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Proteins known as intermediate filaments help to provide structure to cells, and are involved in cell movement. Vimentin is one such protein, and it is often found in mesenchymal cells in eukaryotes, or cells that contain a distinct nucleus. Mesenchymal cells are essential to growth and development since they can differentiate into other cell types. This protein is found not only in eukaryotic cells, but also in bacteria, where it helps form the cytoskeleton.
As part of the cytoskeleton, vimentin plays a vital role in holding cellular structures, called organelles, in place. This protein has a flexible nature, allowing it to respond to mechanical stress. It interacts with other structural proteins, like microtubules, to make the cell rigid and sturdy. Studies performed on cells without vimentin found that they were functional, but very easily damaged when exposed to pressure.
Moving molecules inside of the cell is essential to proper functioning. In the case of at least one molecule, low-density lipoprotein (LDL) cholesterol, vimentin assists in transport duties. This filament protein has been shown to help move LDL cholesterol from organelles called lysosomes to other cell areas. Cells rely on this transport to utilize LDL cholesterol by incorporating it into chemical reactions.
Structural proteins can sometimes be found outside of cells, where they can assist in such actions as healing wounds. In the event of an injury, white blood cells known as macrophages move to the site of the damage as a normal part of the body's immune response. Macrophages have been found to produce vimentin and release it outside into the site, known as the extracellular matrix. These cells are induced to secrete this protein by inflammatory proteins called cytokines. As the wound is repaired and sealed, anti-inflammatory cytokine signals cause macrophages to stop producing intermediate filaments.
Mesenchymal cells are capable of movement in the body, due in part to their use of vimentin. In some forms of cancer, cells change from epithelial cells to mesenchymal cells, allowing them to spread through the body. As a result, the expression of this protein is used as a tumor marker for some cancers, which confirms the presence of a tumor. Antibodies that bind to this protein can help doctors locate tumors in this way.
In addition to being a tumor marker, cancer therapies that target this structural protein have been created. Compounds such as Withaferin-A destroy tumor cells with high levels of this protein when they are locally administered. In some studies, nearby healthy cells that did not contain as much vimentin were left unharmed.