Kang Kyoung Ah, Zhang Rui, Kim Gi Young, Bae Suk Chul, Hyun Jin Won
Division of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Seoul, 139-706, Republic of Korea.
Tumour Biol. 2012 Apr;33(2):403-12. doi: 10.1007/s13277-012-0322-6. Epub 2012 Jan 25.
Runt domain transcription factor 3 (RUNX3) is a tumor suppressor that is silenced in cancer via hypermethylation of its promoter. This study investigated the mechanisms involved in reactive oxygen species (ROS)-induced silencing of RUNX3 in terms of epigenetic alteration since the effects of oxidative stress in tumor suppressor gene transcription are largely unknown. RUNX3 mRNA and protein expressions were down-regulated in response to hydrogen peroxide (H(2)O(2)) in the human colorectal cancer cell line SNU-407. This down-regulation was abolished with pretreatment of the ROS scavenger, N-acetylcysteine (NAC). Moreover, methylation-specific PCR data revealed that H(2)O(2) treatment increased RUNX3 promoter methylation; however, NAC and the cytosine methylation inhibitor, 5-aza-2-deoxycytidine (5-Aza-dC), decreased it, suggesting that an epigenetic regulatory mechanism by ROS-induced methylation may be involved in RUNX3 silencing. H(2)O(2) treatment resulted in DNA methyltransferase 1 (DNMT1) and histone deacetylase 1 (HDAC1) up-regulation with increased expression and activity, increased binding of DNMT1 to HADC1, and increased DNMT1 binding to the RUNX3 promoter. In addition, 5-Aza-dC treatment prevented the decrease in RUNX3 mRNA and protein levels by H(2)O(2) treatment. Additionally, H(2)O(2) treatment inhibited the nuclear localization and expression of RUNX3, which was abolished by NAC treatment. Furthermore, the down-regulation of RUNX3 expression by H(2)O(2) also influenced cell proliferation. Taken together, the data suggested that ROS silenced the tumor suppressor, RUNX3, by epigenetic regulation and may therefore be associated with the progression of colorectal cancer.
runt结构域转录因子3（RUNX3）是一种肿瘤抑制因子，在癌症中其启动子因高甲基化而沉默。由于氧化应激对肿瘤抑制基因转录的影响在很大程度上尚不清楚，本研究从表观遗传改变方面探讨了活性氧（ROS）诱导RUNX3沉默的机制。在人结肠癌细胞系SNU - 407中，过氧化氢（H₂O₂）可使RUNX3 mRNA和蛋白表达下调。活性氧清除剂N - 乙酰半胱氨酸（NAC）预处理可消除这种下调。此外，甲基化特异性PCR数据显示，H₂O₂处理可增加RUNX3启动子甲基化；然而，NAC和胞嘧啶甲基化抑制剂5 - 氮杂 - 2 - 脱氧胞苷（5 - Aza - dC）可使其降低，这表明ROS诱导的甲基化表观遗传调控机制可能参与了RUNX3沉默。H₂O₂处理导致DNA甲基转移酶1（DNMT1）和组蛋白去乙酰化酶1（HDAC1）表达和活性上调，DNMT1与HADC1的结合增加，以及DNMT1与RUNX3启动子的结合增加。此外，5 - Aza - dC处理可防止H₂O₂处理导致的RUNX3 mRNA和蛋白水平降低。另外，H₂O₂处理抑制了RUNX3的核定位和表达，NAC处理可消除这种抑制。此外，H₂O₂对RUNX3表达的下调也影响了细胞增殖。综上所述，数据表明ROS通过表观遗传调控使肿瘤抑制因子RUNX3沉默，因此可能与结直肠癌的进展有关。
