An increase in autophagy characterizes pancreatic carcinogenesis, but the signals that regulate this process are incompletely understood. Because canonical Wnt/β-catenin signaling is necessary for the transition from early to advanced pancreatic intraepithelial neoplasia (PanIN) lesions, we assessed whether Wnt ligands and endogenous inhibitors of Wnt signaling modulate autophagy. In this study, canonical Wnt3a ligand induced autophagy markers and vacuoles in murine PanIN cells. Furthermore, pigment epithelium-derived factor (PEDF), a secreted glycoprotein known for its anti-tumor properties, blocked Wnt3a-directed induction of autophagy proteins. Autophagy inhibition was complemented by reciprocal regulation of the oxidative stress enzymes, superoxide dismutase 2 (SOD2) and catalase. Transcriptional control of Sod2 expression was mediated by PEDF-induced NFκB nuclear translocation. PEDF-dependent SOD2 expression in PanIN lesions was recapitulated in a murine model of PanIN formation where PEDF was deleted. In human PanIN lesions, co-expression of PEDF and SOD2 was observed in the majority of early PanIN lesions (47/50, 94%), whereas PEDF and SOD2 immunolocalization in high-grade human PanIN-2/3 was uncommon (7/50, 14%). These results indicate that PEDF regulates autophagy through coordinate Wnt signaling blockade and NFκB activation.
PEDF is a secreted glycoprotein that is widely expressed by multiple organs. Numerous functional contributions have been attributed to PEDF with antiangiogenic, antitumor, anti-inflammatory, and neurotrophic properties among the most prominent. The discovery that null mutations in the PEDF gene results in Osteogenesis Imperfecta Type VI, a rare autosomal recessive bone disease characterized by multiple fractures, highlights a critical developmental function for this protein. This ultra-rare orphan disease has provided biological insights into previous studies that noted PEDF’s effects on various stem cell populations. In addition to bone development, PEDF modulates resident stem cell populations in the brain, muscle, and eye. Functional effects on human embryonic stem cells have also been demonstrated. An overview of recent advances in our understanding by which PEDF regulates stem cells and their potential clinical applications will be evaluated in this review.
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