Research Article: Parvovirus B19 NS1 protein induces cell cycle arrest at G2-phase by activating the ATR-CDC25C-CDK1 pathway

Date Published: March 6, 2017

Publisher: Public Library of Science

Author(s): Peng Xu, Zhe Zhou, Min Xiong, Wei Zou, Xuefeng Deng, Safder S. Ganaie, Steve Kleiboeker, Jianxin Peng, Kaiyu Liu, Shengqi Wang, Shui Qing Ye, Jianming Qiu, Colin Parrish.

http://doi.org/10.1371/journal.ppat.1006266

Abstract

Human parvovirus B19 (B19V) infection of primary human erythroid progenitor cells (EPCs) arrests infected cells at both late S-phase and G2-phase, which contain 4N DNA. B19V infection induces a DNA damage response (DDR) that facilitates viral DNA replication but is dispensable for cell cycle arrest at G2-phase; however, a putative C-terminal transactivation domain (TAD2) within NS1 is responsible for G2-phase arrest. To fully understand the mechanism underlying B19V NS1-induced G2-phase arrest, we established two doxycycline-inducible B19V-permissive UT7/Epo-S1 cell lines that express NS1 or NS1mTAD2, and examined the function of the TAD2 domain during G2-phase arrest. The results confirm that the NS1 TAD2 domain plays a pivotal role in NS1-induced G2-phase arrest. Mechanistically, NS1 transactivated cellular gene expression through the TAD2 domain, which was itself responsible for ATR (ataxia-telangiectasia mutated and Rad3-related) activation. Activated ATR phosphorylated CDC25C at serine 216, which in turn inactivated the cyclin B/CDK1 complex without affecting nuclear import of the complex. Importantly, we found that the ATR-CHK1-CDC25C-CDK1 pathway was activated during B19V infection of EPCs, and that ATR activation played an important role in B19V infection-induced G2-phase arrest.

Partial Text

Human parvovirus B19 (B19V) is a small, non-enveloped, single stranded DNA (ssDNA) virus belonging to the genus Erythroparvovirus within the family Parvoviridae [1]. B19V causes fifth disease or slapped cheek syndrome in children; however, B19V infection can cause hematological disorders [2–6]. B19V infection of immunocompromised patients, such as those with HIV/AIDS, transplant recipients, and infants, leads to a persistent viremia that is associated with chronic anemia and pure red-cell aplasia. Acute B19V infection of patients experiencing increased destruction of erythrocytes, and therefore having a high demand for erythrocyte production (e.g., those with sickle-cell disease), can cause a transient aplastic crisis, whereas B19V infection of pregnant women can cause non-immune hydrops fetalis. B19V infects human erythroid progenitors at the burst-forming unit (BFU)- and colony-forming unit (CFU)-erythroid stages in the bone marrow [7–9] and fetal liver [10,11], which results in the death of infected cells [12–15]. Currently, there are no vaccines or specific antiviral therapeutics that can prevent or treat B19V-induced hematological disorders.

Here, we identified the key mechanism underlying B19V NS1-induced G2-phase arrest in NS1-expressing B19V-permissive cells. We found that the TAD2 domain at the C-terminus of NS1 plays a key role in transactivating cellular gene expression, and that it is essential for NS1-induced G2-phase arrest. We also identified a de novo role for NS1: activation of ATR. NS1 expression results in ATR phosphorylation at threonine 1989; this then inactivates CDC25C via phosphorylation at serine 216. Phosphorylated CDC25C prevents dephosphorylation of CDK1 at tyrosine15; thus, an inactive cyclin B1/CDK1 complex is imported to the nucleus, thereby blocking progression from G2- to M-phase (Fig 11). Finally, we showed that the ATR-CHK1-CDC25C-CDK1 pathway is activated in both NS1(alone)-expressing and B19V-infected CD36+ EPCs.

 

Source:

http://doi.org/10.1371/journal.ppat.1006266

 

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