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Mitochondrial DNA (mtDNA) mutations are often observed in various cancer types. Although the correlation between mitochondrial dysfunction and cancer malignancy has been demonstrated by several studies, further research is required to elucidate the molecular mechanisms underlying accelerated tumor development and progression due to mitochondrial mutations. We generated an mtDNA-depleted cell line, ρ⁰, via long-term ethidium bromide treatment to define the molecular mechanisms of tumor malignancy induced by mitochondrial dysfunction. Mitochondrial dysfunction in ρ⁰ cells reduced drug-induced cell death and decreased the expression of pro-apoptotic proteins including p53. The p53 expression was reduced by activation of nuclear factor-κB that depended on elevated levels of free calcium in HCT116/ρ⁰ cells. Overall, these data provide a novel mechanism for tumor development and drug resistance due to mitochondrial dysfunction. [BMB Reports 2018; 51(6): 296-301].

Mitochondria are major organelles that play various roles in cells, and mitochondrial dysfunction is the main cause of numerous diseases. Mitochondrial dysfunction also occurs in many cancer cells, and these changes are known to affect malignancy. The mitochondria of normal embryonic stem cells (ESCs) exist in an undifferentiated state and do not function properly. We hypothesized that mitochondrial dysfunction in cancer cells caused by the depletion of mitochondrial DNA might be similar to the mitochondrial state of ESCs. We generated mitochondria dysfunctional (ρ0) cells from the Hep3B hepatocellular carcinoma cell line and tested whether these ρ0 cells show cancer stem-like properties, such as self-renewal, chemotherapy resistance, and angiogenesis. Compared with Hep3B cells, the characteristics of each cancer stem-like cell were increased in Hep3B/ρ0 cells. The Hep3B/ρ0 cells formed a continuous and large sphere from a single cell. Additionally, the Hep3B/ρ0 cells showed resistance to the anticancer drug doxorubicin because of the increased expression of ATP-binding cassette Subfamily B Member 1. The Hep3B/ρ0 conditioned medium induced more and thicker blood vessels and increased the mobility and invasiveness of the blood vessel cells. Therefore, our data suggest that mitochondrial dysfunction can transform cancer cells into cancer stem-like cells.

Hepatitis B virus (HBV) encoding the HBV x protein (HBx) is a known causative agent of hepatocellular carcinoma (HCC). Its pathogenic activities in HCC include interference with several signaling pathways associated with cell proliferation and apoptosis. Mutant C-terminal-truncated HBx isoforms are frequently found in human HCC and have been shown to enhance proliferation and invasiveness leading to HCC malignancy. We investigated the molecular mechanism of the reduced doxorubicin cytotoxicity by C-terminal truncated HBx. Cells transfected with C-terminal truncated HBx exhibited reduced cytotoxicity to doxorubicin compared to those transfected with full-length HBx. The doxorubicin resistance of cells expressing C-terminal truncated HBx correlated with upregulation of the ATP binding cassette subfamily B member 1(ABCB1) transporter, resulting in the enhanced efflux of doxorubicin. Inhibiting the activity of ABCB1 and silencing ABCB1 expression by small interfering ribonucleic acid (siRNA) increased the cytotoxicity of doxorubicin. These results indicate that elevated ABCB1 expression induced by C-terminal truncation of HBx was responsible for doxorubicin resistance in HCC. Hence, co-treatment with an ABCB1 inhibitor and an anticancer agent may be effective for the treatment of patients with liver cancer containing the C-terminal truncated HBx. [BMB Reports 2019; 52(5): 330-335].

Cancer stem cells (CSCs) are a small population of cancer cells that possess characteristics associated with normal stem cells such as self-renewal and differentiation into multiple cell types. Additionally, CSCs have been reported to relationship on tumor relapse after cancer therapy. Mitochondrial dysfunction (MD) has also been known to be associated with cancer malignancy. In this report, the relation of MD and CSCs were initially investigated using mitochondrial-depleted rho0 cells derived from Hep3B hepatocellular carcinoma cell line. The Hep3B/rho0 cells showed cancer stem-like phenotypes including tumor initiation, tumor malignancy, stem cell-related signaling, chemotherapies and radiotherapy resistance. These results suggest that mitochondrial dysfunction induces cancer stem-like phenotypes. Taken together, mitochondrial dysfunction plays an important role in the acquisition of cancer stem-like phenotypes and could be a novel therapeutic target to cancer therapy. Citation Format: Yu-Seon Han, Eui-Yeun Yi, Yung-Jin Kim. Mitochondrial dysfunction induces cancer stem-like phenotypes in Hep3B hepatocellular carcinoma cell line. [abstract]. In: Proceedings of the AACR Special Conference on Translation of the Cancer Genome; Feb 7-9, 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 1):Abstract nr A2-22.

Mitochondria dysfunctional cells are useful models in studies for mitochondrial diseases, apoptosis, cancer and aging, but their functional aspects have not been fully understood. Mitochondrial dysfunction (MD) is found in many type of cancer such as colorectal, liver, pancreatic, breast, prostate, ovarian cancer etc. MD has also been known to be associated with cancer malignancy, especially apoptosis resistance (therapy resistance). Using mitochondrial-depleted P0 derived from Hep3B, we have tested the effects of mitochondrial dysfunction on the chemical and radiation resistance. When compared to parental cells, Hep3B/P0 cells were much less sensitive to doxorubicin and sorafenib and irradiation. Hep3B/P0 cells also showed increased efflux, decreased target molecules, rapid repair and DNA protection. These results suggest that mitochondrial dysfunction confers therapy resistance on the cancer cells, which could be a novel therapeutic target for cancer therapy. Citation Format: YuSeon Han, MyeongEun Je Gal, EuiYeun Yi, YungJin Kim. Mitochondrial dysfunction confers therapy resistance in Hep3B hepatocellular carcinoma cell line. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C67.