title: Keratin impact on PKCδ- and ASMase-mediated regulation of hepatocyte lipid raft size - implication for FasR-associated apoptosis.
abstract: Keratins are epithelial cell intermediate filament (IF) proteins that are expressed as pairs in a cell-differentiation-regulated manner. Hepatocytes express the keratin 8 and 18 pair (denoted K8/K18) of IFs, and a loss of K8 or K18, as in K8-null mice, leads to degradation of the keratin partner. We have previously reported that a K8/K18 loss in hepatocytes leads to altered cell surface lipid raft distribution and more efficient Fas receptor (FasR, also known as TNFRSF6)-mediated apoptosis. We demonstrate here that the absence of K8 or transgenic expression of the K8 G62C mutant in mouse hepatocytes reduces lipid raft size. Mechanistically, we find that the lipid raft size is dependent on acid sphingomyelinase (ASMase, also known as SMPD1) enzyme activity, which is reduced in absence of K8/K18. Notably, the reduction of ASMase activity appears to be caused by a less efficient redistribution of surface membrane PKCδ toward lysosomes. Moreover, we delineate the lipid raft volume range that is required for an optimal FasR-mediated apoptosis. Hence, K8/K18-dependent PKCδ- and ASMase-mediated modulation of lipid raft size can explain the more prominent FasR-mediated signaling resulting from K8/K18 loss. The fine-tuning of ASMase-mediated regulation of lipid rafts might provide a therapeutic target for death-receptor-related liver diseases.
authors.affiliation: Centre de recherche sur le cancer de l'Université Laval and Centre de recherche du CHU de Québec (HDQ), Québec, Canada G1R 2J6.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Gilbert
authors.affiliation: Centre de recherche sur le cancer de l'Université Laval and Centre de recherche du CHU de Québec (HDQ), Québec, Canada G1R 2J6.
authors.forename: Anne
authors.initials: A
authors.lastname: Loranger
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: M Bishr
authors.initials: MB
authors.lastname: Omary
authors.affiliation: Centre de recherche sur le cancer de l'Université Laval and Centre de recherche du CHU de Québec (HDQ), Québec, Canada G1R 2J6 normand.marceau@crchudequebec.ulaval.ca.
authors.forename: Normand
authors.identifier: 0000-0003-4582-2561
authors.initials: N
authors.lastname: Marceau
mesh_terms: D000818:Animals; D017209:Apoptosis; D004705:Endocytosis; D004789:Enzyme Activation; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D007382:Intermediate Filaments / Q000378:metabolism; D053538:Keratin-18 / Q000378:metabolism*; D053533:Keratin-8 / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D051745:Protein Kinase C-delta / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D053538:Keratin-18; D053533:Keratin-8; D019014:fas Receptor; D051745:Protein Kinase C-delta; C577975:ASMase, mouse; D013108:Sphingomyelin Phosphodiesterase
keywords: ASMase; FasR; Hepatocyte; Keratin; Lipid raft; PKC