Faculty of Pharmacy, Autonomous University of Morelos State (UAEM), Cuernavaca, Morelos CP 62209, México.
Department of Developmental Genetics and Molecular Physiology, National Autonomous University of Mexico, Cuernavaca, Morelos, CP 62210, México.
Mol Med Rep. 2019 Mar;19(3):2097-2106. doi: 10.3892/mmr.2019.9850. Epub 2019 Jan 11.
Cervical cancer is the second most common cancer in women worldwide. Human papillomavirus (HPV) infection appears to be a necessary factor in the development of almost all cases (>95%) of cervical cancer. HPV E6 induces a change of control of p53 stabilization from Hdm2 to E6/E6AP in HPV‑infected cells. It is well known that the LxxLL motif of cellular ubiquitin ligase E6AP binds to the pocket of E6 and causes a conformational change to enable E6 to bind p53 competently. In the ternary complex E6/E6AP/p53, p53 is polyubiquitinated by E6AP and subsequently degraded by a proteasome. Therefore, these cells are deficient in the processes regulated by p53, including apoptosis, damaged DNA repair, and the cell cycle. In the present study, it was demonstrated that quercetin induced G2 phase cell cycle arrest and apoptosis in both HeLa and SiHa cells, accompanied by an increase of p53 and its nuclear signal. It was also observed that quercetin increased the level of the p21 transcript and the pro‑apoptotic Bax protein, which are two p53‑downstream effectors. However, quercetin did not alter the expression of the HPV E6 protein in cervical cancer cells; therefore, the increase in p53 occurred in an E6 expression‑independent manner. Furthermore, molecular docking demonstrated that quercetin binds stably in the central pocket of E6, the binding site of E6AP. These data suggest that quercetin increases the nuclear localization of p53 by interrupting E6/E6AP complex formation in cervical cancer cells.
宫颈癌是全球女性中第二常见的癌症。人乳头瘤病毒（HPV）感染似乎是几乎所有宫颈癌病例（>95%）发展的必要因素。HPV E6 诱导 HPV 感染细胞中 p53 稳定性控制从 Hdm2 向 E6/E6AP 的改变。众所周知，细胞泛素连接酶 E6AP 的 LxxLL 基序与 E6 的口袋结合，导致构象变化，使 E6 能够有效地与 p53 结合。在三元复合物 E6/E6AP/p53 中，E6AP 使 p53 多泛素化，随后被蛋白酶体降解。因此，这些细胞缺乏受 p53 调节的过程，包括细胞凋亡、受损的 DNA 修复和细胞周期。在本研究中，证明了槲皮素诱导 HeLa 和 SiHa 细胞的 G2 期细胞周期停滞和细胞凋亡，同时 p53 及其核信号增加。还观察到槲皮素增加了 p21 转录本和促凋亡 Bax 蛋白的水平，这是 p53 的两个下游效应物。然而，槲皮素并未改变宫颈癌细胞中 HPV E6 蛋白的表达；因此，p53 的增加是在 E6 表达不依赖的方式下发生的。此外，分子对接表明，槲皮素通过中断宫颈癌细胞中 E6/E6AP 复合物的形成，稳定地结合在 E6 的中央口袋中，即 E6AP 的结合位点。这些数据表明，槲皮素通过中断 E6/E6AP 复合物的形成，增加了宫颈癌细胞中 p53 的核定位。
