Periostin ( POSTN ), also known as OSF2 (osteoblast specific factor 2), is a heterofunctional secreted extracellular matrix (ECM) protein comprised of four fasciclin domains that promotes cellular adhesion and movement, as well as collagen fibrillogenesis. Postn is expressed in unique growth centers during embryonic development where it facilitates epithelial-mesenchymal transition (EMT) of select cell populations undergoing reorganization. In the adult, Postn expression is specifically induced in areas of tissue injury or areas with ongoing cellular re-organization. In the adult heart Postn is induced in the ventricles following myocardial infarction, pressure overload stimulation, or generalized cardiomyopathy. Although the detailed function of Postn is still unclear, Postn-integrin interaction is thought to be involved in tumor development. Postn is frequently overexpressed in various types of human cancers, stimulating metastatic growth by promoting cancer cell survival, invasion and angiogenesis, and can be a useful marker to predict the behavior of cancer.
Periostin (POSTN,PN),originally named as osteoblast-specific factor 2 (OSF-2),is a 90-kDa secreted protein which is now classified as a matricellular protein. It is present in a wide variety of normal adult tissues and fetal tissues,and has a role in bone,tooth and heart development and function. Studies show that periostin is overexpressed in a broad range of human cancer types,includidng lung,ovary,breast and colon cancers. Recent evidence reveals that periostin is expressed by fibroblasts in the normal tissue and in the stroma of the primary tumour,and it is required to allow cancer stem cell maintenance.
Protein Phosphatase 2A (PP2A) is an enzyme that removes phosphates covalently attached to serine and threonine residues in proteins. It contains three subunits, a catalytic subunit C (PP2Ac), an assembly/structural subunit A (PP2Aa), and a regulatory subunit B (PP2Ab). PP2A is a ubiquitous enzyme that plays a role in regulating many cellular activities varying from ion transport in erythrocytes to suppressing tumor growth. Binding of the SV40 small T antigen to the PP2A phosphatase complex is known to cause oncogenic transformation.
PPA1 (Inorganic pyrophosphatase 1, also PPase and IOPPP) is a 32-36 kDa cytoplasmic member of the PPase family of enzymes. It is ubiquitously expressed, and acts on di-(or pyro) phosphate, generating orthophosphate in a Mg+-dependent manner. This activity can both generate energy for cells, or in the case of osteoblasts, provide raw material for calcification. The consumption of pyrophosphate may also remove inhibitors of enzymes such as guanylyl cyclase, and PPA1 itself is also reported to stimulate gene expression. Human PPA1 is 289 amino acids (aa) in length. There is one pyrophosphatase domain between aa 42-255, and two utilized acetylation sites at Lys 57 and Lys228. PPA1 is known to form homodimers. There is one potential alternative start site at Met46. Full-length human PPA1 shares 94% aa sequence identity with mouse PPA1.
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