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Induction of apoptosis in breast cancer cells by TPA
Y Li1, M Bhuiyan, R M Mohammad
1Department of Pathology, Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan, USA.
Abstract:
Bcl-2, Bax and p53 gene products have been linked to programmed cell death pathways. p21WAF1 has been shown to mediate p53-induced cell cycle arrest and to inhibit cyclin-dependent kinase activity. We have analysed the expression of these genes and apoptosis induced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in several human breast cancer cell line. We found up-regulation of p21WAF1 and Bax expressions, however, the expressions of p53 and Bcl-2 genes remained unchanged in TPA-treated cells. Furthermore, DNA ladder formation and PARP cleavage were observed after treatment for 24 h, indicating apoptotic cell death. Flow cytometry with 7-amino actinomycin D staining showed that the number of apoptotic cells increased with longer treatment of TPA. From these results, we conclude that TPA is not only a tumor promoter, but also induces apoptosis in breast cancer cells. TPA-induced apoptosis appears to be mediated through a p53-independent pathway, and the up-regulation of p21WAF1 and Bax may be the molecular mechanisms by which TPA induces apoptosis.
Insights
The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induces programmed cell death (apoptosis) in human breast cancer cells. This TPA-induced apoptosis involves increased p21WAF1 and Bax gene expression via a p53-independent pathway.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Death Pathways
Background:
- Bcl-2, Bax, and p53 proteins are crucial in regulating programmed cell death.
- p21WAF1 mediates p53-induced cell cycle arrest and inhibits cyclin-dependent kinases.
Purpose of the Study:
- To investigate the role of TPA in inducing apoptosis in human breast cancer cell lines.
- To analyze the expression of Bcl-2, Bax, p53, and p21WAF1 genes during TPA treatment.
Main Methods:
- Analysis of gene expression in human breast cancer cell lines treated with TPA.
- Assessment of apoptosis using DNA ladder formation, PARP cleavage, and flow cytometry with 7-amino actinomycin D staining.
Main Results:
- TPA treatment led to the up-regulation of p21WAF1 and Bax gene expression.
- p53 and Bcl-2 gene expressions remained unchanged.
- DNA ladder formation and PARP cleavage indicated TPA-induced apoptosis.
- Apoptotic cell count increased with prolonged TPA exposure.
Conclusions:
- TPA acts as both a tumor promoter and an inducer of apoptosis in breast cancer cells.
- TPA-induced apoptosis occurs through a p53-independent mechanism.
- Up-regulation of p21WAF1 and Bax are likely molecular mediators of TPA-induced apoptosis.