Abstract
The platelet-derived growth factors (PDGF A, B, C, and D) and their receptors (α-PDGFR and β-PDGFR) play an indispensible role in physiologic and pathologic conditions, including tumorigenesis. The transformative β-PDGFR is overexpressed and activated during prostate cancer progression, but the identification and functional significance of its complementary ligand have not been elucidated. This study examined potential oncogenic functions of β-PDGFR ligands PDGF B and PDGF D, using nonmalignant prostate epithelial cells engineered to overexpress these ligands. In our models, PDGF D induced cell migration and invasion more effectively than PDGF B in vitro. Importantly, PDGF D supported prostate epithelial cell tumorigenesis in vivo and showed increased tumor angiogenesis compared with PDGF B. Autocrine signaling analysis of the mitogen-activated protein kinase and phosphoinositide 3-kinase pathways found PDGF D-specific activation of the c-jun-NH2-kinase (JNK) signaling cascade. Using short hairpin RNA and pharmacologic inhibitors, we showed that PDGFD-mediated phenotypic transformation is β-PDGFR and JNK dependent. Importantly, we made a novel finding of PDGF D-specific increase in the shedding and activation of the serine protease matriptase in prostate epithelial cells. Our study, for the first time to our knowledge, showed ligand-specific β-PDGFR signaling as well as PDGF D-specific regulation of matriptase activity and its spatial distribution through shedding. Taken together with our previous finding that matriptase is a proteolytic activator of PDGF D, this study provides a molecular insight into signal amplification of the proteolytic network and PDGF signaling loop during cancer progression.