G1 arrest and expression of cyclin-dependent kinase inhibitors in tamoxifen-treated MCF-7 human breast cancer cells.

Abstract

Treatment of exponentially growing MCF-7 human breast carcinoma cells with tamoxifen (TAM) inhibits cell growth in a dose-dependent manner. However, the molecular basis for the drug's activity and its relationship to the cell cycle have not yet been clearly established. In this study, we analyzed cell cycle-related proteins used for immunoblotting and flow cytometry in TAM-treated MCF-7 cells. In addition, the ratio of apoptosis in the cell was analyzed using labeling of DNA strand breaks (TdT assay). In flow-cytometric DNA distribution analysis, the S-phase fraction showed a marked decrease and a concomitant increase in G1- and G2-phase cells accompanying the inhibitory effect of TAM; these changes were time- and dose-dependent. Immunoblotting revealed that the levels of p53 and p21(WAF1/CIP1) in TAM-treated cells increased in a time- and dose-dependent manner, whereas those of p27(KIP1) and p16 slightly increased or remained unchanged. Furthermore, cyclin D3 and B showed sharp decreases, in contrast with p53 and p21(WAF1/CIP1) DNA-apoptosis dual analysis using flow cytometry revealed that the TAM-treated samples contained apoptotic cells, the majority of which were arrested in G1 or G2 and showed suppression of Bcl-2 protein. These results suggest that the tumorigenic effect of TAM on MCF-7 cells arises through antitumor effects that are due to the expression of cyclin-dependent kinase inhibitors, especially p21(WAF1/CIP1) and these are regulated by the decrease of wild-type p53. The proposed mechanism is similar to that underlying the cytotoxic effects of other agents and ionizing irradiation that cause DNA damage.

• Authors: Akira Ichikawa, Jiro Ando, Koichi Suda
• Journal: Human cell (Hum Cell) Vol. 21 Issue 2 Pg. 28-37 (May 2008) ISSN: 0914-7470 [Print] Japan
• PMID: 18397472 (Publication Type: Journal Article)

Chemical References

• Antineoplastic Agents, Hormonal
• CDKN1A protein, human
• Cyclin-Dependent Kinase Inhibitor Proteins
• Cyclin-Dependent Kinase Inhibitor p21
• Tumor Suppressor Protein p53
• Tamoxifen

Topics

• Antineoplastic Agents, Hormonal (pharmacology)
• Apoptosis
• Breast Neoplasms (metabolism, pathology)
• Carcinoma (metabolism, pathology)
• Cyclin-Dependent Kinase Inhibitor Proteins (metabolism)
• Cyclin-Dependent Kinase Inhibitor p21 (metabolism)
• Dose-Response Relationship, Drug
• Female
• G1 Phase (drug effects)
• Gene Expression Regulation, Neoplastic
• Humans
• Tamoxifen (pharmacology)
• Time Factors
• Tumor Cells, Cultured
• Tumor Suppressor Protein p53 (metabolism)