# Cultured cells activate IRE1 during attachment and flattening after routine passaging

## TL;DR

This study shows that cultured cells activate an ER stress response during routine passaging, even without added stressors.

## Contribution

The study reveals that Xbp1 splicing occurs during cell passaging, indicating an unfolded protein response during reattachment.

## Key findings

- Xbp1 mRNA is spliced in MC3T3-E1 cells after routine passaging without canonical ER stressors.
- Xbp1 splicing is reduced when cells are plated on non-adherent culture dishes.
- The splicing is independent of the dissociation buffer used.

## Abstract

During endoplasmic reticulum (ER) stress, the ER membrane protein IRE1 initiates the regulated splicing of
Xbp1
mRNA, leading to the production of a potent transcription factor that helps cells restore proteostasis. We report that
Xbp1
is also spliced following the routine passaging of mouse MC3T3-E1 cells, without the addition of canonical ER stressors. This splicing was independent of the type of dissociation buffer used to release cells from the surface, but was reduced when cells were plated on non-adherent culture dishes. These findings suggest that certain cultured mammalian cells induce an unfolded protein response during reattachment and spreading after passaging.