Sortilin is an important regulator with potential tumour-suppressor function by limiting EGFR signalling. In this study, we undertook a comprehensive expression analysis of sortilin transcript variants and the DNA methylation status of their corresponding promoters in human non-small cell carcinomas (NSCLCs). RNA/DNA was extracted from 81 NSCLC samples and paired normal tissue. mRNA expression was measured by qPCR and DNA methylation determined by pyrosequencing. BigDye-terminator sequencing was used to confirm exon-8 alternative splicing. Results demonstrated that both SORT1A and SORT1B variants were downregulated in lung tumours. The SORT1A/SORT1B expression ratio was higher in tumours compared to normal tissue. SORT1B promoter hypermethylation was detected in lung tumours compared to normal lung (median difference 14%, Mann–Whitney testp= 10−6). Interestingly, SORT1B is hypermethylated in white blood cells, but a small and very consistent drop in methylation (6%,p= 10−15) was observed in the lung cancer cases compared to control subjects. We demonstrate that the SORT1B exon-8 splice variation, reported in sequence databases, is also a feature of SORT1A. The significantly altered quantitative and qualitative characteristics of sortilin mRNA in NSCLC indicate a significant involvement in tumour pathogenesis and may have significant impact for its utility as a predictive marker in lung cancer management.
分拣蛋白是一种重要的调节因子，通过限制表皮生长因子受体信号通路发挥潜在的肿瘤抑制功能。本研究对非小细胞肺癌中分拣蛋白转录变体及其对应启动子的DNA甲基化状态进行了全面表达分析。从81例非小细胞肺癌样本及配对正常组织中提取RNA/DNA，采用定量聚合酶链反应检测mRNA表达水平，焦磷酸测序法测定DNA甲基化状态，并通过BigDye末端测序验证第8外显子选择性剪接。结果显示SORT1A和SORT1B变体在肺肿瘤组织中均呈下调表达，且肿瘤组织中SORT1A/SORT1B表达比值显著高于正常组织。与正常肺组织相比，肺肿瘤组织呈现SORT1B启动子高甲基化状态（中位差异14%，曼-惠特尼检验p=10^-6）。值得注意的是，白细胞中虽存在SORT1B高甲基化现象，但肺癌病例较对照组仍观察到甲基化水平出现小幅而高度一致的下降（6%，p=10^-15）。本研究证实序列数据库中报道的SORT1B第8外显子剪接变异同样存在于SORT1A。非小细胞肺癌中分拣蛋白mRNA表达量与质特征的显著改变，表明其在肿瘤发病机制中具有重要作用，并可能对其作为肺癌诊疗预测标志物的应用价值产生重要影响。
Novel Transcriptional and DNA Methylation Abnormalities of SORT1 Gene in Non-Small Cell Lung Cancer
肿瘤(癌症)患者之家