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Butyrate inhibits mouse fibroblasts at a control point in the G1 phase
Abstract:
Butyrate block 3T6 cells in the G1 phase of the cell cycle approximately 5--6 h prior to the start of the S phase. Serum factors are required before as well as after the butyrate-sensitive steps in G1 in order to allow cells to start DNA synthesis. 3T6 cells infected with SV40 or with polyoma virus are also blocked at the same stage in G1 in the presence of the fatty acid. However, events before as well as after the butyrate-sensitive step do not require serum in virus-infected cells. The sensitivity of the initiation of cellular DNA synthesis to increasing concentrations of butyrate is the same for serum-stimulated or for virus-infected cells. A similar and parallel effect on DNA synthesis is observed if cells are incubated in the presence of very small amounts of cycloheximide. After release of the cycloheximide-induced G1 arrest about 4--6 h have to pass before cells enter the S phase. Cells stably transformed by SV40 are considerably more resistant to low cycloheximide concentrations and to butyrate. These data are discussed in the light of the hypothesis that both low concentrations of cycloheximide and sodium butyrate block cells at a control point in G1 by interference with the synthesis of one or more rapidly turning over, cell cycle-specific proteins.
Insights
Sodium butyrate and cycloheximide block cells in G1 phase, preventing DNA synthesis. This occurs by interfering with essential cell cycle proteins, with virus-infected cells showing altered serum factor requirements.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cell cycle progression is tightly regulated by specific proteins.
- Growth factors and viral infections can influence cell cycle control.
Purpose of the Study:
- To investigate the effects of sodium butyrate and cycloheximide on cell cycle progression.
- To elucidate the mechanism by which these agents inhibit DNA synthesis.
Main Methods:
- Treatment of 3T6 cells with sodium butyrate and cycloheximide.
- Analysis of cell cycle phase distribution using DNA synthesis markers.
- Comparison of normal and virus-infected cells, including SV40-transformed cells.
Main Results:
- Sodium butyrate and cycloheximide induce a G1 phase block, delaying S phase entry.
- Serum factors are required for DNA synthesis initiation in normal cells but not in virus-infected cells.
- SV40-transformed cells exhibit resistance to butyrate and cycloheximide.
Conclusions:
- Butyrate and cycloheximide likely inhibit DNA synthesis by interfering with the production of short-lived, cell cycle-specific proteins.
- Viral transformation alters cellular responses to cell cycle inhibitors.