Vimentin is an intermediate filament composed of protein that strengthens the cytoskeleton. In addition, it is found in the plasma of certain cells, such as smooth muscle cells and endothelial cells. In addition, because soft tissue tumors produce more vimentin, medicine uses it as a marker for neoplasms.
What is vimentin?
Vimentin is one of the intermediate filaments (filamenta intermedialia) found in the cytoskeleton and, in addition, exists in the plasma of certain cells. Intermediate filaments are small structures that contribute to the stability of cells. In addition to vimentin, other types exist; they can be grouped into five types – vimentin belongs to type III, which also includes desmin, peripherin and gliafilament protein (GFAP). Vimentin appears to have a high functional similarity to desmin in particular. It is possible that desmin can take over the role of desmin in early developmental stages when the organism does not form this protein structure due to a genetic defect. The extent to which these results, which researchers obtained in animal experiments, can be transferred to humans has not yet been conclusively clarified. Mice lacking the vimentin gene show only minor physiological abnormalities, for example in the form of incorrect alignment of the muscle fibers. Overall, there is still a lot of research to be done on the biomolecule. Vimentin is not only found in the human body, but also in all other vertebrates.
Anatomy and structure
A single vimentin particle is composed of 465 amino acids. In its primary structure, the amino acids are strung together as a long chain, with peptide bonds acting as couplings between each two building blocks. The sequence depends on the specifications laid down in the DNA; in humans, the genes encoding vimentin are located on the tenth chromosome. In the human body, however, vimentin in its final form does not exist as a one-dimensional chain. Therefore, the macromolecule subsequently folds and gradually assumes a spatial structure. The shape depends on the physical properties of the amino acids used, which differ from each other only with respect to their residual group and otherwise follow the same structure. In the secondary structure, the amino acid chain folds and solidifies with the help of hydrogen bonds, and enzymes can support the process. In this process, vimentin takes the form of an α-helix, which is stabilized in its tertiary structure by additional bonds between the residues of the amino acids. A stretched section remains at the head and tail ends of the particle. Only in its completed spatial shape does the protein structure possess its characteristic properties, which include specific interactions with other molecules. Vimentin represents a dimer, as a completed molecule is composed of two similar subunits.
Function and tasks
Intermediate filaments such as vimentin strengthen the cytoskeleton and the shape of the cell as a whole, and in this way contribute to the stability of the cell. The cytoskeleton, or cellular skeleton, is an adaptable structure and can expand, restructure, or degrade into specific areas of the cell as needed. This flexibility allows the cytoskeleton to support movements of the entire cell. In addition, the structure serves as a transport pathway; like the endoplasmic reticulum, the cytoskeleton thus contributes to the distribution of substances within the cell. In addition to intermediate filaments, the cytoskeleton has two other important components on which it depends as a building substance. These are the tubular T-tubules on the one hand and actin filaments on the other. Vimentin is also found in the plasma of certain cells. These include smooth muscle cells, for example. Smooth muscle surrounds organs and occurs as a contractile unit in the walls of blood vessels. Vimentin, together with desmin, stabilizes the fibrils of muscle fibers, which consist primarily of actin and myosin – these are also found in striated muscle. Endothelial cells are another example of vimentin carriers. They coat the interior of hollow organs of the lymphatic system as well as blood vessels. Both cell types arise from the mesenchyme, i.e. from embryonic connective tissue. Another function of vimentin is to protect the cell nucleus, the endoplasmic reticulum and mitochondria from mechanical overload.
Diseases
Medicine uses vimentin as a marker to detect certain tumors that produce more vimentin than other tissues. Elevated levels may indicate neoplasms in soft tissue, which includes muscle, connective tissue, and fat. Sarcomas can occur in these areas. These are malignant neoplasms that grow from mesenchymal cells and are not only soft tissue sarcomas, but can in principle also affect bone or cartilage. Sarcomas can be divided into numerous subtypes: For example, if it grows from smooth muscle, it is a leiomyosarcoma, which can spread throughout the body primarily via the blood. In contrast, fibrosarcoma arises from connective tissue and rarely occurs, while liposarcoma originates in fatty tissue. One-fifth of all malignant soft tissue tumors are liposarcomas; they arise particularly frequently in the retroperitoneal space, which lies between the posterior abdominal wall and part of the ‘peritoneum (the parietal peritoneum), as well as on the back and thigh. Treatment options include, in principle, surgical excision, radiotherapy and/or chemotherapy, all of which aim to destroy the tumor. However, depending on the location, individual risks and type of neoplasm, not all treatment options are indicated in every case. Even with successful treatment, physicians recommend regular follow-up examinations to detect recurrences at an early stage.
