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MVM(p) NS-2 protein expression is required with NS-1 for maximal cytotoxicity in human transformed cells
C Legrand1, J Rommelaere, P Caillet-Fauquet
1Département de Biologie Moléculaire, Faculté des Sciences, Université Libre de Bruxelles, Rhode St. Gen ese, Belgium.
Abstract:
The parvovirus-encoded nonstructural (NS) proteins have been implicated in the cytopathogenicity of these agents. Although protein NS-1 of minute virus of mice (MVM) has been shown to be toxic, little is known about the role of NS-2 in this process. In order to determine the contribution of NS-1 and NS-2 to cytotoxicity, we took advantage of an expression system controlled by the mouse mammary tumor virus promoter which responds to glucocorticoid stimulation and which controls the expression of both MVM(p) NS proteins. Different mutations were introduced in NS genes so as to affect the NS-1 or NS-2 protein. Neoplastic human cell lines expressing only NS-1 protein after induction by dexamethasone undergo a smaller lethality compared to lines expressing both wild-type proteins. Mutations that were introduced in NS-1 coding sequence and did not affect NS-2 were found to drastically suppress the cytotoxic effect. It is concluded that the NS-2 protein has little cytotoxic activity by itself but is required for the full expression of the viral cytopathic effect on transformed human cells. Furthermore these results lead us to suggest that the NS-2 cytotoxic domain is localized in the amino-terminal portion of the protein.
Insights
Minute virus of mice (MVM) nonstructural protein NS-2 is crucial for full viral cytopathic effect on human cells. While NS-1 has toxicity, NS-2 is required for maximal cytotoxicity, with its domain located in the amino-terminal region.
Area of Science:
- Virology
- Cell Biology
- Molecular Biology
Background:
- Parvovirus nonstructural (NS) proteins are linked to cytopathogenicity.
- Minute virus of mice (MVM) NS-1 is known to be toxic, but NS-2's role is unclear.
Purpose of the Study:
- To investigate the individual and combined roles of MVM NS-1 and NS-2 proteins in viral cytotoxicity.
- To identify the specific contributions of each NS protein to the cytopathic effect.
Main Methods:
- Utilized a glucocorticoid-inducible expression system for MVM(p) NS proteins.
- Introduced specific mutations in NS-1 and NS-2 genes to assess their functional impact.
- Compared cytotoxicity in neoplastic human cell lines expressing different combinations of NS proteins.
Main Results:
- Cell lines expressing only NS-1 showed less lethality than those expressing both wild-type NS-1 and NS-2.
- Mutations in NS-1 that did not affect NS-2 significantly reduced the cytotoxic effect.
- NS-2 alone exhibited minimal cytotoxic activity.
Conclusions:
- NS-2 protein is essential for the full expression of the MVM cytopathic effect in transformed human cells.
- The cytotoxic domain of NS-2 is likely located in its amino-terminal portion.
- NS-1 contributes to toxicity, but NS-2 is required for maximal viral-induced cell death.