Quercetin induces G2 phase arrest and apoptosis with the activation of p53 in an E6 expression‑independent manner in HPV‑positive human cervical cancer‑derived cells

Mol Med Rep. 2019 Mar;19(3):2097-2106. doi: 10.3892/mmr.2019.9850. Epub 2019 Jan 11.

Abstract

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.

MeSH terms

  • Apoptosis / drug effects
  • Binding Sites
  • Female
  • G2 Phase Cell Cycle Checkpoints / drug effects
  • HeLa Cells
  • Humans
  • Molecular Docking Simulation
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Oncogene Proteins, Viral / chemistry
  • Oncogene Proteins, Viral / genetics*
  • Papillomavirus Infections / drug therapy*
  • Papillomavirus Infections / genetics
  • Papillomavirus Infections / pathology
  • Papillomavirus Infections / virology
  • Protein Binding
  • Proto-Oncogene Proteins c-mdm2 / chemistry
  • Proto-Oncogene Proteins c-mdm2 / genetics
  • Quercetin / pharmacology
  • Repressor Proteins / chemistry
  • Repressor Proteins / genetics*
  • Tumor Suppressor Protein p53 / chemistry
  • Tumor Suppressor Protein p53 / genetics*
  • Ubiquitin-Protein Ligases / chemistry
  • Ubiquitin-Protein Ligases / genetics*
  • Uterine Cervical Neoplasms / drug therapy*
  • Uterine Cervical Neoplasms / genetics
  • Uterine Cervical Neoplasms / pathology
  • Uterine Cervical Neoplasms / virology

Substances

  • E6 protein, Human papillomavirus type 16
  • Multiprotein Complexes
  • Oncogene Proteins, Viral
  • Repressor Proteins
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • Quercetin
  • UBE3A protein, human
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2
  • Ubiquitin-Protein Ligases