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Viral fusogenic membrane glycoprotein expression causes syncytia formation with bioenergetic cell death: implications
H Higuchi1, S F Bronk, A Bateman
1Center for Basic Research in Digestive Diseases, Mayo Clinic, Rochester Minnesota 55905, USA.
Abstract:
Viral fusogenic membrane glycoproteins (FMGs) are candidates for gene therapy of solid tumors because they cause cell fusion, leading to formation of lethal multinucleated syncytia. However, the cellular mechanisms mediating cell death after FMG-induced cell fusion remain unclear. The present study was designed to examine the mechanisms by which FMG expression in hepatocellular carcinoma cells lead to cell death. Transfection of Hep3B cells with the Gibbon Ape leukemia virus hyperfusogenic envelope protein (GALV-FMG) resulted in the formation of multinucleated syncytia that reached a maximum 5 days after transfection (100 nuclei/syncytia). The syncytia were viable for a period of 2 days and then rapidly lost viability by day 5. Mitochondrial dysfunction occurred in GALV-FMG-induced syncytia prior to loss of viability with loss of the mitochondrial membrane potential, cellular ATP depletion, and release of mitochondrial cytochrome c-GFP into the cytosol. The pan-caspase inhibitor, Z-VAD-fmk, did not prevent cell death. However, glycolytic generation of ATP with fructose effectively increased cellular ATP and preserved syncytial viability. These data suggest that expression of FMG in hepatoma cells results in the formation of multinucleated syncytia, causing mitochondrial failure with ATP depletion, a bioenergetic form of cell death with necrosis. This form of cell death should be effective in vivo and enhance the bystander effect, suggesting that FMG-based gene therapy deserves further study for the treatment of hepatocellular and other cancers.
Insights
Viral fusogenic membrane glycoproteins (FMGs) cause cell fusion in cancer gene therapy. This study reveals FMGs induce cell death via mitochondrial failure and ATP depletion, suggesting a promising therapeutic strategy for hepatocellular carcinoma.
Area of Science:
- Oncology
- Molecular Biology
- Gene Therapy
Background:
- Viral fusogenic membrane glycoproteins (FMGs) induce cell fusion, forming syncytia, and are investigated for solid tumor gene therapy.
- The precise mechanisms of cell death following FMG-induced syncytia formation are not fully understood.
Purpose of the Study:
- To investigate the cellular mechanisms of cell death induced by FMG expression in hepatocellular carcinoma cells.
Main Methods:
- Hep3B cells were transfected with Gibbon Ape leukemia virus hyperfusogenic envelope protein (GALV-FMG).
- Syncytia formation, viability, mitochondrial function (membrane potential, ATP levels, cytochrome c release), and response to caspase inhibition and glycolytic enhancement were assessed.
Main Results:
- GALV-FMG expression led to multinucleated syncytia formation, which were viable for 2 days before rapid death by day 5.
- Mitochondrial dysfunction, including loss of membrane potential and ATP depletion, preceded syncytia death.
- Caspase inhibition did not prevent cell death, but fructose supplementation preserved syncytia viability by boosting ATP levels.
Conclusions:
- FMG expression in hepatoma cells induces syncytia formation, leading to bioenergetic cell death via mitochondrial failure and ATP depletion.
- This necrosis-like cell death mechanism is potentially effective in vivo and may enhance the bystander effect.
- FMG-based gene therapy warrants further investigation for treating hepatocellular carcinoma and other cancers.