# Mechanistic dissection of GRHL2 and PR transcriptional co-regulation in breast cells

## TL;DR

The study reveals how GRHL2 and the progesterone receptor work together to control gene activity in breast cells, using both direct interactions and DNA looping.

## Contribution

The novel discovery is that GRHL2 acts as a progesterone receptor co-regulator through chromatin binding and 3D genome architecture modification.

## Key findings

- GRHL2 interacts with the progesterone receptor independently of hormone stimulation.
- GRHL2 and the progesterone receptor bind to shared enhancer elements upon progesterone exposure.
- GRHL2 and progesterone receptor-bound elements connect through chromatin looping to regulate gene expression.

## Abstract

Gene expression is controlled by complex transcriptional networks in which transcription factors and their cognate enhancer elements integrate developmental and environmental cues. The progesterone receptor (PR), a hormone-activated transcription factor, is essential for breast development and physiology, yet how it engages with the chromatin and lineage-specific cofactors remains unclear. Using an unbiased approach, we identify the epithelial transcription factor grainyhead-like 2 (GRHL2) as a key co-regulator of PR activity in hormone responsive breast cancer cells. We show that GRHL2 interacts with PR in a progesterone-independent manner. Upon progesterone stimulation, GRHL2 and PR are both recruited to distal enhancer elements of target genes. Furthermore, GRHL2- and PR-bound elements connect spatially through chromatin looping to regulate shared targets. These findings uncover a previously unrecognized mechanism by which GRHL2 and PR coordinate gene regulation through both chromatin binding and 3D genome architecture modification, positioning GRHL2 as a crucial modulator of steroid hormone receptor function.

Gene expression is tightly controlled by regulatory networks in which transcription factors integrate developmental and environmental cues. Hormones are one important class of such signals. In breast tissue, the hormone progesterone is essential for normal development and function. Progesterone binds to its receptor, the progesterone receptor, a DNA-binding protein that regulates the activity of progesterone-responsive genes. However, whether and how the progesterone receptor collaborates with lineage-specific cofactors to control gene expression has remained incompletely understood. In this study, we identified GRHL2 as a key co-regulator of the progesterone receptor in hormone-responsive breast cancer cells. We found that these two proteins interact even in the absence of hormone stimulation. Upon progesterone exposure, both proteins are recruited to regulatory regions that control shared target genes. Importantly, we demonstrate that these regulatory regions physically connect through long-range DNA looping, enabling coordinated gene expression. Together, our findings provide new insight into hormone-driven gene regulation and highlight GRHL2 as an important contributor to progesterone receptor function in breast cells.