# Cell density–dependent nuclear‐cytoplasmic shuttling of SETDB1 integrates with Hippo signaling to regulate YAP1‐mediated transcription

## TL;DR

This study shows how cell density controls SETDB1 localization, which in turn affects Hippo signaling and YAP1 activity to regulate gene expression.

## Contribution

The novel finding is that SETDB1 shuttles between the nucleus and cytoplasm in a cell density-dependent manner, modulating Hippo signaling and YAP1 transcriptional activity.

## Key findings

- SETDB1 localization shifts from nucleus to cytoplasm at high cell density, leading to its degradation.
- SETDB1 depletion increases nuclear YAP1 and upregulates YAP1–TEAD1 target genes.
- SETDB1 competes with YAP1 for TEAD1 binding, influencing Hippo pathway output through transcriptional repression.

## Abstract

SETDB1, a H3K9 methyltransferase involved in nuclear transcriptional silencing, also localizes to the cytoplasm through unclear mechanisms. Here, we identify cell density as key regulator of SETDB1 subcellular localization and demonstrate its role in modulating the Hippo signaling pathway. Under low‐density culture, SETDB1 distributes between nucleus and cytoplasm, whereas high‐density culture triggers nuclear exclusion and proteasomal degradation. SETDB1 depletion reduces YAP1 phosphorylation and increases nuclear YAP1 accumulation. Transcriptomic analysis of SETDB1 knockout cells revealed upregulation of YAP1–TEAD1 target genes (YTGs). Immunoprecipitation experiments showed that SETDB1 is recruited to YTG promoters via TEAD1 and competes with YAP1 for TEAD1 binding. These findings reveal that SETDB1 regulates Hippo pathway output through YAP1 phosphorylation modulation and competitive transcriptional repression.

At low cell density, SETDB1 and YAP1 accumulate in the nucleus. As cell density increases, the Hippo pathway is gradually activated, and SETDB1 is associated with increased YAP1 phosphorylation. At high cell density, phosphorylated YAP1 is sequestered in the cytoplasm, while SETDB1 becomes polyubiquitinated and degraded by the ubiquitin–proteasome system.