Received for publication January 19, 2005.
Revised April 26, 2005.
Accepted for publication May 18, 2005.

Chemotherapy Compounds in Cervical Cancer Cells Primed by Reconstitution of p53 Function After Short Interfering RNA-mediated Degradation of Human Papillomavirus 18 E6 mRNA. Opposite Effect of siRNA in Combination With Different Drugs

Abstract

Constant expression of E6 and E7 mRNA by high-risk human papillomaviruses (HPV) abrogates p53 and pRb function, respectively, and is essential for the development of cervical cancer. Despite E6, some chemotherapy drugs can stabilize p53 in cervical cancer cells. It is not known how chemotherapy-induced p53 activation and cytotoxicity is affected when the amount of E6 mRNA is decreased before the drug treatment. Here, HPV 18 positive HeLa cervical cancer cells were transfected with short interfering RNA (siRNA) molecules targeting HPV 18 E6 mRNA before treatment with carboplatin, cisplatin, doxorubicin, etoposide, gemcitabine, mitomycin, mitoxantrone, oxaliplatin, paclitaxel and topotecan. Transfection with siRNA was followed by nuclear accumulation of p53, but the effect was transient despite continuously suppressed HPV mRNA levels. When treatment with E6 siRNA was coupled with chemotherapy, the p53 activity after treatment with carboplatin and paclitaxel was additively increased, whereas the p53 activation induced by the rest of the drugs was synergistically increased. Treatment with E6 siRNA alone moderately inhibited HeLa cell proliferation, but did not induce detectable apoptosis. The combined cytotoxic effect of E6 siRNA and chemotherapy ranged from subadditive to synergistic, depending on the drug. The decrease of E6 mRNA sensitized HeLa cells for example to doxorubicin and gemcitabine, but counteracted the cytotoxicity of cisplatin and etoposide. In conclusion, activating p53 by degrading E6 mRNA may either increase or decrease the chemosensitivity of cervical cancer cells, depending on the chemotherapy compound.

Key words: RNA/siRNA, Mechanisms of cell killing/apoptosis, Oncogenes, Resistance, Tumor suppressors

This article has been cited by other articles:

				J. Courtete, A.-P. Sibler, G. Zeder-Lutz, D. Dalkara, M. Oulad-Abdelghani, G. Zuber, and E. Weiss Suppression of cervical carcinoma cell growth by intracytoplasmic codelivery of anti-oncoprotein E6 antibody and small interfering RNA Mol. Cancer Ther., June 1, 2007; 6(6): 1728 - 1735. [Abstract] [Full Text] [PDF]

				R. Koivusalo, A. Mialon, H. Pitkanen, J. Westermarck, and S. Hietanen Activation of p53 in Cervical Cancer Cells by Human Papillomavirus E6 RNA Interference Is Transient, but Can Be Sustained by Inhibiting Endogenous Nuclear Export-Dependent p53 Antagonists Cancer Res., December 15, 2006; 66(24): 11817 - 11824. [Abstract] [Full Text] [PDF]

				L. N. Putral, M. J. Bywater, W. Gu, N. A. Saunders, B. G. Gabrielli, G. R. Leggatt, and N. A. J. McMillan RNA Interference against Human Papillomavirus Oncogenes in Cervical Cancer Cells Results in Increased Sensitivity to Cisplatin Mol. Pharmacol., November 1, 2005; 68(5): 1311 - 1319. [Abstract] [Full Text] [PDF]