Mallory body formation in primary biliary cirrhosis is associated with increased amounts and abnormal phosphorylation and ubiquitination of cytokeratins

Abstract

Background/aims: Animal studies revealed a key role of toxic bile acids in the regulation of hepatocytic cytokeratin (CK) expression and Mallory body (MB) formation. In this study, we compared CK expression, phosphorylation, and ubiquitination in primary biliary cirrhosis (PBC), chronic hepatitis C (CHC) and control livers to determine whether bile acid-induced CK alterations are associated with cytoskeletal alterations and MB formation in a prototypic chronic cholestatic liver disease.

Methods: CK 8 and CK 18 mRNA and protein levels were investigated by reverse transcriptase-polymerase chain reaction and Western blotting. Intermediate filament (IF) cytoskeletal alterations were assessed by immunofluorescence microscopy using antibodies against CKs, CK phosphoepitopes, MBs, and ubiquitin.

Results: Despite unchanged mRNA levels, CK 8 and CK 18 protein levels were significantly elevated in PBC suggesting stabilization of CKs, possibly due to decreased degradation. CK-IF alterations in PBC comprised increased density with abnormal phosphorylation of the IF network of hepatocytes in acinar zone 1 and in the periphery of cirrhotic nodules. In addition, in these areas hepatocytes with diminished IF network containing MBs consisting of abnormally phosphorylated and ubiquitinated CK were observed.

Conclusions: These findings support our concept that IF cytoskeletal alterations and MB formation in cholestatic liver diseases are related to bile acid-induced cell stress.