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

p53 is degraded in cervical cancer cells by the human papillornavirus E6 and can be stabilized with short interfering RINIA (siRNA) molecules targeting E6 mRNA. In this in vitro study. we show that E6 siRINIA-induced p53 activation is transient in HeLa cervical cancer cells despite continuous suppression of E6 mR-NLA; activation can be sustained if the endogenous p53 antagonists COP1, MDM2, Pirh2, and e-jun-NH2-kinase are also targeted by siRNAs or by inhibiting the nuclear export of p53 with leptomvcin B. The direct targeting of any one of these four cellular p53 antagonists had no effect on p53 activity when E6 was intact, but inhibited the fading off of E6 siRNA-induced p53 activation in nonstress conditions. The effect -was additive when multiple cellular antagonists were concomitantIv inhibited, indicating that all these proteins degrade p53 when E6 is inactivated. The antiproliferative effect induced bv E6 silencing iwas enhanced when the endogenous p53 antagonists were additionally targeted. In conclusion, if human papillomavirus E6 is inhibited under nonstress conditions, the subsequent p53 activation is quickly reversed by the endogenous p53 degenerative machinery. The present results indicate that several cellular p53 antagonists must be inhibited for sustained p53 activity if E6 siRNA therapy is attempted and if no combined genotoxic therapy is applied.