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siRNA silencing of proteasome maturation protein (POMP) activates the unfolded protein response and constitutes a model for KLICK genodermatosis
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Genetics. Uppsala University, Science for Life Laboratory, SciLifeLab.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Dermatology and Venereology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Genetics. Uppsala University, Science for Life Laboratory, SciLifeLab.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Genetics. Uppsala University, Science for Life Laboratory, SciLifeLab.
2012 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 7, no 1, e29471- p.Article in journal (Refereed) Published
Abstract [en]

Keratosis linearis with ichthyosis congenita and keratoderma (KLICK) is an autosomal recessive skin disorder associated with a single-nucleotide deletion in the 5'untranslated region of the proteasome maturation protein (POMP) gene. The deletion causes a relative switch in transcription start sites for POMP, predicted to decrease levels of POMP protein in terminally differentiated keratinocytes. To investigate the pathophysiology behind KLICK we created an in vitro model of the disease using siRNA silencing of POMP in epidermal air-liquid cultures. Immunohistochemical analysis of the tissue constructs revealed aberrant staining of POMP, proteasome subunits and the skin differentiation marker filaggrin when compared to control tissue constructs. The staining patterns of POMP siRNA tissue constructs showed strong resemblance to those observed in skin biopsies from KLICK patients. Western blot analysis of lysates from the organotypic tissue constructs revealed an aberrant processing of profilaggrin to filaggrin in samples transfected with siRNA against POMP. Knock-down of POMP expression in regular cell cultures resulted in decreased amounts of proteasome subunits. Prolonged silencing of POMP in cultured cells induced C/EBP homologous protein (CHOP) expression consistent with an activation of the unfolded protein response and increased endoplasmic reticulum (ER) stress. The combined results indicate that KLICK is caused by reduced levels of POMP, leading to proteasome insufficiency in differentiating keratinocytes. Proteasome insufficiency disturbs terminal epidermal differentiation, presumably by increased ER stress, and leads to perturbed processing of profilaggrin. Our findings underline a critical role for the proteasome in human epidermal differentiation.

Place, publisher, year, edition, pages
2012. Vol. 7, no 1, e29471- p.
National Category
Medical Genetics
Research subject
Clinical Genetics
Identifiers
URN: urn:nbn:se:uu:diva-149416DOI: 10.1371/journal.pone.0029471ISI: 000301123400059OAI: oai:DiVA.org:uu-149416DiVA: diva2:404953
Available from: 2011-03-19 Created: 2011-03-19 Last updated: 2012-04-18Bibliographically approved
In thesis
1. Genetic and Molecular Studies of Two Hereditary Skin Disorders
Open this publication in new window or tab >>Genetic and Molecular Studies of Two Hereditary Skin Disorders
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Monogenic disorders, i.e., disorders caused by mutations in a single gene, are rare and clinically heterogeneous conditions. Identification of the genetic cause of monogenic traits can bring new insights into molecular pathways and disease mechanisms. The aims of the present study were to identify the mutant genes in two autosomal recessive skin disorders and to characterize the functions of the mutated genes.  In order to identify candidate genes for the two disorders whole-genome SNP analysis, homozygosity mapping and gene sequencing were used.

Autosomal recessive congenital ichthyosis (ARCI) is a group of disorders characterized by extensive scaling and redness of the skin.  A subgroup of ARCI patients (n=27) was selected based on specific ultrastructural aberrations in their skin, revealed by electron microscopy. Mutations were identified in the Ichthyin gene in 93% of the selected patients, indicating a strong association between mutant Ichthyin and the specific morphological abnormalities. Ichthyin mRNA levels were shown to increase during keratinocyte differentiation in cells from healthy and affected individuals. Electron microscopy revealed a localization of ichthyin protein to keratins and desmosomes in epidermis. Staining of epidermal lipids identified aberrant lipid aggregates in skin sections of patients with Ichthyin mutations, indicating a role for Ichthyin in epidermal lipid metabolism.

In twelve KLICK syndrome patients with ichthyosis, palmoplantar keratoderma and keratotic striae on joints, a single-nucleotide deletion was identified in the 5’ region of the proteasome maturation protein (POMP) gene.  The deletion caused an increase in the proportion of POMP transcripts with long 5’ UTR’s in patient keratinocytes.  Immunohistochemical analysis of differentiated skin cell layers revealed aberrant expression of POMP, proteasome subunits and the skin protein filaggrin in patients. CHOP expression, associated with endoplasmic reticulum stress, was increased in the same layers. siRNA silencing of POMP in cell cultures reduced proteasome subunit levels and induced expression of CHOP.  The results indicate that the mutation in KLICK patients causes POMP and proteasome insufficiency with subsequent cellular stress.

This study conclusively contributes to the understanding of epidermal physiology and the pathogenesis of two inherited skin diseases.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 657
Keyword
Monogenic disorder, autosomal recessive congenital ichthyosis, KLICK syndrome, Ichthyin, POMP, proteasome, epidermal differentiation
National Category
Medical Genetics
Research subject
Clinical Genetics
Identifiers
urn:nbn:se:uu:diva-149185 (URN)978-91-554-8038-7 (ISBN)
Public defence
2011-05-06, Rudbecksalen, Rudbecklaboratoriet, Dag Hammarskiölds väg 20, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2011-04-14 Created: 2011-03-15 Last updated: 2011-05-05Bibliographically approved

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Dahlqvist, JohannaTörmä, HansDahl, Niklas
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