Keratins as Susceptibility Genes for End-Stage Liver Disease

Massey University, Palmerston North City, Manawatu-Wanganui, New Zealand
Gastroenterology (Impact Factor: 16.72). 10/2005; 129(3):885-93. DOI: 10.1053/j.gastro.2005.06.065
Source: PubMed


Keratins 8 and 18 protect the liver from stress. Keratin 8 and 18 variants in 17 of 467 liver disease explants and 2 of 349 blood bank controls were previously reported in 5 analyzed exonic regions. We asked whether mutations were present in the remaining 10 exons of keratins 8 and 18.
Exonic regions were polymerase chain reaction-amplified from genomic DNA, isolated from the above-mentioned 2 cohorts, and analyzed for the presence of mutations. Mutant keratins were also studied biochemically.
We identified 10 novel keratin 8 and 18 heterozygous variants in 44 of 467 explants and 11 of 349 controls: keratin 18 deletion (delta64-71), a keratin 8 frameshift that truncates the last 14 amino acids; 8 missense keratin 8 and 18 alterations; and several new polymorphisms. The most common variant, keratin 8 R340H, at the highly conserved R340 was found in 30 of 467 explants and 10 of 349 controls (P = .02) and was confirmed in the diseased livers by generation of an R340H-specific antibody. Germline transmission and variant protein expression were verified. The mutations involved a variety of liver diseases, and some variants had an ethnic background preponderance. Mutations that introduced disulfide bonds (keratin 8 G61C or R453C) decreased keratin solubility, particularly after oxidative stress, whereas others decreased keratin 8 phosphorylation (keratin 8 G433S).
The overall frequency of keratin 8 and 18 variants was 12.4% in 467 liver disease explants and 3.7% in 349 blood bank controls (P < .0001). Variants can alter keratin solubility or phosphorylation and may render individuals susceptible to end-stage liver disease, depending on their genetic background and exposure to other insults, such as alcohol or viral infection.

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    • "Non-diseased and diabetic human liver tissues were obtained from the National Disease Research Interchange. Cirrhotic liver explants were obtained from patients who underwent liver transplantation for end-stage liver disease (Ku et al., 2005). Animal use was approved by, and performed in accordance with, the University Committee on Use and Care of Animals at the University of Michigan. "
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    ABSTRACT: Lysine acetylation is an important posttranslational modification that regulates microtubules and microfilaments, but its effects on intermediate filament proteins (IFs) are unknown. We investigated the regulation of keratin 8 (K8), a type II simple epithelial IF, by lysine acetylation. K8 was basally acetylated and the highly conserved Lys-207 was a major acetylation site. K8 acetylation regulated filament organization and decreased keratin solubility. Acetylation of K8 was rapidly responsive to changes in glucose levels and was up-regulated in response to nicotinamide adenine dinucleotide (NAD) depletion and in diabetic mouse and human livers. The NAD-dependent deacetylase sirtuin 2 (SIRT2) associated with and deacetylated K8. Pharmacologic or genetic inhibition of SIRT2 decreased K8 solubility and affected filament organization. Inhibition of K8 Lys-207 acetylation resulted in site-specific phosphorylation changes of K8. Therefore, K8 acetylation at Lys-207, a highly conserved residue among type II keratins and other IFs, is up-regulated upon hyperglycemia and down-regulated by SIRT2. Keratin acetylation provides a new mechanism to regulate keratin filaments, possibly via modulating keratin phosphorylation.
    The Journal of Cell Biology 01/2013; 200(3). DOI:10.1083/jcb.201209028 · 9.83 Impact Factor
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    • "K8 R341H variant was the most common variant and was found in 8 subjects (variant frequency 3.1%), which lies well below the frequencies seen in US Caucasians with end-stage liver disease or acute liver failure (5.1 and 7.2%, respectively, Table 3) [6,19]. On the other hand, similar variant frequencies were observed in US control subjects as well as in a German cohort of patients with chronic hepatitis C (Table 3) [18,19]. Similarly, the frequency of K8 G62C variant found in our cohort is comparable to their occurrence in a large cohort of German control subjects (1.9 vs 1.6-1.8%, "
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    ABSTRACT: Background Keratins 8/18 (K8/K18) are established hepatoprotective proteins and K8/K18 variants predispose to development and adverse outcome of multiple liver disorders. The importance of K8/K18 in alcoholic liver disease as well as in established cirrhosis remains unknown. Methods We analyzed the K8 mutational hot-spots in 261 prospectively followed-up patients with alcoholic cirrhosis (mean follow-up 65 months). PCR-amplified samples were pre-screened by denaturing high-performance liquid chromatography and conspicuous samples were sequenced. Results 67 patients developed hepatocellular carcinoma (HCC) and 133 died. Fourteen patients harbored amino-acid-altering K8 variants (5xG62C, 8xR341H). The presence of K8 variants did not associate with development of HCC (log-rank=0.5) or death (log-rank=0.7) and no significant associations were obtained for the single K8 variants after a correction for multiple testing was performed. Conclusions Keratin variants are expressed in a low percentage of patients with alcoholic cirrhosis and do not influence HCC development. Further studies conducted in larger prospective cohorts are needed to find out whether presence of K8 R341H variant predispose to non-HCC-related liver mortality.
    BMC Gastroenterology 10/2012; 12(1):147. DOI:10.1186/1471-230X-12-147 · 2.37 Impact Factor
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    • "Next we wanted to identify the site(s) in keratins that become phosphorylated in response to SPC. SPC stimulated phosphorylation of K8 at Ser431 in both epithelial cancer cell lines – a site that is also phosphorylated by active ERK (Omary et al., 1998; Ku et al., 2005). K8(S431) phosphorylation in response to SPC was prevented when cells were incubated with either MEK inhibitor (Fig. 4A). "
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    ABSTRACT: Cell migration and invasion are largely dependent on the complex organization of the various cytoskeletal components. Whereas the role of actin filaments and microtubules in cell motility is well established, the role of intermediate filaments in this process is incompletely understood. Organization and structure of the keratin cytoskeleton, which consists of heteropolymers of at least one type 1 and one type 2 intermediate filament, are in part regulated by post-translational modifications. In particular, phosphorylation events influence the properties of the keratin network. Sphingosylphosphorylcholine (SPC) is a bioactive lipid with the exceptional ability to change the organization of the keratin cytoskeleton, leading to reorganization of keratin filaments, increased elasticity, and subsequently increased migration of epithelial tumor cells. Here we investigate the signaling pathways that mediate SPC-induced keratin reorganization and the role of keratin phosphorylation in this process. We establish that the MEK-ERK signaling cascade regulates both SPC-induced keratin phosphorylation and reorganization in human pancreatic and gastric cancer cells and identify Ser431 in keratin 8 as the crucial residue whose phosphorylation is required and sufficient to induce keratin reorganization and consequently enhanced migration of human epithelial tumor cells.
    Journal of Cell Science 02/2012; 125(Pt 9):2148-59. DOI:10.1242/jcs.080127 · 5.43 Impact Factor
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