Hepatocyte Cytokeratins Are Hyperphosphorylated at Multiple Sites in Human Alcoholic Hepatitis and in a Mallory Body Mouse Model

Abstract

Alcoholic hepatitis (AH) is associated with cytokeratin 8 and 18 (CK8/18) accumulation as cytoplasmic inclusion bodies , termed Mallory bodies (MBs).Cytokeratins are members of the large family of intermediate filament (IF) cytoskeletal proteins, which are normally expressed in a tissue-specific manner and assembled as cytoplasmic filamentous arrays. Neurofilaments, ␣-internexin, desmin, vimentin, glial filaments, and the nuclear lamins 1,2 also belong to the IF family. The diverse cell biological functions of IFs are still poorly understood. However, a diversity of human diseases is associated with severe alterations of IFs. A common pathological feature of many IF-related diseases is the accumulation of intracytoplasmic inclusions consisting of modified IF proteins, for example in neurodegenerative diseases such as amyotrophic lateral sclerosis, Parkinson's disease, and Lewy body dementia 3-6 ; in neuromuscular disorders (eg, spheroid body myositis 7 ); and the formation of Mallory bodies (MBs) in alcoholic hepatitis (AH) and other liver disorders (eg, non-alcoholic steatohepatitis, Wilson's disease, primary biliary cirrhosis, Indian childhood cirrhosis, hepatocellular neoplasms 8 -11 ). Although the underlying pathogenetic mechanisms are as yet unclear, posttranslational modifications of IF proteins, such as phosphorylation, limited proteolysis, and crosslinking, may play a major role. For example, the presence of hyperphosphorylated neurofilament epitopes in some neuronal inclusion bodies 12-15 and of abnormally phosphorylated desmin in muscle fibers 16 were reported. Furthermore, a possible association of cytokeratin hyperphosphorylation with the formation of MBs in hepatocytes, a hallmark of AH, was suggested by in vitro and animal studies performed by our own group and others. [17][18][19][20] AH follows chronic alcohol abuse and occurs in 20 to 40% of heavy drinkers. Although reversible at the beginning, most cases of AH progress to irreversible cirrhosis. Besides the amount of alcohol ingested per day, a variety of other factors such as dietary habits, genetic factors influencing alcohol metabolism, viral infections, and additional toxins or drugs seem to determine the extent of liver damage. Classical morphological features of AH are liver cell ballooning and necrosis, inflammation, steatosis, and the formation of cytokeratin-containing MBs, which is associated with severe derangement (ie, diminution or even loss) of the hepatocyte cytokeratin IF network. 8 -11,22-26 Diverse animal models have been generated to study in more detail and under defined conditions mechanisms involved in the pathogenesis of this alcoholic liver disease. Experimental long-term intoxication of mice with Supported by the grants of the Austrian Science Foundation S7401-MOB (to K. Z.) and 7628-MED (to H. D.) and by a U.S. Veterans Affairs Merit and Career Development Award (to M. B. O.).

Keratin 8 and 18 hyperphosphorylation is a marker of progression of human liver disease

“…Increased protein phosphorylation is a common finding in several diseases, which has positioned protein kinases as attractive drug targets and led to the emerging clinical utilization of kinase inhibitors for therapeutic purposes. 33,34 Increases in IF protein phosphorylation in disease states has been reported for neurofilaments in amyotrophic lateral sclerosis 35 and Alzheimer disease 36,37 ; desmin in animal and human cardiomyopathies 38 -40 ; lamin B2 in human leukemia cells 41 ; epidermal K5 and K6 in psoriasis and squamous cell carcinoma 19 ; K8/18 in Mallory bodies of human alcoholic liver disease and animal models with similar hyaline inclusions, 20 primary biliary cirrhosis, 22 in vascular smooth-muscle cells of atherosclerotic lesions and umbilical cord vessels 42 ; and vimentin after rat glomerular cell injury. 43 In most cases the increase in phosphorylation was demonstrated by immunofluorescence staining using phospho-specific antibodies.…”

Tau phosphorylation in Alzheimer's disease: pathogen or protector?

“…Although much remains unknown, it is clear that cytoskeletal phosphorylation and other inclusions could, in fact, be beneficial because similar phosphorylation occurs in cytokeratins in response to various stressors, such as heat shock and toxins [77]. In particular, the administration of hepatotoxins to mice causes the phosphorylation of cytokeratin and its aggregation into Mallory bodies, which are highly insoluble inclusions [78]. Cytokeratins, which are normally expressed in a tissue-specific manner, are, like neurofilaments, members of the large family of intermediate-filament cytoskeletal proteins [79,80].…”

Keratin 20 Serine 13 Phosphorylation Is a Stress and Intestinal Goblet Cell Marker

“…6) as demonstrated by its hyperphosphorylation in response to DSS-induced colitis in mice and to anisomycin in cultured cells, respectively. The association of keratin phosphorylation with cell injury and apoptosis is a uniform finding that is seen in various tissue culture models (11,52,53) and in patients with liver disease (18,54). However, specific phosphorylation FIGURE 9.…”