Periostin, also known as POSTN, is a protein that is encoded by the POSTN gene in humans. These POSTN functions as a ligand for alpha-V/beta-3 and alpha-V/beta-5 integrins and supports adhesion and migration of epithelial cells. POSTN is known as a gla domain vitamin K dependant factor.
POSTN is a secreted extracellular matrix protein that has been identified in cells from the mesenchymal lineage which is osteoblasts and osteoblast-derived cells. It has been linked with the epithelial-mesenchymal transition in cancer, in addition with the differentiation of mesenchyme in the developing heart. Something that this protein shares a homology with is fasciclin I, which is a secreted cell adhesion molecule that is found in insects.
In the case of many cancers, POSTN is able to bind to integrins on cancer cells, activating Akt/PKB and FAK-mediated signalling routes. This can lead to increased cell survival, invasion, angiogenesis, metastasis, and also the epithelial-mesenchymal change. In humans and mice, POSTN can undergo unique splicing in its C terminal region, which results in specific isoforms that can be seen in a wide range of cancers, including pancreatic, colon, and breast cancer.
While POSTN plays a wide range of roles in the development of tissue for disease, it’s function in tissue remodelling as a reaction to injury is a common underlying role in these mechanisms. POSTN is upregulated in the cell fate changes process, regardless of whether they are related to changes in physiology or to pathological changes. The fact is that it has an impact on extracellular matrix structuring, tissue remodeling, and also epithelial-mesenchymal transition, all of these things can be linked to tissue healing. This therefore means that it can act as a mediator, monitoring and balancing appropriate and inappropriate responses to tissue damage.
POSTN plays a vital role in the development of heart valves and also in degenerative valvular heart disease. While POSTN is usually localized to one area in healthy heart valves, its levels are increased in infiltrated inflammatory cells and myofibroblasts in areas with atheroscleoritc and rheumatic valvular heart disease.
As a matricellular protein, POSTN is also vital for regeneration of tissue. In healthy skin, POSTN is exposed at basal levels and is expressed in the epidermis and hair follicles. It is involved in wound healing and speeding up the process.
POSTN is also associated with asthma, a fact that is used in experimental asthma medication, such as lebrikizumab.
In several types of cancer, it was reported that over-expression of POSTN was found, more frequently this was found in the environment of tumor cells. It has most recently been suggested that POSTN is a component of the extracellular matrix expressed by fibroblasts in normal tissues, and also in stomas of tumors. Studies have shown that the metastatic colony creation requires the induction of POSTN in the foreign stoma by infiltrating cancer cells. POSTN is often unregulated in lung fibroblasts, for instance.