The Biflavonoid Amentoflavone Induces Apoptosis via Suppressing E7 Expression, Cell Cycle Arrest at Sub-G(1) Phase, and Mitochondria-Emanated Intrinsic Pathways in Human Cervical Cancer Cells

Abstract

Amentoflavone, a biflavonoid from Selaginella tamariscina, is known to possess several bioactivities such as antitumor, anti-inflammatory, and antifungal effects. However, the mechanism of the anticancer effects of amentoflavone on human cervical cancer cells has not been studied in detail. In this study, we demonstrated that amentoflavone induces apoptosis in SiHa and CaSki cervical cancer cells by suppressing human papillomavirus protein E7 expression. The cyclins and tumor suppressors were modulated by amentoflavone in SiHa and CaSki human cervical cancer cells: cyclin and hyperphosphorylated retinoblastoma (p-pRb) were down-regulated, whereas cyclin-dependent kinase inhibitors and p53 were enhanced. Amentoflavone up-regulated peroxisome proliferator-activated receptor gamma (PPAR gamma) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression levels while inhibiting E7-mediated cyclooxygenase-2 (COX-2)/interleukin-32 (IL-32) expressions were downregulated, and Akt phosphorlylation was decreased in an amentoflavone-induced apoptotic process, suggesting that amentoflavone may be a PPAR gamma activator. Additionally, the expression of the antiapoptotic factor Bcl-2 was decreased, whereas that of the well-known apoptotic factor Bax was increased, thereby releasing cytochrome c into cytosol in amentoflavone-treated cervical cancer cells. Furthermore, amentoflavone treatment led to the activation of caspase-3 and -9 and proteolytic cleavage of poly(ADP-ribose) polymerase. The expression level of the extrinsic death receptor Fas (CD95) was not altered by amentoflavone treatment. When these findings are taken together, the biflavonoid amentoflavone activates PPAR gamma/PTEN expressions and induces apoptosis via suppressing E7 expression, cell cycle arrest at sub-G(1) phase, and mitochondria-emanated intrinsic pathways in SiHa and CaSki human cervical cancer cells. These findings suggest that amentoflavone has potential for development as a therapeutic agent for human cervical cancer.