A Novel Mechanism for NF-κB-activation via IκB-aggregation: Implications for Hepatic Mallory-Denk-Body Induced...

Area of Science:

• Hepatology
• Molecular Biology
• Immunology

Background:

• Mallory-Denk-bodies (MDBs) are hepatic protein aggregates linked to inflammation.
• Protein aggregation in neurodegenerative diseases also triggers inflammation via NF-κB activation.
• The precise mechanism linking protein aggregation to NF-κB activation and inflammation remains unclear.

Purpose of the Study:

• To elucidate the mechanism by which MDBs induce NF-κB activation and inflammation.
• To identify novel therapeutic targets for MDB-associated liver inflammation and protoporphyria.

Main Methods:

• Primary hepatocytes were treated with MDB-inducing agents (NMPP, PPIX, ZnPP).
• IκBα-loss mechanisms were investigated, including proteasomal degradation, autophagy, calpain degradation, and translational inhibition.
• Immunofluorescence, urea/CHAPS-extraction, affinity pulldown, proximity biotinylation, and proteomic analyses were employed.
• RNA-interference was used to identify key protein mediators.

Main Results:

• MDB-inducing agents caused IκBα-loss and NF-κB activation, excluding known degradation pathways.
• IκBα and IκBβ were sequestered into insoluble aggregates, releasing NF-κB.
• NF-κB subunit p65 no longer bound to IκBα upon MDB induction.
• Nucleoporins Nup153 and RanBP2 were identified as mediators of IκBα nuclear import.
• Aggregation of IκBα, Nup153, and RanBP2 blocked IκBα nuclear entry, sustaining NF-κB activation.

Conclusions:

• Protein aggregate-induced liver inflammation involves IκBα sequestration into insoluble aggregates, mediated by nucleoporins.
• This novel mechanism explains MDB-associated inflammation and is relevant to protoporphyria.
• Targeting IκBα aggregation or nucleoporin interactions offers potential therapeutic strategies for liver inflammation.