Hypoxia negatively regulates antimetastatic PEDF in melanoma cells by a hypoxia inducible factor-independent, autophagy dependent mechanism

Autophagy in BRAF-mutant cutaneous melanoma: recent advances and therapeutic perspective

Macroautophagy, hereafter referred to as autophagy, represents a highly conserved catabolic process that maintains cellular homeostasis. At present, the role of autophagy in cutaneous melanoma (CM) is still controversial, since it appears to be tumor-suppressive at early stages of malignant transformation and cancer-promoting during disease progression. Interestingly, autophagy has been found to be often increased in CM harboring BRAF mutation and to impair the response to targeted therapy. In addition to autophagy, numerous studies have recently conducted in cancer to elucidate the molecular mechanisms of mitophagy, a selective form of mitochondria autophagy, and secretory autophagy, a process that facilitates unconventional cellular secretion. Although several aspects of mitophagy and secretory autophagy have been investigated in depth, their involvement in BRAF-mutant CM biology has only recently emerged. In this review, we aim to overview autophagy dysregulation in BRAF-mutant CM, along with the therapeutic advantages that may arise from combining autophagy inhibitors with targeted therapy. In addition, the recent advances on mitophagy and secretory autophagy involvement in BRAF-mutant CM will be also discussed. Finally, since a number of autophagy-related non-coding RNAs (ncRNAs) have been identified so far, we will briefly discussed recent advances linking ncRNAs to autophagy regulation in BRAF-mutant CM.

Newly identified form of phenotypic plasticity of cancer: immunogenic mimicry

Cancer plasticity is now a recognized new hallmark of cancer which is due to disturbances of cell differentiation programs. It is manifested not only in various forms like the best-known epithelial-mesenchymal transition (EMT) but also in vasculogenic and megakaryocytic mimicries regulated by EMT-specific or less-specific transcription factors such as HIF1a or STAT1/2. Studies in the past decades provided ample data that cancer plasticity can be manifested also in the expression of a vast array of immune cell genes; best-known examples are PDL1/CD274, CD47, or IDO, and we termed it immunogenic mimicry (IGM). However, unlike other types of plasticities which are epigenetically regulated, expression of IGM genes are frequently due to gene amplifications. It is important that the majority of the IGM genes are regulated by interferons (IFNs) suggesting that their protein expressions are regulated by the immune microenvironment. Most of the IGM genes have been shown to be involved in immune escape of cancers broadening the repertoire of these mechanisms and offering novel targets for immunotherapeutics.

[Vasculogenic mimicry]

Anti-angiogenic drugs are used as an established approach of malignant neoplasms therapy. It has been established that the development of the phenomenon of vasculogenic mimicry - a specific variant of tumor neoangiogenesis, which is formed in highly aggressive solid tumors, is associated with a decrease in the effectiveness of antitumor therapy. This review highlights the mechanisms of development of vasculogenic mimicry in malignant neoplasms, which is one of the alternative options for tumor blood supply. In the formation of vasculogenic mimicry, an important role is assigned to the tumor microenvironment, primarily tumor-associated macrophages and fibroblasts. The signaling pathways that regulate the formation of vasculogenic mimicry channels in tumors have been characterized. The prospects for a targeted impact on molecular targets that initiate and promote vasculogenic mimicry, the impact on which can increase the effectiveness of antitumor therapy, are shown. The review discusses experimental studies of the mechanisms of vasculogenic mimicry formation in malignant neoplasms and the prospects for targeted action on molecules that are components of signaling cascades involved in the development of this model of neoangiogenesis.

CircSERPINA3 regulates SERPINA3-mediated apoptosis, autophagy and aerobic glycolysis of prostate cancer cells by competitively binding to MiR-653-5p and recruiting BUD13

BACKGROUND

Prostate cancer (PCa) belongs to an epithelial malignancy that occurs in the prostate gland and is the most common malignancy of the male genitourinary system. Referring to related literature, circSERPINA3 has been reported to be up-regulated in PCa. However, its biological function remains unclear.

PURPOSE

This study aimed to reveal the specific role and relevant molecular mechanism of circSERPINA3 in PCa.

METHODS

RT-qPCR was used to examine gene expression and functional analyses were conducted to verify the effect of circSERPINA3 on cell apoptosis, autophagy and aerobic glycolysis in PCa cells. Mechanism assays were applied to evaluate the relationship among circSERPINA3/miR-653-5p/SERPINA3/BUD13.

RESULTS

CircSERPINA3 was verified to be up-regulated in PCa cells and to inhibit cell apoptosis while promoting aerobic glycolysis and autophagy in PCa cells. CircSERPINA3 and SERPINA3 were also testified to bind to miR-653-5p through a line of mechanism experiments. Moreover, it was discovered that circSERPINA3 could stabilize SERPINA3 mRNA via recruiting BUD13. Additionally, SERPINA3 was verified to inhibit cell apoptosis, while promoting aerobic glycolysis and autophagy in PCa cells.

CONCLUSIONS

Our study suggested that circSERPINA3 regulated apoptosis, autophagy and aerobic glycolysis of PCa cells by competitively binding to miR-653-5p and recruiting BUD13.

The increasing role of pigment epithelium-derived factor in metastasis: from biological importance to a promising target

Pigment epithelium-derived factor (PEDF) is a non-inhibitory member of the serpin (serine protease inhibitor) family and is a well-known potent anti-tumor factor in a variety of cancers. It has been ascertained that PEDF regulates multiple metastatic processes through various plausible mechanisms, including inhibiting angiogenesis, inducing apoptosis, stimulating extracellular matrix (ECM) degradation, and suppressing the epithelial-to-mesenchymal transition (EMT) process. Although PEDF has been recognized as an anti-metastatic marker in most studies, its role remains controversial with conflicting reports of PEDF as a metastatic marker. The emerging insights into the mechanism(s) of PEDF in tumor progression and its therapeutic effects are discussed systematically in this review, aiming to improve our understanding in the context of metastasis and drug development.

Hypoxia-dependent drivers of melanoma progression

Hypoxia, a condition of low oxygen availability, is a hallmark of tumour microenvironment and promotes cancer progression and resistance to therapy. Many studies reported the essential role of hypoxia in regulating invasiveness, angiogenesis, vasculogenic mimicry and response to therapy in melanoma. Melanoma is an aggressive cancer originating from melanocytes located in the skin (cutaneous melanoma), in the uveal tract of the eye (uveal melanoma) or in mucosal membranes (mucosal melanoma). These three subtypes of melanoma represent distinct neoplasms in terms of biology, epidemiology, aetiology, molecular profile and clinical features.In this review, the latest progress in hypoxia-regulated pathways involved in the development and progression of all melanoma subtypes were discussed. We also summarized current knowledge on preclinical studies with drugs targeting Hypoxia-Inducible Factor-1, angiogenesis or vasculogenic mimicry. Finally, we described available evidence on clinical studies investigating the use of Hypoxia-Inducible Factor-1 inhibitors or antiangiogenic drugs, alone or in combination with other strategies, in metastatic and adjuvant settings of cutaneous, uveal and mucosal melanoma.Hypoxia-Inducible Factor-independent pathways have been also reported to regulate melanoma progression, but this issue is beyond the scope of this review.As evident from the numerous studies discussed in this review, the increasing knowledge of hypoxia-regulated pathways in melanoma progression and the promising results obtained from novel antiangiogenic therapies, could offer new perspectives in clinical practice in order to improve survival outcomes of melanoma patients.

Hypoxia and Extracellular Acidification as Drivers of Melanoma Progression and Drug Resistance

Hypoxia and elevated extracellular acidification are prevalent features of solid tumors and they are often shown to facilitate cancer progression and drug resistance. In this review, we have compiled recent and most relevant research pertaining to the role of hypoxia and acidification in melanoma growth, invasiveness, and response to therapy. Melanoma represents a highly aggressive and heterogeneous type of skin cancer. Currently employed treatments, including BRAF V600E inhibitors and immune therapy, often are not effective due to a rapidly developing drug resistance. A variety of intracellular mechanisms impeding the treatment were discovered. However, the tumor microenvironment encompassing stromal and immune cells, extracellular matrix, and physicochemical conditions such as oxygen level or acidity, may also influence the therapy effectiveness. Hypoxia and acidification are able to reprogram the metabolism of melanoma cells, enhance their survival and invasiveness, as well as promote the immunosuppressive environment. For this reason, these physicochemical features of the melanoma niche and signaling pathways related to them emerge as potential therapeutic targets.

Therapeutic Potential of Pigment Epithelium-derived Factor in Cancer

Pigment epithelium-derived factor (PEDF) is one of the serine protease inhibitors with multifunctional properties, which is produced by various types of organs and tissues. There is an accumulating body of evidence that PEDF plays an important role in the maintenance of tissue homeostasis. Indeed, PEDF not only works as an endogenous inhibitor of angiogenesis, but also suppresses oxidative stress, inflammatory and thrombotic reactions in cell culture systems, animal models, and humans. Furthermore, we, along with others, have found that PEDF inhibits proliferation of, and induces apoptotic cell death in, numerous kinds of tumors. In addition, circulating as well as tumor expression levels of PEDF have been inversely associated with tumor growth and metastasis. These observations suggest that supplementation of PEDF proteins and/or enhancement of endogenous PEDF expression could be a novel therapeutic strategy for the treatment of cancer. Therefore, in this paper, we review the effects of PEDF on diverse types of cancer, and discuss its therapeutic perspectives.

Pigment Epithelium-Derived Factor Promotes the Growth and Migration of Human Esophageal Squamous Cell Carcinoma

Pigment epithelium-derived factor (PEDF) is an oncogene found in various types of cancers. However, how PEDF affects the development of human esophageal squamous cell carcinoma (ESCC) is unknown. This study investigates the role of PEDF in ESCC cell proliferation, migration, and cell cycle both in vitro and in vivo. The PEDF expression was examined in patient tumor samples and ESCC cell lines. Short hairpin RNA technology was used to inhibit the PEDF expression in ESCC EC9706 and KYSE150 cells. In vitro cell proliferation and migration assays were performed. The effects of PEDF on tumor growth and progression were examined in vivo in murine subcutaneous xenograft tumor models. It was found that PEDF was overexpressed in esophageal cancer cells and patient tumor tissues compared to normal control samples. PEDF enhanced cell cycle progression and inhibited cell apoptosis. Knock down of PEDF inhibited esophageal cell proliferation and migration in vitro. Moreover, Inhibition of PEDF significantly reduced tumor growth and tumor size in vivo. These results indicate that PEDF induce tumorigenesis in ESCC and can be a potential therapeutic target for cancer treatment.

Endothelial cell-specific redox gene modulation inhibits angiogenesis but promotes B16F0 tumor growth in mice

Glutaredoxin-1 (Glrx) is a small cytosolic enzyme that removes S-glutathionylation, glutathione adducts of protein cysteine residues, thus modulating redox signaling and gene transcription. Although Glrx up-regulation prevented endothelial cell (EC) migration and global Glrx transgenic mice had impaired ischemic vascularization, the effects of cell-specific Glrx overexpression remained unknown. Here, we examined the role of EC-specific Glrx up-regulation in distinct models of angiogenesis; namely, hind limb ischemia and tumor angiogenesis. EC-specific Glrx transgenic (EC-Glrx TG) overexpression in mice significantly impaired EC migration in Matrigel implants and hind limb revascularization after femoral artery ligation. Additionally, ECs migrated less into subcutaneously implanted B16F0 melanoma tumors as assessed by decreased staining of EC markers. Despite reduced angiogenesis, EC-Glrx TG mice unexpectedly developed larger tumors compared with control mice. EC-Glrx TG mice showed higher levels of VEGF-A in the tumors, indicating hypoxia, which may stimulate tumor cells to form vascular channels without EC, referred to as vasculogenic mimicry. These data suggest that impaired ischemic vascularization does not necessarily associate with suppression of tumor growth, and that antiangiogenic therapies may be ineffective for melanoma tumors because of their ability to implement vasculogenic mimicry during hypoxia.-Yura, Y., Chong, B. S. H., Johnson, R. D., Watanabe, Y., Tsukahara, Y., Ferran, B., Murdoch, C. E., Behring, J. B., McComb, M. E., Costello, C. E., Janssen-Heininger, Y. M. W., Cohen, R. A., Bachschmid, M. M., Matsui, R. Endothelial cell-specific redox gene modulation inhibits angiogenesis but promotes B16F0 tumor growth in mice.

Critical Functionality Effects from Storage Temperature on Human Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium Cell Suspensions

Human induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (hiPSC-RPE) cells suspension have the potential for regenerative treatment. However, practical regenerative applications with hiPSC-RPE cells require the development of simple and cost-effective non-freezing preservation methods. We investigated the effect of non-freezing temperatures on suspended hiPSC-RPE cells in various conditions and analysed mechanisms of cell death, anoikis, Rho GTPases, hypoxia, microtubule destruction, and cell metabolism. Cells stored at 37 °C had the lowest viability due to hypoxia from high cell metabolism and cell deposits, and cells preserved at 4 °C were damaged via microtubule fragility. Cell suspensions at 16 °C were optimal with drastically reduced apoptosis and negligible necrosis. Moreover, surviving cells proliferated and secreted key proteins normally, compared to cells without preservation. hiPSC-RPE cell suspensions were optimally preserved at 16 °C. Temperatures above or below the optimal temperature decreased cell viability significantly yet differentially by mechanisms of cell death, cellular metabolism, microtubule destruction, and oxygen tension, all relevant to cell conditions. Surviving cells are expected to function as grafts where high cell death is often reported. This study provides new insight into various non-freezing temperature effects on hiPSC-RPE cells that are highly relevant to clinical applications and may improve cooperation between laboratories and hospitals.

Pigment epithelium-derived factor: a key mediator in bone homeostasis and potential for bone regenerative therapy

Objectives

Pigment epithelium-derived factor (PEDF), a multifunctional endogenous glycoprotein, has a very wide range of biological actions, notably in bone homeostasis. The question has been raised regarding the place of PEDF in the treatment of bone disorders and osteosarcoma, and its potential for tumour growth suppression.

Methods

The PubMed database was used to compile this review.

Key findings

Pigment epithelium-derived factor's actions in osteoid tissues include promoting mesenchymal stem cell commitment to osteoblasts, increasing matrix mineralisation, and promoting osteoblast proliferation. It shows potential to improve therapeutic outcomes in treatment of multiple cancer types and regrowth of bone after trauma or resection in animal studies. PEDF may possibly have a reduced adverse effect profile compared with current osteo-regenerative treatments; however, there is currently very limited evidence regarding the safety or efficacy in human models.

Summary

Pigment epithelium-derived factor is very active within the body, particularly in osseous tissue, and its physiological actions give it potential for treatment of both bone disorders and multiple tumour types. Further research is needed to ascertain the adverse effects and safety profile of PEDF as a therapeutic agent.

HIF-2α promotes the formation of vasculogenic mimicry in pancreatic cancer by regulating the binding of Twist1 to the VE-cadherin promoter

Vasculogenic mimicry (VM) is a blood supply modality that occurs independently of endothelial cell angiogenesis. Hypoxia and the epithelial-mesenchymal transition (EMT) induce VM formation by remodeling the extracellular matrix. Our previous study demonstrated that hypoxia-inducible factor-2 alpha (HIF-2α) promotes the progress of EMT in pancreatic cancer; however, whether HIF-2α promotes VM formation in pancreatic cancer remains unknown. In this study, we investigated HIF-2α expression and VM by immunohistochemistry in 70 pancreatic cancer patients as well as the role of Twist1and Twist2 in HIF-2α-induced VM in vitro and in vivo. We found that the overexpression of HIF-2α and VM were correlated with poor tumor differentiation, late clinical stage and lymph node metastasis, and a poor prognosis in pancreatic cancer. Moreover, the upregulation of HIF-2α in SW1990 cells induced VM formation, whereas the opposite results were found after silencing HIF-2α in AsPC-1 cells. A mechanistic study indicated that HIF-2α might regulate the binding of twist1 to vascular endothelial cadherin (VE-cadherin) to promote VM formation in pancreatic cancer cells, and that the P1 (-421bp) and P4 (-2110bp) regions of the Twist1 binding sequences are positive regulatory elements for VE-cadherin. In addition, we confirmed that the overexpression of HIF-2α increased Twist1 expression and promoted tumor growth and VM formation in pancreatic cancer xenografts in nude mice. These findings indicated that HIF-2α might play a critical role in VM and that HIF-2α and the pathway of HIF-2α inducing VM formation are potential therapeutic targets for pancreatic cancer.

Collateral Damage Intended-Cancer-Associated Fibroblasts and Vasculature Are Potential Targets in Cancer Therapy

After oncogenic transformation, tumor cells rewire their metabolism to obtain sufficient energy and biochemical building blocks for cell proliferation, even under hypoxic conditions. Glucose and glutamine become their major limiting nutritional demands. Instead of being autonomous, tumor cells change their immediate environment not only by their metabolites but also by mediators, such as juxtacrine cell contacts, chemokines and other cytokines. Thus, the tumor cells shape their microenvironment as well as induce resident cells, such as fibroblasts and endothelial cells (ECs), to support them. Fibroblasts differentiate into cancer-associated fibroblasts (CAFs), which produce a qualitatively and quantitatively different extracellular matrix (ECM). By their contractile power, they exert tensile forces onto this ECM, leading to increased intratumoral pressure. Moreover, along with enhanced cross-linkage of the ECM components, CAFs thus stiffen the ECM. Attracted by tumor cell- and CAF-secreted vascular endothelial growth factor (VEGF), ECs sprout from pre-existing blood vessels during tumor-induced angiogenesis. Tumor vessels are distinct from EC-lined vessels, because tumor cells integrate into the endothelium or even mimic and replace it in vasculogenic mimicry (VM) vessels. Not only the VM vessels but also the characteristically malformed EC-lined tumor vessels are typical for tumor tissue and may represent promising targets in cancer therapy.

Disrupting Tumor Angiogenesis and "the Hunger Games" for Breast Cancer

Angiogenesis, one of the hallmarks of cancers, has become an attractive target for cancer therapy since decades ago. It is broadly thought that upregulation of angiogenesis is involved in tumor progression and metastasis. Though tumor vessels are tortuous, disorganized, and leaky, they deliver oxygen and nutrients for tumor development. Based on this knowledge, many kinds of drugs targeting angiogenesis pathways have been developed, such as bevacizumab. However, the clinical outcomes of anti-angiogenesis therapies are moderate in metastatic breast cancer as well as in metastatic colorectal cancer and non-small cell lung cancer, even combined with traditional chemotherapy. In this chapter, the morphologic angiogenesis patterns and the key molecular pathways regulating angiogenesis are elaborated. The FDA-approved anti-angiogenesis drugs and current challenges of anti-angiogenesis therapy are described. The strategies to overcome the barriers will also be elucidated.

Tumor cell vascular mimicry: Novel targeting opportunity in melanoma

In 1999, the American Journal of Pathology published an article, entitled "Vascular channel formation by human melanoma cells in vivo and in vitro: vasculogenic mimicry" by Maniotis and colleagues, which ignited a spirited debate for several years and earned the journal's distinction of a "citation classic" (Maniotis et al., 1999). Tumor cell vasculogenic mimicry (VM), also known as vascular mimicry, describes the plasticity of aggressive cancer cells forming de novo vascular networks and is associated with the malignant phenotype and poor clinical outcome. The tumor cells capable of VM share the commonality of a stem cell-like, transendothelial phenotype, which may be induced by hypoxia. Since its introduction as a novel paradigm for melanoma tumor perfusion, many studies have contributed new findings illuminating the underlying molecular pathways supporting VM in a variety of tumors, including carcinomas, sarcomas, glioblastomas, astrocytomas, and melanomas. Of special significance is the lack of effectiveness of angiogenesis inhibitors on tumor cell VM, suggesting a selective resistance by this phenotype to conventional therapy. Facilitating the functional plasticity of tumor cell VM are key proteins associated with vascular, stem cell, extracellular matrix, and hypoxia-related signaling pathways--each deserving serious consideration as potential therapeutic targets and diagnostic indicators of the aggressive, metastatic phenotype. This review highlights seminal findings pertinent to VM, including the effects of a novel, small molecular compound, CVM-1118, currently under clinical development to target VM, and illuminates important molecular pathways involved in the suppression of this plastic, aggressive phenotype, using melanoma as a model.

Melanoma Cells Block PEDF Production in Fibroblasts to Induce the Tumor-Promoting Phenotype of Cancer-Associated Fibroblasts

Loss of pigment epithelium-derived factor (PEDF, SERPINF1) in cancer cells is associated with poor prognosis and metastasis, but the contribution of stromal PEDF to cancer evolution is poorly understood. Therefore, we investigated the role of fibroblast-derived PEDF in melanoma progression. We demonstrate that normal dermal fibroblasts expressing high PEDF levels attenuated melanoma growth and angiogenesis in vivo, whereas PEDF-depleted fibroblasts exerted tumor-promoting effects. Accordingly, mice with global PEDF knockout were more susceptible to melanoma metastasis. We also demonstrate that normal fibroblasts in close contact with PEDF-null melanoma cells lost PEDF expression and tumor-suppressive properties. Further mechanistic investigations underlying the crosstalk between tumor and stromal cells revealed that melanoma cells produced PDGF-BB and TGFβ, which blocked PEDF production in fibroblasts. Notably, cancer-associated fibroblasts (CAF) isolated from patient-derived tumors expressed markedly low levels of PEDF. Treatment of patient CAF and TGFβ-treated normal fibroblasts with exogenous PEDF decreased the expression of CAF markers and restored PEDF expression. Finally, expression profiling of PEDF-depleted fibroblasts revealed induction of IL8, SERPINB2, hyaluronan synthase-2, and other genes associated with tumor promotion and metastasis. Collectively, our results demonstrate that PEDF maintains tumor-suppressive functions in fibroblasts to prevent CAF conversion and illustrate the mechanisms by which melanoma cells silence stromal PEDF to promote malignancy. Cancer Res; 76(8); 2265-76. ©2016 AACR.

Downregulation of pyrroline-5-carboxylate reductase-2 induces the autophagy of melanoma cells via AMPK/mTOR pathway

Melanoma is the most aggressive form of skin cancer and causes 50,000 deaths annually worldwide. The roles of proline-dependent process and autophagy have both been reported in studies on melanoma. In the present study, we focused on the effect of pyrroline-5-carboxylate reductase-2 (PYCR2) on inducing autophagy process in melanoma. The expression of PYCR2 was regulated by an RNAi technique, and the cell proliferation of A375 cell line was determined by methyl thiazolyl tetrazolium test; the effect of PYCR2 on the apoptosis process and AMPK/mTOR pathway was evaluated by flow cytometry assay and Western blot. It was found that silence of PYCR2 resulted in the decrease of proliferative ability and activation of AMPK/mTOR-induced autophagy of A375 cells. PYCR2 silencing also activated AMPK/mTOR pathway in another melanoma cell line, CHL-1. However, the overexpression of PYCR2 seemed to make no difference to the cell viability and targeted pathway. Our results offered a preliminary illustration on the mechanism of the PYCR2-dependent autophagy and showed that PYCR2 was a potential therapeutic target of melanoma.

PEDF and its roles in physiological and pathological conditions: implication in diabetic and hypoxia-induced angiogenic diseases

Pigment epithelium-derived factor (PEDF) is a broadly expressed multifunctional member of the serine proteinase inhibitor (serpin) family. This widely studied protein plays critical roles in many physiological and pathophysiological processes, including neuroprotection, angiogenesis, fibrogenesis and inflammation. The present review summarizes the temporal and spatial distribution patterns of PEDF in a variety of developing and adult organs, and discusses its functions in maintaining physiological homoeostasis. The major focus of the present review is to discuss the implication of PEDF in diabetic and hypoxia-induced angiogenesis, and the pathways mediating PEDF's effects under these conditions. Furthermore, the regulatory mechanisms of PEDF expression, function and degradation are also reviewed. Finally, the therapeutic potential of PEDF as an anti-angiogenic drug is briefly summarized.

Chronic intermittent hypoxia increases encoding pigment epithelium-derived factor gene expression, although not that of the protein itself, in the temporal cortex of rats

Objective:

Obstructive sleep apnea syndrome is mainly characterized by intermittent hypoxia (IH) during sleep, being associated with several complications. Exposure to IH is the most widely used animal model of sleep apnea, short-term IH exposure resulting in cognitive and neuronal impairment. Pigment epithelium-derived factor (PEDF) is a hypoxia-sensitive factor acting as a neurotrophic, neuroprotective, and antiangiogenic agent. Our study analyzed performance on learning and cognitive tasks, as well as PEDF gene expression and PEDF protein expression in specific brain structures, in rats exposed to long-term IH.

Methods:

Male Wistar rats were exposed to IH (oxygen concentrations of 21-5%) for 6 weeks-the chronic IH (CIH) group-or normoxia for 6 weeks-the control group. After CIH exposure, a group of rats were allowed to recover under normoxic conditions for 2 weeks (the CIH+N group). All rats underwent the Morris water maze test for learning and memory, PEDF gene expression and PEDF protein expression in the hippocampus, frontal cortex, and temporal cortex being subsequently assessed.

Results:

The CIH and CIH+N groups showed increased PEDF gene expression in the temporal cortex, PEDF protein expression remaining unaltered. PEDF gene expression and PEDF protein expression remained unaltered in the frontal cortex and hippocampus. Long-term exposure to IH did not affect cognitive function.

Conclusions:

Long-term exposure to IH selectively increases PEDF gene expression at the transcriptional level, although only in the temporal cortex. This increase is probably a protective mechanism against IH-induced injury.

Regulatory and functional connection of microphthalmia-associated transcription factor and anti-metastatic pigment epithelium derived factor in melanoma

Pigment epithelium-derived factor (PEDF), a member of the serine protease inhibitor superfamily, has potent anti-metastatic effects in cutaneous melanoma through its direct actions on endothelial and melanoma cells. Here we show that PEDF expression positively correlates with microphthalmia-associated transcription factor (MITF) in melanoma cell lines and human samples. High PEDF and MITF expression is characteristic of low aggressive melanomas classified according to molecular and pathological criteria, whereas both factors are decreased in senescent melanocytes and naevi. Importantly, MITF silencing down-regulates PEDF expression in melanoma cell lines and primary melanocytes, suggesting that the correlation in the expression reflects a causal relationship. In agreement, analysis of Chromatin immunoprecipitation coupled to high throughput sequencing (ChIP-seq) data sets revealed three MITF binding regions within the first intron of SERPINF1, and reporter assays demonstrated that the binding of MITF to these regions is sufficient to drive transcription. Finally, we demonstrate that exogenous PEDF expression efficiently halts in vitro migration and invasion, as well as in vivo dissemination of melanoma cells induced by MITF silencing. In summary, these results identify PEDF as a novel transcriptional target of MITF and support a relevant functional role for the MITF-PEDF axis in the biology of melanoma.

Fibrocyte-like cells from intrauterine growth restriction placentas have a reduced ability to stimulate angiogenesis

Intrauterine growth restriction (IUGR) is a common complication of pregnancy whereby the fetus fails to achieve its genetic growth potential. Malformation of the placental vasculature is observed in IUGR and may be due to the development of the placenta in a chronically hypoxic environment. Recently, we identified that the predominant stromal cells in the angiogenic zones of the placenta are fibrocyte-like cells. The conditioned medium from fibrocyte-like cells (FcCM) has been shown to stimulate angiogenesis in vitro. Thus, we hypothesized that FcCM from IUGR cells would have a reduced ability to stimulate angiogenesis and that chronic hypoxia would decrease the ability of both normal and IUGR fibrocyte-like cells to stimulate angiogenesis. IUGR FcCM had a reduced ability to stimulate endothelial tubule-like structure formation and an increased ability to stimulate endothelial migration compared with normal FcCM. However, normal and IUGR FcCM produced in chronic hypoxia did not alter endothelial proliferation, migration, or tubule-like structure formation. IUGR FcCM was found to have reduced levels of the pro-angiogenic cytokine IL-8 and increased levels of the anti-angiogenic factors activin-A and pigment epithelium-derived growth factor. Thus, alterations in the ability of IUGR fibrocyte-like cells to stimulate angiogenesis may contribute to the development of vascular malformation in IUGR, but in vitro these changes cannot be attributed to a chronically hypoxic environment.

Targeting autophagy as a potential therapeutic approach for melanoma therapy

Melanoma, occurring as a rapidly progressive skin cancer, is resistant to current chemo- and radiotherapy, especially after metastases to distant organs has taken place. Most chemotherapeutic drugs exert their cytotoxic effect by inducing apoptosis, which, however, is often deficient in cancer cells. Thus, it is appropriate to attempt the targeting of alternative pathways, which regulate cellular viability. Recent studies of autophagy, a well-conserved cellular catabolic process, promise to improve the therapeutic outcome in melanoma patients. Although a dual role for autophagy in cancer therapy has been reported, both protecting against and promoting cell death, the potential for using autophagy in cancer therapy seems to be promising. Here, we review the recent literature on the role of autophagy in melanoma with respect to the expression of autophagic markers, the involvement of autophagy in chemo- and immunotherapy, as well as the role of autophagy in hypoxia and altered metabolic pathways employed for melanoma therapy.

Host pigment epithelium-derived factor (PEDF) prevents progression of liver metastasis in a mouse model of uveal melanoma

Uveal melanoma (UM) has a 30 % 5-year mortality rate, primarily due to liver metastasis. Both angiogenesis and stromagenesis are important mechanisms for the progression of liver metastasis. Pigment epithelium-derived factor (PEDF), an anti-angiogenic and anti-stromagenic protein, is produced by hepatocytes. Exogenous PEDF suppresses metastasis progression; however, the effects of host-produced PEDF on metastasis progression are unknown. We hypothesize that host PEDF inhibits liver metastasis progression through a mechanism involving angiogenesis and stromagenesis. Mouse melanoma cells were injected into the posterior ocular compartment of PEDF-null mice and control mice. After 1 month, the number, size, and mean vascular density (MVD) of liver metastases were determined. The stromal component of hepatic stellate cells (HSCs) and the type III collagen they produce was evaluated by immunohistochemistry. Host PEDF inhibited the total area of liver metastasis and the frequency of macrometastases (diameter >200 μm) but did not affect the total number of metastases. Mice expressing PEDF exhibited significantly lower MVD and less type III collagen production in metastases. An increase in activated HSCs was seen in the absence of PEDF, but this result was not statistically significant. In conclusion, host PEDF inhibits the progression of hepatic metastases in a mouse model of UM, and loss of PEDF is accompanied by an increase in tumor blood vessel density and type III collagen.

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.

Tumor cell vasculogenic mimicry: from controversy to therapeutic promise

In 1999, The American Journal of Pathology published an article entitled "Vascular channel formation by human melanoma cells in vivo and in vitro: vasculogenic mimicry," by Maniotis and colleagues, which ignited a spirited debate for several years and earned distinction as a citation classic. Tumor cell vasculogenic mimicry (VM) refers to the plasticity of aggressive cancer cells forming de novo vascular networks, which thereby contribute to perfusion of rapidly growing tumors, transporting fluid from leaky vessels, and/or connecting with the constitutional endothelial-lined vasculature. The tumor cells capable of VM share a plastic, transendothelial phenotype, which may be induced by hypoxia. Since VM was introduced as a novel paradigm for melanoma tumor perfusion, many studies have contributed new findings illuminating the underlying molecular pathways supporting VM in a variety of tumors, including carcinomas, sarcomas, glioblastomas, astrocytomas, and melanomas. Facilitating the functional plasticity of tumor cell VM are key proteins associated with vascular, stem cell, and hypoxia-related signaling pathways, each deserving serious consideration as potential therapeutic targets and diagnostic indicators of the aggressive, metastatic phenotype.