Hepatitis B virus X protein inhibits p53-mediated upregulation of mitofusin-2 in hepatocellular carcinoma cells

Mitofusin-2 in cancer: Friend or foe?

Cancer is a category of disorders characterized by excessive cell proliferation with the ability to infiltrate or disseminate to other organs of the body. Mitochondrial dysfunction, as one of the most prominent hallmarks of cancer cells, has been related to the onset and development of various cancers. Mitofusin 2 (MFN2) is a major mediator of mitochondrial fusion, endoplasmic reticulum (ER)-mitochondria interaction, mitophagy and axonal transport of mitochondria. Available data have shown that MFN2, which its alterations have been associated with mitochondrial dysfunction, could affect cancer initiation and progression. In fact, it showed that MFN2 may have a double-edged sword effect on cancer fate. Precisely, it demonstrated that MFN2, as a tumor suppressor, induces cancer cell apoptosis and inhibits cell proliferation via Ca²⁺ and Bax-mediated apoptosis and increases P21 and p27 levels, respectively. It also could suppress cell survival via inhibiting PI3K/Akt, Ras-ERK1/2-cyclin D1 and mTORC2/Akt signaling pathways. On the other hand, MFN2, as an oncogene, could increase cancer invasion via snail-mediated epithelial-mesenchymal transition (EMT) and in vivo tumorigenesis. While remarkable progress has been achieved in recent decades, further exploration is required to elucidate whether MFN2 could be a friend or it's an enemy. This study aimed to highlight the different functions of MFN2 in various cancers.

Targeting p53 as a promising therapeutic option for cancer by re-activating the wt or mutant p53’s tumor suppression

p53 protein, a product of the TP53 tumor suppressor gene, controls the cellular genome’s integrity and is an important regulator of cell cycling, proliferation, apoptosis and metabolism. Mutations of TP53 or inactivation of its gene product are among the first events initiating malignant transformation. The consequent loss of control over the cell cycle, resulting in accelerated cell proliferation and facilitating metabolic reprogramming, gives the initiated (premalignant) cells numerous advantages over healthy cells. Interestingly, p53 status is not only an important marker in cancer diagnosis; it has also become a promising target of personalized therapy. Depending on the TP53 status different therapeutic options have been developed. (Re)-activation of p53 functionality in cancer cells offers promising new alternatives to existing oncological therapies.

The anti-tumor effects of Mfn2 in breast cancer are dependent on promoter DNA methylation, the P21Ras motif and PKA phosphorylation site

Mitofusin 2 (Mfn2) is expressed in numerous human tissues and serves a pivotal role in cell proliferation. However, Mfn2 is considered as an anti-tumor gene, and is silenced in human malignant tumors, including those of breast cancer. However, the mechanisms contributing to Mfn2 silencing and the mechanism of its anti-tumor function in breast cancer remain unclear. In the present study, hypoexpression of Mfn2, and hypermethylation of its promoter, was confirmed in human breast cancer cells and in breast cancer tissues by reverse transcription-quantitative polymerase chain reaction (PCR) and methylation specific PCR, respectively. Chemical demethylation treatment with 5-aza-2'-deoxycytidine upregulated the mRNA expression level of Mfn2 in MCF-7 cells in a dose-dependent manner. In addition, overexpression of Mfn2 repressed the proliferation, migration and invasion of MCF-7 cells, mediated by inhibition of the Ras-extracellular signal-regulated kinase (ERK)1/2 signaling pathway. However, overexpression of Mfn2 with deletion of the p21^Ras motif (Mfn2^ΔRas) and protein kinase A (PKA) phosphorylation site (Mfn2^ΔPKA) partially reduced the anti-tumor function of Mfn2, and inhibited the Ras-ERK1/2 signaling pathway. Taken together, the present study confirmed the anti-tumor effects of Mfn2 in human breast cancer and clarified that the mechanism of its anti-tumor functions includes promoter DNA methylation, the P21^Ras binding site and PKA phosphorylation.

Overexpression of Mitochondrial GTPase MFN2 Represents a Negative Prognostic Marker in Human Gastric Cancer and Its Inhibition Exerts Anti-Cancer Effects

Background: As one of the most common malignancies in the world, little is known about the molecular mechanism underlying gastric cancer (GC) and its progression. In this study, we aimed to investigate the clinical impact of the mitochondrial GTPase mitofusin 2 (MFN2) in GC.

Methods: Immunohistochemistry was used to examine the expression levels of MFN2 in gastric tissues obtained from 141 patients with GC. The correlations between MFN2 protein level and clinicopathologic parameters, as well as the significance of MFN2 protein level for overall and disease-free survival were assessed. siRNA technology was used to study the effect of MFN2 knockdown on cell proliferation and invasion.

Results: The overexpression of MFN2 was positively associated with depth of invasion (P = 0.0430), stage (P = 0.0325) and vascular invasion (P = 0.0077). Patients with high expression levels of MFN2 had a significantly lower overall survival rate and disease-free survival rate compared with those with low expression levels (P = 0.003 and 0.001, respectively). Multivariate Cox regression analysis showed that the overexpression of MFN2 was an independent prognostic marker for inferior overall survival and disease-free survival (P = 0.015 and 0.025, respectively). In addition, studies conducted in GC cells indicated that knockdown of MFN2 suppressed cell proliferation and invasion.

Conclusions: Overexpression of MFN2 can be used as a marker to predict the outcome of patients with GC. Furthermore, targeting MFN2 might provide a new therapeutic modality for the treatment of GC.

Clinical significance of mitofusin-2 and its signaling pathways in hepatocellular carcinoma

BACKGROUND

The mitochondrial GTPase mitofusin-2 (MFN2) gene encodes a mitochondrial membrane protein that can induce apoptosis of hepatocellular carcinoma (HCC) via the mitochondrial apoptotic pathway, as validated in our previous research. However, little is known of the clinical significance of MFN2 expression and its signaling pathways in HCC.

METHODS

MFN2 mRNA expression in tumor and adjacent non-tumor tissues from 115 patients with HCC was investigated using quantitative real-time PCR. The association of the MFN2 mRNA expression level with clinical and pathological parameters was evaluated statistically, while a comparative microarray analysis was used to identify MFN2 signaling pathways in HepG2 cells.

RESULTS

MFN2 was significantly (p < 0.0001) downregulated in HCC tissues. Low MFN2 expression was significantly correlated with sex and preoperative alpha-fetoprotein (p < 0.05). Both a Kaplan-Meier survival curve and multivariate analyses showed that MFN2 was related to overall survival. A comparative gene expression microarray revealed 211 upregulated (58 %) and 153 downregulated (42 %) genes. Eighteen pathways were identified as the most significant pathways correlated with MFN2.

CONCLUSIONS

Low MFN2 expression in HCC indicated a worse overall survival. Crucial signaling molecules such as PI3K-AKT, cytokine receptor, and focal adhesion may participate in MFN2-mediated signaling pathway changes in HCC.

Mitofusin-2 over-expresses and leads to dysregulation of cell cycle and cell invasion in lung adenocarcinoma

Mitofusin-2 (MFN2) is a mitochondrial protein associated with mitochondrial fusion process. It was initially identified as a hyperplasia suppressor and implicated in Charcot-Marie-Tooth disease. Recent studies showed that MFN2 played important roles in the development of multiple tumors. Here we examined MFN2 expression in 30 lung adenocarcinoma samples and revealed that the expression of MFN2 was significantly higher in lung adenocarcinoma tissues as compared to adjacent normal tissues. We then investigated the impact of MFN2 knockdown on A549 human lung adenocarcinoma cells and showed that cell proliferation, cell cycle and invasion behavior were all deregulated by MFN2 knockdown. And deregulation of cell cycle pathway after MFN2 knockdown was confirmed by microarray analysis. Furthermore, microarray analysis also revealed that different oncogenes such as RAP1A, RALB and ITGA2 were oppositely regulated by MFN2, which provided molecular clues for the paradoxical functions of MFN2 in tumor development. Taken together, our study unraveled the tumor-promoting functions of MFN2 in lung adenocarcinoma and implicated that the role of MFN2 in cancer development might be more complicated than expected and should be explored in detail in the future.

Frequent losses of heterozygosity in the mitofusin 2 gene in hepatocellular carcinoma: their relationship to clinicopathological features

BACKGROUND

The aim of the study was to determine the features of loss of heterozygosity in the mitofusin 2 gene and their association with clinicopathological characteristics of hepatocellular carcinoma.

METHODOLOGY

Loss of heterozygosity of four microsatellite loci were detected in tumors and their adjacent normal tissues of 29 surgically resected hepatocellular carcinomas using an ABI3130xl automated sequencer.

RESULTS

The results showed the incidences of loss of heterozygosity on microsatellite loci D1S2667, D1S2740, D1S434, and D1S228 were 21%, 23%, 21%, and 22%, respectively. Loss of heterozygosity in the mitofusin 2 gene was closely correlated with age, degree of differentiation, capsule integrity, and tumor size (P <0.05) but was not correlated with gender, thrombosis, liver cirrhosis, or alpha-fetoprotein levels (P >0.05).

CONCLUSIONS

Frequent loss of heterozygosity in the mitofusin 2 gene exists in hepatocellular carcinoma. Loss of heterozygosity, which represents a tumor suppressor gene pathway, may play a critical role in the occurrence and development of hepatocellular carcinoma.

Hepatitis B virus-induced hepatocellular carcinoma

Many factors are considered to contribute to hepatitis B virus (HBV) associated hepatocellular carcinoma (HCC), including products of HBV, HBV integration and mutation, and host susceptibility. HBV X protein (HBx) can interfere with several signal pathways that associated with cell proliferation and apoptosis, and the impact of HBx C-terminal truncation in the development of HCC has been implicated. Recent studies by advanced sequencing technologies have revealed recurrent HBV DNA integration sites in hepatoma cells and susceptible genes/SNPs play an important role in the pathogenesis of liver cancer. Epigenetic changes, immune and inflammatory factors are also important contributing factors for liver cancer. This mini-review provides an overview on the recent development of HBV induced HCC.