FANCD2 Binds Human Papillomavirus Genomes and Associates with a Distinct Set of DNA Repair Proteins to Regulate Viral Replication.

Chelsey C. Spriggs,Laimonis A. Laimins,Michael J. Imperiale

doi:10.1128/mbio.02340-16

Abstract

ABSTRACTThe life cycle of human papillomavirus (HPV) is dependent on the differentiation state of its host cell. HPV genomes are maintained as low-copy episomes in basal epithelial cells and amplified to thousands of copies per cell in differentiated layers. Replication of high-risk HPVs requires the activation of the ataxia telangiectasia-mutated (ATM) and ATM and Rad3-related (ATR) DNA repair pathways. The Fanconi anemia (FA) pathway is a part of the DNA damage response and mediates cross talk between the ATM and ATR pathways. Our studies show that HPV activates the FA pathway, leading to the accumulation of a key regulatory protein, FANCD2, in large nuclear foci. These HPV-dependent foci colocalize with a distinct population of DNA repair proteins, including ATM components γH2AX and BRCA1, but infrequently with p-SMC1, which is required for viral genome amplification in differentiated cells. Furthermore, FANCD2 is found at viral replication foci, where it is preferentially recruited to viral genomes compared to cellular chromosomes and is required for maintenance of HPV episomes in undifferentiated cells. These findings identify FANCD2 as an important regulator of HPV replication and provide insight into the role of the DNA damage response in the differentiation-dependent life cycle of HPV.

Highlights

IMPORTANCE High-risk human papillomaviruses (HPVs) are the etiological agents of cervical cancer and are linked to the development of many other anogenital and oropharyngeal cancers
As the life cycle of HPV is closely linked to the differentiation state of its host cell, we investigated if FANCD2 levels are altered in HPV-positive cells upon epithelial differentiation induced by the addition of medium containing 1.5 mM calcium
The Fanconi anemia pathway is a critical component of the DNA damage response, as it regulates the repair of interstrand cross-links [43]

Summary

Introduction

IMPORTANCE High-risk human papillomaviruses (HPVs) are the etiological agents of cervical cancer and are linked to the development of many other anogenital and oropharyngeal cancers. Our studies demonstrate that FA pathway component FANCD2 is recruited to HPV DNA, associates with members of the ATM DNA repair pathway, and is essential for the maintenance of viral episomes in basal epithelial cells. High-risk HPVs have been shown to selectively activate and repress components of these signaling pathways to promote viral replication [19]; which members of these pathways are involved in regulating episomal maintenance as well as differentiation-dependent genome amplification is still not fully understood. Interstrand cross-links are covalent linkages between opposite strands of DNA that are generated by mistakes in replication or the action of DNA-alkylating agents These toxic lesions block both replication and transcription, making their resolution essential for cell survival [21]. FANCD2 is phosphorylated by ATM, but this leads to an S-phase arrest and is not involved in FA pathway-mediated repair [26]

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