Department and Institute of Pharmacology, National Yang-Ming University, Taipei, Taiwan.
Center for Infectious Disease and Cancer Research (CICAR), Kaohsiung Medical University, Kaohsiung, Taiwan.
Sci Rep. 2018 Aug 16;8(1):12284. doi: 10.1038/s41598-018-30682-5.
Glycine N-methyltransferase (GNMT) is a tumor suppressor for HCC. It is down-regulated in HCC, but the mechanism is not fully understood. MicroRNA-224 (miR-224) acts as an onco-miR in HCC. This study is the first to investigate miR-224 targeting the coding region of GNMT transcript. The GNMT-MT plasmid containing a miR-224 binding site silent mutation of the GNMT coding sequence can escape the suppression of miR-224 in HEK293T cells. Expression of both exogenous and endogenous GNMT was suppressed by miR-224, while miR-224 inhibitor enhanced GNMT expression. miR-224 counteracts the effects of GNMT on the reduction of cell proliferation and tumor growth. The levels of miR-224 and GNMT mRNA showed a significant inverse relationship in tumor specimens from HCC patients. Utilizing CCl4-treated hepatoma cells and mice as a cell damage of inflammatory or liver injury model, we observed that the decreased expression levels of GNMT were accompanied with the elevated expression levels of miR-224 in hepatoma cells and mouse liver. Finally, hepatic AAV-mediated GNMT also reduced CCl4-induced miR-224 expression and liver fibrosis. These results indicated that AAV-mediated GNMT has potential liver protection activity. miR-224 can target the GNMT mRNA coding sequence and plays an important role in GNMT suppression during liver tumorigenesis.
甘氨酸 N-甲基转移酶（GNMT）是 HCC 的肿瘤抑制因子。它在 HCC 中下调，但机制尚不完全清楚。microRNA-224（miR-224）在 HCC 中作为癌基因 microRNA。本研究首次探讨了 miR-224 靶向 GNMT 转录本编码区的作用。含有 GNMT 编码序列 miR-224 结合位点沉默突变的 GNMT-MT 质粒可逃避 miR-224 在 HEK293T 细胞中的抑制作用。外源性和内源性 GNMT 的表达均被 miR-224 抑制，而 miR-224 抑制剂增强了 GNMT 的表达。miR-224 拮抗了 GNMT 对细胞增殖和肿瘤生长减少的作用。肝癌患者肿瘤标本中 miR-224 和 GNMT mRNA 的水平呈显著负相关。利用 CCl4 处理的肝癌细胞和小鼠作为细胞损伤的炎症或肝损伤模型，我们观察到在肝癌细胞和小鼠肝中，GNMT 的表达水平降低伴随着 miR-224 的表达水平升高。最后，肝 AAV 介导的 GNMT 也降低了 CCl4 诱导的 miR-224 表达和肝纤维化。这些结果表明，AAV 介导的 GNMT 具有潜在的肝脏保护活性。miR-224 可以靶向 GNMT mRNA 编码序列，并在肝肿瘤发生过程中对 GNMT 抑制发挥重要作用。
