Disturbance of keratin homeostasis in griseofulvin-intoxicated mouse liver.

BACKGROUND Alterations of the hepatocytic intermediate filament (IF) cytoskeleton, i.e., derangement and diminution of the keratin network and appearance of cytoplasmic aggregates of keratin-containing material, termed Mallory bodies, are characteristic features of human alcoholic hepatitis. Mallory bodies can be experimentally produced in mouse liver by chronic griseofulvin (GF) administration. GF intoxication of mice is, therefore, a suitable model to study the mechanisms of Mallory body formation and related cytoskeletal changes. EXPERIMENTAL DESIGN To investigate the correlation between morphologic alterations of the keratin cytoskeletal network and the mRNA levels for liver keratins A (8) and D (18) in this pathologic situation immunohistochemical studies and northern blot analyses were performed. The amount of mRNA for both keratins was also analyzed by nuclease S1 protection assay. RESULTS In GF-treated livers (4 months of treatment) an increase of mRNA for both liver keratins was found. This increase of mRNA was unexpected under these conditions, since in longterm GF-fed animals, the amount of keratin IFs was reduced as revealed by immunofluorescence and electron microscopy and by biochemical analysis of keratin proteins. In livers treated for 2 months with GF the IF meshwork seemed to be still intact, but the increase of RNA was already detectable indicating that alterations of keratin mRNA precede detectable morphologic alterations. When using this mRNA for in vitro translation experiments, strong keratin polypeptide spots could be detected by autoradiography of 2-dimensional gels. CONCLUSIONS These results strongly suggest that in vivo under the conditions of GF intoxication posttranslational modifications, like phosphorylation, proteolysis and covalent cross-linking, could influence IF homeostasis and interfere with IF assembly. Increase of mRNA for liver keratins despite IF protein reduction might be due to negative feedback regulation.