Department of Gastroenterological Surgery, Graduate School of Medicine, Osaka University, 2-2 E2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
J Transl Med. 2022 Aug 29;20(1):383. doi: 10.1186/s12967-022-03594-2.
Esophageal squamous cell carcinoma (ESCC) is one of the most severe cancers and is characterized by chemotherapy resistance and poor prognosis associated with epithelial-mesenchymal transition (EMT). In a previous study, a low mitochondrial DNA (mtDNA) copy number was associated with poorer prognosis and induced EMT in ESCC. However, the detailed mechanism related to mtDNA copy number and EMT is unclear. The aim of this study was to clarify the mechanism by which a change in mtDNA copy number contributes to EMT and to examine treatment of chemotherapy resistance in ESCC.
The association between low mtDNA copy number and chemotherapy resistance was investigated using specimens from 88 patients who underwent surgery after neoadjuvant chemotherapy. Then, the mtDNA content of human ESCC cell lines, TE8 and TE11, was depleted by knockdown of mitochondrial transcription factor A expression. The present study focused on modulation of mitochondrial membrane potential (MMP) and DNA methylation as the mechanisms by which mtDNA copy number affects EMT. mRNA and protein expression, chemotherapy sensitivity, proliferation, MMP and DNA methylation were evaluated, and in vitro and in vivo assays were conducted to clarify these mechanisms.
ESCC patients with decreased mtDNA copy number who underwent R0 resection after neoadjuvant chemotherapy had significantly worse pathological response and recurrence-free survival. Additionally, low mtDNA copy number was associated with resistance to chemotherapy in vitro and in vivo. mtDNA controlled MMP, and MMP depolarization induced EMT. Depletion of mtDNA and low MMP induced DNA methylation via a DNA methylation transcription factor (DNMT), and a DNMT inhibitor suppressed EMT and improved chemotherapy sensitivity in mtDNA-depleted ESCC cells, as shown by in vitro and in vivo assays.
This study showed that decreased mtDNA copy number induced EMT via modulation of MMP and DNA methylation in ESCC. Therapeutic strategies increasing mtDNA copy number and DNMT inhibitors may be effective in preventing EMT and chemosensitivity resistance.
食管鳞状细胞癌（ESCC）是最严重的癌症之一，其特征是化疗耐药和预后不良，与上皮-间充质转化（EMT）有关。在之前的研究中，低线粒体 DNA（mtDNA）拷贝数与 ESCC 预后较差和诱导 EMT 有关。然而，与 mtDNA 拷贝数和 EMT 相关的详细机制尚不清楚。本研究旨在阐明 mtDNA 拷贝数变化导致 EMT 的机制，并研究 ESCC 化疗耐药的治疗方法。
通过对 88 例接受新辅助化疗后手术的患者标本进行研究，调查低 mtDNA 拷贝数与化疗耐药的关系。然后，通过敲低线粒体转录因子 A 表达来耗尽人 ESCC 细胞系 TE8 和 TE11 的 mtDNA 含量。本研究重点研究 mtDNA 拷贝数影响 EMT 的机制，即调节线粒体膜电位（MMP）和 DNA 甲基化。评估 mRNA 和蛋白质表达、化疗敏感性、增殖、MMP 和 DNA 甲基化，并进行体外和体内实验以阐明这些机制。
接受新辅助化疗后 R0 切除的 ESCC 患者 mtDNA 拷贝数降低，病理反应和无复发生存明显较差。此外，低 mtDNA 拷贝数与体外和体内的化疗耐药有关。mtDNA 控制 MMP，MMP 去极化诱导 EMT。mtDNA 耗竭和低 MMP 通过 DNA 甲基化转录因子（DNMT）诱导 DNA 甲基化，DNMT 抑制剂抑制 mtDNA 耗竭的 ESCC 细胞中的 EMT，并提高化疗敏感性，这在体外和体内实验中得到证实。
本研究表明，ESCC 中 mtDNA 拷贝数降低通过调节 MMP 和 DNA 甲基化诱导 EMT。增加 mtDNA 拷贝数和 DNMT 抑制剂的治疗策略可能有效预防 EMT 和化疗耐药。
