脑胶质瘤全基因组SNP芯片扫描筛选与EGFR相关联基因的研究

Cancer is a result of genomic DNA alterations. Glioblastoma multiforme (GBM) is the most common primary brain tumor. In previous studies, we used SNP-Chip technique to screen copy number alterations (CNAs) of the whole genome in GBM and found that EGFR/VEGFR-PTEN, p16(INK4A)/p15(INK4B)-CDK4/6-pRb and p14(ARF)-MDM2/4-p53 were three core signaling pathways in GBM. 91% of GBM patients had at least one pathway with genetic alterations. We also found that deletions of 1p36.23, 6q26-27 accounted for 35%, 27% respectively in GBMs. According to results of SNP-Chip analysis, the common minimum deletion region (CMDR) of 1p36.23 and 6q26-27 merely contain three genes (mir-34a, GPR157, H6PD) and four genes (PARK2, PACRG, QKI, PDE10A) respectively. Interestingly, 22% of GBM cases with both EGFR gene amplification and 1p36.23 deletion had a significantly shortened survival time. We hypothesized that genes in 1p36.23 region may negatively regulate EGFR. Our preliminary experimental results demonstrated that mature mir-34a down-regulated expression of EGFR. In this project, we will study on molecular mechanism of mir-34a regulating expression of EGFR and investigate relationship between GPR157, H6PD and EGFR. We also will survey association between genes in 6q26-27 region and EGFR. EGFR signaling pathway is very important in GBM. The new finding of EGFR-regulating mechanism is helpful for understanding the molecular genetic pathogenesis of GBM and providing new therapeutic strategies in GBM.

我们利用SNP-Chip对脑胶质瘤全基因组拷贝数进行扫描，发现1p36.23和6q26-27 缺失分别占脑胶质瘤的35% 和27%。根据SNP-Chip分析结果，1p36.23和6q26-27最小公共缺失片段中仅分别包含三个基因（mir-34a、GPR157、H6PD）和四个基因(PARK2, PACRG, QKI, PDE10A)。有趣的是22%病例中EGFR基因扩增与1p36.23缺失同时发生，而且这部分病人的生存时间明显缩短，因此我们提出1p36.23中的基因对EGFR基因有负调节作用的假设。初步的实验结果显示mir-34a对EGFR表达有负调节功能。本课题将研究mir-34a对EGFR的调节机制和GPR157、H6PD与EGFR的关系，以及以类似的方法研究6q26-27中的基因与EGFR基因的关联性。如果能找到调控EGFR表达的新基因，将有助于进一步阐明脑胶质瘤的分子遗传发病机制。

EGFR基因的异常是驱动很多肿瘤发生发展的重要的分子因素。找到调控EGFR 表达的新基因，对研究肿瘤的治疗将有重要意义。本研究首先对55 例脑胶质瘤（GBM）组织样本和6 个GBM 细胞株中的DNA 进行了全基因组的SNP-Chip 扫描检测，结果发现1p36.23和6q26-27是最小公共缺失片段，仅分别包含三个基因（mir-34a、GPR157、H6PD）和四个基因（PARK2、PACRG、QKI、PDE10A），而EGFR在脑胶质瘤是扩增率最高的基因，我们根据临床表征确定这些缺失片段中的基因是否与EGFR的扩增存在相关性，并探索这些缺失基因对EGFR是否存在调控或被调控关系。我们进一步对531例恶性胶质瘤的affymetry SNP-CHIP数字化染色体型图谱进行了整合分析，探索可能存在的EGFR的相关联的基因。并且我们的研究结果揭示了：1）EGFR扩增与1p36.23 片段缺失同时发生的患者与单独EGFR扩增或单独1p36.23 片段缺失相比生存时间最短；2）EGFR受转录因子YY1的转录活化，mir-34a通过靶向YY1的mRNA的水平抑制EGFR的表达；3）PARK2可通过多途径抑制EGFR通路活性，一方面通过泛素化蛋白酶体途径降解EGFR，一方面通过抑制EGFR的mRNA的表达水平。通过本课题的完成，我们发表了7篇有重要意义的SCI论文，并鉴定出来一些重要的参与肿瘤发生发展的基因，为临床诊治和预后提供应用基础。