Isoliquiritigenin Induces Caspase-Dependent Apoptosis via Downregulation of HPV16 E6 Expression in Cervical Cancer Ca Ski Cells

Abstract

Flavonoids have antitumoral properties and may be attractive candidates as anticancer therapy. Isoliquiritigenin which is a constituent of licorice (Glycyrrhiza inflata), a plant commonly used in traditional Uyghur medicine in Xinjiang, China, was studied for antiproliferative and apoptotic activity in human cervical cancer cells, Ca Ski, SiHa, HeLa, and C-33A. Its molecular mechanism of action was specifically examined in Ca Ski cells. Isoliquiritigenin decreased cell viability, induced cell accumulation in G2/M and morphological and biochemical features of apoptosis in the four cancer cell lines. In Ca Ski cells, isoliquiritigenin led to a downregulation of HPV16 E6 expression associated with an increase of p53 and p21 levels, enhanced expression of Bax and decreased expression of Bcl-2 and Bid proform triggering dissipation of the mitochondrial membrane potential, released cytochrome c to the cytosol followed by activation of caspase cascade with cleavage of caspase-9, caspase-3, and PARP. Caspase-8 was also cleaved. Moreover treatment with a pan-caspase inhibitor prevented apoptosis. As Ca Ski cells are representative of carcinoma naturally occurring in the cervix, our results suggest a potential benefit of isoliquiritigenin for cervical cancer prevention and treatment.

Characteristic Features of Cytotoxic Activity of Flavonoids on Human Cervical Cancer Cells

“…There are more than 200 types of HPVs described to date from which about 15 are designed as high-risk strains according to the propensity of malignant progression of virus-associated lesions (Di Domenico et al, 2012;Yuan CH, 2012;Hirchaud et al, 2013;Moga et al, 2014). The most prevalent high risk type is HPV16 that is responsible for the development of about 50-60% of all cervical cancers.…”

“…The most prevalent high risk type is HPV16 that is responsible for the development of about 50-60% of all cervical cancers. It is followed by HPV18 that harbors about 10-20% of cervical carcinomas worldwide Cherry et al, 2013;Hirchaud et al, 2013;Kim MS et al, 2013). The oncogenic function of HPVs can be primarily attributed to the two encoded oncoproteins, E6 and E7 (Kim et al, 2012;Kim MS et al, 2013).…”

“…The E6 protein target the wild-type tumor suppressor p53, binding to it and stimulating its degradation; the E7 protein interacts to the other tumor suppressor, retinoblastoma (Rb). These two oncoproteins induce cervical cancer progression by disturbing the functions of tumor suppressors on cell cycle regulation and apoptosis, thereby enhancing the proliferation of infected cells and promoting their immortality (Lee et al, 2005;Shin et al, 2008;Lee et al, 2011;Di Domenico et al, 2012;Kim et al, 2012;Hirchaud et al, 2013;Kim MS et al, 2013). Downregulation of these oncoproteins could thus enhance the stabilization and increase the level of tumor suppressors, engaging cancer cells in cell death.…”

“…Numerous effective anticancer drugs are either isolated from botanical sources or are modifications of natural molecules (Csapi et al, 2010;Al-Hazzani and Alshatwi, 2011;Hirchaud et al, 2013;Kitdamrongtham et al, 2013;Muthusami et al, 2013). Plants have received extensive attention as a source of potential antitumor agents in the past few decades and currently, most of the modern anticancer drugs such as camptothecin, vincristine, vinblastine, adriamycin, taxol, etoposide and paclitaxel are plant-derived compounds (Koppikas et al, 2010;Vidya Priyadarsini et al, 2010;Krifa et al, 2013).…”

“…The common dietary licorice chalcone isoliquiritigenin has shown to reduce the cell viability by inducing cell cycle arrest and morphological and biochemical features of apoptosis in both HPV16-(CaSki, SiHa) and HPV18-positive (HeLa) cell lines as well as HPV-negative cervical cancer cells (C33A) (Li et al, 2008;Hsu et al, 2009;Park et al, 2009;Hirchaud et al, 2013). Increase in intracellular reactive oxygen species (ROS) and triggering oxidative stress may play a critical role in isoliquiritigenin induced HeLa cell apoptosis (Yuan X et al, 2012;Yuan et al, 2013).…”