Role of NF2 tumor suppressor gene promoter in the tumorigenesis

背景资料：虽然NF 2基因的突变失活和等位基因丢失似乎是大多数前庭神经鞘瘤的因果事件，但另一个潜在的重要机制，转录失活的参与尚未调查。结果如下：我们克隆了人NF 2基因的5 '侧翼区，并对其进行了功能鉴定，确定了调节NF 2表达的分子机制。荧光素酶分析和定点突变表明，一个70碱基对（bp）的区域（从翻译起始位点的-591到-522 bp）是NF 2基因的基本表达所必需的。凝胶迁移率变动分析表明，识别核蛋白的异常长（约66 bp）的序列在这一地区。识别被抑制的结合核心序列的突变或甲基化的三个CpG位点。这些CpG位点的点突变显著降低了启动子活性，表明这些位点的重要性。在23例前庭神经鞘瘤中，14例该区域内的3个CpG位点以位点特异性方式甲基化，甲基化状态与NF 2 mRNA的表达一致。结论：通过异常甲基化或启动子元件突变抑制NF 2基因的表达可能是NF 2基因失活的另一种机制。

Background : Although mutational inactivation and allelic loss in the NF2 gene appear to be causal events in the majority of vestibular schwannomas, involvement of another potentially important mechanism, transcriptional inactivation, has not been investigated. Results : We cloned and functionally characterized the 5'-flanking region of the human NF2 gene and identified the molecular mechanisms that regulate NF2 expression. Luciferase assay and site-directed mutagenesis demonstrated that a 70-base pair (bp) region (-591 to -522 bp from the translation start site) was essential for the basic expression of the NF2 gene. Gel mobility shift assay indicated recognition by nuclear protein(s) of the unusually long (〜66 bp) sequences in this region. Recognition was inhibited by either mutation of the binding core sequence or by methylation of three CpG sites. Point mutations at these CpG sites significantly decreased promoter activity, suggesting the importance of these sites. In 14 of 23 vestibular schwannomas, these 3 CpG sites within this region were methylated in a site-specific manner and the methylation status was consistent with the expression of NF2 mRNA.Conclusions : Suppressed expression by aberrant methylation or mutation of the promoter elements could be an alternative mechanism for inactivation of the NF2 gene.