Cytoskeleton keratin regulation of FasR signaling through modulation of actin/ezrin interplay at lipid rafts in hepatocytes

• Published in: Apoptosis (London) 2012-08, Vol.17 (8), p.880-894
• Main Authors: Gilbert, Stéphane, Loranger, Anne, Lavoie, Josée N., Marceau, Normand
• Format: Article
• Language: English
• Subjects: Actins - metabolism; Animals; Apoptosis; Biochemistry; Biomedical and Life Sciences; Biomedicine; Cancer Research; Caveolin 1 - metabolism; Cell Biology; Cells, Cultured; Cytochalasin D - pharmacology; Cytoskeletal Proteins - metabolism; Cytoskeleton - metabolism; Diffusion; fas Receptor - metabolism; Hepatocytes - drug effects; Hepatocytes - metabolism; Hepatocytes - ultrastructure; Intermediate Filaments - metabolism; Keratin-18 - metabolism; Keratin-8 - deficiency; Keratin-8 - genetics; Membrane Microdomains - metabolism; Membrane Proteins - metabolism; Mice; Mortality; Oncology; Original Paper; Protein Multimerization - drug effects; Signal Transduction; Virology
• ISSN: 1360-8185; 1573-675X
• DOI: 10.1007/s10495-012-0733-2

FasR stimulation by Fas ligand leads to rapid formation of FasR microaggregates, which become signaling protein oligomerization transduction structures (SPOTS), through interactions with actin and ezrin, a structural step that triggers death-inducing signaling complex formation, in association with procaspase-8 activation. In some cells, designated as type I, caspase 8 directly activates effector caspases, whereas in others, known as type II, the caspase-mediated death signaling is amplified through mitochondria. Keratins are the intermediate filament (IF) proteins of epithelial cells, expressed as pairs in a lineage/differentiation manner. Hepatocyte IFs are made solely of keratins 8/18 (K8/K18), the hallmark of all simple epithelia. We have shown recently that in comparison to type II wild-type (WT) mouse hepatocytes, the absence of K8/K18 IFs in K8-null hepatocytes leads to more efficient FasR-mediated apoptosis, in link with a type II/type I-like switch in FasR-death signaling. Here, we demonstrate that the apoptotic process occurring in type I-like K8-null hepatocytes is associated with accelerated SPOTS elaboration at surface membrane, along with manifestation of FasR cap formation and internalization. In addition, the lipid raft organization is altered in K8-null hepatocytes. While lipid raft inhibition impairs SPOTS formation in both WT and K8-null hepatocytes, the absence of K8/K18 IFs in the latter sensitizes SPOTS to actin de-polymerization, and perturbs ezrin compartmentalization. Overall, the results indicate that the K8/K18 IF loss in hepatocytes alters the initial FasR activation steps through perturbation of ezrin/actin interplay and lipid raft organization, which leads to a type II/type I switch in FasR-death signaling.