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bcl-2 suppresses expression of p21WAF1/CIP1 in breast epithelial cells
S Upadhyay1, G Li, H Liu
1Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Abstract:
The tumor suppressor gene p53 regulates G1 checkpoint prior to the initiation of DNA synthesis, which can either induce G1 arrest or signal apoptosis. The involvement of p53 in apoptosis may also be related to its ability to down-regulate transcription of the bcl-2 gene. The bcl-2 gene product prevents most types of apoptotic cell death, suggesting that bcl-2 interferes with an essential signaling molecule involved in the apoptotic cell death pathway. Although the bcl-2 protein is shown to be overexpressed in many types of human tumor including breast cancer, its biochemical or pathological consequences are poorly understood. To determine the effects of bcl-2 overexpression on apoptosis and transformation of breast epithelial cells and to investigate whether bcl-2 interferes with the p53 pathway, we introduced the bcl-2 expression vector into MCF10A cells, which were derived from diploid human breast epithelial cells containing the wild-type p53 gene. Overexpression of bcl-2 prevented free radical-induced apoptosis and induced a partially transformed phenotype in MCF10A cells. Although overexpression of bcl-2 did not affect the expression of the p53 gene, p53-dependent gene transcription such as p21WAF1/CIP1 was suppressed. These results suggest that bcl-2 may inhibit p53 functional activity and is involved in the regulation of an early commitment step either to proliferate or suicide.
Insights
Overexpressing the bcl-2 gene in breast cells inhibits apoptosis and interferes with the p53 tumor suppressor pathway, promoting cell proliferation. This suggests bcl-2 plays a role in cancer development.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- The p53 tumor suppressor gene controls cell cycle checkpoints and apoptosis.
- The bcl-2 gene product inhibits apoptosis and is often overexpressed in human tumors, including breast cancer.
- The precise role of bcl-2 in cancer and its interaction with p53 are not fully understood.
Purpose of the Study:
- To investigate the effects of bcl-2 overexpression on apoptosis and transformation in breast epithelial cells.
- To determine if bcl-2 interferes with the p53 signaling pathway.
Main Methods:
- Introduced a bcl-2 expression vector into MCF10A human breast epithelial cells with wild-type p53.
- Assessed apoptosis induction by free radicals.
- Evaluated cell transformation.
- Analyzed p53 gene expression and p53-dependent gene transcription (e.g., p21WAF1/CIP1).
Main Results:
- bcl-2 overexpression prevented free radical-induced apoptosis in MCF10A cells.
- Overexpression of bcl-2 led to a partially transformed phenotype in these cells.
- While bcl-2 did not alter p53 gene expression, it suppressed p53-dependent transcription of genes like p21WAF1/CIP1.
Conclusions:
- bcl-2 overexpression can inhibit apoptosis and promote transformation in breast epithelial cells.
- bcl-2 appears to interfere with p53's functional activity, potentially by suppressing downstream targets.
- These findings suggest bcl-2 is involved in regulating the cell's decision between proliferation and apoptosis, contributing to tumorigenesis.