Human Papilloma Virus 16 E6 RNA Interference Enhances Cisplatin and Death Receptor-Mediated Apoptosis in Human Cervical Carcinoma Cells

Abstract

In cervical cancer, the p53 and retinoblastoma (pRb) tumor suppressor pathways are disrupted by the human papilloma virus (HPV) E6 and E7 oncoproteins, because E6 targets p53 and E7 targets pRb for rapid proteasome-mediated degradation. We have investigated whether E6 suppression with small interfering RNA (siRNA) restores p53 functionality and sensitizes the HPV16-positive cervical cancer cell line SiHa to apoptosis by cisplatin, irradiation, recombinant human tumor necrosis factor-related apoptosis-inducing ligand (rhTRAIL), or agonistic anti-Fas antibody. E6 siRNA resulted in decreased E6 mRNA levels and enhanced p53 and p21 expression, demonstrating the restoration of p53 functionality in SiHa cells, without inducing high levels of apoptosis (Ͻ10%). Cell surface expression of the proapoptotic death receptors (DRs) DR4, DR5, and Fas was not affected by E6 suppression. E6 suppression conferred susceptibility to cisplatin-induced apoptosis but not to irradiation-, rhTRAIL-, or anti-Fas antibody-induced apoptosis. Combining cisplatin with rhTRAIL or anti-Fas antibody induced even higher apoptosis levels in E6-suppressed cells. At the molecular level, cisplatin treatment resulted in elevated p53 levels, enhanced caspase-3 activation, and reduced p21 levels in E6-suppressed cells. Cisplatin in combination with death receptor ligands enhanced caspase-8 and caspase-3 activation and reduced X-linked inhibitor-of-apoptosis protein (XIAP) levels in these cells. We showed using siRNA that the enhanced apoptosis in E6-supressed cells was related to reduced XIAP levels and not due to reduced p21 levels. In conclusion, targeting E6 or XIAP in combination with cisplatin can efficiently potentiate rhTRAIL-induced apoptosis in HPV-positive cervical cancer cells.

Human Papillomavirus E6 Knockdown Restores Adenovirus Mediated-estrogen Response Element Linked p53 Gene Transfer in HeLa Cells

“…These findings indicate that intrinsic p53 expression is suppressed by HPV E6 and that knockdown of E6 is essential for p53 expression. However, additional treatments were required to induce apoptosis of cervical cancer cells (Hougardy et al, 2006;Tan et al, 2012).…”

The PEI-introduced CS shell/PMMA core nanoparticle for silencing the expression of E6/E7 oncogenes in human cervical cells

“…Therefore, the use of RNAi to inhibit the expression of E6/E7 genes has been studied intensively (Alvarez-Salas, BenitezHess, & DiPaolo, 2003;Butz et al, 2003). Furthermore, several studies revealed that treatment of cancer with siRNA was able to enhance the effect of anti-tumor drugs such as cisplatin (Tan et al, 2012), doxorubicin, and gemcitabine (Koivusalo, Krausz, Helenius, & Hietanen, 2005).…”

Artificial microRNAs against the viral E6 protein provoke apoptosis in HPV positive cancer cells

“…E7 is responsible for pRb degradation, a negative regulator of the cell cycle, leading to S-phase entry, viral replication and maintenance [6]. E6 and E7 inhibition or knockdown is a promising therapeutical strategy to act on cancer cells to potentially induce cell death or growth arrest [7][8][9][10][11].…”

“…The efficiency in vivo could be improved by transferring the miRNA expression cassettes into conditionally replicative adenoviruses (CRAd) which should allow a better killing of tumor cells and an improved vector dissemination[20]. Another possibility would be the use of a combinatorial treatment with Ad18_2 and Cisplatin[8]. Very recently we designed a high affinity bivalent ligand able to bind specifically to E6 of all high risk HPV[21].…”