Deregulation of Internal Ribosome Entry Site-Mediated p53 Translation in Cancer Cells with Defective p53 Response to DNA Damage

Abstract

Synthesis of the p53 tumor suppressor and its subsequent activation following DNA damage are critical for its protection against tumorigenesis. We previously discovered an internal ribosome entry site (IRES) at the 5′ untranslated region of the p53 mRNA. However, the connection between IRES-mediated p53 translation and p53's tumor suppressive function is unknown. In this study, we identified two p53 IRES trans-acting factors, translational control protein 80 (TCP80), and RNA helicase A (RHA), which positively regulate p53 IRES activity. Overexpression of TCP80 and RHA also leads to increased expression and synthesis of p53. Furthermore, we discovered two breast cancer cell lines that retain wild-type p53 but exhibit defective p53 induction and synthesis following DNA damage. The levels of TCP80 and RHA are extremely low in both cell lines, and expression of both proteins is required to significantly increase the p53 IRES activity in these cells. Moreover, we found cancer cells transfected with a shRNA against TCP80 not only exhibit decreased expression of TCP80 and RHA but also display defective p53 induction and diminished ability to induce senescence following DNA damage. Therefore, our findings reveal a novel mechanism of p53 inactivation that links deregulation of IRES-mediated p53 translation with tumorigenesis.

ACKNOWLEDGMENTS

We thank Vitaly Polunovsky and Peter Bitterman (University of Minnesota) for helpful comments on the results presented in the manuscript. We also thank Suisheng Zhang (Institute of Molecular Biotechnology, Germany) and Michael B. Matthews (University of Medicine and Dentistry of New Jersey) for providing the pcDNA3.1/RHA and pcDNA3.1/HisB/TCP80 expression vectors, respectively.

Funding for this research was provided by an Idea Award (BC051719) from the Department of Defense, three research grants (1RO1 CA084325, 1RO3 ES017869, and 1RO3 CA177954) from the National Institutes of Health, an Institutional Research Grant (118198-IRG-58-001-52-IRG99) from American Cancer Society, and the Hormel Foundation.