肺肿瘤抑制基因GPRC5A在肺癌中表达下调的机制研究

Loss or inactivation of tumor suppressor genes drives tumorigenesis.GPRC5A is a newly identified lung tumor suppressor gene, its deletion leads to spontaneous lung tumorigenesis in mice. In addition, the expression of GPRC5A was generally down-regulated in human lung cancer tissue, which is associate with poor prognosis; but the regulatory mechanism of GPRC5A in lung cancer is not clear. Inflammation is closely associate with lung tumor initiation and development. In this study, We found that in cell and animal models, inflammatory stimuli significantly inhibited GPRC5A expression and depended on the activation of NF-kB. In human lung cancer and adjacent normal tissues, the activation level of NF-kB was negatively correlated with the expression of GPRC5A .Further, we found that the inhibition of GPRC5A by NF-kB occurred at the transcriptional level. Preliminary mechanism studies showed that activation of NF-kB could change histone acetylation modification in GPRC5A promoter region. Therefore, we hypothesize that inflammation inhibits the expression of GPRC5A through an epigenetic mechanism. On the basis of these important findings, we will study GPRC5A at three levels: cell, animal model and clinical samples of lung cancer, clarify the mediating role of GPRC5A between inflammation and lung cancer, and explore the specific molecular mechanism of NF-kB inhibiting GPRC5A expression. These work may not only provide new clues for the pathogenesis of lung cancer, but also may provide a new way for the prevention and treatment of inflammation-mediated lung cancer.

肿瘤抑制基因的丢失或失活驱动肿瘤的发生。GRPC5A是新发现的肺肿瘤抑制基因,其缺失会导致小鼠自发产生肺癌。人肺癌组织中GPRC5A的表达普遍下调，并与预后不良相关，但其下调机制不明。炎症与肺癌的发生密切相关。我们发现，在细胞和动物模型上，炎症刺激可以显著抑制GPRC5A的表达，且依赖于NF-kB的激活。在人肺癌组织中，NF-kB的活化水平与GPRC5A的表达存在明显负相关。进一步，我们发现NF-kB对GPRC5A的抑制发生在转录水平；并且与GPRC5A启动子区组蛋白乙酰化修饰改变有关。因此我们假设，炎症通过表观调控机制抑制GPRC5A的表达。本课题将在前期发现的基础上，从细胞、动物模型和肺癌临床样本三个水平展开研究，明确GPRC5A在炎症和肺癌发生之间的介导作用，并深入探寻炎症抑制GPRC5A表达的具体分子机制，这不仅可能为肺癌的发生机制提供新线索，还可望为炎症介导肺癌的防治提供新思路。

肿瘤抑制基因的缺失或失活驱动肿瘤的发生。GRPC5A是新发现的肺肿瘤抑制基因,其缺失会导致小鼠自发产生肺癌。人肺癌组织中GPRC5A的表达普遍下调，并与预后不良相关，但其下调机制并不清楚。炎症与肺癌的发生密切相关。慢性阻塞性肺病（COPD）是一种肺部慢性炎症疾病，COPD患者发生肺癌的概率比正常人要高3~5倍。我们发现在人肺癌组织和COPD组织中，NF-kB的活化水平与GPRC5A的表达水平显著负相关。在细胞和动物模型上，炎症刺激可以显著抑制GPRC5A的表达，且依赖于NF-kB的激活。在此基础上，本课题进一步研究发现1）NF-kB对GPRC5A的抑制发生在转录水平；其对GPRC5A的抑制作用虽然不需要其转录活性激活下游靶基因，但是p65的转录激活区域却是必需的；2）p65并不结合在GPRC5A启动子区上的潜在NF-kB结合位点，而是通过与RARa/b相互作用结合在GPRC5A启动子区的视黄酸反应元件（RARE）上，并减少了RNA聚合酶II在GPRC5A启动子区的结合；3）p65上第276位丝氨酸的磷酸化对于其发挥抑制GPRC5A的作用至关重要，该位点的磷酸化影响了其与RARa/b的相互作用；4）p65对GPRC5A的抑制并不改变其启动子区DNA的甲基化水平，而主要通过减少GPRC5A启动子区组蛋白H3K9的乙酰化修饰水平来实现。5）使用组蛋白去乙酰化酶的抑制剂SAHA对肺肿瘤细胞进行体外和在体处理，均可以恢复GPRC5A的表达。综上可知，在具有炎症的肺组织中，NF-kB通过与RARa/b相互作用，降低GPRC5A启动子区域组蛋白上H3K9的乙酰化修饰，减少RNA聚合酶II的结合来降低GPRC5A的表达。本课题在细胞、动物模型和肺癌临床样本三个水平展开研究，明确了GPRC5A在炎症和肺癌发生之间的介导作用，阐明了炎症抑制GPRC5A表达的具体机制，这不仅为肺癌的发生机制提供了新线索，还可望为炎症介导肺癌的防治提供新思路。