Abstract
Keratins 8 and 18 (K8 and K18) are heteropolymeric intermediate filament phosphoglycoproteins of simple-type epithelia. Mutations in K8 and K18 predispose the affected individual to liver disease as they protect hepatocytes from apoptosis. K18 undergoes dynamic O-linked N-acetylglucosamine glycosylation at Ser 30, 31 and 49. We investigated the function of K18 glycosylation by generating mice that overexpress human K18 S30/31/49A substitution mutants that cannot be glycosylated (K18-Gly(-)), and compared the susceptibility of these mice to injury with wild-type and other keratin-mutant mice. K18-Gly(-) mice are more susceptible to liver and pancreatic injury and apoptosis induced by streptozotocin or to liver injury by combined N-acetyl-D-glucosaminidase inhibition and Fas administration. The enhanced apoptosis in the livers of mice that express K18-Gly(-) involves the inactivation of Akt1 and protein kinase Ctheta as a result of their site-specific hypophosphorylation. Akt1 binds to K8, which probably contributes to the reciprocal hyperglycosylation and hypophosphorylation of Akt1 that occurs on K18 hypoglycosylation, and leads to decreased Akt1 kinase activity. Therefore, K18 glycosylation provides a unique protective role in epithelial injury by promoting the phosphorylation and activation of cell-survival kinases.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Acetylglucosamine / analogs & derivatives
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Acetylglucosamine / pharmacology
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Amino Acid Substitution / genetics
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Animals
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Antibodies, Monoclonal / immunology
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Antibodies, Monoclonal / pharmacology
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Apoptosis / drug effects
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Apoptosis / genetics
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Caspase 3 / metabolism*
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Chemical and Drug Induced Liver Injury / genetics
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Chemical and Drug Induced Liver Injury / metabolism
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Chemical and Drug Induced Liver Injury / pathology*
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Chemical and Drug Induced Liver Injury / prevention & control*
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Cytoskeleton / metabolism
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Cytosol / drug effects
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Cytosol / metabolism
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Enzyme Inhibitors / pharmacology
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Glycogen Synthase Kinase 3 / metabolism
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Glycosylation / drug effects
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HSP70 Heat-Shock Proteins / metabolism
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Hepatocytes / drug effects
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Hepatocytes / metabolism
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Humans
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Keratin-18 / genetics
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Keratin-18 / metabolism
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Keratin-8 / metabolism
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Keratins / chemistry*
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Keratins / genetics
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Keratins / metabolism*
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Liver / drug effects
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Liver / metabolism
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Liver / pathology
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Mice
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Mice, Inbred Strains
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Mice, Knockout
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Mice, Transgenic
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Models, Biological
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Oximes / pharmacology
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Pancreas / drug effects
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Pancreas / injuries*
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Pancreas / metabolism
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Pancreas / pathology*
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Phenylcarbamates / pharmacology
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Phosphorylation / drug effects
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Phosphorylation / genetics
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Protein Binding / physiology
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Protein Kinase C-delta / metabolism
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins c-akt / genetics
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Proto-Oncogene Proteins c-akt / metabolism
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Pyruvate Dehydrogenase Acetyl-Transferring Kinase
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Streptozocin / pharmacology
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beta-N-Acetylhexosaminidases / antagonists & inhibitors
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fas Receptor / agonists
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fas Receptor / immunology
Substances
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Antibodies, Monoclonal
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Enzyme Inhibitors
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HSP70 Heat-Shock Proteins
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KRT18 protein, human
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Keratin-18
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Keratin-8
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Krt8 protein, mouse
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Oximes
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Phenylcarbamates
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Pyruvate Dehydrogenase Acetyl-Transferring Kinase
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fas Receptor
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N-acetylglucosaminono-1,5-lactone O-(phenylcarbamoyl)oxime
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Streptozocin
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Keratins
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Akt1 protein, mouse
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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Protein Kinase C-delta
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Glycogen Synthase Kinase 3
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glycogen synthase kinase 3 alpha
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hexosaminidase C
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beta-N-Acetylhexosaminidases
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Caspase 3
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Acetylglucosamine