title: siRNA silencing of proteasome maturation protein (POMP) activates the unfolded protein response and constitutes a model for KLICK genodermatosis.
abstract: 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.
authors.affiliation: Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Johanna
authors.initials: J
authors.lastname: Dahlqvist
authors.forename: Hans
authors.initials: H
authors.lastname: Törmä
authors.forename: Jitendra
authors.initials: J
authors.lastname: Badhai
authors.forename: Niklas
authors.initials: N
authors.lastname: Dahl
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D004817:Epidermis / Q000378:metabolism / Q000473:pathology; D000091344:Filaggrin Proteins; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D014176:Protein Biosynthesis; D034741:RNA, Small Interfering / Q000235:genetics*; D012871:Skin Diseases / Q000151:congenital* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D056811:Unfolded Protein Response / Q000235:genetics*
chemical_list: D020121:5' Untranslated Regions; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D018832:Molecular Chaperones; D034741:RNA, Small Interfering; C110856:proteasome maturation protein; D046988:Proteasome Endopeptidase Complex