Publications by authors named "Janniche Torsvik"

10 Publications

  • Page 1 of 1

Functional Analyses of HNF1A-MODY Variants Refine the Interpretation of Identified Sequence Variants.

J Clin Endocrinol Metab 2020 04;105(4)

Department of Safety, Chemistry and Biomedical Laboratory Sciences, Western Norway University of Applied Sciences, Bergen, Norway.

Context: While rare variants of the hepatocyte nuclear factor-1 alpha (HNF1A) gene can cause maturity-onset diabetes of the young (HNF1A-MODY), other variants can be risk factors for the development of type 2 diabetes. As has been suggested by the American College of Medical Genetics (ACMG) guidelines for variant interpretation, functional studies provide strong evidence to classify a variant as pathogenic.

Objective: We hypothesized that a functional evaluation can improve the interpretation of the HNF1A variants in our Czech MODY Registry.

Design, Settings, And Participants: We studied 17 HNF1A variants that were identified in 48 individuals (33 female/15 male) from 20 Czech families with diabetes, using bioinformatics in silico tools and functional protein analyses (transactivation, protein expression, DNA binding, and nuclear localization).

Results: Of the 17 variants, 12 variants (p.Lys120Glu, p.Gln130Glu, p.Arg131Pro, p.Leu139Pro, p.Met154Ile, p.Gln170Ter, p.Glu187SerfsTer40, p.Phe215SerfsTer18, p.Gly253Arg, p.Leu383ArgfsTer3, p.Gly437Val, and p.Thr563HisfsTer85) exhibited significantly reduced transcriptional activity or DNA binding (< 40%) and were classified as (likely) pathogenic, 2/17 variants were (likely) benign and 3/17 remained of uncertain significance. Functional analyses allowed for the reclassification of 10/17 variants (59%). Diabetes treatment was improved in 20/29 (69%) carriers of (likely) pathogenic HNF1A variants.

Conclusion: Functional evaluation of the HNF1A variants is necessary to better predict the pathogenic effects and to improve the diagnostic interpretation and treatment, particularly in cases where the cosegregation or family history data are not available or where the phenotype is more diverse and overlaps with other types of diabetes.
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http://dx.doi.org/10.1210/clinem/dgaa051DOI Listing
April 2020

Identification of an alternatively spliced nuclear isoform of human N-terminal acetyltransferase Naa30.

Gene 2018 Feb 13;644:27-37. Epub 2017 Dec 13.

Department of Molecular Biology, University of Bergen, Thormøhlensgate 55, 5006 Bergen, Norway; Department of Surgery, Haukeland University Hospital, Jonas Lies vei 87, 5021 Bergen, Norway. Electronic address:

N-terminal acetylation is a highly abundant and important protein modification in eukaryotes catalyzed by N-terminal acetyltransferases (NATs). In humans, six different NATs have been identified (NatA-NatF), each composed of individual subunits and acetylating a distinct set of substrates. Along with most NATs, NatC acts co-translationally at the ribosome. The NatC complex consists of the catalytic subunit Naa30 and the auxiliary subunits Naa35 and Naa38, and can potentially Nt-acetylate cytoplasmic proteins when the initiator methionine is followed by a bulky hydrophobic/amphipathic residue at position 2. Here, we have identified a splice variant of human NAA30, which encodes a truncated protein named Naa30. The splice variant was abundantly present in thyroid cancer tissues and in several different human cancer cell lines. Surprisingly, Naa30 localized predominantly to the nucleus, as opposed to annotated Naa30 which has a cytoplasmic localization. Full-length Naa30 acetylated a classical NatC substrate peptide in vitro, whereas no significant NAT activity was detected for Naa30 Due to the nuclear localization, we also examined acetyltransferase activity towards lysine residues. Neither full-length Naa30 nor Naa30 displayed any lysine acetyltransferase activity. Overexpression of full-length Naa30 increased cell viability via inhibition of apoptosis. In contrast, Naa30 did not exert an anti-apoptotic effect. In sum, we identified a novel and widely expressed Naa30 isoform with a potential non-catalytic role in the nucleus.
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http://dx.doi.org/10.1016/j.gene.2017.12.019DOI Listing
February 2018

Copy number variants and VNTR length polymorphisms of the carboxyl-ester lipase (CEL) gene as risk factors in pancreatic cancer.

Pancreatology 2017 Jan - Feb;17(1):83-88. Epub 2016 Oct 11.

KG Jebsen Center for Diabetes Research, Department of Clinical Science, University of Bergen, Bergen, Norway; Gade Laboratory for Pathology, Department of Clinical Medicine, University of Bergen, Bergen, Norway; Department of Pathology, Haukeland University Hospital, Bergen, Norway.

Background/objectives: We have recently described copy number variants (CNVs) of the human carboxyl-ester lipase (CEL) gene, including a recombined deletion allele (CEL-HYB) that is a genetic risk factor for chronic pancreatitis. Associations with pancreatic disease have also been reported for the variable number of tandem repeat (VNTR) region located in CEL exon 11. Here, we examined if CEL CNVs and VNTR length polymorphisms affect the risk for developing pancreatic cancer.

Methods: CEL CNVs and VNTR were genotyped in a German family with non-alcoholic chronic pancreatitis and pancreatic cancer, in 265 German and 197 Norwegian patients diagnosed with pancreatic adenocarcinoma, and in 882 controls. CNV screening was performed using PCR assays followed by agarose gel electrophoresis whereas VNTR lengths were determined by DNA fragment analysis.

Results: The investigated family was CEL-HYB-positive. However, an association of CEL-HYB or a duplication CEL allele with pancreatic cancer was not seen in our two patient cohorts. The frequency of the 23-repeat VNTR allele was borderline significant in Norwegian cases compared to controls (1.2% vs. 0.3%; P = 0.05). For all other VNTR lengths, no statistically significant difference in frequency was observed. Moreover, no association with pancreatic cancer was detected when CEL VNTR lengths were pooled into groups of short, normal or long alleles.

Conclusions: We could not demonstrate an association between CEL CNVs and pancreatic cancer. An association is also unlikely for CEL VNTR lengths, although analyses in larger materials are necessary to completely exclude an effect of rare VNTR alleles.
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http://dx.doi.org/10.1016/j.pan.2016.10.006DOI Listing
August 2017

Defective PITRM1 mitochondrial peptidase is associated with Aβ amyloidotic neurodegeneration.

EMBO Mol Med 2016 Mar;8(3):176-90

Department of Neurology, Haukeland University Hospital, Bergen, Norway Department of Clinical Medicine (K1), University of Bergen, Bergen, Norway

Mitochondrial dysfunction and altered proteostasis are central features of neurodegenerative diseases. The pitrilysin metallopeptidase 1 (PITRM1) is a mitochondrial matrix enzyme, which digests oligopeptides, including the mitochondrial targeting sequences that are cleaved from proteins imported across the inner mitochondrial membrane and the mitochondrial fraction of amyloid beta (Aβ). We identified two siblings carrying a homozygous PITRM1 missense mutation (c.548G>A, p.Arg183Gln) associated with an autosomal recessive, slowly progressive syndrome characterised by mental retardation, spinocerebellar ataxia, cognitive decline and psychosis. The pathogenicity of the mutation was tested in vitro, in mutant fibroblasts and skeletal muscle, and in a yeast model. A Pitrm1(+/-) heterozygous mouse showed progressive ataxia associated with brain degenerative lesions, including accumulation of Aβ-positive amyloid deposits. Our results show that PITRM1 is responsible for significant Aβ degradation and that impairment of its activity results in Aβ accumulation, thus providing a mechanistic demonstration of the mitochondrial involvement in amyloidotic neurodegeneration.
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http://dx.doi.org/10.15252/emmm.201505894DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4772954PMC
March 2016

A recombined allele of the lipase gene CEL and its pseudogene CELP confers susceptibility to chronic pancreatitis.

Nat Genet 2015 May 16;47(5):518-522. Epub 2015 Mar 16.

KG Jebsen Center for Diabetes Research, Department of Clinical Science, University of Bergen, Bergen, Norway.

Carboxyl ester lipase is a digestive pancreatic enzyme encoded by the CEL gene. Mutations in CEL cause maturity-onset diabetes of the young as well as pancreatic exocrine dysfunction. Here we describe a hybrid allele (CEL-HYB) originating from a crossover between CEL and its neighboring pseudogene, CELP. In a discovery series of familial chronic pancreatitis cases, we observed CEL-HYB in 14.1% (10/71) of cases compared to 1.0% (5/478) of controls (odds ratio (OR) = 15.5; 95% confidence interval (CI) = 5.1-46.9; P = 1.3 × 10(-6) by two-tailed Fisher's exact test). In three replication studies of nonalcoholic chronic pancreatitis, we identified CEL-HYB in a total of 3.7% (42/1,122) cases and 0.7% (30/4,152) controls (OR = 5.2; 95% CI = 3.2-8.5; P = 1.2 × 10(-11); formal meta-analysis). The allele was also enriched in alcoholic chronic pancreatitis. Expression of CEL-HYB in cellular models showed reduced lipolytic activity, impaired secretion, prominent intracellular accumulation and induced autophagy. These findings implicate a new pathway distinct from the protease-antiprotease system of pancreatic acinar cells in chronic pancreatitis.
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http://dx.doi.org/10.1038/ng.3249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5321495PMC
May 2015

Endocytosis of secreted carboxyl ester lipase in a syndrome of diabetes and pancreatic exocrine dysfunction.

J Biol Chem 2014 Oct 25;289(42):29097-111. Epub 2014 Aug 25.

From the KG Jebsen Center for Diabetes Research, Department of Clinical Science, University of Bergen, Bergen, Norway, Gade Laboratory for Pathology, Department of Clinical Medicine, University of Bergen, N-5021 Bergen, Norway, Department of Pathology, Haukeland University Hospital, Bergen, Norway

Maturity-onset diabetes of the young, type 8 (MODY8) is characterized by a syndrome of autosomal dominantly inherited diabetes and exocrine pancreatic dysfunction. It is caused by deletion mutations in the last exon of the carboxyl ester lipase (CEL) gene, resulting in a CEL protein with increased tendency to aggregate. In this study we investigated the intracellular distribution of the wild type (WT) and mutant (MUT) CEL proteins in cellular models. We found that both CEL-WT and CEL-MUT were secreted via the endoplasmic reticulum and Golgi compartments. However, their subcellular distributions differed, as only CEL-MUT was observed as an aggregate at the cell surface and inside large cytoplasmic vacuoles. Many of the vacuoles were identified as components of the endosomal system, and after its secretion, the mutant CEL protein was re-internalized, transported to the lysosomes, and degraded. Internalization of CEL-MUT also led to reduced viability of pancreatic acinar and beta cells. These findings may have implications for the understanding of how the acinar-specific CEL-MUT protein causes both exocrine and endocrine pancreatic disease.
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http://dx.doi.org/10.1074/jbc.M114.574244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4200264PMC
October 2014

The number of tandem repeats in the carboxyl-ester lipase (CEL) gene as a risk factor in alcoholic and idiopathic chronic pancreatitis.

Pancreatology 2013 Jan-Feb;13(1):29-32. Epub 2012 Dec 20.

KG Jebsen Center for Diabetes Research, Department of Clinical Medicine, University of Bergen, Bergen, Norway.

Background/aims: The variable number of tandem repeats (VNTR) in the last exon of the carboxyl-ester lipase (CEL) gene has been reported to associate with alcohol-induced chronic pancreatitis (ACP) in a Japanese study. Here, we have investigated the association between the number of CEL VNTR repeats and ACP or idiopathic chronic pancreatitis (ICP) in a cohort of German patients.

Methods: Patients diagnosed with ACP (n = 203) or ICP (n = 64) were genotyped using a screening method consisting of PCR followed by DNA fragment analysis. The allele frequencies of different CEL VNTR lengths were compared to the frequencies in healthy controls (n = 390).

Results: We observed no statistical significant associations between CEL VNTR allele frequencies and ACP or ICP.

Conclusion: This study did not find evidence that supported an association between the common length variations of the CEL VNTR and chronic pancreatitis.
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http://dx.doi.org/10.1016/j.pan.2012.12.059DOI Listing
July 2013

Diabetes and pancreatic exocrine dysfunction due to mutations in the carboxyl ester lipase gene-maturity onset diabetes of the young (CEL-MODY): a protein misfolding disease.

J Biol Chem 2011 Oct 22;286(40):34593-605. Epub 2011 Jul 22.

Department of Clinical Medicine, University of Bergen, N-5020 Bergen, Norway.

CEL-maturity onset diabetes of the young (MODY), diabetes with pancreatic lipomatosis and exocrine dysfunction, is due to dominant frameshift mutations in the acinar cell carboxyl ester lipase gene (CEL). As Cel knock-out mice do not express the phenotype and the mutant protein has an altered and intrinsically disordered tandem repeat domain, we hypothesized that the disease mechanism might involve a negative effect of the mutant protein. In silico analysis showed that the pI of the tandem repeat was markedly increased from pH 3.3 in wild-type (WT) to 11.8 in mutant (MUT) human CEL. By stably overexpressing CEL-WT and CEL-MUT in HEK293 cells, we found similar glycosylation, ubiquitination, constitutive secretion, and quality control of the two proteins. The CEL-MUT protein demonstrated, however, a high propensity to form aggregates found intracellularly and extracellularly. Different physicochemical properties of the intrinsically disordered tandem repeat domains of WT and MUT proteins may contribute to different short and long range interactions with the globular core domain and other macromolecules, including cell membranes. Thus, we propose that CEL-MODY is a protein misfolding disease caused by a negative gain-of-function effect of the mutant proteins in pancreatic tissues.
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http://dx.doi.org/10.1074/jbc.M111.222679DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3186416PMC
October 2011

Mutations in the VNTR of the carboxyl-ester lipase gene (CEL) are a rare cause of monogenic diabetes.

Hum Genet 2010 Jan 17;127(1):55-64. Epub 2009 Sep 17.

Department of Clinical Medicine, University of Bergen, Bergen, Norway.

We have previously shown that heterozygous single-base deletions in the carboxyl-ester lipase (CEL) gene cause exocrine and endocrine pancreatic dysfunction in two multigenerational families. These deletions were found in the first and fourth repeats of a variable number of tandem repeats (VNTR), which has proven challenging to sequence due to high GC-content and considerable length variation. We have therefore developed a screening method consisting of a multiplex PCR followed by fragment analysis. The method detected putative disease-causing insertions and deletions in the proximal repeats of the VNTR, and determined the VNTR-length of each allele. When blindly testing 56 members of the two families with known single-base deletions in the CEL VNTR, the method correctly assessed the mutation carriers. Screening of 241 probands from suspected maturity-onset diabetes of the young (MODY) families negative for mutations in known MODY genes (95 individuals from Denmark and 146 individuals from UK) revealed no deletions in the proximal repeats of the CEL VNTR. However, we found one Danish patient with a short, novel CEL allele containing only three VNTR repeats (normal range 7-23 in healthy controls). This allele co-segregated with diabetes or impaired glucose tolerance in the patient's family as six of seven mutation carriers were affected. We also identified individuals who had three copies of a complete CEL VNTR. In conclusion, the CEL gene is highly polymorphic, but mutations in CEL are likely to be a rare cause of monogenic diabetes.
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http://dx.doi.org/10.1007/s00439-009-0740-8DOI Listing
January 2010

Cloning and characterization of hNAT5/hSAN: an evolutionarily conserved component of the NatA protein N-alpha-acetyltransferase complex.

Gene 2006 Apr 28;371(2):291-5. Epub 2006 Feb 28.

Department of Molecular Biology, University of Bergen, N-5020 Bergen, Norway.

The human hARD1-NATH complex, cotranslationally acetylating the alpha-amino groups of proteins, was recently described. In S. cerevisiae and D. melanogaster this NatA complex contains a third subunit, Nat5p or San, respectively. Based on phylogenetic analyses and database searches, we here describe the human homologue, hNAT5, of these proteins. RT-PCR experiments demonstrated that hNat5 mRNA was expressed in several human cell lines. The candidacy of hNAT5 as a third subunit of the hARD1-NATH complex was investigated using anti-NATH or anti-hARD1 in co-immunoprecipitation experiments followed by Mass Spectrometry analysis of tryptic peptides. Oligopeptides specific for hNAT5 were identified. This verified the expression of endogenous hNAT5 protein in human cells and also identified hNAT5 as a NATH and hARD1 interacting partner. hNAT5 localized to the cytoplasm in accordance with hNAT5-hARD1-NATH complexes playing a role in cotranslational N-alpha-acetylation. Sequence alignment revealed a high degree of similarity of the NAT5 protein between species supporting its conserved role as a part of the complex. The predicted acetyltransferase domain within hNAT5 suggested that this protein, like hARD1, is an enzymatically active component. In summary, we present the first description of the human homologue of Nat5p/San, hNAT5, the third component of the human NatA N-alpha-acetyltransferase complex.
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http://dx.doi.org/10.1016/j.gene.2005.12.008DOI Listing
April 2006