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Modulation of cell cycle control by vitamin D3 and its analogue, EB1089, in human breast cancer cells
1Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo 43699-0008, USA.
Abstract:
Examination of a panel of ER positive breast cancer cell lines showed that they were differentially growth inhibited by vitamin D3 and its analogue EB1089. EB1089 treatment of the breast cancer cell lines MCF-7 E, BT20, T47D, and ZR75 demonstrated a correlation between a reduction in Cdk2 kinase activity towards phosphorylation of histone H1 and a decrease in DNA synthesis, while no modulation of Cdk2 activity was observed in the vitamin D3 and EB1089 resistant cell line MCF-7 L. This was accompanied by a time dependent decrease in the percentage of S phase cells in the responsive lines. Characterization of the expression levels of Cdk2 and its related cell cycle proteins in MCF-7 E cells showed that after EB1089 treatment, there was a concentration and time dependent up-regulation of p21 as well as a decrease in cyclin A proteins. Paradoxically, cyclin E levels were increased as a function of treatment. Analysis of cyclin-Cdk2-Cdki complex formation showed that in EB1089 treated MCF-7 E cells, Cdk2, cyclin A and cyclin E immunoprecipitates contained an increased abundance of p21. In contrast to MCF-7 E cells, increases in both p21 and p27 as well as their complex formation with Cdk2 were observed in BT20 and ZR75 cells. These findings indicate that up-regulation of p21 as well as p27 in some cell types may account for the inactivation of Cdk2 activity and a G1 block of the cell cycle following EB1089 treatment.
Insights
Vitamin D3 analogue EB1089 inhibits growth of estrogen receptor-positive breast cancer cells by reducing Cdk2 kinase activity and DNA synthesis. This involves cell cycle regulation via p21 and p27 upregulation, leading to a G1 block.
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- Estrogen receptor-positive (ER+) breast cancer remains a significant health concern.
- Vitamin D3 and its analogues show potential anti-cancer properties.
- Understanding the molecular mechanisms of these agents is crucial for therapeutic development.
Purpose of the Study:
- To investigate the differential effects of vitamin D3 and its analogue EB1089 on ER+ breast cancer cell lines.
- To elucidate the role of Cdk2 kinase activity and cell cycle proteins in EB1089-induced growth inhibition.
Main Methods:
- Treatment of ER+ breast cancer cell lines (MCF-7 E, BT20, T47D, ZR75, MCF-7 L) with vitamin D3 and EB1089.
- Assay of Cdk2 kinase activity, DNA synthesis, and cell cycle phase distribution (S phase).
- Analysis of cell cycle regulatory protein expression (p21, p27, cyclin A, cyclin E) and complex formation.
Main Results:
- EB1089 differentially inhibited growth in ER+ breast cancer cell lines.
- Responsive cell lines showed reduced Cdk2 activity, decreased DNA synthesis, and a G1 cell cycle block.
- EB1089 treatment led to p21 upregulation and cyclin A decrease in MCF-7 E cells, while p21 and p27 increased in BT20 and ZR75 cells, correlating with Cdk2 inactivation.
Conclusions:
- EB1089 effectively inhibits ER+ breast cancer cell growth by modulating Cdk2 activity.
- Upregulation of p21 and p27 is a key mechanism for Cdk2 inactivation and cell cycle arrest at G1 phase.
- These findings support the potential of vitamin D analogues as therapeutic agents in breast cancer treatment.