Platelet-Derived Growth Factor D Is Activated by Urokinase Plasminogen Activator in Prostate Carcinoma Cells

Abstract

Platelet-derived growth factors (PDGFs) regulate a diverse array of cellular processes, including cell proliferation, transformation, migration, survival, and apoptosis of mesenchymal cells, in development as well as during pathogenesis (reviewed in references 31 and 42). For over 2 decades, PDGFs were thought to exist as the homodimers PDGF AA and BB or the heterodimer PDGF AB. These PDGF dimers are processed intracellularly and secreted as active dimers that readily activate PDGF receptors (PDGFRs). Recently, two new PDGF ligands (PDGF CC and DD) were discovered that have a unique two-domain structure with an N-terminal complement subcomponent C1r/C1s, Uegf, Bmp1 (CUB) domain and a C-terminal PDGF/vascular endothelial growth factor domain. PDGF CC and DD are secreted as full-length, latent dimers, and the proteolytic removal of the CUB domain is required for the growth factor domain of PDGF CC or DD to activate the PDGF receptors (4,20,21).PDGFs exert their biological functions through the activation of dimeric receptors made up of two structurally similar protein-tyrosine kinase receptor subunits (␣␣-, ␣␤-, or ␤␤-

The uPA/uPAR system regulates the bioavailability of PDGF-DD: implications for tumour growth

“…We have addressed the possibility that cell surface bound complexes of uPA/uPAR regulate activation of PDGF-DD, partly as a result of a locally increased uPA concentration, but also by the prolonged and directed proteolytic activity of uPAR-bound uPA. Consistent with reports showing a prognostic value of uPA and uPAR in suggested PDGF-DD/PDGFRb driven pathologies such as prostate cancer (Miyake et al, 1999;Ustach and Kim, 2005), this proposed mechanism is likely to be beneficial for regulating the efficacy of PDGF-DD activation in the local milieu. Our results confirmed that the presence of uPAR increased PDGF-DD activation by uPA under certain conditions, but also showed that uPAR was not an absolute requirement for the activation to occur.…”

“…Structural determinants required for PDGF-DD activation were further explored by dissecting the importance of the putative cleavage site region. Recently, the introduction of a double mutation (R247A, R249A) in PDGF-D was shown to effectively reduce uPA-mediated activation of PDGF-DD (Ustach and Kim, 2005) and our data more specifically demonstrated that R249A alone is responsible for this reported phenomenon. However, as tPA-induced activation of PDGF-CC is confined to a conserved tribasic site, it is likely that uPA has preferences for a similar site in PDGF-DD.…”

“…In a sequence comparison between this identified region with the conserved basic stretch of amino acids in PDGF-D, processing may potentially also occur in the -R 254 KSK-site and not only in the -R 247 GR-site, recognized in the initial identification of uPA as a proteolytic activator of PDGF-DD (Ustach and Kim, 2005;Figure 1a). To establish the importance of these basic amino acids for uPA-mediated activation, an alanine scan mutagenesis analysis was performed, where substitutions in the PDGF-D(fl) chain were made as depicted (Figure 1b).…”

“…Recently, we identified the serine protease tissueplasminogen activator (tPA) as a potent activator of latent dimeric PDGF-CC (Fredriksson et al, 2004(Fredriksson et al, , 2005 and soon after, the closely related protease uPA was found to activate latent PDGF-DD (Ustach and Kim, 2005). The findings that the novel PDGFs are substrates for plasminogen activators were surprising as the function of these proteases has long been considered to be to induce plasmin-mediated proteolysis and thereby control fibrinolysis, cell migration and tissue remodelling (Mondino and Blasi, 2004).…”

“…The uPA/uPAR system has been extensively studied and its diverse functions generate a complexity strictly dependent on the microenvironment and presence of cofactors (Hoyer-Hansen et al, 1992;Simon et al, 2000;Liu et al, 2002;Ustach and Kim, 2005). On account of its low zymogenic activity, single-chain (sc) uPA is usually referred to as a 53 kDa pro-enzyme.…”