# Regulation of HPV Replication.

> **NIH NIH R21** · NORTHWESTERN UNIVERSITY · 2022 · $200,000

## Abstract

PROJECT SUMMARY
Human papillomaviruses (HPV) infect stratified squamous epithelia and link their productive life cycles to the
differentiation of the host cell. HPVs infect cells in the basal layer of stratified epithelia and establish genomes
as low copy nuclear episomes. When HPV infected cells migrate from the basal layer, they re-enter S/G2 phases
in the most differentiated layers to allow for vegetative viral DNA replication in a process referred to as
amplification. HPV replication is regulated by viral proteins as well as cellular factors that control cell cycle
progression, differentiation and DNA damage repair pathways. Our recent studies have shown that activation of
both the ataxia telangiectasia (ATM) pathway as well as the ataxia telangiectasia and Rad3-related (ATR)
pathway is necessary for differentiation-dependent amplification of viral genomes and we have identified many
members of these pathways that provide important functions. Our studies further indicate that enhanced levels
of DNA breaks in HPV positive cells are responsible for activation of these pathways but the mechanism behind
this increase has not been identified. DNA breaks can be induced by exposure to exogenous DNA damaging
agents or through endogenous pathways such as through the action of topoisomerases. We have recently
demonstrated that the type II topoisomerase TOP2is responsible for generating over 50% of DNA breaks in
HPV positive cells. Topoisomerases regulate higher order chromatin structures through the transient breaking
and re-ligation of one or both strands of the phosphodiester backbone of duplex DNA. Our studies have shown
that the levels of TOP2 are increased by a 3 to 5-fold in cells with high-risk HPV genomes. Importantly,
knockdown of TOP2 blocks HPV genome replication and moderately reduces viral transcription but has no
effect on cell proliferation. Furthermore, knockdown of TOP2reduced the amount of DNA breaks in HPV
positive cells which results in decreased DDR nuclear repair foci. While our assays demonstrated that over half
of total DNA breaks in HPV positive cells were induced by TOP2 other factors must be responsible for the
remaining breaks. Strong candidates for this activity are two other topoisomerases, TOP2and TOP1, and
investigation of this possibility as well as an examination of the role of these enzymes in viral replication is the
focus of this R21 application. These studies will provide important insights into how the differentiation-dependent
HPV life cycle is regulated.

## Key facts

- **NIH application ID:** 10495235
- **Project number:** 5R21AI165941-02
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Laimonis A. LAIMINS
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $200,000
- **Award type:** 5
- **Project period:** 2021-09-24 → 2024-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10495235

## Citation

> US National Institutes of Health, RePORTER application 10495235, Regulation of HPV Replication. (5R21AI165941-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10495235. Licensed CC0.

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