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Oncogenic H-ras induces cyclin B1 expression in a p53-independent manner
Carla Santana1, Enrique Ortega, Alejandro García-Carrancá
1Department of Molecular Biology and Biotechnology, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico.
Abstract:
The role of p53 in controlling the G2 checkpoint, in part by repressing cyclin B1 transcription, has been well established. However, accumulating evidence indicate that p53-independent pathways may also play an important role. Ras proteins have been shown to regulate G1/S, but also G2/M transitions. Since cyclin B1/cdc2 complex is the key regulator controlling the G2/M checkpoint, we were interested in addressing if the H-ras oncogene could regulate cyclin B1 expression in a p53-independent manner. We observed an induction of cyclin B1 promoter activity in the presence of H-ras oncogene in SW480 cells, which contain null p53 alleles. In addition, HeLa cells known to express the HPV18 E6 oncogene that inactivates p53, exhibited increased levels of cyclin B1 mRNA and protein when transfected with the H-ras oncogene. Higher expression of cyclin B1 correlated with higher levels of cyclin B1/cdc2 complex and kinase activity that interestingly, showed no inhibition at G2/M after DNA damage. These data suggest that H-ras participates in pathways that regulate cyclin B1 expression and therefore controls the G2/M checkpoint in a p53-independent manner.
Insights
The H-ras oncogene regulates cyclin B1 expression and G2/M checkpoint control independently of p53. This suggests H-ras influences cell cycle progression through novel p53-independent pathways.
Area of Science:
- Cell Biology
- Molecular Oncology
- Cancer Research
Background:
- The p53 tumor suppressor is crucial for G2 checkpoint control, often by repressing cyclin B1 transcription.
- Emerging evidence highlights p53-independent mechanisms regulating cell cycle progression.
- Ras proteins are implicated in controlling both G1/S and G2/M transitions.
Purpose of the Study:
- To investigate whether the H-ras oncogene can regulate cyclin B1 expression in a p53-independent manner.
- To elucidate the role of H-ras in G2/M checkpoint control independent of p53 function.
Main Methods:
- Assessed cyclin B1 promoter activity in SW480 cells with null p53 alleles upon H-ras oncogene expression.
- Examined cyclin B1 mRNA and protein levels in HeLa cells (expressing HPV18 E6 to inactivate p53) transfected with H-ras.
- Measured cyclin B1/cdc2 complex levels and kinase activity.
- Evaluated G2/M checkpoint response to DNA damage.
Main Results:
- H-ras oncogene induced cyclin B1 promoter activity in p53-null SW480 cells.
- Transfection with H-ras increased cyclin B1 mRNA and protein in p53-inactivated HeLa cells.
- Elevated cyclin B1 expression correlated with increased cyclin B1/cdc2 complex and kinase activity.
- The cyclin B1/cdc2 complex showed no inhibition at G2/M following DNA damage.
Conclusions:
- H-ras oncogene plays a role in regulating cyclin B1 expression through p53-independent pathways.
- H-ras influences G2/M checkpoint control via modulation of cyclin B1, independent of p53 status.
- These findings reveal a novel mechanism for cell cycle regulation by H-ras in the context of compromised p53 function.