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Decreased intracellular superoxide levels activate Sindbis virus-induced apoptosis
K I Lin1, P Pasinelli, R H Brown
1Department of Neurology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
Infection of many cultured cell types with Sindbis virus (SV), an alphavirus, triggers apoptosis through a commonly utilized caspase activation pathway. However, the upstream signals by which SV activates downstream apoptotic effectors, including caspases, remain unclear. Here we report that in AT-3 prostate carcinoma cells, SV infection decreases superoxide (O-2) levels within minutes of infection as monitored by an aconitase activity assay. This SV-induced decrease in O-2 levels appears to activate or modulate cell death, as a recombinant SV expressing the O-2 scavenging enzyme, copper/zinc superoxide dismutase (SOD), potentiates SV-induced apoptosis. A recombinant SV expressing a mutant form of SOD, which has reduced SOD activity, has no effect. The potentiation of SV-induced apoptosis by wild type SOD is because of its ability to scavenge intracellular O-2 rather than its ability to promote the generation of hydrogen peroxide. Pyruvate, a peroxide scavenger, does not affect the ability of wild type SOD to potentiate cell death; and increasing the intracellular catalase activity via a recombinant SV vector has no effect on SV-induced apoptosis. Moreover, increasing intracellular O-2 by treatment of 3T3 cells with paraquat protects them from SV-induced death. Altogether, our results suggest that SV may activate apoptosis by reducing intracellular superoxide levels and define a novel redox signaling pathway by which viruses can trigger cell death.
Insights
Sindbis virus (SV) infection triggers apoptosis by decreasing cellular superoxide levels. Enhancing superoxide scavenging with superoxide dismutase (SOD) potentiates SV-induced cell death, revealing a novel viral apoptosis pathway.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Sindbis virus (SV) infection induces apoptosis via caspase activation.
- The upstream signaling events triggering SV-induced apoptosis are not fully understood.
Purpose of the Study:
- To investigate the role of superoxide (O-2) in SV-induced apoptosis.
- To elucidate the upstream redox signaling pathway involved in viral apoptosis.
Main Methods:
- Monitoring O-2 levels using aconitase activity assays in SV-infected AT-3 prostate carcinoma cells.
- Utilizing recombinant SV expressing copper/zinc superoxide dismutase (SOD) and mutant SOD.
- Assessing the effects of pyruvate and catalase on SV-induced apoptosis.
- Examining the impact of paraquat-induced O-2 increase on SV-induced cell death in 3T3 cells.
Main Results:
- SV infection rapidly decreases intracellular O-2 levels.
- Overexpression of wild-type SOD potentiates SV-induced apoptosis by scavenging O-2.
- A catalytically inactive SOD mutant or peroxide scavenging (pyruvate, catalase) did not affect apoptosis.
- Increasing intracellular O-2 with paraquat protected cells from SV-induced death.
Conclusions:
- SV activates apoptosis by reducing intracellular O-2 levels.
- A novel redox signaling pathway involving decreased O-2 mediates SV-induced cell death.