Modifications in cytokeratin and actin in cultured liver cells derived from griseofulvin-fed mice.
BACKGROUND: Hepatocytes from mice fed griseofulvin (GF) for 8 months form Mallory bodies (MBs), which represent a pathologic state of intermediate filaments (IFs). The cellular mechanisms that lead to MB formation are not known. EXPERIMENTAL DESIGN: This study was aimed to investigate if MB formation could be related to modification in cytokeratin (CK) metabolism. Primary cultures of hepatocytes from control and GF livers were studied. Immunofluorescence microscopy was used to study the organization of the cytoskeleton in these cells. The hepatocytes were labeled with [35S]methionine or [32P]orthophosphate to study, respectively, the level of amino acid incorporation into IF proteins (CK 8 and CK 18) and their phosphorylation levels. The response to the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate stimulation of the phosphorylation of CK 8 and CK 18 was also elicited in contrast to control hepatocytes. RESULTS: We found that there was a change in the organization of actin and the IF network in the hepatocytes from GF-treated animals. This was associated with an increase in labeled amino acid incorporation into CK 8 and CK 18 as well as in actin. Although there was no significant difference in the absolute level of CK phosphorylation, we found modifications in the phosphorylated isomers of CK 8, the more phosphorylated isomers becoming more prominent. The treatment of the hepatocytes with 12-O-tetradecanoyl-phorbol-13-acetate did not induce changes in the level of CK phosphorylation in GF-pretreated hepatocytes. CONCLUSIONS: These results suggest that the modification of the IF network and MB formation are the consequences of increased CK synthesis and the modification of phosphorylation. They could alter the normal interaction of the IFs with different cellular components, which results in conformational changes of CKs and the reorganization of the IF network to the form of MBs.