ABSTRACT

Superoxide dismutase 3 (SOD3) is a secreted antioxidant enzyme that regulates reactive oxygen species in the microenvironment. It is also a potential tumour suppressor gene that is significantly downregulated in breast cancer. We have previously shown that its mRNA expression is inversely correlated with relapse free survival in breast cancer patients. This study aimed to investigate the correlation of SOD3 promoter DNA methylation with its expression in different molecular subtypes of breast carcinoma. We found that SOD3 expression was significantly reduced in breast carcinoma samples compared to normal tissues with the lowest levels observed in Luminal B subtype. Pyrosequencing analysis showed significant increase in methylation levels in the SOD3 promoter region (−108 and −19 from the TSS) in tumours vs normal tissues (53.6% vs 25.2%). The highest degree of correlation between methylation and SOD3 expression levels was observed in Luminal B subtype (Spearman’s R = −0.540, P < 0.00093). In this subtype, the −78 CpG position is the most significantly methylated site. The Spearman’s coefficient analysis also indicated the most significant correlation of DNA methylation at this site with SOD3 gene expression levels in tumours vs. normal tissues (R = −0.5816, P < 6.9E-12). Moreover, copy number variation analysis of TCGA database revealed that the more aggressive Triple Negative and Her2+ subtypes had higher levels of SOD3 gene deletion. The predominantly down-regulated expression pattern of SOD3 and the various genetic and epigenetic deregulations of its expression suggest that loss of this antioxidant promotes an advantageous tumour-promoting microenvironment in breast cancer.

摘要

超氧化物歧化酶3（SOD3）是一种分泌的抗氧化酶，可调节微环境中的活性氧。它也是潜在的抑癌基因，在乳腺癌中被显着下调。先前我们已经表明，其mRNA表达与乳腺癌患者的无复发生存率呈负相关。这项研究旨在调查SOD3启动子DNA甲基化与其在乳腺癌不同分子亚型中表达的相关性。我们发现，与正常组织相比，在Luminal B亚型中观察到的最低水平，乳腺癌组织中的SOD3表达显着降低。焦磷酸测序分析显示，与正常组织相比，肿瘤中SOD3启动子区域的甲基化水平显着增加（TSS为−108和-19）（53.6％比25.2％）。在Luminal B亚型中观察到甲基化与SOD3表达水平之间的最高相关度（Spearman R = -0.540，P <0.00093）。在此亚型中，-78 CpG位置是最明显的甲基化位点。Spearman系数分析还表明，与正常组织相比，此部位的DNA甲基化与SOD3基因表达水平之间存在最显着的相关性（R = -0.5816，P <6.9E-12）。此外，TCGA数据库的拷贝数变异分析表明，更具攻击性的三阴性和Her2 +亚型的SOD3基因缺失水平更高。