Intermediate-sized filaments in cultured rat liver tumor cells with Mallory body-like cytoplasm abnormalities

The endoskeletal structure of tumor cells with a characteristic cytoplasmic abnormality initiated in rat liver by the in vivo adminisration of the carcinogen diethylnitrosamine was studied in clonal cell lines established and propagated in vitro. The bulk of the cytoplasmic and plasma membrane protein was removed by extraction with Triton X-100, and subsequently the juxtanuclear detergent-insoluble fraction containing filaments of 100-150 A was released into citrate buffer at pH 2.8. Analysis of this fraction by sodium dodecyl sulfate acrylamide gel electrophoresis revealed the pressence of five major proteins that banded with apparent molecular weights of about 66, 57, 52, 48 , and 43 x 10(3), the last of which comigrated with actin. The proteins thus resembled those from intermediate-sized filaments of both the vimentin (57 x 10(3)) and the prekeratin types obtained from various vertebrate cells. They also appeared to be related to the polypeptides of intermediate-sized filaments from Mallory bodies induced by griseofulvin in the livers of mice and to some of the polypeptides seen in isolates of Mallory bodies from human alcoholics. These results indicated that a major component of the carcinogen-induced lesion consisted of intermediate-sized filaments. The possible significance in cell transformation of this stably maintained aggregate of filaments that binds concanavalin A and displaces the nucleus is discussed. The close resemblance of this lesion to that seen in the cells of cirrhotic livers of alcoholics (Mallory's alcoholic hyalin) raises a question regarding the possible oncogenic status of such cells in humans.