IFN-alfa AFFECTS CELL CYCLE PROGRESSION AND INDUCES APOPTOSIS IN HPV-POSITIVE HUMAN CERVICAL CARCINOMA CELLS. STUDIES ON E6 GENE SILENCED CELLS BY EXPRESSION OF HPV16-E6 SPECIFIC siRNA.

Interferon (IFN)-alfa induces a significant antiproliferative action in cervical carcinoma cells, expressing E6, E7 and E1 Human Papilloma Virus (HPV) genes. The knowledge of the signalling and cell death machineries by which IFN can counteract the activity of oncogenic viral protein E6 and E7 in cervical carcinoma cells appears of primary importance for new IFN-based therapeutic strategies to circumvent cancer disease progression or improve clinical outcome. We observed that IFN-alfa induces S-phase slowing and cell death in HPV-positive cervical carcinoma cell lines SiHa and ME-180, where p53 function is inhibited by HPV E6 oncoprotein. In this respect, we are setting up a molecular approach of RNA interference against HPV oncoproteins, to activate a specific interference in the deregulation of cell proliferation due to HPV oncogenic proteins. To date, we silenced HPV-E6 using siRNA to target the specific mRNA. Following a single dose of E6 siRNA treatment of SiHa cells, we observed selective silencing of E6. E6 silencing induces a consequent accumulation of p53 protein. The restored p53 protein transactivates cell cycle control gene CDKI-p21, thus suggesting the recovery of cellular regulatory system in these experimental conditions. Interestingly, IFN alfa appears unable to inhibit cell proliferation via cell cycle S-phase slowing and apoptosis, in E6 silenced cervical carcinoma cells. This suggests that in HPV-positive cells IFN-beta effect on cell cycle alteration is related to p53 inhibition by E6 oncoprotein.