Mallory Bodies (MB) are cytoplasmic filamentous inclusions seen primarily in alcoholic liver disease, although they may also be found in association with other liver diseases. The primary structural components of MB are a group of epithelial specific intermediate filament cytoskeletal proteins termed keratin polypeptides 8 and 18 (K8/18). The biochemical basis for these abnormally aggregated keratins is presently unknown. A basic understanding of the nature of keratin modification in MB should allow designing rational experiments to determine if changes in keratins are essential for alcohol induced injury and if such changes can be reversed. Our hypothesis is that Mallory Body formation may result from alterations in glycosylation and/or phosphorylation of hepatocyte keratins. This hypothesis is based on finding discrete keratin cytoplasmic dots, that are morphologically similar to MB, when keratin phosphorylation and glycosylation increases during cell mitosis. In addition, desmin bodies which are found in familial myopathy and are derived from the intermediate filament protein desmin, were found to be hyperphosphorlated. In carrying out this proposal, we plan to take advantage of our studies involving the characterization of normal epithelial keratin glycosylation and phosphorylation. For example, we recently showed that keratins 8 and 18 are O-linked glycoproteins with glycosylation sites consisting of single N-acetylglucosamine (GlcNAc) residues. To test our hypothesis, we plan to study the phosphorylation and glycosylation of K8/18 in experimentally induced Mallory Bodies in mice, and in human liver specimen obtained from biopsies or surgical specimen. We also plan to determine at a detailed molecular level if other forms of posttranslational modification such as transglutamination account for MB formation. Finally, we plan to explore the possibility that primary amino acid structural changes occur in keratins of MB.
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