O-GlcNAcylation of RBM14 contributes to elevated cellular O-GlcNAc through regulation of OGA protein stability.

Dysregulation of O-GlcNAcylation has emerged as a potential biomarker for several diseases, particularly cancer. The role of OGT (O-GlcNAc transferase) in maintaining O-GlcNAc homeostasis has been extensively studied; nevertheless, the regulation of OGA (O-GlcNAcase) in cancer remains elusive. Here, we demonstrated that the multifunctional protein RBM14 is a regulator of cellular O-GlcNAcylation.

Roles of Keratins in Intestine.

Keratins make up a major portion of epithelial intermediate filament proteins. The widely diverse keratins are found in both the small and large intestines. The human intestine mainly expresses keratins 8, 18, 19, and 20.

Keratin 8/18 Regulate the Akt Signaling Pathway.

Keratin 8 and keratin 18 (K8/K18) are intermediate filament proteins that form the obligate heteropolymers in hepatocytes and protect the liver against toxins. The mechanisms of protection include the regulation of signaling pathway associated with cell survival. Previous studies show K8/K18 binding with Akt, which is a well-known protein kinase involved in the cell survival signaling pathway.

Keratin 8 mutations in transgenic mice predispose to lung injury.

Keratin 8 (K8) is the cytoskeletal intermediate filament protein of simple-type epithelia. Mutations in K8 predispose the affected individual and transgenic mouse to liver disease. However, the role of K8 in the lung has not been reported in mutant transgenic mouse models.

Revealing the Roles of Keratin 8/18-Associated Signaling Proteins Involved in the Development of Hepatocellular Carcinoma.

Although hepatocellular carcinoma (HCC) is developed with various etiologies, protection of hepatocytes seems basically essential to prevent the incidence of HCC. Keratin 8 and keratin 18 (K8/K18) are cytoskeletal intermediate filament proteins that are expressed in hepatocytes. They maintain the cell shape and protect cells under stress conditions.

Keratins regulate Hsp70-mediated nuclear localization of p38 mitogen-activated protein kinase.

Intermediate filament protein keratin 8 (K8) binds to heat shock protein 70 (Hsp70) and p38 MAPK, and is phosphorylated at Ser74 by p38α (MAPK14, hereafter p38). However, a p38 binding site on K8 and the molecular mechanism of K8-p38 interaction related to Hsp70 are unknown. Here, we identify a p38 docking site on K8 (Arg148/149 and Leu159/161) that is highly conserved in other intermediate filaments.

Liver disease-associated keratin 8 and 18 mutations modulate keratin acetylation and methylation.

Keratin 8 (K8) and keratin 18 (K18) are the intermediate filament proteins whose phosphorylation/transamidation associate with their aggregation in Mallory-Denk bodies found in patients with various liver diseases. However, the functions of other post-translational modifications in keratins related to liver diseases have not been fully elucidated. Here, using a site-specific mutation assay combined with nano-liquid chromatography-tandem mass spectrometry, we identified K8-Lys108 and K18-Lys187/426 as acetylation sites, and K8-Arg47 and K18-Arg55 as methylation sites.

The role of keratins in the digestive system: lessons from transgenic mouse models.

Keratins are the largest subfamily of intermediate filament proteins. They are either type I acidic or type II basic keratins. Keratins form obligate heteropolymer in epithelial cells and their expression patterns are tissue-specific.

The sweet side of vimentin.

A protein modification called O-linked glycosylation regulates the interactions between vimentin molecules under normal conditions, and the ability of bacteria to replicate after they infect cells.

A mutation in keratin 18 that causes caspase-digestion resistance protects homozygous transgenic mice from hepatic apoptosis and injury.

Cytoskeletal keratin 18 (K18) undergoes caspase-mediated digestion during apoptosis, which leads to dramatic disassembly of keratin filaments. We studied the significance of K18 caspase digestion in a mouse model and generated transgenic mice expressing the human K18 caspase digestion-resistant double-mutant K18-D238/397E in a mouse (m) K18-null background, and compared their response to injury mediated by administration of antibody against tumor necrosis factor receptor superfamily member 6 (Fas), anti-FasAb. Notably, K18-D238/397E;mK18-null mice were significantly more resistant to anti-FasAb-induced injury as compared with K18-WT;mK18-null mice (23% vs 57% lethality, respectively; <0.

Keratins: Biomarkers and modulators of apoptotic and necrotic cell death in the liver.

Unlabelled: Keratins, formerly known as cytokeratins, are the major epithelial-specific subgroup of intermediate filament proteins. Adult hepatocytes express keratin polypeptides 8 and 18 (K8/K18), whereas cholangiocytes express K8/K18 and keratins 7 and 19 (K7/K19). Keratins function primarily to protect hepatocytes from apoptosis and necrosis, which was revealed using several genetic mouse models.

Mutation of caspase-digestion sites in keratin 18 interferes with filament reorganization, and predisposes to hepatocyte necrosis and loss of membrane integrity.

Keratin 18 (K18 or KRT18) undergoes caspase-mediated cleavage during apoptosis, the significance of which is poorly understood. Here, we mutated the two caspase-cleavage sites (D238E and D397E) in K18 (K18-DE), followed by transgenic overexpression of the resulting mutant. We found that K18-DE mice develop extensive Fas-mediated liver damage compared to wild-type mice overexpressing K18 (K18-WT).

Predisposition to apoptosis in keratin 8-null liver is related to inactivation of NF-κB and SAPKs but not decreased c-Flip.

Keratin 8 and 18 (K8/K18) are major intermediate filament proteins of liver hepatocytes. They provide mechanical and nonmechanical stability, thereby protecting cells from stress. Hence, K8-null mice are highly sensitive to Fas-mediated liver cell apoptosis.

Intermediate filaments of the lung.

Intermediate filaments (IF), a subfamily of the cytoskeletal filaments, provide structural support to cells. Human diseases related to mutations in IF proteins in which their tissue-specific expression is reflected have been found in a broad range of patients. The properties of identified IF mutants are well-studied in vitro in cultured cells and in vivo using transgenic mice expressing IF mutants.

Keratins: markers and modulators of liver disease.

Purpose Of Review: Keratins are a subgroup of intermediate filaments expressed in the epithelia. Keratins emerged as important tissue-protecting genes and keratin variants cause/predispose to development of more than 50 human disorders. Our review focuses on the importance of keratins in context of liver disease.

Characterization of in vivo keratin 19 phosphorylation on tyrosine-391.

Background: Keratin polypeptide 19 (K19) is a type I intermediate filament protein that is expressed in stratified and simple-type epithelia. Although K19 is known to be phosphorylated on tyrosine residue(s), conclusive site-specific characterization of these residue(s) and identification potential kinases that may be involved has not been reported.

Methodology/principal Findings: In this study, biochemical, molecular and immunological approaches were undertaken in order to identify and characterize K19 tyrosine phosphorylation.

Cytoskeletal keratin glycosylation protects epithelial tissue from injury.

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.

Toward unraveling the complexity of simple epithelial keratins in human disease.

Simple epithelial keratins (SEKs) are found primarily in single-layered simple epithelia and include keratin 7 (K7), K8, K18-K20, and K23. Genetically engineered mice that lack SEKs or overexpress mutant SEKs have helped illuminate several keratin functions and served as important disease models. Insight into the contribution of SEKs to human disease has indicated that K8 and K18 are the major constituents of Mallory-Denk bodies, hepatic inclusions associated with several liver diseases, and are essential for inclusion formation.

Keratins let liver live: Mutations predispose to liver disease and crosslinking generates Mallory-Denk bodies.

Keratin polypeptides 8 and 18 (K8/K18) are the cytoskeletal intermediate filament proteins of hepatocytes while K8/K18/K19 are the keratins of hepatobiliary ductal cells. Hepatocyte K8/K18 are highly abundant and behave as stress proteins with injury-inducible expression. Human association studies show that K8/K18 germline heterozygous mutations predispose to end-stage liver disease of multiple etiologies ( approximately 3 fold increased risk), and to liver disease progression in patients with chronic hepatitis C infection.

Keratin 18 overexpression but not phosphorylation or filament organization blocks mouse Mallory body formation.

Unlabelled: Several human liver diseases are associated with formation of Mallory body (MB) inclusions. These hepatocyte cytoplasmic deposits are composed primarily of hyperphosphorylated keratins 8 and 18 (K8/K18). Feeding a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet is a well-established mouse model of MBs.

A disease- and phosphorylation-related nonmechanical function for keratin 8.

Keratin 8 (K8) variants predispose to human liver injury via poorly understood mechanisms. We generated transgenic mice that overexpress the human disease-associated K8 Gly61-to-Cys (G61C) variant and showed that G61C predisposes to liver injury and apoptosis and dramatically inhibits K8 phosphorylation at serine 73 (S73) via stress-activated kinases. This led us to generate mice that overexpress K8 S73-to-Ala (S73A), which mimicked the susceptibility of K8 G61C mice to injury, thereby providing a molecular link between K8 phosphorylation and disease-associated mutation.

"Heads and tails" of intermediate filament phosphorylation: multiple sites and functional insights.

Intermediate filaments (IFs) are major components of the mammalian cytoskeleton. They are among the most abundant cellular phosphoproteins; their phosphorylation typically involves multiple sites at repeat or unique motifs, preferentially within the "head" or "tail" domains. Phosphorylation and dephosphorylation are essential for the regulation of IF dynamics by modulating the intrinsic properties of IFs: solubility, conformation and filament organization, and, in addition, for the regulation of other IF post-translational modifications.

Denaturing temperature selection may underestimate keratin mutation detection by DHPLC.

Keratins 8 and 18 (KRT8 and KRT18 genes; K8 and K18 proteins) variants are risk factors for developing end-stage liver disease and may be associated with inflammatory bowel disease and chronic pancreatitis. The frequency of K8/K18 variants in American, British, German, and Italian populations differs. For example, one study showed no amino acid-altering K8/K18 mutations in 256 German patients with liver disorders, while another found 58 out of 467 American liver disease patients with K8/K18 mutations.

Bispecific and human disease-related anti-keratin rabbit monoclonal antibodies.

Rabbit antibodies may have favorable properties compared to mouse antibodies, including high affinities and better antigen recognition. We used a biochemical and reverse immunologic approach to generate and characterize rabbit anti-phospho-keratin and anti-keratin monoclonal antibodies (MAb). Human keratins 8 and 18 (K8/K18) were used as immunogens after isolation from cells pretreated with okadaic acid or pervanadate to promote Ser/Thr or Tyr hyperphosphorylation, respectively.