title: Stress-induced recruitment of epiplakin to keratin networks increases their resistance to hyperphosphorylation-induced disruption.
abstract: Epiplakin is a large (>725 kDa) cytoskeletal protein exclusively expressed in epithelial tissues. It has a unique structure, consisting entirely of plakin repeat domains (PRDs), one of the hallmarks of spectraplakin protein family members. Previous studies, including the phenotypic analyses of knockout mice, failed to reveal the biological function of epiplakin. Using in vitro binding assays, we show here that all but one of the 16 PRDs of mouse epiplakin bind to keratins of basal keratinocytes. Nevertheless, in primary keratinocyte cell cultures, epiplakin only partially colocalized with keratin intermediate filament networks. However, upon application of cellular stress in the form of keratin hyperphosphorylation, osmotic shock or UV irradiation, the entire cytoplasmic epiplakin pool became associated with keratin. In response to such types of stress, epiplakin initially translocated to the still-intact keratin filament network and remained associated with keratin after its disruption and transformation into granular aggregates. Time-course experiments revealed that serine/threonine (okadaic acid) and tyrosine (orthovanadate) phosphatase inhibitor-induced filament disruption in differentiated keratinocytes proceeded faster in epiplakin-deficient cells compared with wild-type cells. Our data suggest that epiplakin plays a role in keratin filament reorganization in response to stress, probably by protecting keratin filaments against disruption in a chaperone-like fashion.
authors.affiliation: Department of Molecular Cell Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria.
authors.forename: Daniel
authors.initials: D
authors.lastname: Spazierer
authors.forename: Julia
authors.initials: J
authors.lastname: Raberger
authors.forename: Karin
authors.initials: K
authors.lastname: Gross
authors.forename: Peter
authors.initials: P
authors.lastname: Fuchs
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wiche
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007382:Intermediate Filaments / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D007633:Keratins / Q000032:analysis / Q000378:metabolism*; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D009997:Osmotic Pressure; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D014466:Ultraviolet Rays
chemical_list: D001324:Autoantigens; D004791:Enzyme Inhibitors; C426678:epiplakin; D019319:Okadaic Acid; D007633:Keratins; D002118:Calcium