[Platelet- derived growth factor--the construction, role and it's receptors].

CONSTRUCTION: The platelet- derived growth factor (PDGF) is a small protein which is produced by many cells. PDGF was originally identified in platelets and in serum. It is a dimeric molecule consisting of disulfide- bonded, structurally similar A- and B- polypeptide chains. There are four isoforms of PDGF: PDGF A, PDGF B, PDFG C and PDGF D. There are purified from the alpha-granules of the platelets. ROLE: PDGF is a critical regulator of mesenchymal cell migration and proliferation. It is essential for angiogenesis, embryogenesis and cancer development and progression. Clinical studies reveal that aberrant expression of PDGF and its receptors is often associated with a variety of disorders including atherosclerosis, fibroproliferative diseases of lungs and kidneys. RECEPTORS: There are two structurally related PDGF- receptors, each with its own variation in signaling mechanism. Each subunit of PDGF binds one receptor subunit, leading to receptor dimerization. The receptors are tyrosine kinases. PDGFR alpha binds all types of isoforms. PDGFR beta can bind only polypeptide B.