Osteopontin

• OMIM: 166490
• UniProt: P10451

Osteopontin (OPN ) ( Gen: SPP1 ) is a protein found in all higher mammals, which is involved in the maintenance of bone substance and some immune processes. It binds hydroxyapatite and provides the basic structure (matrix) for bone, but also for kidney stones.

It is encoded by a gene of the same name, located in the long arm of human chromosome 4q. Osteopontin belongs to the family of so-called " siblings " (small integrin binding ligand N -linked glycoprotein ), with whose members it has genetic and biochemical similarities.

Osteopontin was discovered as a glycoprotein in 1986 in osteoblasts and consists of about 300 amino acids.

Osteo the prefix indicates that the protein is produced in the bone tissue. Osteopontin as an extracellular structural protein is a part of the bone marrow and bone matrix (see also the bones). Synonymous terms of the protein are sialoprotein I and 44K BPP (English bone phosphoprotein ). A functional characteristic is the ability to bind to integrins. This property is mediated by the RGD motif.

Osteopontin is produced in a variety of tissue types, such as osteoblasts, osteocytes, in the inner ear, brain, kidney, placenta, odontoblasts, some bone marrow cells, cartilage cells, macrophages, in smooth muscle and endothelial cells. The formation of the osteopontin is stimulated by calcitriol ( 1,25- dihydroxy -vitamin D3).

Osteopontin may be overexpressed in various cancers such as lung cancer, breast cancer, colon cancer, stomach cancer, ovarian cancer, skin cancer and pleural mesothelioma. It is also involved in the development of kidney stones.

Tumors do not grow in isolation, they need new blood vessels to supply oxygen, nutrients, and supporting tissues. Signals which promote tumor growth, mediated through long distances throughout the body. One of the neurotransmitters involved therein is the protein osteopontin. Cancer patients with aggressive tumors have very high Osteopontinwerte in blood serum.

In multiple sclerosis, especially in the relapsing form, osteopontin seems to play an important role. It was found in studies that Osteopontinwerte are just before and increased during an attack. In addition, the protein seems to have a positive effect on the survival of autoimmune T cells, which are blamed for the disease by inhibiting the natural apoptosis of these cells.