Pigment Epithelium-derived Factor and Its Phosphomimetic Mutant Induce JNK-dependent Apoptosis and p38-mediated Migration Arrest

Abstract

Pigment epithelium-derived factor (PEDF) is a potent endogenous inhibitor of angiogenesis and a promising anticancer agent. We have previously shown that PEDF can be phosphorylated and that distinct phosphorylations differentially regulate its physiological functions. We also demonstrated that triple phosphomimetic mutant (EEE-PEDF), has significantly increased antiangiogenic activity and is much more efficient than WT-PEDF in inhibiting neovascularization and tumor growth. The enhanced antiangiogenic effect was associated with a direct ability to facilitate apoptosis of tumor-residing endothelial cells (ECs), and subsequently, disruption of intratumoral vascularization. In the present report, we elucidated the molecular mechanism by which EEE-PEDF exerts more profound effects at the cellular level. We found that EEE-PEDF suppresses EC proliferation due to caspase-3-dependent apoptosis and also inhibits migration of the EC much better than WT-PEDF. Although WT-PEDF and EEE-PEDF did not affect proliferation and did not induce apoptosis of cancer cells, these agents efficiently inhibited cancer cell motility, with EEE-PEDF showing a stronger effect. The stronger activity of EEE-PEDF was correlated with a better binding to laminin receptors. Furthermore, the proapoptotic and antimigratory activities of WT-PEDF and EEE-PEDF were found regulated by differential activation of two distinct MAPK pathways, namely JNK and p38, respectively. We show that JNK and p38 phosphorylation is much higher in cells treated with EEE-PEDF. JNK leads to apoptosis of ECs, whereas p38 leads to anti-migratory effect in both EC and cancer cells. These results reveal the molecular signaling mechanism by which the phosphorylated PEDF exerts its stronger antiangiogenic, antitumor activities. Pigment epithelium-derived factor (PEDF)2 is a 46-kDa secreted glycoprotein that can act either as a neurotrophic or an antiangiogenic factor (1, 2). PEDF has been originally identified in the retina; however, it has now become evident that it is expressed throughout the human body and is constantly present in the systemic circulation (3, 4). Studies of the past decade have implicated PEDF in the pathophysiology of a wide range of angiogenesis-associated disorders, including diabetic complications (5), macular degeneration (6), and the growth of many types of solid tumors (7-10). Furthermore, the natural antiangiogenic activity of PEDF, which is far greater than that of any other known endogenously produced factor (2, 11), has turned it into a highly potent therapeutic agent for the inhibition of pathological neovascularization and, therefore, a promising tumor suppressor. To date, a number of studies have shown that exogenous administration of PEDF results in tumor regression, decreased intratumoral microvessel density, and prolonged survival in various animal cancer models (12-15). The underlying molecular mechanism of anticancer activity of PEDF has been under extensive investigation recently (13,16). Yet, the signaling pathways that mediate the effect...

The effects of PEDF on cancer biology: mechanisms of action and therapeutic potential

“…The exciting observation was that PEDF also exhibits its known survival effect on the neurons that shielded the brain from tumour-induced damage. In culture, PEDF exhibits potent antimigratory activity on human breast tumour cells 77,78 and neuroprotectant activity on neurons. These observations emphasize the dual role of PEDF as both a metastatic suppressor and a neuroprotectant in the brain.…”

“…They also showed that PEDF upregulated presenilin 1, which facilitates the association between protein tyrosine phosphatases and VEGFR1 to inhibit VEGF-induced phosphorylation of VEGFR1. Konson and co-workers 77 reported that different tumour-suppressive activities of PEDF are independently regulated by two different MAPK pathways: the JUN N-terminal kinase (JNK) pathway regulates the endothelial pro-apoptotic activity and the p38 MAPK pathway regulates antimigratory activities. The contributions of the Volpert laboratory elucidated how PEDF regulates CD95 ligand (CD95L; also known as FAS ligand) and cellular FLICE-like inhibitory protein (FLIP) to inhibit neovascularization in activated endothelial cells 66,88 .…”

“…PEDF and its variants act on intratumoural endothelial apoptosis, but in contrast to results from other groups, the Seger group reported that the variant forms do not affect the survival of cancer cells in vitro , hence they concluded that the anti-angiogenic activity of these agents is the main property of the observed antitumour effect. More recently, the same group reported the molecular mechanism by which phosphomimetic PEDF exerts more-profound effects at the cellular level by inducing JNK-dependent apoptosis and p38-mediated migration arrest 77 . More recently, Feng and co-workers 126 demonstrated that the triple phospho mimetic EEE-PEDF significantly reduced the growth and metastasis of choroidal melanoma xenografts in nude mice, and this effect was associated with inhibiting VEGF and NF-κB expression.…”

“…PEDF is a ligand of cell-surface F ATP synthase, and its 34-mer peptide region inhibits ATP production and reduces endothelial and tumour cell viability and angiogenesis 107,108 . PEDF, through interaction with a yet unknown receptor, can sequentially activate MKK3, MKK6 and p38α MAPK to inhibit cell migration 77 . FA, fatty acid; LPA, lysophosphatidic acid.…”

“…PEDF inhibits VEGF-driven angiogenesis and permeability through the regulated intracellular proteolysis of VEGFR. PEDF can activate the p38 MAPK pathway to inhibit endothelial cell migration 77 . It can also activate peroxisome proliferator-activated receptor-γ (PPARγ) through cytosolic phospholipase A2α (PLA2α) to induce the expression of TP53 , which encodes the pro-apoptotic protein p53 (REF.…”