肠的杂合缺失率高 ,但差异无显著性 ;远端结肠、直肠癌的杂合缺失率 (14 / 30 ,4 7% )高于近端结肠癌 (2 / 15 ,13% ,P =0 .0 15 ) ,提示远端结肠、直肠癌与近端结肠癌发生机制可能有所不同。结论 在 2 2号染色体长臂上可能存在与结直肠癌发生相关的抑癌基因 。

Objective The loss of heterozygosity (LOH) on tumor suppressor genes is believed to play a key role in the carcinogenesis of colorectal cancer. When LOH occurs at a tumor suppressor gene locus where one of the alleles is already abnormal, it can result in neoplastic transformation. In this study, we analyzed the LOH on the chromosome 22 in sporadic colorectal cancer to identify additional loci involved in colorectal tumorigenesis. Methods Six polymorphic microsatellite markers were analyzed in 83 cases of colorectal cancer and normal tissue DNA by PCR. PCR products were eletrophoresed on an ABI Prism 377 DNA sequencer; Genescan 3.1 and Genotype 2.1 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological data were performed by χ 2 test. Results The average LOH frequency on chromosome 22 was 27.27%. The region between markers D22S280 and D22S274 (22q12.2-q13.33) exhibited relatively high LOH frequency. The two highest LOH loci with frequencies of 35.09% and 34.04% was identified on D22S280 (22q12.2-q12.3) and D22S274 (22q13.32-q13.33). On D22S274 locus, LOH frequency of rectal cancer was 50% (9/18), which was higher than that of proximal colon cancer (12%, 2/17) ( P =0.018). The frequency of distal colon cancer was 42% (5/12), also higher than that of proximal colon cancer. But there was no statistical significance. Putting both the tumors in distal colon and rectum together into consideration, the frequency, 47% (14/30), was higher than that of proximal colon cancer ( P = 0.015 ),suggested the mechanism of carcinogenesis was different in both groups.Conclusion This study provided evidence for the involvement of putative tumor suppressor genes related to the sporadic colorectal carcinoma on chromosome 22q. The tumor suppressor gene(s) might locate on the 22q12.2-q12.3 and/or 22q13.32 -q13.33.