Membrane curvature elastic stress triggers recruitment of PML-II onto the inner nuclear membrane

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Promyelocytic leukemia (PML) protein isoform II is found in PML nuclear bodies (PML NBs), nuclear lipid droplets (nLDs), and the inner nuclear membrane (INM).
• Metabolic treatments can induce membrane curvature elastic stress (CES) in the INM, indicated by CTP:phosphocholine cytidylyltransferase α (CCTα) recruitment and nuclear diacylglycerol (DAG) biosensor activity.

Purpose of the Study:

• To determine if CES in the INM is a prerequisite for PML-II membrane association.
• To investigate the role of CES in the formation of PML-II patches on the INM.

Main Methods:

• Treatment of U2OS cells with unsaturated fatty acids and DAG acyltransferase inhibitors to induce CES.
• Monitoring DAG enrichment and CCTα recruitment using biosensors.
• Genetic manipulation, including knockout of CDP-choline pathway enzymes.
• Analysis of PML patch composition and localization relative to lamin and nLDs.

Main Results:

• Metabolic treatments inducing CES caused rapid PML-II patch formation on the INM, correlating with DAG enrichment and CCTα stabilization.
• PML patches were specific to the PML-II isoform, depleted of canonical PML NB proteins, and found at lamin-depleted sites.
• CES induction via genetic manipulation also promoted PML patches and CCTα stabilization.
• PML patch formation was independent of nLD assembly capacity.

Conclusions:

• Curvature elastic stress (CES) in the INM promotes the reversible assembly of PML-II-dependent membrane-associated patches.
• PML-II membrane association is regulated by INM physical forces, specifically CES.
• The findings reveal a novel mechanism for PML protein localization and potential function at the INM.