HPV-mediated nuclear export of HP1\u03b3 drives cervical tumorigenesis by downregulation of p53

Sang Ah Yi,Jeung-Whan Han,Dong Hoon Lee,Junjeong Choi,Hwamok Oh,Go Woon Kim,Hyun-Wook Ryu,Jueng Soo You,Jong Woo Park,Jihoon Han,Hyeok Gu Kang,Jee Hun Park,Jaecheol Lee,Kyung-Hee Chun,So Hee Kwon,Hyun-Soo Kim,Da-Hyun Kim,Jieun Lee

doi:10.1038/s41418-020-0520-5

Abstract

E6 oncoprotein derived from high-risk human papillomavirus (HPV) drives the development of cervical cancer through p53 degradation. Because cervical cancer therapies to inactivate HPV or E6 protein are not available, alternative strategies are required. Here, we show that HPV-mediated nuclear export of human heterochromatin protein 1γ (HP1γ) reduces the stability of p53 through UBE2L3-mediated p53 polyubiquitination during cervical cancer progression. In general, HP1 plays a key role in heterochromatin formation and transcription in the nucleus. However, our immunostaining data showed that the majority of HP1γ is localized in the cytoplasm in HPV-mediated cervical cancer. We found that HPV E6 protein drives unusual nuclear export of HP1γ through the interaction between the NES sequence of HP1γ and exportin-1. The mutation of the NES sequence in HP1γ led to nuclear retention of HP1γ and reduced cervical cancer cell growth and tumor generation. We further discovered that HP1γ directly suppresses the expression of UBE2L3 which drives E6-mediated proteasomal degradation of p53 in cervical cancer. Downregulation of UBE2L3 by overexpression of HP1γ suppressed UBE2L3-dependent p53 degradation-promoting apoptosis of cervical cancer cells. Our findings propose a useful strategy to overcome p53 degradation in cervical cancer through the blockage of nuclear export of HP1γ.

Highlights

Cervical carcinogenesis is induced by persistent high-risk human papillomavirus (HPV) infection, which is different from other cancers or malignant diseases [1]
The DNA constructs used in this study were pcDNA-EGFPHP1β, pcDNA-EGFP-heterochromatin protein 1γ (HP1γ), pcDNA-EGFP-HP1γ V32A, Cells were transfected with siRNA targeting HP1α, HP1β, HP1γ, UBE2L3, or HPV16 E6 using Lipofectamine 2000 reagent (Life Technologies) according to the manufacturer’s protocol
Based on the hypothesis that the three Heterochromatin protein 1 (HP1) isoforms differentially regulate gene expression, we explored the effects of HP1 depletion on gene regulation throughout the human genome

Summary

Introduction

Cervical carcinogenesis is induced by persistent high-risk human papillomavirus (HPV) infection, which is different from other cancers or malignant diseases [1]. Several studies have shown that HP1 contributes to the progression of several cancers [24,25,26], while there are evidences demonstrating that expression of HP1 isoforms is decreased in diverse tumor tissues [17] Adding to these controversial findings, an indepth understanding of the role of HP1 in cancer progression would provide an interesting target for therapy. Overexpression of HP1γ suppressed UBE2L3 and restored p53 stability, further inducing apoptosis of cervical cancer cells. These observations prompted us to take a closer look at the role of HP1γ in the cervical cancer and provide a pathogenic rationale to treat cervical cancer. After incubation with or without doxycycline (1 μg/ml) for additional 48 h, the cells were harvested for analyses

Materials and methods

Discussion

Findings

Compliance with ethical standards