Keratin, fas, and cryptogenic liver failure
Authors: Sorom Abraham J. , Nyberg Scott L. , Gores Gregory J. 
Published: December 2002

Abstract

Background:
About 10 percent of patients who undergo liver transplantation have cryptogenic liver disease. In animal models, the absence of heteropolymeric keratins 8 and 18 or the presence of mutant keratins in hepatocytes causes or promotes liver disease. We have previously described a mutation in the keratin 18 gene in a patient with cryptogenic cirrhosis, but the importance of mutations in the keratin 8 and keratin 18 genes in such patients is unclear.

Methods:
We tested for mutations in the keratin 8 and keratin 18 genes in purified genomic DNA isolated from 150 explanted livers and 89 peripheral-blood specimens from three groups of patients: 55 patients with cryptogenic liver disease; 98 patients with non-cryptogenic liver disease, with causes that included alcohol use, autoimmunity, drug use, and viral infections; and 86 randomly selected inpatients and outpatients who provided blood to the hematology laboratory.

Results:
Of the 55 patients with cryptogenic liver disease, 3 had glycine-to-cysteine mutations at position 61 (a highly conserved glycine) of keratin 8, and 2 had tyrosine-to-histidine mutations at position 53 of keratin 8. These mutations were not detected in the patients with other liver diseases or in the randomly selected patients. We verified the presence of the mutations in specimens of explanted livers by protein analysis and by the detection of unique restriction-enzyme cleavage sites. In transfected cells, the glycine-to-cysteine mutation limited keratin-filament reorganization when the cells were exposed to oxidative stress. In contrast, the tyrosine-to-histidine mutation destabilized keratin filaments when transfected cells were exposed to heat or okadaic acid stress.

Conclusions:
Mutations in the keratin 8 gene may predispose people to liver disease and may account for cryptogenic liver disease in some patients. (N Engl J Med 2001;344:1580-1587.) Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation.

Gilbert S, Loranger A, Daigle N, Marceau N
. J Cell Biol 2001;154:763-773. (Reproduced from the Journal of Cell Biology, by copyright permission of the Rockefeller University Press.) Keratins 8 and 18 belong to the keratin family of intermediate filament (IF) proteins and constitute a hallmark for all simple epithelia, including the liver. Hepatocyte IFs are made solely of keratins 8 and 18 (K8/K18). In these cells, the loss of one partner via a targeted null mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins. Here, we report that K8-null mouse hepatocytes in primary culture and in vivo are three- to fourfold more sensitive than wild-type (WT) mouse hepatocytes to Fas-mediated apoptosis after stimulation with Jo2, an agonistic antibody of Fas ligand. This increased sensitivity is associated with a higher and more rapid caspase-3 activation and DNA fragmentation. In contrast, no difference in apoptosis is observed between cultured K8-null and WT hepatocytes after addition of the Fas-related death-factors tumor necrosis factor (TNF) alpha or TNF-related apoptosis-inducing ligand. Analyses of the Fas distribution in K8-null and WT hepatocytes in culture and in situ demonstrate a more prominent targeting of the receptor to the surface membrane of K8-null hepatocytes. Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8-null versus WT hepatocytes. Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface. (J Cell Biol 2001;154:763-773.)