Keratins are intermediate filament–forming proteins that provide mechanical support and fulfill a variety of additional functions in epithelial cells. In 1982, a nomenclature was devised to name the keratin proteins that were known at that point. The systematic sequencing of the human genome in recent years uncovered the existence of several novel keratin genes and their encoded proteins. Their naming could not be adequately handled in the context of the original system. We propose a new consensus nomenclature for keratin genes and proteins that relies upon and extends the 1982 system and adheres to the guidelines issued by the Human and Mouse Genome Nomenclature Committees. This revised nomenclature accommodates functional genes and pseudogenes, and although designed specifically for the full complement of human keratins, it offers the flexibility needed to incorporate additional keratins from other mammalian species.
Preface
Intermediate filaments (IFs) are cytoskeletal and nucleoskeletal structures that provide mechanical and stress-coping resilience to cells, contribute to subcellular and tissue-specific biological functions, and facilitate intracellular communication. IF proteins, including nuclear lamins and cytoplasmic keratins, vimentin, desmin, neurofilaments, and glial fibrillary acidic protein, undergo various functionally important post-translational modifications (PTMs). Proteomic advances highlight the enormous complexity of IF PTMs, which include phosphorylation, glycosylation, sumoylation, acetylation, and prenylation, as well as their ability to regulate IF proteins, and are likely to reveal novel modifications. We would like to keep the original statement, since the revised version seems to imply that proteomic advances provide insight into the ability of PTMs to regulate IF proteins, which is not the case. Future studies will need to characterize their on–off mechanisms, cross-talk, and utility as biomarkers and targets for diseases involving the IF cytoskeleton.
Simple epithelial keratins (SEKs) are found primarily in single-layered simple epithelia and include keratin 7 (K7), K8, K18-K20, and K23. Genetically engineered mice that lack SEKs or overexpress mutant SEKs have helped illuminate several keratin functions and served as important disease models. Insight into the contribution of SEKs to human disease has indicated that K8 and K18 are the major constituents of Mallory-Denk bodies, hepatic inclusions associated with several liver diseases, and are essential for inclusion formation. Furthermore, mutations in the genes encoding K8, K18, and K19 predispose individuals to a variety of liver diseases. Hence, as we discuss here, the SEK cytoskeleton is involved in the orchestration of several important cellular functions and contributes to the pathogenesis of human liver disease.
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