Periostin, also known as OSF-2, is a secreted matricellular protein with functions in extracellular matrix formation, cell migration, and inflammation (1). It is secreted as a 90 kDa monomer that can aggregate into >170 kDa higher-order multimers (2). Periostin contains an N-terminal EMI domain followed by four tandem FAS1 domains (3). Alternative splicing generates additional isoforms of rat Periostin with various deletions in the C-terminal region following the FAS domains. This recombinant protein corresponds to the isoform of rat Periostin that lacks aa 785-812. It shares 90% and 97% aa sequence identity with comparable isoforms of human and mouse Periostin, respectively. Periostin is expressed by mesenchymal cells such as vascular smooth muscle cells, fibroblasts, osteoblasts, and odontoblasts in developing teeth (4-7). It is up-regulated in many carcinomas (2, 8). Periostin binds to Integrins alpha _v beta ₃ and alpha _v beta ₅ (2, 9), leading to enhanced cell adhesion and cell migration (2, 5, 6). It enhances Fibronectin and Collagen I production and promotes collagen fibrillogenesis (10, 11). It also induces epithelial-mesenchymal transition, tumor growth, invasion, and metastasis (9). Periostin induces the expression of VEGF R2 on endothelial cells and VEGF-C in tumor cells, and it can induce tumor lymphangiogenesis (8, 12). Periostin plays an important role in heart valve development and tissue healing after myocardial infarction (5, 13, 14). In asthma, it is
up-regulated in bronchial epithelium and plays both destructive and protective roles by inducing eosinophil infiltration and inhibiting goblet cell metaplasia and mucus production, respectively (15, 16).