Jennifer A. Doll

Pigment epithelium-derived factor regulates the vasculature and mass of the prostate and pancreas

Angiogenesis sustains tumor growth and metastasis, and recent studies indicate that the vascular endothelium regulates tissue mass. In the prostate, androgens drive angiogenic inducers to stimulate growth, whereas androgen withdrawal leads to decreased vascular endothelial growth factor, vascular regression and epithelial cell apoptosis. Here, we identify the angiogenesis inhibitor pigment epithelium–derived factor (PEDF) as a key inhibitor of stromal vasculature and epithelial tissue growth in mouse prostate and pancreas. In PEDF-deficient mice, stromal vessels were increased and associated with epithelial cell hyperplasia. Androgens inhibited prostatic PEDF expression in cultured cells. In vivo, androgen ablation increased PEDF in normal rat prostates and in human cancer biopsies. Exogenous PEDF induced tumor epithelial apoptosis in vitro and limited in vivo tumor xenograft growth, triggering endothelial apoptosis. Thus, PEDF regulates normal pancreas and prostate mass. Its androgen sensitivity makes PEDF a likely contributor to the anticancer effects of androgen ablation.

TGF-β: Duality of Function Between Tumor Prevention and Carcinogenesis

Several mechanisms underlying tumor progression have remained elusive, particularly in relation to transforming growth factor beta (TGF-β). Although TGF-β initially inhibits epithelial growth, it appears to promote the progression of advanced tumors. Defects in normal TGF-β pathways partially explain this paradox, which can lead to a cascade of downstream events that drive multiple oncogenic pathways, manifesting as several key features of tumorigenesis (uncontrolled proliferation, loss of apoptosis, epithelial-to-mesenchymal transition, sustained angiogenesis, evasion of immune surveillance, and metastasis). Understanding the mechanisms of TGF-β dysregulation will likely reveal novel points of convergence between TGF-β and other pathways that can be specifically targeted for therapy.

Mutations in SERPINF1 cause osteogenesis imperfecta type VI

Osteogenesis imperfecta (OI) is a spectrum of genetic disorders characterized by bone fragility. It is caused by dominant mutations affecting the synthesis and/or structure of type I procollagen or by recessively inherited mutations in genes responsible for the posttranslational processing/trafficking of type I procollagen. Recessive OI type VI is unique among OI types in that it is characterized by an increased amount of unmineralized osteoid, thereby suggesting a distinct disease mechanism. In a large consanguineous family with OI type VI, we performed homozygosity mapping and next‐generation sequencing of the candidate gene region to isolate and identify the causative gene. We describe loss of function mutations in serpin peptidase inhibitor, clade F, member 1 (SERPINF1) in two affected members of this family and in an additional unrelated patient with OI type VI. SERPINF1 encodes pigment epithelium–derived factor. Hence, loss of pigment epithelium–derived factor function constitutes a novel mechanism for OI and shows its involvement in bone mineralization.

Anti-angiogenic pigment epithelium-derived factor regulates hepatocyte triglyceride content through adipose triglyceride lipase (ATGL) ☆

BACKGROUND/AIMS Anti-angiogenic pigment epithelium-derived factor (PEDF) is a 50 kDa secreted glycoprotein that is highly expressed in hepatocytes. Adipose triglyceride lipase (ATGL), a novel lipase critical for triglyceride metabolism, is a receptor for PEDF. We postulated that hepatocyte triglyceride metabolism was dependent on interactions between PEDF and ATGL, and loss of PEDF would impair mobilization of triglycerides in the liver. METHODS Immunoprecipitation studies were performed in PEDF null and control hepatocytes with recombinant PEDF (rPEDF) as bait. Immunofluorescent microscopy was used to localize ATGL. Triglyceride content was analyzed in hepatocytes and in whole liver with and without rPEDF. ATGL was blocked using an inhibitor, (R)-bromoenol lactone. RESULTS PEDF co-immunoprecipitated with ATGL in hepatic and HCC lysates. All PEDF deficient livers demonstrated steatosis. Triglyceride content was significantly increased in PEDF null livers compared to wildtype (p<0.05) and in isolated hepatocytes (p<0.01). Treatment of PEDF null hepatocytes with rPEDF decreased TG content (p<0.05) and this activity was dependent on ATGL. CONCLUSIONS Our results identify a novel role for PEDF in hepatic triglyceride homeostasis through binding to ATGL and demonstrate that rPEDF and ATGL localize to adiposomes in hepatocytes. Dysregulation of this pathway may be one mechanism underlying fatty liver disease.

Alternatively spliced human tissue factor promotes tumor growth and angiogenesis in a pancreatic cancer tumor model

INTRODUCTION Tissue Factor (TF) expression is observed in many types of cancer, associated with more aggressive disease, and thrombosis. Alternatively-spliced human tissue factor (asHTF) has recently been identified in which exon 5 is deleted. asHTF is soluble due to the substitution of the transmembrane and cytoplasmic domains of exon 6 with a unique COOH-terminal domain. MATERIALS AND METHODS We examine the expression and function of asHTF and full-length Tissue Factor ((FL)TF) in six human pancreatic cancer cells. Further, we transfected asHTF, (FL)TF, and control expression vectors into a non-expressing, human pancreatic cancer line (MiaPaCa-2). We studied the procoagulant activity of asHTF and (FL)TF and the effect on tumor growth in mice. RESULTS asHTF is expressed in 5 of 6 human pancreatic cancer cell lines, but not in normal human fibroblasts, nor the MiaPaCa-2 line. (FL)TF conferred procoagulant activity, but asHTF did not. Transfected cells were injected subcutaneously in athymic mice. Interestingly, compared with control transfection, (FL)TF expression was associated with reduced tumor growth (mean 7 mg vs 85 mg), while asHTF-expression was associated with enhanced tumor growth (mean 389 mg vs. 85 mg). asHTF expression resulted in increased mitotic index and microvascular density. CONCLUSIONS These data suggests that asHTF expression promotes tumor growth, and is associated with increased tumor cell proliferation and angiogenesis in vivo. Our results raise a new perspective on the understanding of the relationship between TF expression and cancer growth, by showing a dissociation of the procoagulant activity of (FL)TF and the cancer-promoting activity of asHTF.

Decreased Pigment Epithelium-Derived Factor Is Associated with Metastatic Phenotype in Human and Rat Prostate Tumors

Pigment epithelium-derived factor, a potent angiogenesis inhibitor in the eye, is also expressed in the prostate. Prostate size and angiogenesis is increased in pigment epithelium-derived factor knockout mice, and pigment epithelium-derived factor is down-regulated in some prostate cancers. To investigate whether pigment epithelium-derived factor expression correlates with tumor progression, we examined 5 Dunning rat prostate sublines with different growth rates, differentiation, androgen dependence, vascular density, and metastatic ability and 26 human prostate cancers of Gleason score 8–10 obtained from patients at transurethral resection selected to represent two groups, with and without metastases at diagnosis. By Western blot, real-time quantitative reverse transcription-PCR, and immunostaining, pigment epithelium-derived factor was detected in highly differentiated, nonmetastatic, androgen-sensitive Dunning tumors and in the anaplastic, androgen insensitive but nonmetastatic Dunning tumors. In contrast, the metastatic Dunning tumor sublines showed very low pigment epithelium-derived factor expression levels. In human cancer tissues, by immunohistochemistry and real-time quantitative reverse transcription-PCR, patients without metastases at diagnosis had higher tumor pigment epithelium-derived factor levels than tumors from patients with metastases at diagnosis. In both the rat model and in the human tumors, the proliferation index and vascular count, as determined by Ki-67 staining and endoglin and/or factor VIII-related antigen staining, inversely correlated with pigment epithelium-derived factor mRNA levels. These observations indicate that loss of pigment epithelium-derived factor expression could be associated with the progression toward a metastatic phenotype in prostate cancer.

Ethanol Exposure Depletes Hepatic Pigment Epithelium-Derived Factor, a Novel Lipid Regulator

BACKGROUND & AIMS Ethanol abuse can lead to hepatic steatosis and evolve into cirrhosis and hepatocellular carcinoma. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that is expressed by hepatocytes. Proteomic, experimental, and clinical studies implicate PEDFs role in lipid regulation. Because matrix metalloproteinase (MMP)-2/9 activity regulates PEDF levels, we investigated whether PEDF degradation by MMPs has a permissive role in ethanol-induced hepatic steatosis. METHODS PEDF levels were examined in liver biopsy specimens from patients with ethanol-induced steatosis. Hepatic PEDF levels and MMP activity were assessed in 2 animal models of ethanol feeding (rats on an alcohol-containing liquid diet and mice given intragastric infusion of ethanol). The consequences of PEDF depletion in the liver were examined in PEDF-null mice. RESULTS Liver biopsy samples from patients with ethanol-induced steatosis had reduced PEDF levels, compared with normal liver samples. Ethanol-fed animals had histologic steatosis and increased liver triglyceride content (P< .05), as well as reduced levels of hepatic PEDF and increased MMP-2/9 activity. Ethanol-exposed hepatic lysates degraded PEDF in a MMP-2/9-dependent manner, and liver sections demonstrated abundant MMP-2/9 activity in situ. Addition of recombinant PEDF to PEDF-null hepatocytes, reduced their triglyceride content. CONCLUSIONS Ethanol exposure leads to marked loss of hepatic PEDF in human livers and in 2 animal models of ethanol feeding. Loss of PEDF contributes to the accumulation of lipids in ethanol-induced hepatic steatosis.

Role of alternatively spliced tissue factor in pancreatic cancer growth and angiogenesis.

Increased tissue factor (TF) expression is observed in many types of cancer, associated with more aggressive disease, and in thrombosis. The mechanism by which TF promotes tumor growth remains unclear. Anticoagulation has been shown to result in a trend toward improved survival; no direct antitumor effect has been shown in cancer patients. Alternatively spliced tissue factor (asTF) was recently described, in which exon 5 is deleted. Because of a frame-shift in exon 6, the transmembrane and cytoplasmic domains are replaced with a unique COOH-terminal domain, making asTF soluble. Both alternatively spliced human tissue factor (asHTF) and full-length tissue factor (flTF) are expressed in human pancreatic cancer lines and in pancreatic cancer specimens. We studied the role of asHTF and flTF in a mouse model of pancreatic cancer. Although lacking procoagulant activity, asTF promotes primary growth of human pancreatic cancer cells in mice and augments tumor-associated angiogenesis. This body of work suggests a new paradigm for the role of TF in pancreatic cancer: that asHTF contributes to cancer growth, independent of procoagulant activity.

In vivo generation of angiostatin isoforms by administration of a plasminogen activator and a free sulfhydryl donor: a phase I study of an angiostatic cocktail of tissue plasminogen activator and mesna.

Purpose: Angiostatin4.5 (AS4.5), the endogenous human angiostatin, is derived from plasminogen in a two-step process. A plasminogen activator converts plasminogen to plasmin, then plasmin undergoes autoproteolysis to AS4.5. A free sulfhydryl donor can mediate plasmin autoproteolysis. To translate this process to human cancer therapy, we conducted a phase I trial of administration of a tissue plasminogen activator (tPA) with a free sulfhydryl donor (mesna). Patients and Methods: Fifteen patients with advanced solid tumors were treated. The dose of tPA was escalated (cohorts; 1, 2, 3, 5, and 7.5 mg/h for 6 hours). Mesna was administered as a 240 mg/m2 bolus followed by an infusion of 50 mg/h, concurrent with tPA. Both tPA and mesna were administered 3 consecutive days every 14 days. Results: No dose-limiting toxicity was observed. Two AS4.5 isoforms were generated, Lys-AS4.5 and Glu-AS4.5. Mean baseline Lys-AS4.5 level was 20.4 nmol/L (SE, 2.9). In the 5 mg/h tPA cohort, Lys-AS4.5 levels increased by an average of 143% or 24 nmol/L (SE, 4.9) above baseline. Glu-AS4.5 (Mr ∼ 62,000) was also generated (additional 77 amino acids at amino terminus compared with Lys-AS4.5). Glu-AS4.5 level at baseline was undetectable in four of five patients in the 5 mg/h tPA cohort, but at end of infusion, was ∼67 nmol/L (SE, 20). Two patients in the 5 mg/h tPA cohort experienced decreases in tumor markers with treatment, although no clinical objective responses were observed. Conclusion: This study shows that in vivo generation of AS4.5 is safe in humans and may provide a practical approach to achieve antiangiogenic therapy.

Differential binding of plasminogen, plasmin, and angiostatin4.5 to cell surface β-actin : Implications for cancer-mediated angiogenesis

Angiostatin4.5 (AS4.5) is the product of plasmin autoproteolysis and consists of kringles 1 to 4 and approximately 85% of kringle 5. In culture, cancer cell surface globular beta-actin mediates plasmin autoproteolysis to AS4.5. We now show that plasminogen binds to prostate cancer cells and that the binding colocalizes with surface beta-actin, but AS4.5 does not bind to the cell surface. Plasminogen and plasmin bind to immobilized beta-actin similarly, with a Kd of approximately 140 nmol/L. The binding is inhibited by epsilon-aminocaproic acid (epsilonACA), indicating the requirement for a lysine-kringle domain interaction. Using a series of peptides derived from beta-actin in competitive binding studies, we show that the domain necessary for plasminogen binding is within amino acids 55 to 69 (GDEAQSKRGILTLKY). Substitution of Lys61 or Lys68 with arginine results in the loss of the ability of the peptide to block plasminogen binding, indicating that Lys61 and Lys68 are essential for plasminogen binding. Other actin peptides, including peptides with lysine, did not inhibit the plasminogen-actin interaction. AS4.5 did not bind actin at concentrations up to 40 micromol/L. Plasminogen, plasmin, and AS4.5 all contain kringles 1 to 4; however, kringle 5 is truncated in AS4.5. Isolated kringle 5 binds to actin, suggesting intact kringle 5 is necessary for plasminogen and plasmin to bind to cell surface beta-actin, and the truncated kringle 5 in AS4.5 results in its release from beta-actin. These data may explain the mechanism by which AS4.5 is formed locally on cancer cell surfaces and yet acts on distant sites.