Abstract
Vimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn’s disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspectives.
Highlights
Campus D2 2, Leibniz-Institut für Neue Materialien gGmbH (INM) and Experimental Physics, NT Faculty, Department of Medical Biochemistry and Microbiology, Uppsala University, 75237 Uppsala, Sweden
This indicates that different domains of vimentin might have evolved independently of each other, and would have clearly defined, and distinct functions, which might contribute to the functional diversity of this protein
Vimentin has been shown to promote factors that can enhance integrin activation, such as the clustering and ligand affinity for β3 integrins [161] and ligand affinity of β1 integrins [162]. These studies suggest that vimentin promotes integrin clustering and activation, and thereby controls the organisation and dynamics of focal adhesions. This concept is supported by a number of additional observation, e.g., vimentin stabilises cell-matrix adhesions that are subjected to shear stress [163]; the focal contacts of fibroblasts from vimentin-null mouse cells are more irregular, less distinct and less mechanically stable, compared to wild-type control cells [140]; and thick vimentin bundles have been associated with large focal contacts, while decreased vimentin levels result in reduced sizes of focal contacts [163]
Summary
The early studies of vimentin showed that the protein was present in bovine eye lenses [76,77]. In the Human Protein Atlas database, the vimentin protein was found to be expressed in the majority of the 44 tissues analysed, 14 of which showed high levels of vimentin expression. Vimentin forms a network that surrounds the nucleus It extends throughout the entire cytoplasm, with shorter soluble forms more abundant in the cell periphery [8,23,84]. The organisation of the filamentous intracellular network of vimentin varies in different cells. It can form relatively homogenous distributions within the cytoplasm of primary, senescent or non-dividing mesenchymal cells, and is rapidly reorganised towards the nucleus upon exposure to PDGF, oncogenes or viruses [87,88]. The many different forms of vimentin can result in binding of different types of associated proteins and protein complexes
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