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Cyclin B1 availability is a rate-limiting component of the radiation-induced G2 delay in HeLa cells
G D Kao1, W G McKenna, A Maity
1Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Abstract:
Irradiation of tumor cells results in a G2 delay, which has been postulated to allow DNA repair and cell survival. The G2 delay after irradiation is marked in HeLa and other cells by delayed expression of cyclin B1. To test whether this depression of cyclin B1 contributes to the G2 delay, we induced cyclin B1 expression in irradiated HeLa cells using a dexamethasone-inducible promoter. Induction of cyclin B1 after radiation abrogated the G2 delay by approximately doubling the rate at which the cells reentered mitosis, whereas dexamethasone itself had no effect. However, overexpression of cyclin B1 did not eliminate the G2 delay in irradiated cells. In unirradiated cells, overexpression of cyclin B1 had no effect on cell cycle progression. Confirmation that reduction of cyclin B1 levels would prolong G2 was provided using antisense oligonucleotides to cyclin B1. These results demonstrate that cyclin B1 levels control the length of the G2 delay following irradiation in HeLa cells but do not exclude additional mechanisms controlling the mitotic delay after irradiation.
Insights
Cyclin B1 levels regulate the G2 cell cycle delay after irradiation in HeLa cells. Manipulating cyclin B1 expression affects mitotic reentry, suggesting its crucial role in DNA repair and cell survival post-irradiation.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Cancer Research
Background:
- Irradiation of tumor cells induces a G2 cell cycle delay, hypothesized to facilitate DNA repair and enhance cell survival.
- Delayed cyclin B1 expression is a hallmark of the G2 delay in HeLa and other cell types following irradiation.
Purpose of the Study:
- To investigate the role of cyclin B1 expression in mediating the G2 delay observed after tumor cell irradiation.
- To determine if modulating cyclin B1 levels can influence the duration of the G2 delay and subsequent cell cycle progression.
Main Methods:
- Utilized a dexamethasone-inducible promoter to control cyclin B1 expression in irradiated HeLa cells.
- Administered dexamethasone to induce cyclin B1 expression and observed its effect on G2 delay.
- Employed antisense oligonucleotides to reduce cyclin B1 levels and assess the impact on G2 delay.
Main Results:
- Induction of cyclin B1 in irradiated HeLa cells abrogated the G2 delay, approximately doubling the rate of mitotic reentry.
- Dexamethasone alone did not affect the G2 delay, indicating cyclin B1's specific role.
- Overexpression of cyclin B1 did not completely eliminate the G2 delay, and had no effect in unirradiated cells.
- Reduction of cyclin B1 levels using antisense oligonucleotides prolonged the G2 delay.
Conclusions:
- Cyclin B1 levels are a key determinant of the G2 delay duration following irradiation in HeLa cells.
- These findings highlight cyclin B1's critical role in controlling cell cycle progression after DNA damage.
- The study suggests that while cyclin B1 is a major factor, other mechanisms may also contribute to the post-irradiation mitotic delay.