Low mitochondrial DNA copy number induces chemotherapy resistance via epithelial-mesenchymal transition by DNA methylation in esophageal squamous cancer cells

Abstract

Background 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. Methods 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. Results 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. Conclusion 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.

Ovarian cancer cells regulate their mitochondrial content and high mitochondrial content is associated with a poor prognosis

“…These results indicate that ovarian cancer cells to change their mitochondrial number according to their environment, e. g. whether they grow in 2D in vitro or in 3D in vivo and thus indicates that they adopt to their metabolic and survival needs. This in turn may have consequences in for the success of chemotherapy as it has been described in oesophageal cancer cells where low mitochondrial DNA number induces chemotherapy resistance via the induction of EMT [ 32 ]. Cells with initially low mitochondrial content are spared during a course of chemotherapy and can restore high mitochondrial number once chemotherapy has stopped and can thus grow more aggressively again.…”

“…Mitochondria primarily act as energy providers in metastasising ovarian cancer cells, while their function as inducers of apoptosis is of lesser importance. The ability of ovarian cancer cells to regulate their mitochondrial content may also add to their resistance to chemotherapy as low mitochondrial content is associated with chemotherapy resistance [ 32 ].…”

The Role of Mitochondrial Copy Number in Neurodegenerative Diseases: Present Insights and Future Directions

“…Depletion of mtDNA-CN reduced mitochondrial membrane potential (MMP) and increased DNA methylation by upregulation of DNA methyltransferase (DNMT), causing epithelial–mesenchymal transition (EMT) and chemoresistance. The use of a DNMT inhibitor reduced EMT and improved chemotherapy sensitivity in ESCC cell models, suggesting that mechanisms aiming to restore mtDNA-CN content represent a paradigm shift in therapeutic strategies for cancers [ 67 ].…”

Linc01614 Regulates the Proliferation, Apoptosis, and Chemotherapy Resistance in Esophageal Squamous Cell Carcinoma by Targeting Mir-4775

“…Tunel staining were performed as described previously ( 15 ). In brief, after paraffin section samples were deparaffinized and hydrated, the samples were biotin-labeled with tunel solution, then incubated with DAB for 15 min, then in hematoxylin solution for 15 min, and finally observed under a light microscope (Olympus, Tokyo, Japan).…”