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Platelet-derived growth factor (PDGF) was originally identified as a constituent of blood serum and subsequently purified from human platelets. PDGF ligand is a dimeric molecule consisting of two disulfide-bonded chains from A-, B-, Cand D-polypeptide chains, which combine to homoand heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors. PDGF is a potent mitogen and chemoattractant for mesenchymal cells and also a chemoattractant for neutrophils and monocytes. In radiation oncology, PDGF are important for several pathologic processes, including oncogenesis, angiogenesis and fibrogenesis. Autocrine activation of PDGF was observed and interpreted as an important mechanism involved in brain and other tumors. PDGF has been shown to be fundamental for the stability of normal blood vessel formation, and may be essential for the angiogenesis in tumor tissue. PDGF also plays an important role in the proliferative disease, such as atherosclerosis and radiation-induced fibrosis, regarding its proliferative stimulation of fibroblast cells. Moreover, PDGF was also shown to stimulate production of extracellular matrix proteins, which are mainly responsible for the irreversibility of these diseases. This review introduces the structural and functional properties of PDGF and PDGF receptors and discusses the role and mechanism of PDGF signaling in normal and tumor tissues under different conditions in radiation oncology. Background PDGF was originally identified as a constituent of whole blood serum that was absent in cell-free plasma [1,2] and subsequently purified from human platelets [3,4]. Although the α-granules of platelets are a major storage site for PDGF, recent studies have shown that PDGF can be synthesized by a number of different cell types such as macrophages, epithelial and endothelial cells [5-8]. Studies have shown that PDGF has important physiologic functions in organ development [9,10]. PDGF has also been implicated in a wide variety of pathological processes, including fibrosis, atherosclerosis, glomerulonephritis and aggressive fibromatosis [11-15]. Moreover, aberrant production of PDGF and autocrine stimulation may be an important mechanism in the neoplastic conversion of PDGF receptor-positive cells [16-18]. Here, we point out the most important features of PDGF and PDGF receptors concerning their roles in radiation oncology. PDGF structure and signaling PDGF is a disulfide-linked dimer of two related polypeptide chains, designated A, B, C and D, which are assembled as heterodimers (PDGF-AB) or homodimers (PDGFAA, PDGF-BB, PDGF-CC and PDGF-DD) [19-21]. PDGF exerts its biological activity by binding to structurally similar PDGF receptors (PDGFR-α and -β). The PDGFR-α Published: 11 January 2007 Radiation Oncology 2007, 2:5 doi:10.1186/1748-717X-2-5 Received: 15 November 2006 Accepted: 11 January 2007 This article is available from: http://www.ro-journal.com/content/2/1/5 © 2007 Li et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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