Keratin Isotypes Control Desmosome Stability and Dynamics through PKCα

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 a major determinant of adhesive strength. In support, wound healing is characterized by a transient decrease in desmosomal adhesion accompanied by increased expression of keratins K6/K16/K17 at the expense of K1/K10. The significance of altered keratin expression for desmosomal composition and adhesion remains incompletely understood at a mechanistic and functional level. Here, we investigated the respective contribution of K5/K14 or K6/K17 to desmosome adhesion, on their stable re-expression in keratinocytes lacking all keratins. This revealed that K5/K14 filaments support stable desmosomes, whereas “wound healing” keratins K6/K17 induce elevated protein kinase C alpha–mediated desmosome disassembly and subsequent destabilization of epithelial sheets. Moreover, our data suggest that K5/K14 sequester protein kinase C alpha in the cytoplasm, whereas K6/K17 or the absence of all keratins enables protein kinase C alpha translocation to the plasma membrane and induction of desmosome disassembly. Gain- and loss-of-function experiments support a major role of K5 in desmosome stability control via protein kinase C alpha. Our data show that keratin isotypes differently and specifically regulate wound healing and invasion by modulating intercellular adhesion

Contribution of keratins to junction dynamics and stability in keratinocytes: Contribution of keratinsto junction dynamics and stability in keratinocytes

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

Structure-property relations in multiblock copoly(ether-urea)s studied by SAXS, DSC and thermo-mechanical techniques

3 páginas, 4 figuras, 1 tabla.-- Trabajo presentado a la 1ª Conferencia Europea sobre Synchrotron Radiation in Materials Science celebrada en Chester (UK/1994).The morphology of four copoly(ether-urea)s was studied by using synchrotron radiation in order to relate the changes of morphology with temperature to the transitions in mechanical and thermal properties. Very different behaviour was found for copolyureas synthesised from aromatic isocyanates and from aliphatic isocyanates. Whilst the former retain the phase separated structure above the hard segment glass transition, the latter did not show evidence of phase separation above the hard segment transition and it did not reappear on cooling.Peer reviewe

Keratins Mediate Localization of Hemidesmosomes and Repress Cell Motility

The keratin (K)–hemidesmosome (HD) interaction is crucial for cell-matrix adhesion and migration in several epithelia, including the epidermis. Mutations in constituent proteins cause severe blistering skin disorders by disrupting the adhesion complex. Despite extensive studies, the role of keratins in HD assembly and maintenance is only partially understood. Here we address this issue in keratinocytes in which all keratins are depleted by genome engineering. Unexpectedly, such keratinocytes maintain many characteristics of their normal counterparts. However, the absence of the entire keratin cytoskeleton leads to loss of plectin from the hemidesmosomal plaque and scattering of the HD transmembrane core along the basement membrane zone. To investigate the functional consequences, we performed migration and adhesion assays. These revealed that, in the absence of keratins, keratinocytes adhere much faster to extracellular matrix substrates and migrate approximately two times faster compared with wild-type cells. Reexpression of the single keratin pair K5 and K14 fully reversed the above phenotype. Our data uncover a role of keratins, which to our knowledge is previously unreported, in the maintenance of HDs upstream of plectin, with implications for epidermal homeostasis and pathogenesis. They support the view that the downregulation of keratins observed during epithelial–mesenchymal transition supports the migratory and invasive behavior of tumor cells