食管癌新肿瘤易感基因SLC22A3生物学功能及临床意义研究

Esophageal squamous cell carcinomas (ESCC) occur with the highest frequencies amongst the Chinese, especially the high-risk Northern Chinese, where the incidence rates of 121 per 100,000 population are over 20 times higher than those in low-risk regions worldwide. Although environmental factors are crucial for varied distribution of ESCC in high-incidence area, only a minor proportion of the population develops ESCC, suggesting the importance of host susceptibility factors for developing the disease in the population at risk. With an aim to isolate esophageal cancer susceptibility genes, our group recently performed Affymetrix cDNA microarrays to compare the genome-wide expression profiles of pooled ESCC tumors with family history (FH+; n=5) and pooled ESCC tumors without family history (FH-; n=10), relative to pooled adjacent non-tumor tissues (n=15). One significantly down-regulated gene in FH+ ESCCs, SLC22A3 (solute carrier family 22, member 3 or OCT3) becomes an attractive candidate for a tumor susceptibility gene based on the following evidence: 1) SLC22A3 showed a significant lower fold-change (-4.5) in FH+ ESCCs than that (-2.2) in FH- ESCCs; 2) SLC22A3 downregulation was validated in 4/5 (80%) of FH+ ESCCs and 5/10 (50%) of FH- ESCCs compared with their paired non-tumor tissues by qPCR; 3) Different methylation frequencies have been detected in blood leukocytes of controls and cases from different regions of China, with highest frequency (65%) recorded in ESCC patients from Henan province (high-risk region), and the lowest (5%) in healthy people from Guangdong province (low-risk region); and 4) SLC22A3 was able to inhibit foci and colony formation in ESCC cell line KYSE30. Collectively, we propose to investigate the role of SLC22A3 as a candidate tumor susceptibility gene in ESCC development with three specific objectives: 1) to further investigate the methylation frequencies of SLC22A3 in ESCC high- and low-risk population; 2) to investigate the imprinting status of SLC22A3 and its correlation with methylation in ESCC; and 3) to investigate the functional role of SLC22A3 and its clinical significance in ESCC. A better understanding of the molecular genetic basis of SLC22A3 will significantly improve our knowledge in ESCC initiation and progression, and its epigenetic inactivation may serve as a tumor marker for the early identification of individuals in high-risk ESCC population.

河南林州是世界上食管鳞状细胞癌发病率最高的地区，约121/10万，是低发区的20倍。在高发区，虽然环境因素对食管癌的发生具有非常重要的作用，但仍只有少数人发病，说明宿主易感性因素在疾病发生中也起着重要作用。前期工作中，我们发现SLC22A3是食管鳞癌潜在的肿瘤易感基因。本研究拟通过高低发区对比，应用BGS,MSP分析SLC22A3甲基化状态，应用SLC22A3+387C>T多态性DNA PCR扩增分析SLC22A3印记状态，并探讨两者相互关系；应用重组质粒转染及RNAi技术改变SLC22A3在食管鳞癌细胞系中的表达水平，观察其对食管鳞癌细胞生物学行为影响；采用qPCR，Western blot及免疫组化检测SLC22A3在食管鳞癌组织中的表达水平，分析其与临床病理学特征的关系。本研究不仅有助于阐明高发区食管癌发生发展的分子遗传学基础，还可望为其早期诊断、分子靶向治疗及预后分析提供理论依据。