Molecular SIBLINGs in Health and Disease
What is Osteopontin?
Osteopontin (OPN) is a protein that has also been called bone sialoprotein-1, bone phosphoprotein, tumor-secreted phosphoprotein 1, early T-lymphocyte activation-1, transformation-associated phosphoprotein, uropontin, nephropontin  which reflects identification of the molecule with distinct biological steps and tissues. OPN is expressed in multiple tissue types and once secreted can bind to cell surface receptors such as αVβ3, α4β1, α9β1 integrins, CD44 as well as to extracellular matrix components such as collagen and matrix metalloproteinases. 
Osteopontin belongs to the SIBLING family of five identically oriented tandem genes within a 375,000 bp region on chromosome 4. Underlying OPN physiology are sentinel areas of high research interest, including malignant disease, neovascularization and angiogenesis, wound healing, innate and adaptive immunity, embryo implantation, hypoxia, stress response, and apoptosis. One can identify in pathological states where osteopontin plays a role, the common theme of stress response/chronic immune activation. Chronic immune activation and inflammation are ‘hot’ topics of research and are associated with a number of pathologies such as autoimmune disease, cardiovascular disease, cancer, aging, diabetes, obesity and metabolic syndrome.