GWAS发现的胰腺癌易感基因功能研究

Pancreatic cancer (PC) has the worst survival rate among any human cancer and there are no effective markers for screening and early diagnosis. Our previous GWAS (Wu et al, Nat Genet 2012) has identified 7 genes or loci associated with PC risk. Among them, the most significant signal was rs372883T>C in the 3′UTR of BACH1, whose roles in cancer has not been elucidated yet. Our preliminary results show that the rs372883T (not C)-containing BACH13′UTR is able to bind miR-1257 and thus suppress reporter gene expression. The BACH1 mRNA levels in human pancreatic tissues are significantly associated with rs372883 genotype (CC genotype > CT genotype > TT genotype); the BACH1 expression is significantly lower in PC tissues than in adjacent normal tissues. We also found a reverse association between BACH1 levels in PC tissue with patients’ survival, suggesting that BACH1 may not only play a role in the development but also involve in the progression of PC. Our preliminary results also indicated that knockdown of BACH1 enhances melignant phenotypes of cells such as proliferation, colony formation, migration, and invasion in vitro, and tumor growth and metastasis of xenograft in mice. Having these interesting and promising results, this project will further investigate and elucidate the underlying mechanism of the effect of BACH1 on pancreatic cancer. The findings of this project will be of significance for prevention and target therapy of pancreatic cancer.

我们通过全基因组关联研究发现7个胰腺癌易感等位基因，其中BACH1 3′UTR的rs372883T>C变异是最重要易感信号。BACH1在肿瘤发生发展中的作用尚不清楚。预实验结果表明，含rs372883T的3′UTR可与miR-1257结合并降低报告基因表达；不同rs372883基因型的人胰腺组织中BACH1 RNA表达差异显著，即CC基因型>CT基因型>TT基因型；癌组织的BACH1表达水平显著低于癌旁组织，而低表达患者的生存时间显著低于高表达患者，提示BACH1不但与胰腺癌发生相关而且还涉及胰腺癌进展。细胞恶性表型和动物移植瘤实验证明，BACH1低表达显著促进胰腺细胞恶性表型。在这些工作基础上，本项目拟进一步研究并阐明BACH1在胰腺癌发生发展中的作用机制。此项目是基于我们全基因组分析的发现进行的深入研究，既具重要性又具原创性，研究结果对胰腺癌的防治及寻找药物靶点都将具有重要意义。

胰腺癌是一种发病率相对较低的消化系统恶性肿瘤，但是其预后极差，提示胰腺癌恶性程度非常高。我们前期采用全基因组关联研究的方法，从2972例胰腺癌患者和正常对照中 (981例胰腺癌患者，1991例正常人对照) 鉴定了5个新的与胰腺癌发病风险相关的染色体区段，其中rs372883 (位于基因BACH1的3’UTR) 在胰腺癌易感中具有显著意义 (T>C, odds ratio (OR) = 0.69, 95% confidence interval (CI), 0.62−0.70; P = 2.10 × 10–10)，提示BACH1在胰腺癌易感中可能具有重要作用，然而其作用机制尚不清楚。本项目运用生化及分子生物学、细胞生物学等研究策略，首先证明了BACH1在胰腺癌组织中低表达，在胰腺癌细胞中高表达BACH1能显著抑制细胞的增殖及血管生成能力，而这些表型改变是由BACH1直接调控的下游基因HMOX1介导的。此外，高表达BACH1还能显著增强胰腺癌细胞对吉西他滨处理的敏感性，提示BACH1的差异表达还可能与胰腺癌患者的化疗敏感性相关。接着我们阐明了rs372883多态是与miRNA-1257选择性结合来调控BACH1的表达，进而调节下游增殖及促血管生成信号通路，使个体对胰腺癌具有不同的遗传易感性。同时，临床数据分析结果也表明携带rs372883CC基因型的患者对吉西他滨的治疗较TT基因型的患者更为敏感，且生存时间显著延长。这说明rs372883多态不仅与胰腺癌的易感性的相关，也可能是反映胰腺癌患者后续治疗敏感性的标志物。本项目是基于我们先前关联分析研究的进一步生物学功能机制探讨，具有原创性和系统性。研究结果对于阐明胰腺癌病因、分析胰腺癌预后及判断胰腺癌患者对吉西他滨治疗的应答反应具有重要理论意义和潜在的应用价值。