Vimentin has been shown to be involved in wound healing, but its functional contribution to this process is poorly understood. Here we describe a previously unrecognized function of vimentin in coordinating fibroblast proliferation and keratinocyte differentiation during wound healing. Loss of vimentin led to a severe deficiency in fibroblast growth, which in turn inhibited the activation of two major initiators of epithelial–mesenchymal transition (EMT), TGF-β1 signaling and the Zinc finger transcriptional repressor protein Slug, in vimentin-deficient (VIM^−/−) wounds. Correspondingly, VIM^−/− wounds exhibited loss of EMT-like keratinocyte activation, limited keratinization, and slow reepithelialization. Furthermore, the fibroblast deficiency abolished collagen accumulation in the VIM^−/− wounds. Vimentin reconstitution in VIM^−/− fibroblasts restored both their proliferation and TGF-β1 production. Similarly, restoring paracrine TGF-β–Slug–EMT signaling reactivated the transdifferentiation of keratinocytes, reviving their migratory properties, a critical feature for efficient healing. Our results demonstrate that vimentin orchestrates the healing by controlling fibroblast proliferation, TGF-β1–Slug signaling, collagen accumulation, and EMT processing, all of which in turn govern the required keratinocyte activation. Significance The central concept in this study is that a major cytoskeletal component, vimentin, acts as a signal integrator during wound healing, operating in both signal-triggering and signal-receiving cells. This is a previously unreported concept for intermediate filaments, with an evolving paradigm according to which intermediate filaments emerge as integrators of regeneration with specific functions in the particular tissues for which individual intermediate filaments are characteristic. Our study reveals the underlying molecular and cellular control functions of vimentin in vimentin-dependent epithelial–mesenchymal transition, regeneration, and healing.

It took more than 100 years before it was established that the proteins that form intermediate filaments (IFs) comprise a unified protein family, the members of which are ubiquitous in virtually all differentiated cells and present both in the cytoplasm and in the nucleus. However, during the past 2 decades, knowledge regarding the functions of these structures has been expanding rapidly. Many disease-related roles of IFs have been revealed. In some cases, the molecular mechanisms underlying these diseases reflect disturbances in the functions traditionally assigned to IFs, i.e., maintenance of structural and mechanical integrity of cells and tissues. However, many disease conditions seem to link to the nonmechanical functions of IFs, many of which have been defined only in the past few years.

Nuclear lamins form the major structural elements comprising the nuclear lamina. While loss of nuclear structural integrity has been implicated as a key factor in the lamin A gene mutations causing laminopathies, the normal regulation of lamin A/C (LA/C) assembly and organization in interphase cells is still undefined. We assumed phosphorylation to be a major determinant, identifying 21 prime interphase phosphorylation sites, with 8 high turnover sites. The roles of these latter sites were examined by site-directed mutagenesis, followed by detailed microscopic analysis, including fluorescence recovery after photobleaching, fluorescence correlation spectroscopy, and nuclear extraction techniques. Results reveal three phosphorylation regions, each with dominant sites, together controlling LA/C structure and dynamics. Interestingly, two of these interphase sites are hyperphosphorylated in mitotic cells and one is within the sequence missing in progerin of the Hutchinson Gilford Progeria Syndrome. A model is presented where different phosphorylation combinations will yield markedly different effects on the assembly, subunit turnover, and mobility of LA/C between and within the lamina, the nucleoplasm, and the cytoplasm of interphase cells.

Intermediate filaments (IFs) comprise a diverse group of flexible cytoskeletal structures, the assembly, dynamics, and functions of which are regulated by posttranslational modifications. Characteristically, the expression of IF proteins is specific for tissues, differentiation stages, cell types, and functional contexts. Recent research has rapidly expanded the knowledge of IF protein functions. From being regarded as primarily structural proteins, it is now well established that IFs act as powerful modulators of cell motility and migration, playing crucial roles in wound healing and tissue regeneration, as well as inflammatory and immune responses. Although many of these IF-associated functions are essential for tissue repair, the involvement of IF proteins has been established in many additional facets of tissue healing and regeneration. Here, we review the recent progress in understanding the multiple functions of cytoplasmic IFs that relate to cell motility in the context of wound healing, taking examples from studies on keratin, vimentin, and nestin. Wound healing and regeneration include orchestration of a broad range of cellular processes, including regulation of cell attachment and migration, proliferation, differentiation, immune responses, angiogenesis, and remodeling of the extracellular matrix. In this respect, IF proteins now emerge as multifactorial and tissue-specific integrators of tissue regeneration, thereby acting as essential guardian biopolymers at the interface between health and disease, the failing of which contributes to a diverse range of pathologies.

Lamin A/C is part of the nuclear lamina, a meshwork of intermediate filaments underlying the inner nuclear membrane. The lamin network is anchoring a complex set of structural and linker proteins and is either directly or through partner proteins also associated or interacting with a number of signaling protein and transcription factors. During mitosis the nuclear lamina is dissociated by well established phosphorylation- dependent mechanisms. A-type lamins are, however, also phosphorylated during interphase. A recent study identified 20 interphase phosphorylation sites on lamin A/C and explored their functions related to lamin dynamics; movements, localization and solubility. Here we discuss these findings in the light of lamin functions in health and disease.