Structure and biological function

PERIOSTIN (UniProtKB - Q15063), also known as osteoblast specific factor 2 (OSF-2), is a cell adhesion protein belonging to the fasciclin domain-containing protein family. It consists of 836 amino acids (aa) starting with a 21 aa long signaling sequence, followed by an Emilin-like domain rich in cysteine, four repeated fasiclin 1 and a C-terminal variable domain, which is different among the 7 splice variants (isoforms) in humans. PERIOSTIN is expressed during ontogenesis and especially in adult connective tissues submitted to mechanical stress such as bone, tendons, heart valves, skin and the periodontal ligaments. Further, it is widely expressed in aorta, stomach, lower gastrointestinal tract, placenta, uterus, thyroid and breast tissue. In bone, PERIOSTIN directly interacts with collagen type I, fibronectin, Notch 1, tenascin-C and BMP-1, resulting in enhanced proteolytic activation of lysyl oxidase for collagen cross-linking, thus stabilising the bone matrix. Next to its role in developing, maintaining and repairing of tissue, PERIOSTIN plays a vital role in tumorigenesis by interacting with various cell-surface receptors and signaling pathways e.g. resulting in inactivation of integrin- mediated signaling, leading to promoting cell adhesion and motility which is of relevance for tumor progression and metastasis.