Altered cytokeratin expression and differentiation induction during neoplastic transformation of cultured rat liver cells by nickel subsulfide

Cytokeratin expression, fibrillar organization, and subtle function in liver cells

Cytokeratins (CKs) constitute a diverse group of intermediate filament (IF) proteins, expressed as pairs in keratinized and nonkeratinizing epithelial cells. Much is known now about the expression, assembly, and function of CKs in keratinized epithelial cells, the main features being the tight coupling between CK pair switch and cell terminal differentiation (protection barrier) and the vital role of CK IFs in cell mechanical integrity. However, the picture about nonkeratinizing epithelia, like the hepatic tissue, remains quite unclear. The liver forms a multicellular system, where parenchymal cells (i.e., hepatocytes) exert diverse metabolic function(s) and nonparenchymal epithelial cells (e.g., biliary epithelial cells) usually serve structural (or accessory) purposes. In terms of differential CK gene expression, the data accumulated so far demonstrated that parenchymal cells can contain as few as one single CK pair, whereas nonparenchymal cells contain more than two CKs, one of them being a representative of those found in epidermis. Moreover, the distribution of the CK IF networks present in the different cell types varies a lot and can often be linked to the cell specialization. However, the function(s) played by these IF proteins in this multicellular tissue remains a major issue. The use of new experimental approaches, largely based on gene transfer technology, indicates that it is quite subtle.

The Mallory body: morphological, clinical and experimental studies (Part 1 of a literature survey)

To aid understanding of markers of disease and predictors of outcome in alcohol-exposed systems, we undertook a literature survey of more than 700 articles to view the morphological characteristics and the clinical and experimental epidemiology of the Mallory body. Mallory bodies are filaments of intermediate diameter that contain intermediate filament components (e.g., cytokeratins) observable by conventional light microscopy or immunohistochemical methods, identical in structure regardless of initiating factors or putative pathogenesis. Although three morphological types can be identified under electron microscopy (with fibrillar structure parallel, random or absent), they remain stereotypical manifestations of hepatocyte injury. A summary of the conditions associated with Mallory bodies in the literature and their validity and potential etiological relationships is presented and discussed, including estimates on the combined light microscopic and immunohistochemical prevalences and kinetics. Emphasis is placed on proper confounder control (in particular, alcohol history), which is highly essential but often inadequate. These conditions include (mean prevalence of Mallory bodies in parentheses): Indian childhood cirrhosis (73%), alcoholic hepatitis (65%), alcoholic cirrhosis (51%), Wilson's disease (25%), primary biliary cirrhosis (24%), nonalcoholic cirrhosis (24%), hepatocellular carcinoma (23%), morbid obesity (8%) and intestinal bypass surgery (6%). Studies in alcoholic hepatitis strongly suggest a hit-and-run effect of alcohol, whereas other chronic liver diseases show evidence of gradual increase in prevalence of Mallory bodies with severity of hepatic pathology. Mallory bodies in cirrhosis do not imply alcoholic pathogenesis. Obesity, however, is associated with alcoholism and diabetes, and Mallory bodies are only present in diabetic patients if alcoholism or obesity complicates the condition. In addition, case studies on diseases in which Mallory bodies have been identified, along with pharmacological side effects and experimental induction of Mallory bodies by various antimitotic and oncogenic chemicals, are presented. Mallory bodies occur only sporadically in abetalipoproteinemia, von Gierke's disease and focal nodular hyperplasia and during hepatitis due to calcium antagonists or perhexiline maleate. Other conditions and clinical drug side effects are still putative. Finally, a variety of experimental drugs have been developed that cause Mallory body formation, but markedly different cell dynamics and metabolic pathways may raise questions about the relevance of such animal models for human Mallory body formation. In conclusion, the Mallory body is indicative but not pathognomonic of alcohol involvement. A discussion on theories of development and pathological significance transcending the clinical frameworks will be presented in a future paper.