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Induction of apoptosis by cadmium and the adeno-associated virus Rep proteins
1Department of Biochemistry and Molecular Biology, Medical College of Ohio, 3035 Arlington Ave., Toledo, Ohio 43614-5804, USA.
Abstract:
The parvoviruses exert antiproliferative effects on transformed cells in culture. The development of cell lines that inducibly express the parvovirus nonstructural proteins have implicated these proteins in the limitation of cell growth. To study the host cell interactions of the nonstructural proteins we have developed a human 293 cell line that expresses the adeno-associated virus (AAV) rep gene upon induction with heavy metal salts. When induced with both Zn(2+) and Cd(2+), Rep protein expression correlates with a cell cycle block in S phase (Yang, Q., Chen, F., and Trempe, J. P. (1994). J. Virology 68,7169-7177). However when induced with Cd(2+) alone, the Rep proteins are expressed and the cells are killed. Production of a nucleosomal DNA repeat pattern and degradation of poly-ADP ribose polymerase (PARP) suggest that killing occurs by apoptosis. These results demonstrate that AAV Rep protein expression in chemically stressed cells is cytotoxic due to induction of apoptotic pathways.
Insights
Adeno-associated virus (AAV) Rep protein expression halts cell growth and can trigger programmed cell death (apoptosis) in human cells, particularly under chemical stress. This highlights the cytotoxic potential of AAV Rep proteins.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Parvoviruses are known to inhibit the proliferation of cancer cells.
- Nonstructural proteins of parvoviruses have been linked to cell growth limitation.
- Understanding the host cell interactions of these viral proteins is crucial.
Purpose of the Study:
- To investigate the role of adeno-associated virus (AAV) Rep proteins in host cell cycle regulation and cell death.
- To develop a human cell line model for inducible expression of AAV Rep proteins.
Main Methods:
- Developed a human 293 cell line with inducible expression of the AAV rep gene using heavy metal salts (Zn(2+) and Cd(2+)).
- Analyzed cell cycle progression and cell viability upon induction.
- Assessed DNA fragmentation and poly-ADP ribose polymerase (PARP) degradation to identify mechanisms of cell death.
Main Results:
- Rep protein expression induced by Zn(2+) and Cd(2+) resulted in an S-phase cell cycle block.
- Cd(2+) induction alone led to Rep protein expression and significant cell death.
- Evidence of nucleosomal DNA fragmentation and PARP degradation indicated apoptosis induction.
Conclusions:
- AAV Rep protein expression can induce apoptosis in chemically stressed human cells.
- The cytotoxic effects of AAV Rep proteins are mediated through the activation of apoptotic pathways.
- This study provides insights into the dual role of AAV Rep proteins in cell cycle arrest and apoptosis.