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Hepatocyte cytokeratins are hyperphosphorylated at multiple sites in human alcoholic hepatitis and in a mallory body
C Stumptner1, M B Omary, P Fickert
1Departments of Pathology and Medicine, University of Graz, Graz, Austria.
Abstract:
Alcoholic hepatitis (AH) is associated with cytokeratin 8 and 18 (CK8/18) accumulation as cytoplasmic inclusion bodies, termed Mallory bodies (MBs). Studies with MB mouse models and cultured hepatocytes suggested that CK8/18 hyperphosphorylation might be involved in MB formation. However, no data exist on phosphorylation of CK8/18 in human AH. In this study, antibodies that selectively recognize phosphorylated epitopes of CK8 or CK18 were used to analyze CK8/18 phosphorylation states in normal human and murine livers, human AH biopsies, and livers of 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC)-intoxicated mice, the last serving as model for MB induction. Hepatocyte cytokeratins become hyperphosphorylated at multiple sites in AH and in DDC-intoxicated mice. Hyperphosphorylation of CK8/18 occurred rapidly, after 1 day of DDC intoxication and preceded architectural changes of the cytoskeleton. In long-term DDC-intoxicated mice as well as in human AH, MBs preferentially contain hyperphosphorylated CK8/18 as compared with the cytoplasmic cytokeratin intermediate filament network suggesting that CK8/18 hyperphosphorylation may play a contributing role in MB pathogenesis. Furthermore, the site-specific phosphorylation of cytokeratin in different stages of MB induction provides indirect evidence for the involvement of a variety of protein kinases known to be activated in stress responses, mitosis, and apoptosis.
Insights
Alcoholic hepatitis involves Mallory body formation due to cytokeratin 8 and 18 (CK8/18) hyperphosphorylation. This study confirms CK8/18 hyperphosphorylation in human AH and DDC mouse models, suggesting its role in Mallory body pathogenesis.
Area of Science:
- Hepatology
- Cell Biology
- Biochemistry
Background:
- Alcoholic hepatitis (AH) is characterized by Mallory body (MB) formation, involving cytokeratin 8 and 18 (CK8/18) accumulation.
- Previous studies suggested CK8/18 hyperphosphorylation contributes to MB formation, but this remained unconfirmed in human AH.
Purpose of the Study:
- To investigate CK8/18 phosphorylation states in human AH and a mouse model of MB induction.
- To determine if CK8/18 hyperphosphorylation is associated with MB formation in human disease.
Main Methods:
- Utilized antibodies specific to phosphorylated CK8 and CK18 epitopes.
- Analyzed liver biopsies from human AH patients and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-intoxicated mice.
- Compared phosphorylation levels in MBs versus the general cytokeratin network.
Main Results:
- Hepatocyte CK8/18 becomes hyperphosphorylated in both human AH and DDC-intoxicated mice.
- CK8/18 hyperphosphorylation occurred rapidly in DDC mice, preceding cytoskeletal changes.
- Mallory bodies preferentially contained hyperphosphorylated CK8/18 compared to the surrounding cytokeratin network.
Conclusions:
- CK8/18 hyperphosphorylation is a significant feature of human AH and a DDC-induced MB model.
- These findings support a contributing role for CK8/18 hyperphosphorylation in Mallory body pathogenesis.
- Site-specific phosphorylation patterns suggest involvement of various stress-activated protein kinases.