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Modulation of intrinsic P-glycoprotein expression in multicellular prostate tumor spheroids by cell cycle inhibitors
Maria Wartenberg1, Kerstin Fischer, Jürgen Hescheler
1Department of Neurophysiology, University of Cologne, Robert-Koch-Strasse 39, D-50931 Cologne, Germany.
Abstract:
The effects of cell cycle inhibition on the expression of the multidrug resistance transporter P-glycoprotein (P-gp) as well as of the cyclin-dependent kinase (CDK) inhibitors p27(Kip1) and p21(WAF-1) were investigated in DU-145 prostate tumor spheroids. With increasing spheroid size the number of cells in the G0/G1 phase augmented, whereas the number of cells in the G2/M phase and the S phase of the cell cycle declined. The number of G0/G1 cells was elevated after incubation with either mimosine, staurosporine or serum-free medium. Mitomycin C and roscovitine increased the number of S phase cells. Roscovitine additionally increased cells in the G2/M phase. Incubation in serum-free medium upregulated p21(WAF-1), p27(Kip1) and P-gp. Mimosine treatment resulted in upregulation of p27(Kip1) and P-gp, whereas p21(WAF-1) remained unchanged. Upon roscovitine treatment p27(Kip1) and p21(WAF-1) were downregulated, whereas P-gp was unaltered. Mitomycin C treatment resulted in downregulation of p27(Kip1) and p21(WAF-1); no significant change in P-gp levels was observed. Staurosporine induced upregulation of p21(WAF-1) whereas p27(Kip1) remained unaltered. P-gp was downregulated upon staurosporine treatment, which was owing to an elevation of intracellular reactive oxygen species by this compound. It is concluded that upregulation of P-gp in G0/G1 phase cells requires coexpression of the CDK inhibitor p27(Kip1) but not the CDK inhibitor p21(WAF-1).
Insights
Cell cycle inhibition affects multidrug resistance P-glycoprotein (P-gp) expression in prostate cancer. Upregulation of P-gp in G0/G1 phase cells requires p27(Kip1) but not p21(WAF-1) CDK inhibitors.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- The multidrug resistance transporter P-glycoprotein (P-gp) plays a crucial role in cancer treatment failure.
- Cell cycle regulation is altered in tumor spheroids, impacting cellular functions.
- Cyclin-dependent kinase (CDK) inhibitors like p27(Kip1) and p21(WAF-1) are key regulators of the cell cycle.
Purpose of the Study:
- To investigate the effects of cell cycle inhibition on P-glycoprotein (P-gp) expression.
- To determine the role of CDK inhibitors p27(Kip1) and p21(WAF-1) in P-gp regulation within prostate tumor spheroids.
Main Methods:
- DU-145 prostate tumor spheroids were treated with various agents (mimosine, staurosporine, serum-free medium, mitomycin C, roscovitine) to induce cell cycle arrest or progression.
- Flow cytometry was used to analyze cell cycle distribution (G0/G1, S, G2/M phases).
- Expression levels of P-gp, p27(Kip1), and p21(WAF-1) were assessed using techniques likely involving Western blotting or similar methods.
Main Results:
- Increasing spheroid size correlated with more cells in G0/G1 and fewer in G2/M and S phases.
- Serum-free medium, mimosine, and staurosporine increased G0/G1 phase cells.
- Mitomycin C and roscovitine increased S phase cells, with roscovitine also increasing G2/M phase cells.
- Serum-free medium and mimosine upregulated p27(Kip1) and P-gp; mimosine did not alter p21(WAF-1).
- Roscovitine downregulated p27(Kip1) and p21(WAF-1) but did not affect P-gp.
- Mitomycin C downregulated p27(Kip1) and p21(WAF-1) without significant P-gp change.
- Staurosporine upregulated p21(WAF-1), did not alter p27(Kip1), and downregulated P-gp due to reactive oxygen species.
Conclusions:
- P-glycoprotein (P-gp) upregulation in G0/G1 phase prostate cancer cells is dependent on the co-expression of the CDK inhibitor p27(Kip1).
- The CDK inhibitor p21(WAF-1) is not required for P-gp upregulation in G0/G1 phase cells.
- Cell cycle phase and specific CDK inhibitors differentially regulate P-gp expression in prostate tumor models.