Keratin 8 phosphorylation regulates its transamidation and hepatocyte Mallory-Denk body formation

Area of Science:

• Hepatology and molecular biology
• Intermediate filament protein research
• Cellular inclusions and disease pathogenesis

Background:

• Mallory-Denk bodies (MDBs) are hepatic cellular inclusions linked to poor liver disease outcomes.
• Keratin 8 (K8) and its cross-linking by transglutaminase-2 (TG2) are critical for MDB formation.
• The role of keratin phosphorylation in MDB development remains unclear.

Purpose of the Study:

• To elucidate the relationship between keratin phosphorylation and MDB formation.
• To identify specific keratin residues involved in MDB pathogenesis.
• To investigate the mechanism linking K8 phosphorylation to TG2-mediated cross-linking.

Main Methods:

• Utilized a mutational approach to analyze keratin 8 (K8) function.
• Investigated K8 cross-linking in cells treated with phosphatase inhibitors.
• Generated transgenic mice expressing specific K8 variants (S74A, G62C).

Main Results:

• Identified K8 Q70 as crucial for K8 self-cross-linking.
• Demonstrated that K8 S74 phosphorylation promotes K8 Q70 cross-linking.
• Showed that K8 S74A and G62C mutations significantly reduce MDB formation in mice.
• Phosphatase inhibition enhances K8 cross-linking, while specific mutations decrease it.

Conclusions:

• Stress-induced phosphorylation of K8 at S74 triggers K8 cross-linking by TG2, initiating MDB formation.
• This mechanism provides insight into MDB pathogenesis in liver disease.
• Findings may have implications for understanding intermediate filament inclusions in neuropathies and myopathies.