Keratin function and regulation in tissue homeostasis and pathogenesis.

Abstract Epithelial tissues act as hubs in metabolism and communication and protect the organism against dehydration, infections, pharmacological and physical stress. Keratin intermediate filament proteins are well established as major cytoskeletal players in maintaining epithelial integrity. More recently, an involvement of keratins in growth control and organelle functions has emerged. Disruption of the keratin cytoskeleton by mutations or its reorganization following posttranslational modifications can render epithelia susceptible to tissue damage and various stresses, while loss of keratin expression is a hallmark of epithelial-mesenchymal transition (EMT). To understand the molecular mechanisms by which keratins perform their functions remains a formidable challenge. Based on selected examples, we will discuss how cell-specific expression of keratin isotypes affects cytoarchitecture and cell behavior. Further, we ask how posttranslational modifications alter keratin organization and interactions during signaling. Next, we discuss pathomechanisms of epidermal keratin disorders in the light of novel data. Finally, we raise open questions and point out future directives.