Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation.
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.
Gilbert
S
S
Centre de recherche en cancérologie et Département de médecine, Université Laval, Québec, G1K 7P4, Canada.
Loranger
A
A
Daigle
N
N
Marceau
N
N
D000818:Animals; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D007381:Intermediate Filament Proteins / Q000235:genetics / Q000378:metabolism*; D053533:Keratin-8; D007633:Keratins / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D008954:Models, Biological; D021381:Protein Transport; D015398:Signal Transduction; D019014:fas Receptor / Q000378:metabolism*
D007381:Intermediate Filament Proteins; D053533:Keratin-8; C486595:Krt8 protein, mouse; D019014:fas Receptor; D007633:Keratins