Abstract

p53 is frequently mutated in patients with prostate cancer, especially in those with advanced disease. Therefore, the selective elimination of p53 mutant cells will likely have an impact in the treatment of prostate cancer. Because p53 has important roles in cell cycle checkpoints, it has been anticipated that modulation of checkpoint pathways should sensitize p53-defective cells to chemotherapy while sparing normal cells. To test this idea, we knocked down ataxia telangiectasia mutated (ATM) gene by RNA interference in prostate cancer cell lines and in normal human diploid fibroblasts IMR90. ATM knockdown in p53-defective PC3 prostate cancer cells accelerated their cell cycle transition, increased both E2F activity and proliferating cell nuclear antigen expression, and compromised cell cycle checkpoints, which are normally induced by DNA damage. Consequently, PC3 cells were sensitized to the killing effects of the DNA-damaging drug doxorubicin. Combining ATM knockdown with the Chk1 inhibitor UCN-01 further increased doxorubicin sensitivity in these cells. In contrast, the same strategy did not sensitize either IMR90 or LNCaP prostate cancer cells, both of which have normal p53. However, IMR90 and LNCaP cells became more sensitive to doxorubicin or doxorubicin plus UCN-01 when both p53 and ATM functions were suppressed. In addition, knockdown of the G(2) checkpoint regulators ATR and Chk1 also sensitized PC3 cells to doxorubicin and increased the expression of the E2F target gene PCNA. Together, our data support the concept of selective elimination of p53 mutant cells by combining DNA damage with checkpoint inhibitors and suggest a novel mechanistic insight into how such treatment may selectively kill tumor cells.

Highlights

  • Cell cycle checkpoints are signaling pathways that sense the state of the cell and the progression of cell cycle events to orchestrate a cellular response to damage [1]

  • We found that ataxia telangiectasia mutated (ATM) knockdown increased the mitotic index of PC3 prostate cancer cells, augmented E2F activity and proliferating cell nuclear antigen (PCNA) expression, and inhibited G2 arrest in response to DNA damage

  • The ability of the most efficient small hairpin RNAs (shRNA) to interfere with the ATM pathway was verified by measuring the phosphorylation of the ATM target Chk2 at Thr68 (Fig. 1B)

Read more

Summary

Introduction

Cell cycle checkpoints are signaling pathways that sense the state of the cell and the progression of cell cycle events to orchestrate a cellular response to damage [1]. Moderate injury generally triggers a cell cycle arrest to allow time for repair, dissipation of stressors, or accumulation of essential factors for cell cycle progression. Significant damage induces programmed cell death to protect the organism from the expansion of cells with extensive genomic alterations that. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Could eventually lead to neoplastic transformation [2]. Failure to activate these checkpoint pathways may cause the development of cancer and other diseases [2]. A major issue in cancer therapeutics is to find targets whose modulation will exploit these checkpoint defects in tumor cells to make them more sensitive to chemotherapy [3]

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call