腎細胞癌標的抗原MN/CA IXの臨床的意義

Abstract

腎細胞癌の進展機序に関して癌関連抗原MN/CA IX抗原発現について解析した.腎細胞癌の進展と共にMN/CA9の発現の減弱傾向が認められ, その原因としてプロモーター領域のDNAメチル化やMN/CA9遺伝子の変異の関与が示唆された.腎細胞癌の予後因子として循環血液中MN/CA9陽性細胞の検出は今後有望であると思われた

MN/CA IX is considered as a carbonic anhydrase isoenzyme expressed in the normal alimentary tract in a tissue-specific manner. This antigen is activated in the majority of renal cell carcinomas (RCC) but not in the normal kidney tissues. Our previous study revealed that increase of malignant potential is related to down-regulation of MN/CA9. To investigate the mechanism of MN activation in RCC, we examined the methylation status of this gene (MN/CA9) in RCC cell lines (SKRC-1, 6, 10, 12, 14, 44, 59). Moreover, we analyzed the circulating blood of patients for the presence of RCC cells by RT-PCR, to determine whether detection of circulating RCC cells could be useful as a biomarker. CpG methylation was investigated at 7 CpG sites in the MN/CA9 5' region. Clear mRNA signals were observed in 5 cell lines (SKRC-1, 6, 10, 44, 59), e.g., MN/CA9 positive. These 5 MN-positive cell lines showed hypomethylation in the 5' region. In contrast, all CpG sites were methylated in the remaining 2 lines and 3 normal kidney tissue samples. These results suggest that hypomethylation in the 5' region may play an important role in the expression of MN/CA9 in RCC. RT-PCR analysis of blood samples from RCC patients revealed the presence of circulating MN-positive cancer cells in the blood. Although a significant correlation with tumor stage and grade was not observed, the analysis of blood samples from patients with metastases resulted in a high detection rate of 82%. These findings suggest the usefulness of MN/CA IX as a potential diagnostic marker for detection of RCC.