Differentiation of Y79 retinoblastoma cells with pigment epithelial-derived factor and interphotoreceptor matrix wash: effects on tumorigenicity

UHRF1 downmodulation enhances antitumor effects of histone deacetylase inhibitors in retinoblastoma by augmenting oxidative stress-mediated apoptosis

Identification of new genetic pathways or molecular targets that sensitize cancer cells to chemotherapeutic drugs may improve the efficacy of current chemotherapy. Here, we report that downmodulation of UHRF1 (ubiquitin-like with PHD and RING finger domains 1) in retinoblastoma (RB) cells increases the sensitivity to histone deacetylase (HDAC) inhibitors, augmenting apoptotic cell death. We found that UHRF1 depletion downregulates two redox-responsive genes GSTA4 (glutathione S-transferase α4) and TXN2 (thioredoxin-2) in RB cells, and increases the basal level of intracellular oxidative stress. Antioxidant treatment significantly reduced both basal and HDAC inhibitor-induced DNA damage and apoptosis in UHRF1-depleted cells. Knockdown of GSTA4 or TXN2 sensitized RB cells to HDAC inhibitors, demonstrating that GSTA4 and TXN2 play key roles in redox homeostasis in RB cells and the susceptibility to HDAC inhibitor treatment upon UHRF1 depletion. In human primary RB, GSTA4 and TXN2 proteins were found to be mostly elevated along with high UHRF1 expression. In addition to augmentation of apoptosis in UHRF1-depleted RB cells, we also show that UHRF1 downmodulation derepresses the expression of photoreceptor-specific genes in RB cells in cooperation with a HDAC inhibitor MS-275 and promotes neuron-like differentiation. However, further investigation revealed that the enhanced growth-inhibitory effects of MS-275 in UHRF1-depleted cells were still mainly due to robust apoptosis induction rather than differentiation-mediated growth arrest. Consistent with our findings, UHRF1 depletion in RB cells increased the therapeutic efficacy of MS-275 in murine orthotopic xenografts. These results provide a novel basis for potential benefits of UHRF1 targeting for RB treatment.

Regulated differentiation of WERI-Rb-1 cells into retinal neuron-like cells

The encouraging response and improved survival of acute promyelocytic leukemia patients following retinoic acid treatment has rendered differentiation therapy an attractive option in cancer treatment. Given that terminal differentiation represents a considerable barrier in retinoblastoma tumorigenesis and that retinoblastoma has a significantly higher spontaneous degeneration rate compared with other tumors (1,000-fold change), differentiation therapy represents a promising alternative in the treatment of retinoblastoma. However, the full differentiation potential of retinoblastoma still unknown. The present study was designed to investigate the extend differentiation of the classical retinoblastoma cell line WERI-Rb-1 (W-RBCs). Several critical cell signaling pathways and key genes related to cell proliferation and differentiation were comprehensively regulated to control the fate of W-RBCs. Various strategies were applied to optimize simple and time-saving methods to induce W-RBCs into different types of retinal neuron-like cells (RNLCs) in vitro. Further, the tumorigenesis of these differentiated W-RBCs was tested in nude mice in vivo. W-RBCs were found to inherently express both retinal progenitor cell- and embryonic stem cell-related genes or proteins. Moreover, the addition of antagonists of critical cell signals (Wnt, Nodal, BMP4 and Notch), even without atonal bHLH transcription factor 7 gene transfection, could directly induce W-RBCs into RNLCs, and especially into photoreceptor-like and retinal ganglion-like cells. Interestingly, the differentiated cells showed remarkably poorer tumorigenesis in vivo. These findings may offer new insights on the oriented differentiation of W-RBCs into RNLCs with low tumorigenicity and provide potential targets for retinoblastoma differentiation therapy.

Intraocular Transplantation of E1A-Immortalized Retinal Precursor Cells

The purpose of this study was to examine the effect of the ocular environment on the survival, tumorigenicity, and phenotypic marker expression of immortalized retinal precursor cells transplanted into immunocompetent adult and neonatal Sprague–Dawley rats. E1A-NR.3, a rat immortalized retinal precursor cell culture, was used as an inexhaustible source of experimental graft material. These cells were prelabeled with the fluorescent marker diI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) and transplanted intravitreally (50,000 cells per μL) into 11 adult and 31 neonatal Sprague–Dawley rat eyes. At 1 mo posttransplant, animals were sacrificed and retinal tissue sections examined histologically for the presence of grafted cells, signs of tumor formation, and retinal phenotypic marker expression. No obvious signs of tumor formation or rejection were seen in a total of 42 eyes in the immunocompetent hosts. Our results indicate that E1A-NR.3 cells survive at least 1 month in vivo, and can migrate from the vitreous into neuroretinal cell layers. Subpopulations of surviving grafted cells were seen to express photoreceptor markers rhodopsin and recoverin comparably between in vitro and in vivo conditions. However, the number of cells immunoreactive for vimentin and E1A decreased significantly under in vivo conditions. This report represents the first experimental intravitreal transplantation of E1A-immortalized retinal precursor cells into adult and neonatal rats. The intraocular location and environment appears to affect phenotypic expression of surviving grafted cells, especially with respect to vimentin and E1A expression. The fact that E1A-NR.3 cells survived intraocularly at least 1 mo without tumor formation suggests that the cells may continue to be useful for further in vivo studies of experimental retinal transplantation, and effects of histological location on retinal cell phenotype and histogenesis in immunocompetent hosts. © 1998 Elsevier Science Inc.

Pigment epithelium-derived factor (PEDF) normalizes matrix defects in iPSCs derived from Osteogenesis imperfecta Type VI

Osteogenesis imperfecta (OI) Type VI is characterized by a defect in bone mineralization, which results in multiple fractures early in life. Null mutations in the PEDF gene, Serpinf1, are the cause of OI VI. Whether PEDF restoration in a murine model of OI Type VI could improve bone mass and function was previously unknown. In Belinsky et al, we provided evidence that PEDF delivery enhanced bone mass and improved parameters of bone function in vivo. Further, we demonstrated that PEDF temporally inhibits Wnt signaling to enhance osteoblast differentiation. Here, we demonstrate that generation of induced pluripotent stem cells (iPSCs) from a PEDF null patient provides additional evidence for PEDF's role in regulating extracellular matrix proteins secreted from osteoblasts. PEDF null iPSCs have marked abnormalities in secreted matrix proteins, capturing a key feature of human OI Type VI, which were normalized by exogenous PEDF. Lastly, we place our recent findings within the broader context of PEDF biology and the developmental signaling pathways that are implicated in its actions.

Metformin inhibits prostate cancer cell proliferation, migration, and tumor growth through upregulation of PEDF expression

Metformin has been reported to inhibit the growth of various types of cancers, including prostate cancer. Yet the mode of anti-cancer action of metformin and the underlying mechanisms remain not fully elucidated. We hypothesized that the antitumorigenic effects of metformin are mediated through upregulation of pigment epithelium-derived factor (PEDF) expression in prostate cancer cells. In this report, metformin treatment significantly inhibited the proliferation and colony formation of prostate cancer cells, in a dose- and time-dependent manner. Meanwhile, Metformin markedly suppressed migration and invasion and induced apoptosis of both LNCaP and PC3 cancer cells. Metformin also reduced PC3 tumor growth in BALB/c nude mice in vivo. Furthermore, metformin treatment was associated with higher PEDF expression in both prostate cancer cells and tumor tissue. Taken together, metformin inhibits prostate cancer cell proliferation, migration, invasion and tumor growth, and these activities are mediated by upregulation of PEDF expression. These findings provide a novel insight into the molecular functions of metformin as an anticancer agent.

Pigment Epithelium-Derived Factor (PEDF) is a Determinant of Stem Cell Fate: Lessons from an Ultra-Rare Disease

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.

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

The potent actions of pigment epithelium-derived factor (PEDF) on tumour-associated cells, and its extracellular localization and secretion, stimulated research on this multifunctional serpin. Such studies have identified several PEDF receptors and downstream signalling pathways. Known cellular PEDF responses have expanded from the initial discovery that PEDF induces retinoblastoma cell differentiation to its anti-angiogenic, antitumorigenic and antimetastatic properties. Although the diversity of PEDF activities seems to be complex, they are consistent with the varied mechanisms that regulate this multimodal factor. If PEDF is to be used for cancer management, a deeper appreciation of its many functions and mechanisms of action is needed.

Expression of pigment epithelium-derived factor in human melanocytes and malignant melanoma cells and tissues: Is loss of pigment epithelium-derived factor associated with melanoma?

BACKGROUND

Pigment epithelium-derived factor (PEDF) was first isolated from the medium conditioned by human fetal retinal pigment epithelial cells and has been detected in a broad range of human fetal and adult tissues. Recent studies have indicated that PEDF activity is inhibitory to angiogenesis.

OBJECTIVE

To study the expression and distribution of pigment epithelium-derived factor (PEDF) in human melanocytes, malignant melanoma cells and tissues.

RESULTS

PEDF was expressed in human melanocytes. The expression of PEDF protein diminished in the following orders healthy skin, pigmented nevus and human malignant melanoma (p < 0.001). Both the expression of PEDF mRNA and protein was much lower or almost absent in the malignant melanoma cell line A375 than that in human melanocytes (p < 0.001).

METHODS

The expression and distribution of PEDF in human healthy skin, pigmented nevus and malignant melanoma were studied. The expression of PEDF mRNA in human melanocytes and malignant melanoma cell line A375 was measured by reverse transcription polymerase chain reaction (RT-PCR) and PEDF protein was detected by immunohistochemical method and Western blotting analysis.

CONCLUSION

The lack of PEDF expression may contribute to the pathogenesis of malignant melanoma.

Polarized secretion of PEDF from human embryonic stem cell-derived RPE promotes retinal progenitor cell survival

PURPOSE

Human embryonic stem cell-derived RPE (hES-RPE) transplantation is a promising therapy for atrophic age-related macular degeneration (AMD); however, future therapeutic approaches may consider co-transplantation of hES-RPE with retinal progenitor cells (RPCs) as a replacement source for lost photoreceptors. The purpose of this study was to determine the effect of polarization of hES-RPE monolayers on their ability to promote survival of RPCs.

METHODS

The hES-3 cell line was used for derivation of RPE. Polarization of hES-RPE was achieved by prolonged growth on permeable inserts. RPCs were isolated from 16- to 18-week-gestation human fetal eyes. ELISA was performed to measure pigment epithelium-derived factor (PEDF) levels from conditioned media.

RESULTS

Pigmented RPE-like cells appeared as early as 4 weeks in culture and were subcultured at 8 weeks. Differentiated hES-RPE had a normal chromosomal karyotype. Phenotypically polarized hES-RPE cells showed expression of RPE-specific genes. Polarized hES-RPE showed prominent expression of PEDF in apical cytoplasm and a marked increase in secretion of PEDF into the medium compared with nonpolarized culture. RPCs grown in the presence of supernatants from polarized hES-RPE showed enhanced survival, which was ablated by the presence of anti-PEDF antibody.

CONCLUSIONS

hES-3 cells can be differentiated into functionally polarized hES-RPE cells that exhibit characteristics similar to those of native RPE. On polarization, hES-RPE cells secrete high levels of PEDF that can support RPC survival. These experiments suggest that polarization of hES-RPE would be an important feature for promotion of RPC survival in future cell therapy for atrophic AMD.

'Loss of pigment epithelium-derived factor enables migration, invasion and metastatic spread of human melanoma'

Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that displays broad anti-tumor activity based on dual targeting of the tumor microenvironment (anti-angiogenic action) and the tumor cells (direct anti-tumor action). Here, we show that PEDF expression is high in melanocytes, but it is lost during malignant progression of human melanoma. Using a high-throughput analysis of the data from microarray studies of molecular profiling of human melanoma, we found that PEDF expression is lost in highly invasive melanomas. In paired cell lines established from the same lesion but representing the high and low extremes of malignant potential, abundant PEDF expression was restricted to the poorly aggressive counterparts. We used RNA interference to directly address the functional consequences of PEDF silencing. PEDF knockdown in poorly aggressive melanoma cell lines augmented migration, invasion and vasculogenic mimicry, which translated into an increased in vivo metastatic potential. PEDF interference also significantly enhanced the migratory and invasive capability of normal melanocytes and moderately increased their proliferative potential. Our results show that loss of PEDF enables melanoma cells to acquire an invasive phenotype and, therefore, modulation of this multifunctional factor could be critical for the malignant progression of human melanoma.

Pigment epithelium-derived factor binds to hyaluronan. Mapping of a hyaluronan binding site

Pigment epithelium-derived factor (PEDF) is a multifunctional serpin with antitumorigenic, antimetastatic, and differentiating activities. PEDF is found within tissues rich in the glycosaminoglycan hyaluronan (HA), and its amino acid sequence contains putative HA-binding motifs. We show that PEDF coprecipitation with glycosaminoglycans in media conditioned by human retinoblastoma Y-79 cells decreased after pretreatments with hyaluronidase, implying an association between HA and PEDF. Direct binding of human recombinant PEDF to highly purified HA was demonstrated by coprecipitation in the presence of cetylpyridinium chloride. Binding of PEDF to HA was concentration-dependent and saturable. The PEDF-HA interactions were sensitive to increasing NaCl concentrations, indicating an ionic nature of these interactions and having affinity higher than PEDF-heparin. Competition assays showed that PEDF can bind heparin and HA simultaneously. PEDF chemically modified with fluorescein retained the capacity for interacting with HA but lacked heparin affinity, suggesting one or more distinct HA-binding regions on PEDF. The HA-binding region was examined by site-directed mutagenesis. Single-point and cumulative alterations at basic residues within the putative HA-binding motif K189A/K191A/R194A/K197A drastically reduced the HA-binding activity without affecting heparin- or collagen I binding of PEDF. Cumulative alterations at sites critical for heparin binding (K146A/K147A/R149A) decreased HA affinity but not collagen I binding. Thus these clusters of basic residues (BXBXXBXXB and BX3AB2XB motifs) in PEDF are functional regions for binding HA. In the spatial PEDF structure they are located in distinct areas away from the collagen-binding site. The HA-binding activity of PEDF may contribute to deposition in the extracellular matrix and to its reported antitumor/antimetastatic effects.

Pigment epithelium-derived factor targets endothelial and epithelial cells in Wilms' tumor

PURPOSE

Loss of pigment epithelium-derived factor (PEDF), a potent inhibitor of angiogenesis, has been linked to progression of angiogenesis-dependent diseases. We postulated that decreased levels of endogenous PEDF in the kidney creates a tumor permissive environment for Wilms' tumor.

METHODS

Fresh and frozen Wilms' tumor (n = 28), adjacent (n = 3), and normal kidney (n = 8) were immunostained and graded. The Wilms' tumor cells (SK-NEP-1), renal epithelial cells (NRK-52), and fresh tumor samples were grown in culture. Condition media were collected and analyzed by an in vitro angiogenesis assay and Western blot. The SK-NEP-1 cells were treated with PEDF and cell viability assessed.

RESULTS

Wilms' tumors expressed less PEDF than normal and adjacent kidney. Pigment epithelium-derived factor protein secretion was abundant in NRK-52 cells but significantly decreased in Wilms' tumor. Pigment epithelium-derived factor acted as blockade to angiogenesis and it had a dose-dependent cytotoxic effect on Wilms' tumor epithelial cells.

CONCLUSION

Renal tubular epithelial cells are a rich source of PEDF in the normal kidney. Reduced levels of PEDF in Wilms' tumor remove a critical endogenous renal barrier to angiogenesis and tumor cell survival. Therapeutic replacement of PEDF may prove to be an effective strategy to combat Wilms' tumor progression.

Proteomic analysis of the porcine interphotoreceptor matrix

The interphotoreceptor matrix (IPM) is located between photoreceptors and pigment epithelium in the retina and is involved in fundamental functions of the visual cycle. These include visual pigment chromophore exchange, retinal adhesion, metabolite trafficking, and growth factor presentation. In general, IPM preparations are contaminated with intracellular proteins, as has also been described for other body fluids. This study aimed at identifying new components of the IPM by discriminating between truly secreted proteins and proteins that are part of the IPM for secondary reasons. "Soluble" porcine IPM was extracted from retina and pigment epithelium with PBS by two different procedures, followed by extraction with water alone that released "insoluble" IPM matrix sheets. Samples from all preparations were separated by 2-DE and a total of 140 protein spots were identified by MALDI-TOF and/or CapLC Q-TOF MS. Although identified proteins included several already known in the IPM, the majority had not been previously described in this structure. Gene ontology classifications allocated the identified proteins into nine different functional networks. The IPM preparations also included intracellular proteins from cells adjacent to the IPM, which may have resulted from cell disruption. This underlines the experimental difficulties of a biochemical analysis of the IPM as an intact compartment. We show here a strategy for predicting the probability of identified IPM proteins occurring in vivo by combined high-resolution protein separation methods with computational prediction methods. Thus, a set of potentially neuroprotective proteins could be extracted, including PEA-15, peroxiredoxin 5, alpha-B-crystallin, macrophage migration inhibitory factor, 78 kDa glucose-regulated protein (GRP78), protein disulfide-isomerase, and PEP-19, which have not been previously associated with the IPM. Furthermore, with immunohistochemical staining we could confirm the localization of GRP78 in the IPM on porcine eye sections, thus validating the proposed prediction method.

Vitamin A up-regulates the expression of thrombospondin-1 and pigment epithelium-derived factor in retinal pigment epithelial cells

Vitamin A is essential for the visual system. It is metabolized in the retina and the resulting product, retinoic acid (RA), greatly affects the structure and functions of retinal pigment epithelial (RPE) cells. RPE cells produce a variety of extracellular matrix (ECM) proteins and angiogenic factors, both of which are expressed at varying levels in the normal RPE layer. In this study, we investigated the effect of all-trans-retinoic acid on the production of an ECM protein, thrombospondin-1 (TSP-1), and two angiogenic factors, pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) by RPE cells. RA increased the release of TSP-1 and PEDF, but not that of VEGF, from human RPE cells in vitro. In vitamin A-deficient mice, the expression of TSP-1 and PEDF in the RPE layer considerably decreased compared with that of normal control mice. The vitamin A deficiency hardly affected the accumulation of VEGF in the RPE layer. These findings suggest that vitamin A modulates the structure and anti-angiogenic functions of the RPE layer partly by up-regulating the expression of the angiogenesis-related ECM protein, TSP-1, and the anti-angiogenic factor, PEDF.

Localization of pigment epithelium-derived factor in growing mouse bone

Pigment epithelium-derived factor (PEDF) is a potent anti-angiogenic factor found in a wide range of fetal and adult tissues, where it is thought to play a role in the regulation of angiogenesis during development. The temporal expression of PEDF during endochondral bone formation has not previously been reported. In this study, we analysed the expression pattern of PEDF in growing mouse hindlimbs from newborn day one through to maturation at week 9, using immunohistochemistry and in situ hybridization. PEDF expression was demonstrated in chondrocytes within the resting, proliferative and upper hypertrophic zones of the epiphyseal growth plate. The pattern of expression was consistent throughout the developmental stages of the mouse. In addition, PEDF was expressed by osteoblasts lining the bone spicules in the ossification zone of metaphyseal bone, as well as by osteoblasts lining cortical periosteum. These novel results demonstrate that PEDF is developmentally expressed in both cartilage and bone cells during endochondral bone formation, and strongly suggest that it may play a regulatory role in the processes of chondrocyte and osteoblast differentiation, endochondral ossification, and bone remodelling during growth and development of long bones.

Inhibition of glioma invasion by overexpression of pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a potent inhibitor of angiogenesis and an inducer of neural differentiation. We previously reported the loss of PEDF expression in glioma progression. In this study, we investigated whether PEDF overexpression could suppress glioma growth and invasion. Glioma cell line U251 was stably transfected with a full-length human PEDF expression vector. The expression and release of various cytokines and angiogenic factors into the medium were analyzed by real-time reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, and gelatin zymography. Apoptosis was checked by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Growth inhibition was evaluated by using the in vitro Matrigel invasion. Tumorigenicity was examined in vivo by subcutaneous xenotransplantation into severe combined immunodeficient mice. In U251 cells overexpressing PEDF, thrombospondin-1 protein was upregulated (5.3-fold more), but the production of vascular endothelial growth factor (VEGF) (1.8-fold less) and basic fibroblast growth factor (2.5-fold less) was lower than in cells transfected with the vector only. PEDF also downregulated the production of matrix metalloproteinase-9. Conditioned medium collected from the PEDF-transfected U251 cells showed a significant reduction of VEGF expression. In vitro invasiveness was reduced by approximately 40%. PEDF expression prevented the growth of transfected cells and caused a significant increase in the percentage of cells undergoing apoptosis (50.4% in PEDF-transfected cells). Furthermore, the size of xenotransplants was significantly smaller. In conclusion, PEDF overexpression decreased malignancy, and this might be attributed to the promotion of apoptosis and the regulation of expression of angiogenic effectors. Thus, treatment with PEDF may be useful in patients with malignant gliomas. However, the mechanism of apoptosis induction needs to be investigated.

Loss of EPC-1/PEDF expression during skin aging in vivo

EPC-1/PEDF (early population doubling level cDNA-1/retinal pigmented epithelium-derived factor) is a single-copy, quiescence-specific gene that is transcribed into a 1.5 kb mRNA and then translated into a 50 kDa secreted protein that is a potent inhibitor of angiogenesis. EPC-1 expression has been detected in a number of cultured cell lines, including lung and skin fibroblasts, retinal pigmented epithelial cells, and endometrial stromal fibroblasts. Furthermore, its expression has been shown to decline during replicative aging of these cells in culture. In this report, we describe our examination of the age-related changes in EPC-1 expression in situ in skin sections from donors of different ages. EPC-1 mRNA is detected primarily in the dermal layer of the skin and its expression declines with increasing donor age. This decline is statistically significant between young (less than 31 years old) and middle-aged (between 30 and 60 years old) donors, with the decline becoming less dramatic at older ages. This age-related decline in the expression of an angiogenic inhibitor contributes to the imbalance of angiogenic modulators that is observed during aging. In fact, this decline may reflect a compensatory change to help reverse the decline of angiogenesis marked by reduced abundance of microvessels. This downregulation of an angiogenesis inhibitor may, in turn, play a critical role in the development of diseases caused by abnormal vascularization. The potential role of the age-associated decline in EPC-1 expression in tissue remodeling and in the development of skin diseases with excessive angiogenesis may provide new insights into disease prevention.

Identification of the antivasopermeability effect of pigment epithelium-derived factor and its active site

Vascular permeability plays a key role in a wide array of life-threatening and sight-threatening diseases. Vascular endothelial growth factor can increase vascular permeability. Using a model system for nonproliferative diabetic retinopathy, we found that pigment epithelium-derived factor (PEDF) effectively abated vascular endothelial growth factor-induced vascular permeability. A 44-amino acid region of PEDF was sufficient to confer the antivasopermeability activity. Additionally, we identified four amino acids (glutamate-101, isoleucine-103, leucine-112, and serine-115) critical for this activity. PEDF, or a derivative, could potentially abate or restore vision loss from diabetic macular edema. Furthermore, PEDF may represent a superior therapeutic approach to sepsis-associated hypotension, nephrotic syndrome, and other sight-threatening and life-threatening diseases resulting from excessive vascular permeability.

Regulation of the expression of pigment epithelium-derived factor, an anti-angiogenic factor in human oral squamous cell carcinoma cell lines

Angiogenesis plays an important role in tumor growth and metastasis and is regulated by a balance between angiogenic stimulators and inhibitors. We investigated the gene expression profile of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF), a potent endogenous anti-angiogenic factor, in human oral squamous cell carcinoma (SCC) cell lines. The treatment of SCC cells with hypoxia increased the expression of PEDF as well as VEGF. Moreover, the treatment of SCC cells with VEGF enhanced the expression of PEDF mRNA and secretion of PEDF. In LMF-4, a SCC clone producing abundant VEGF and PEDF, the addition of neutralizing VEGF antibody substantially blocked PEDF expression. These data suggest that human oral squamous cell carcinoma cells produce VEGF, which in turn regulates PEDF production, and this balance may be contributing to neovascularization in tumors.

Regulation of alpha1G T-type calcium channel gene (CACNA1G) expression during neuronal differentiation

Down-regulation of T-type Ca channel current and mRNA occurs following differentiation of Y79 retinoblastoma cells. To understand how the decrease in expression is linked to cell differentiation, we examined transcriptional regulation of the Cav3.1 Ca channel gene, CACNA1G. We identified two putative promoters (A and B) in 1.3 kb of cloned genomic DNA. Reverse transcriptase-polymerase chain reaction and 5' rapid amplification of cDNA ends-polymerase chain reaction analyses demonstrated that two transcripts with different 5' untranslated regions are generated by different transcription start sites, with promoter A favoured in undifferentiated cells and promoter B favoured in differentiated cells. Functional analyses of the promoter sequence revealed that both promoters are active. Enhancer and repressor sequences were identified upstream of promoter A and B, respectively. These results suggest that the down-regulation of alpha1G mRNA in differentiated Y79 cells is mediated primarily by decreased activity of promoter A, which could occur in conjunction with repression of the activity of promoter B. The decrease in T-type Ca channel expression in Y79 cells may be an essential signal affecting phenotypic maturation and expression of other ion channel subtypes in the differentiated cells.

Loss of pigment epithelium derived factor expression in glioma progression

BACKGROUND

Pigment epithelium derived factor (PEDF) was first isolated from medium conditioned by human fetal retinal pigment epithelial cells. PEDF was detected in a broad range of human fetal and adult tissues including almost all brain areas. It can also inhibit the proliferation of cultured rat astrocytes. Recent studies have implicated PEDF in activities that are inhibitory to angiogenesis.

AIMS

To investigate the expression of PEDF in gliomas to assess its "gliastatic" effects and its role in anti-angiogenesis.

METHODS

PEDF mRNA values were measured by quantitative real time reverse transcription polymerase chain reaction (RT-PCR) analysis of normal brain tissue and tumour specimens from both low and high grade gliomas. In addition, immunohistochemical staining for PEDF and vascular endothelial growth factor (VEGF) was performed on 32 paraffin wax embedded glioma samples, 10 of them grade IV, 10 grade III, seven grade II, and five grade I.

RESULTS

RT-PCR showed that PEDF mRNA values were 5.0 (p < 0.001) and 15.4 (p < 0.001) times higher in normal human brain specimens (n = 5) than in tumour tissue specimens of low grade glioma (grades I and II; n = 15) and high grade glioma (grades III and IV; n = 10), respectively. VEGF was strongly positive in 90% of grade IV, 70% of grade III, 43% of grade II, and 20% of grade I cases. In contrast, PEDF was positive in none of grade IV, 20% of grade III, 43% of grade II, and 60% of grade I tumours. There was an inverse correlation between VEGF and PEDF expression, and a lack of PEDF in advanced grade gliomas.

CONCLUSIONS

It is possible that the absence of PEDF expression is a potent factor for the enhancement of angiogenesis in glioma.

Unbalanced vitreous levels of pigment epithelium-derived factor and vascular endothelial growth factor in diabetic retinopathy

PURPOSE

To determine the levels of pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in the vitreous of patients with diabetic retinopathy (DR).

DESIGN

Experimental study of PEDF and VEGF levels in vitreous samples collected during vitrectomy.

METHODS

The levels of PEDF and VEGF were measured by enzyme-linked immunosorbent assay in the vitreous of 46 eyes of 43 patients who underwent vitrectomy with diabetic retinopathy (DR) (32 eyes of 29 patients) and an idiopathic macular hole (MH) (14 eyes of 14 patients).

RESULTS

The vitreal concentration of PEDF was significantly lower at 1.11 +/- 0.14 microg/ml (mean +/- standard error) in eyes with DR than in eyes with MH at 1.71 +/- 0.22 microg/ml (P =.021). The VEGF level was 1799 +/- 478 pg/ml in eyes with DR and not detectable in MH. The PEDF level in proliferative DR (PDR) (0.94 +/- 0.12 microg/ml) was lower than that in nonproliferative DR (NPDR) (2.25 +/- 0.32 microg/ml), and that in active DR (0.85 +/- 0.14 microg/ml) was significantly lower than that in inactive DR (1.59 +/- 0.24 microg/ml; P =.01). The VEGF level was 2025 +/- 533 pg/ml in PDR and 215 +/- 201 pg/ml in NPDR and that in active DR (2543 +/- 673 pg/ml) was significantly higher than that in inactive DR (395 +/- 188 pg/ml; P =.0098).

CONCLUSIONS

These results suggest that lower levels of PEDF and higher levels of VEGF may be related to the angiogenesis in DR that leads to active PDR.

Pigment epithelium-derived factor exerts opposite effects on endothelial cells of different phenotypes

The anti-angiogenic activity of pigment epithelium-derived factor (PEDF) has recently been discovered on the basis of its inhibition of ischemia-induced retinal neovascularization in an animal model of retinopathy of the premature. Moreover PEDF inhibits the migration and proliferation of various endothelial cells maintained in culture with FGF(2). Since vascular endothelial growth factor (VEGF) is the main angiogenic factor expressed in hypervascularized retinas, we investigated the functions of PEDF on retinal endothelial cells whose angiogenic phenotype is controlled or not by long term exposure to VEGF as observed in human pathologies such as diabetic retinopathy. Here, we observed that PEDF exerts opposite effects on endothelial cells depending on their phenotype. We determined that when PEDF inhibits endothelial cell growth, it inhibits VEGF-induced MAPK activation. However, in endothelial cells cultured with VEGF, PEDF has a synergistic action on cell proliferation with VEGF, and this corresponds to increased MAPK activation.

Pigment epithelium-derived factor (PEDF) in neuroblastoma: a multifunctional mediator of Schwann cell antitumor activity

Neuroblastoma is notable for its cellular heterogeneity and unpredictable outcome. Tumors are a variable mixture of primitive malignant neuroblasts, more differentiated ganglionic cells, Schwann and endothelial cells. Although often fatal, neuroblastomas can spontaneously regress, possibly due to favorable autocrine and paracrine interactions among these cells. Here, pigment epithelium-derived factor (PEDF), a potent inhibitor of angiogenesis and inducer of neural differentiation, is shown to be produced by ganglionic cells and Schwann cells, but not by more primitive tumor cells. Although undifferentiated neuroblastoma tumor cell secretions were angiogenic primarily due to vascular endothelial growth factor, secretions of Schwann cells were anti-angiogenic due to PEDF. In addition, PEDF was the major factor responsible for Schwann cell’s ability to induce tumor cell differentiation in vitro and recombinant PEDF had the same effect in vitro and in vivo. Both the growth and the survival of Schwann cells were enhanced by PEDF. Thus PEDF may serve as a multifunctional antitumor agent in neuroblastomas, inhibiting angiogenesis while promoting the numbers of Schwann cells and differentiated tumor cells that in turn produce PEDF, suggesting that its clinical administration could stimulate a multifaceted antitumor feedback loop with the potential to limit and possibly regress tumor growth.

Crystal structure of human PEDF, a potent anti-angiogenic and neurite growth-promoting factor

Pigment epithelium-derived factor (PEDF), a noninhibitory member of the serpin superfamily, is the most potent inhibitor of angiogenesis in the mammalian ocular compartment. It also has neurotrophic activity, both in the retina and in the central nervous system, and is highly up-regulated in young versus senescent fibroblasts. To provide a structural basis for understanding its many biological roles, we have solved the crystal structure of glycosylated human PEDF to 2.85 A. The structure revealed the organization of possible receptor and heparin-binding sites, and showed that, unlike any other previously characterized serpin, PEDF has a striking asymmetric charge distribution that might be of functional importance. These results provide a starting point for future detailed structure/function analyses into possible mechanisms of PEDF action that could lead to development of therapeutics against uncontrolled angiogenesis.

Pigment epithelium-derived factor in the vitreous is low in diabetic retinopathy and high in rhegmatogenous retinal detachment

PURPOSE

To report the levels of pigment epithelium-derived factor in the vitreous of patients with diabetic retinopathy, rhegmatogenous retinal detachment, and idiopathic macular hole.

METHODS

Using enzyme-linked immunosorbent assay, we measured the levels of pigment epithelium-derived factor in the vitreous of 34 eyes of 33 patients who underwent vitrectomy for the treatment of diabetic retinopathy (17 eyes of 16 patients), rhegmatogenous retinal detachment (10 eyes), and idiopathic macular hole (seven eyes).

RESULTS

The vitreal concentration of pigment epithelium-derived factor was 1.15 +/- 0.23 microg/ml (mean +/- standard error) in eyes with diabetic retinopathy, 3.28 +/- 0.69 microg/ml in rhegmatogenous retinal detachment, and 1.71 +/- 0.39 microg/ml in idiopathic macular hole. The pigment epithelium-derived factor level in rhegmatogenous retinal detachment was significantly higher than that in diabetic retinopathy (P =.0008) and idiopathic macular hole (P =.034). For eyes with diabetic retinopathy, the pigment epithelium-derived factor level was 0.88 +/- 0.21 microg/ml in proliferative diabetic retinopathy and 2.43 +/- 0.37 microg/ml in nonproliferative diabetic retinopathy (P =.0083). Additionally, the pigment epithelium-derived factor level in active diabetic retinopathy (0.70 +/- 0.22 microg/ml) was significantly lower than the level in inactive diabetic retinopathy (1.79 +/- 0.35 microg/ml; P =.018).

CONCLUSIONS

These results suggest that pigment epithelium-derived factor inhibits angiogenesis and that lower levels of pigment epithelium-derived factor may be related to the angiogenesis in diabetic retinopathy and result in active proliferative diabetic retinopathy. The results also suggest that higher levels of pigment epithelium-derived factor in the eyes with rhegmatogenous retinal detachment may act as a neuroprotective agent for the detached retina.

Pigment epithelium derived factor as a neuroprotective agent against ischemic retinal injury

PURPOSE

Pigment epithelium-derived factor (PEDF) is a protein shown to have neurotrophic activity. The purpose of this study was to determine whether PEDF is neuroprotective of retinal neurons that are exposed to transient ischemia-reperfusion.

METHODS

Transient retinal ischemia was produced by increasing the intraocular pressure for 45 min in albino rats eyes. Immediately after reperfusion, PEDF was injected intravitreally into the experimental eyes. Injury was evaluated morphologically and by measuring the thickness of the inner retinal layers (IRL) and by counting the number of retinal ganglion cells (RGC) in epon embedded sections.

RESULTS

Morphologic and morphometric analysis of the thickness of the IRL and the counting of RGC demonstrated that PEDF injected immediately after reperfusion protected the eyes partially but significantly from the ischemic injury.

CONCLUSIONS

Intravitreal injection of PEDF even after the ischemia can ameliorate retinal injury. PEDF may be useful in preventing neuronal degeneration in the inner retina resulting from ischemia.

Effects of donor age on the expression of a marker of replicative senescence (EPC-1) in human dermal fibroblasts

EPC-1 (early population doubling level cDNA-1) is a quiescence-specific gene expressed at high levels by early passage WI-38 fibroblasts under conditions of either density-dependent growth arrest or serum deprivation. Late passage WI-38 cells lose the ability to express EPC-1 under all conditions tested. The decline in EPC-1 mRNA is gradual during the replicative life span and correlates inversely with the population doubling level (PDL) of the cells. The objective of this study was to determine whether the decline in EPC-7 mRNA abundance observed during proliferative senescence also occurs in cultures derived from donors of different ages. To address this question, we examined the abundance of EPC-1 mRNA in 28 skin fibroblast lines established from healthy donors of different ages ranging from 12 fetal weeks to 94 years. EPC-1 expression was measured, under conditions of growth arrest, prior to the end of the replicative life span of the cultures. Despite some variability in steady-state transcript levels among the cell lines, EPC-1 expression was significantly lower in cells derived from the fetal donor group (12-20 gestational weeks) than in cells derived from adult donors. An in vitro age-dependent decline in EPC-1 expression was observed in all the skin lines examined, independent of donor age; however, no significant difference was observed between the young adult donor group (17-33 years) and the old adult donor group (78-94 years). Thus, expression of EPC-1 is linked to the replicative age of the cells and whether the cells are derived from fetal skin or adult skin. In adults, EPC-1 expression is independent of donor age.

pRb controls proliferation, differentiation, and death of skeletal muscle cells and other lineages during embryogenesis

Mice deficient for the RB gene (RB-/-), prior to death at embryonic day 14.5, show increased cell death in all tissues that normally express RB1: the nervous system, liver, lens, and skeletal muscle precursor cells. We have generated transgenic mice (RBlox) that express low levels of pRb, driven by an RB1 minigene. RBlox/RB-/- mutant fetuses die at birth with specific skeletal muscle defects, including increased cell death prior to myoblast fusion, shorter myotubes with fewer myofibrils, reduced muscle fibers, accumulation of elongated nuclei that actively synthesized DNA within the myotubes, and reduction in expression of the late muscle-specific genes MCK and MRF4. Thus, insufficient pRb results in failure of myogenesis in vivo, manifest in two ways. First, the massive apoptosis of myoblasts implicates a role of pRb in cell survival. Second, surviving myotubes failed to develop normally and accumulated large polyploid nuclei, implicating pRb in permanent withdrawal from the cell cycle. These results demonstrate a role for pRb during terminal differentiation of skeletal muscles in vivo and place pRb at a nodal point that controls cell proliferation, differentiation, and death.

Prevention of activity-dependent neuronal death: vasoactive intestinal polypeptide stimulates astrocytes to secrete the thrombin-inhibiting neurotrophic serpin, protease nexin I

Neuronal cell death occurs as a programmed, naturally occurring mechanism and is the primary regressive event in central nervous system development. Death of neurons also occurs on an injury-induced basis after trauma and in human neurodegenerative diseases. Classical neurotrophic factors can reverse this phenomenon in experimental models prompting initiation of clinical trials in conditions such as amyotrophic lateral sclerosis and Alzheimer's disease. The glial-derived protease nexin I (PNI), a known promoter of neurite outgrowth in cell culture and a potent inhibitor of serine proteases, also enhances neuronal cell survival. PNI, in nanomolar concentrations, rescues spinal cord motor neurons from both naturally-occurring programmed cell death in the chick embryo as well as following injury in the neonatal mouse. The potent neuromodulator, vasoactive intestinal polypeptide (VIP), influences neuronal survival through glial-mediated factors and also induces secretion of newly synthesized astrocyte PNI. We now report that subnanomolar amounts of PNI enhance neuronal survival in mixed spinal cord cell culture, especially when neuronal cells were made electrically silent by administration of tetrodotoxin. The mediation of this effect is by inhibition of the multifunctional serine protease, thrombin, because hirudin, a thrombin-specific inhibitor, has the same effect. In addition, spinal cord neurons are exquisitely sensitive to thrombin because picomolar and lower levels of the coagulation factor causes neuronal death. Thus, PNI is an astrocyte-derived, thrombin-inhibiting, activity-dependent neurotrophic agent, enhanced secretion of which by VIP may be one approach to treat neurological disorders.