Osteopontin information and research

Osteopontin produced by cells of the immune system, epithelial tissue, smooth muscle cells, osteoblasts and tumor cells has been implicated in various pathophysiological functions such as cell binding, spreading and migration, and tumor metastasis.

Control of osteopontin signaling and function by post-translational phosphorylation and protein folding.
J Cell Biochem. 2007 Nov 1; Kazanecki CC, Uzwiak DJ, Denhardt DT. Division of Life Sciences, Rutgers University, Piscataway, New Jersey, USA.
Osteopontin plays roles in a variety of cellular processes from bone resorption and extracellular matrix (ECM) remodeling to immune cell activation and inhibition of apoptosis. Because it binds receptors (integrins, CD44 variants) typically engaged by ECM molecules, Osteopontin acts as a "soluble" ECM molecule. A persistent theme throughout the characterization of how Osteopontin functions has been the importance of phosphorylation. The source of the Osteopontin used in specific experiments and the location of modified sites is an increasingly important consideration for Osteopontin research. We review briefly some of the ways Osteopontin impacts on the biology of mammalian systems with an emphasis on the importance of serine phosphorylation in modulating its signaling ability. We describe experiments that support the hypothesis that differences in the post-translational phosphorylation of Osteopontin expressed by different cell types regulate how it impacts on target cells. Analyses of Osteopontin potential secondary structure reveal a possible beta-sheet conformation that offers an interpretation of certain experimental observations, specifically the effect of thrombin cleavage; it is consistent with an interaction between the C-terminal region of the protein and the central integrin-binding RGD sequence.

Role of osteopontin in regulating hepatic inflammatory responses and toxic liver injury.
Expert Opin Drug Metab Toxicol. 2007 Aug; Ramaiah SK, Rittling S. Texas A & M University, Department of Pathobiology, College of Veterinary Medicine, MS-4467, College Station, TX 77843-4467, USA.
Osteopontin is known to bind to integrins expressed on macrophages through the arginine-glycine-aspartic acid (RGD) motif and promote migration of cells resulting in granuloma. In the liver, it has been reported that hepatic Kupffer cells secrete Osteopontin facilitating macrophage infiltration in necrotic areas following carbon tetrachloride liver toxicity. Recent work has underlined the importance of Osteopontin as a pivotal cytokine/chemokine in the generated hepatic neutrophil response during early phase alcoholic liver injury. Increased hepatobiliary OPN expression correlated well with higher neutrophil infiltration in a rat model of alcoholic steatohepatitis. In the same model of alcoholic steatohepatitis, higher hepatic expression of Osteopontin in females was attributed to the higher neutrophil infiltration and consequent higher female sensitivity to liver damage. Osteopontin as a potential biomarker for inflammatory liver disease has also been recently assessed. This review will focus on studies demonstrating the role of Osteopontin in mediating hepatic inflammation (neutrophils, monocytes/macrophages and lymphocytes) and the ensuing liver toxicity.

tongkat ali home information