Endoplasmic reticulum disruption stimulates nuclear membrane mechanotransduction.

Cytosolic phospholipase A2 (cPLA2) controls some of the most powerful inflammatory lipids in vertebrates by releasing their metabolic precursor, arachidonic acid, from the inner nuclear membrane (INM). Ca2+ and INM tension (TINM) are thought to govern the interactions and activity of cPLA2 at the INM. However, as compensatory membrane flow from the contiguous endoplasmic reticulum (ER) may prevent TINM, the conditions permitting nuclear membrane mechanotransduction by cPLA2 or other mediators remain unclear. To test whether the ER buffers TINM, we created the genetically encoded, Ca²⁺-insensitive TINM biosensor amphipathic lipid-packing domain inside the nucleus (ALPIN). Confocal time-lapse imaging of ALPIN- or cPLA2-INM interactions, along with ER morphology, nuclear shape/volume and cell lysis revealed a link between TINM and disrupted ER-nuclear membrane contiguity in osmotically or ferroptotically stressed mammalian cells and at zebrafish wound margins in vivo. By combining ALPIN imaging with Ca2+-induced ER disruption, we reveal the causality of this correlation, which suggests that compensatory membrane flow from the ER buffers TINM without preventing it. Besides consolidating the biomechanical basis of cPLA2 activation by nuclear deformation, our results identify cell stress- and cell death-induced ER disruption as an additional nuclear membrane mechanotransduction trigger.