Osteopontin Protein Regulates Biomineralization, Immune Function, and Apoptosis
Measuring osteopontin protein using anti-osteopontin antibody products and ELISA as an osteopontin test
Osteopontin protein, also known as bone sialoprotein 1 (BSP-1 or BSNP), is a secreted glycoprotein originally isolated from osteoblasts. Produced as a 33 kDa nascent polypeptide, osteopontin protein can undergo thrombin cleavage and posttranslational modifications including glycosylation and phosphorylation. The gene encoding OPN1 (SPP1) is subject to alternative splicing. As a consequence, osteopontin protein isoforms have been identified that range in size from 44 kDa to 66 kDa.
In addition to its presence in preosteoblasts, osteoblasts, osteocytes, odontoblasts, and bone marrow cells, osteopontin protein expression has been detected in urine, milk, activated T cells, smooth muscle cells, kidney cells, and some tumor cells. Osteopontin protein contains an Arg-Gly-Asp (RGD) motif, which is also present in fibronectin, vitronectin, and other extracellular proteins that bind the integrin family of cell surface receptors such as avb3, a5b1, a8b1, and avb5. It is hypothesized that the RGD motif plays a functional role in processes including cell adhesion, migration, growth, and bone resorption. It also may contribute to regulation of disease processes including cancer metastasis as well as neo-angiogenesis.
Specific detection of osteopontin protein domains
Detection of specific osteopontin protein isoforms may help elucidate their roles. Toward this end, we offer a series of anti-osteopontin antibody products (monoclonal, polyclonal, and directed toward N-terminal domains), as well as osteopontin ELISA kits, that may be used in osteopontin test procedures for research studies. Distinguishing among versions of osteopontin protein may be critical to understanding the physiological or disease state it is involved in. For example, a motif that is N-terminal to the OPN thrombin cleavage site has been reported to bind to the a4 and a9 integrin family. This motif (amino acid sequence SVVYGLR in human osteopontin) has been postulated to be involved in neutrophil erosion of inflammatory cells and neutrophilic migration. Furthermore, the portion of OPN that is N-terminal to the thrombin cleavage site (referred to as OPN N-half or OPN-R) is found at higher levels in joints of rheumatoid arthritis patients. The role of OPN N-half is not clear, however, underscoring the need for further study.
Osteopontin protein has also been reported to be a ligand for CD44. This interaction does not require presence of the RGD motif. OPN interaction with CD44 has been postulated to be involved in the disease progression of lymphoid tumors and bladder carcinoma, but the mechanism remains unknown.
We offer a series of anti-ostopontin antibody products* recognizing various domains. Both polyclonal and monoclonal antibodies are available. Additionally, the osteopontin N-half ELISA kit may be used to detect the N-terminal OPN thrombin cleavage product. A summary of anti-osteopontin antibody and osteopontin test ELISA kits is presented in the illustration below.
*Offered in partnership with IBL Co., Ltd., Japan. Products sold by Clontech Laboratories are for Research Use Only. Not for use in diagnostic procedures.
|Figure 1. Anti-osteopontin antibodies and ELISA kits for quantifying osteopontin protein.|