肺癌抑制基因GPRC5A与肺组织慢性炎症及肺癌发生的关系

Lung cancer is the leading cause of cancer death. Reveal the mechanism of lung carcinogenesis is of great significance for early diagnosis, prevention and therapeutic treatment of lung cancer. Development of lung cancer is frequently associated with chronic inflammation in the lung tissues. However, the underlying molecular mechanism remains illusive. GPRC5A is a target gene of retinoic acid signaling, which is frequently lost or suppressed in human lung cancer. Gprc5a-knockout mice develop spontaneous lung tumors, indicating it is a lung tumor suppressor gene. Importantly, the pathological features of lung cancer developed in this mouse model are very similar to those in human lung cancer, including latency of lung cancer development, association with chronic inflammation, deregulated signaling pathways, gene expression signature, and so on. The proposed project will study the molecular mechanisms and biological significance of lung carcinogenesis in Gprc5a-knockout mouse model, especially on the effect of chronic inflammation on lung carcinogenesis. Gprc5a-knockout mice have aberrantly activated NF-κB activity in lung epithelial cells, suggesting that Gprc5a exhibits an inhibitory regulation on NF-κB signaling pathway. This proposal will analyze the cross-regulation between GPRC5A and NF-κB signaling pathway. We will study the mechanism of GPRC5A in regulation of NF-?B pathway, and the effects of inflammatory cytokines on GPRC5A expression. We will examine the expression of GPRC5A and NF-?B in human lung cancer tissue samples by immunohistochemical staining. Based on the information of clinical and pathological data, we will make a conclusion and propose a model of the cross-regulation between GPRC5A and NF-?B pathway. The proposed study will reveal the mechanism of cross-regulation between GPRC5A and NF-kB, which provide a theoretical basis for anti-inflammation as a strategy for cancer prevention.

肺癌是癌症中的第一杀手。揭示肺癌发生的机理对早期诊断、防治具有十分重要意义。肺癌发生发展往往与肺组织慢性炎症有关，但其分子机理却不十分清楚。GPRC5A是一种新发现的肺癌抑制基因，它在吸烟者和肺癌患者中常被抑制或丢失。Gprc5a敲除小鼠会产生自发性肺癌，且伴有肺组织慢性炎症。Gprc5a-敲除小鼠肺上皮细胞中NF-κB活性异常增高，这表明GPRC5A对NF-κB信号通路有抑制作用，但其机理并不清楚。本课题将研究人GPRC5A对NF-κB信号通路的调控作用与机理，还将研究炎症信号对GPRC5A表达的调控与机制，最后在人肺癌组织样品中对上述分子的表达进行测定，并对照肺癌患者的临床病理资料进行系统分析，确立肿瘤组织中GPRC5A与NF-κB之间及其与临床病理资料之间的相互关系。本研究将为肺部慢性炎症与肺癌发生的相互关系提供分子水平的调控模型，还将为抗炎症药物在肺癌预防中的作用提供理论依据。

GPRC5A是G蛋白偶联受体，是维甲酸信号通路的靶基因，且仅在肺组织中表达，其他组织中基本不表达或表达很低。Gprc5a基因敲除小鼠会发生自发性肺腺癌，这是一种比较接近人肺癌的动物模型。基于这个模型，我们进行了系统研究，并取得了如下几方面进展：1）NF-kB信号通路在Gprc5a基因敲除小鼠肺癌发生过程中起到重要作用，证实了Gprc5a基因缺失所导致的NF-kB通路异常激活是诱发急性肺损伤易感性增强的主要通路；2）通过特异性抗磷酸化GPRC5A抗体的检测，证实了肿瘤组织中表达的GPRC5A，大多呈磷酸化或非活性状态，解释了为何有些肺肿瘤组织仍有肺肿瘤抑制基因GPRC5A的表达。3）GPRC5A可以通过其跨膜区与EGFR发生相互作用，并抑制EGFR信号通路，包括STAT3信号通路。该调控作用不仅发现在体外细胞水平，也发现在动物模型，和人的炎症肺组织中。4）研究了Gprc5a-ko小鼠肺上皮细胞NF-kB信号通路对肺组织炎症和肺癌发生的生物学意义。我们将肺细胞特异性启动子起动的Super Repressor IkBa(SPC-SR-IkBa)转基因小鼠与Gprc5a基因敲除小鼠进行杂交，建立了Gprc5a-ko/ SPC-SR-IkBa杂交小鼠。初步的结果发现，肺肿瘤的发生被推迟了6个月，这相当于小鼠寿命的1/4。目前，本研究中的许多重要突破性发现还在继续深入研究之中。