# Stromal Interferon Regulatory Factor 3 Can Antagonize Human Papillomavirus Replication by Supporting Epithelial-to-Mesenchymal Transition

## TL;DR

Stromal IRF3 helps fight HPV by promoting EMT, which hinders virus replication and connects wound healing with immunity.

## Contribution

Stromal IRF3 is shown to regulate EMT and inhibit HPV replication through TGFβ1 signaling.

## Key findings

- Stromal IRF3 promotes EMT-like gene expression in HPV16-containing epithelium.
- IRF3 binds to the TGFB1 promoter and is necessary for TGFβ1 mRNA production.
- An EMT-like state disrupts HPV16 replication by inhibiting epithelial differentiation.

## Abstract

Epithelia contribute to the innate immune system through barrier formation and through signaling to immune cells. When the barrier is breached, epithelial cells undergo epithelial-to-mesenchymal transition (EMT) as part of the wound healing process. EMT is largely directed by signals from the stromal microenvironment, including transforming growth factor beta (TGFβ1), and antagonizes normal epithelial differentiation. How EMT and innate immunity may be connected molecularly has not been explored, although both processes are likely to occur simultaneously. Keratinocytes are the host cell type for human papillomaviruses (HPV), which can induce EMT in certain conditions but also depend on differentiation for their replication. We previously found that the innate immune factor interferon regulatory factor 3 (IRF3) inhibits epithelial differentiation and reduces the expression of HPV16 late genes. Here we report that IRF3 in the stroma compartment promotes an EMT-like pattern of gene expression in an HPV16-containing epithelium. The depletion of stromal IRF3 resulted in the downregulation of TGFβ1-related signaling in both the stroma and epithelium. IRF3 binds to the TGFB1 promoter in human foreskin fibroblasts and is necessary for TGFB1 mRNA production. Because an EMT-like state is unfavorable for differentiation-dependent HPV16, we observed that all EMT markers examined were reduced in the presence of episomal HPV16. Together, we show that stromal IRF3 can disrupt epithelial differentiation and act as an anti-HPV factor through the regulation of EMT, linking wound healing and immunity.