Expression and interaction of desmosomal components and keratins provide stable cell cohesion and protect the epidermis against various types of stress. The differentiation-specific isotype composition of the keratin cytoskeleton and desmosomes is regarded as major determinant of adhesive strength. However, the functional significance of individual keratins for the composition and adhesion of desmosomes has not been addressed in full. To overcome keratin redundancy following deletion of individual keratin genes, the entire type II or type I keratin cluster was deleted, resulting in the absence of keratin filaments in epidermal keratinocytes. The comparison of mouse keratinocyte cell lines lacking all keratins or re-expressing distinct keratin isotypes provides an excellent model to examine keratin contribution to the formation and stability of desmosomes. In support with the reported phenotype in vivo, desmosomes assemble in the absence of keratins but are endocytosed at accelerated rates. The internalization of desmosomes is regulated by PKCα-mediated desmoplakin phosphorylation, rendering epithelial sheets highly susceptible to mechanical stress in cell culture. Re-expression of the keratin pair K5/K14, inhibition of PKCα activity, or blocking of endocytosis reconstituted both desmosome localization at the plasma membrane and epithelial adhesion. The data support a model whereby K5/K14 sequesters RACK1, which can bind PKCα and thereby limits DP phosphorylation, promoting desmosome stability/maintenance and intercellular adhesive strength. To investigate the isotype-specific function of keratins, the respective contribution of K5/K14 or K6/K17 to desmosome adhesion, upon their stable re-expression in keratinocytes lacking all keratins was analyzed. This revealed that K5/K14 support stable desmosomes, whereas expression of “wound healing” keratins K6/K17 induce PKCα-mediated desmosome disassembly and subsequent destabilization of epithelial sheets accompanied by faster wound closure. Furthermore, analysis of adherens junctions and actin organization in keratin-free keratinocytes demonstrated a role of keratins in reorganization of the actin cytoskeleton and maturation of adherens junctions.
This study identified a hitherto unknown mechanism by which keratins control intercellular adhesion, with potential implications for wound healing, tumor invasion and keratinopathies, settings in which diminished cell adhesion facilitates tissue fragility and neoplastic growth.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:14941 |
| Date | 13 November 2015 |
| Creators | Loschke, Fanny |
| Contributors | Magin, Thomas, Niessen, Carien, Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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