A study of the Effects of Angiotensins 1, 2, 3 and Bradykinin on the Replication of Bovine Retinal Capillary Endothelial Cells and Pericytes

The renin-angiotensin system of the human eye may play a role in the regulation of retinal blood flow and the development of new vessels. We have investigated whether angiotensins 1, 2 and 3 or bradykinin, in concentrations ranging between 1 × 10–12 and 1 × 10–6, have any mitogenic activity on cultured bovine retinal endothelial cells (BREC) and pericytes (BRP). Cell replication was assessed by 3H-thymidine incorporation and, in the case of BREC and A T-2, also by cell counts. A T-2 was also tested on bovine aortic EC (BAEC). None of the substances elicited any response on BREC, BRP or BAEC. Whether angiotensin(s) induce angiogenesis in retinal vessels in vivo remains to be established but this does not appear to occur through direct stimulation of cell replication.

Effect of hypoxia on tissue factor pathway inhibitor expression in breast cancer

ESSENTIALS: A hypoxic microenvironment is a common feature of tumors that may influence activation of coagulation. MCF-7 and SK-BR-3 breast cancer cells and breast cancer tissue samples were used. The results showed transcriptional repression of tissue factor pathway inhibitor expression in hypoxia. Hypoxia-inducible factor 1α may be a target for the therapy of cancer-related coagulation and thrombosis.

BACKGROUND

Activation of coagulation is a common finding in patients with cancer, and is associated with an increased risk of venous thrombosis. As a hypoxic microenvironment is a common feature of solid tumors, we investigated the role of hypoxia in the regulation of tissue factor (TF) pathway inhibitor (TFPI) expression in breast cancer.

OBJECTIVES

To explore the transcriptional regulation of TFPI by hypoxia-inducible factor (HIF)-1α in breast cancer cells and their correlation in breast cancer tissues.

METHODS AND RESULTS

MCF-7 and SK-BR-3 breast cancer cells were cultured in 1% oxygen or treated with cobalt chloride (CoCl2 ) to mimic hypoxia. Time-dependent and dose-dependent downregulation of TFPI mRNA (quantitative RT-PCR) and of free TFPI protein (ELISA) were observed in hypoxia. Western blotting showed parallel increases in the levels of HIF-1α protein and TF. HIF-1α inhibitor abolished or attenuated the hypoxia-induced downregulation of TFPI. Luciferase reporter assay showed that both hypoxia and HIF-1α overexpression caused strong repression of TFPI promoter activity. Subsequent chromatin immunoprecipitation and mutagenesis analysis demonstrated a functional hypoxia response element within the TFPI promoter, located at -1065 to -1060 relative to the transcriptional start point. In breast cancer tissue samples, gene expression analyses showed a positive correlation between the mRNA expression of TFPI and that of HIF-1α.

CONCLUSIONS

This study demonstrates that HIF-1α is involved in the transcriptional regulation of the TFPI gene, and suggests that a hypoxic microenvironment inside a breast tumor may induce a procoagulant state in breast cancer patients.

Inhibition of PDGF-BB by Factor VII-activating protease (FSAP) is neutralized by protease nexin-1, and the FSAP-inhibitor complexes are internalized via LRP

FSAP (Factor VII-activating protease) can inhibit neointima formation and VSMC (vascular smooth-muscle cell) proliferation by cleavage of PDGF-BB (platelet-derived growth factor-BB). Negatively charged polyanions lead to autoactivation of the FSAP, but no information is available concerning the potential regulation of FSAP activity and its metabolism in the vessel wall. In the present study, we demonstrate that the enzymatic activity of FSAP can be inhibited by the serine protease inhibitor, PN-1 (protease nexin-1), that is found in the vasculature. This leads to the loss of the inhibitory effect of FSAP on PDGF-BB-mediated DNA synthesis and mitogen-activated protein kinase phosphorylation in VSMCs. The FSAP-PN-1 complexes bind to the LRP (low-density lipoprotein receptor-related protein) and are subsequently internalized. This binding is inhibited by receptor-associated protein, an antagonist of LRP, as well as heparin. While PDGFbetaR (PDGFbeta receptor) is internalized by an LRP-dependent mechanism after stimulation of cells by PDGF-BB, the FSAP-PN-1 complex neither influenced PDGF-BB-mediated phosphorylation of PDGFbetaR nor its internalization via LRP. Hence, PN-1 inhibits the enzymatic activity of FSAP and neutralizes its effect on PDGF-BB-mediated VSMC proliferation. The FSAP-inhibitor complexes are internalized via LRP without influencing the PDGF-BB signal transduction pathway.

Nucleic acids potentiate Factor VII-activating protease (FSAP)-mediated cleavage of platelet-derived growth factor-BB and inhibition of vascular smooth muscle cell proliferation

FSAP (Factor VII-activating protease) can cleave and inactivate PDGF-BB (platelet-derived growth factor-BB) and thereby inhibits VSMC (vascular smooth-muscle cell) proliferation. The auto-activation of FSAP is facilitated by negatively charged polyanions such as heparin, dextransulfate or extracellular ribonucleic acids. Since auto-activation is essential for the anti-proliferative function of FSAP, the influence of nucleic acids as cofactors for the FSAP-mediated inhibition of PDGF-BB was investigated. Natural or artificial RNA was an effective cofactor for FSAP mediated PDGF-BB degradation, whereas the effect of DNA was weak. RNA-induced cleavage of PDGF-BB was inhibited by serine protease inhibitors. The pattern of PDGF-BB cleavage was identical with either heparin or RNA as a cofactor. One of the cleavage sites in PDGF-BB was at the positions 160-162 (R160KK162), which is an important region for receptor binding and activation. In VSMCs, PDGF-BB-stimulated DNA synthesis was inhibited by FSAP in the presence of RNA. RNA was more effective than DNA and the cofactor activity of RNA was neutralized after pretreatment with RNase. FSAP binding to RNA protected the nucleic acid from degradation by RNase. These data are relevant to situations where extracellular nucleic acids released from necrotic or apoptotic cells could activate local FSAP, leading to inhibition of PDGF-BB.

A positively charged cluster in the epidermal growth factor-like domain of Factor VII-activating protease (FSAP) is essential for polyanion binding

FSAP (Factor VII-activating protease) is a novel plasma-derived serine protease that regulates haemostasis as well as vascular cell proliferation. FSAP undergoes autoactivation in the presence of polyanionic macromolecules such as heparin and RNA. Competition experiments suggest that RNA and heparin bind to the same or overlapping interaction sites. A proteolysis approach, where FSAP was hydrolysed into smaller fragments, was used to identify the polyanion-binding site. The EGF (epidermal growth factor)-like domains EGF2 and EGF3 of FSAP are the major interaction domains for RNA. The amino acids Arg170, Arg171, Ser172 and Lys173 within the EGF3 domain were essential for this binding. This is also the region with the highest positive net charge in the protein and is most probably located in an exposed loop. It is also highly conserved across five species. Disruption of disulphide bridges led to the loss of RNA and heparin binding, indicating that the three-dimensional structure of the EGF3 domain is essential for binding to negatively charged heparin or RNA. The identification of polyanion-binding sites will help to define the role of FSAP in the vasculature.

Developmental patterns of glucagon-like peptide-1-(7-36) amide and peptide-YY in rat pancreas and gut

Glucagon-like peptide-(17-36) amide [GLP-1-(7-36) amide] and peptide tyrosine tyrosine (PYY) are both products of the enteroglucagon cell. To examine the changes occurring during development, we analyzed by RIA the pancreatic concentrations of these two peptides in fetal and neonatal rats. The levels obtained were compared with those of the classical islet hormones, insulin, somatostatin, and glucagon. The total hormone content of the pancreas increased with age for insulin, glucagon, and somatostatin. The amounts of GLP-1-(7-36) amide immunoreactivity (IR) and PYY, however, remained approximately constant in the 3-, 8-, and 30-day-old and adult pancreas. GLP-1-(7-36) amide IR showed only a single peak by gel chromatography, but further analysis by anion exchange chromatography showed that during the fetal period (-18 days) and 3 days postpartum GLP-1-(7-36) amide was the main product, whereas 30 days postpartum and in adult pancreas mainly GLP-1 and an intermediate form were found. Similar analyses of gut extracts revealed that only GLP-1-(7-36) amide is produced during intestinal development. The gut content of GLP-1-(7-36) amide IR and PYY IR increased approximately 100 times between the fetus and the 30-day-old rat. This study reveals a complex and specific regulation of posttranslational processing during maturation for these two peptides.

Characterization of glucagon-like peptide-1-(7-36)amide in the hypothalamus

The distribution of glucagon-like peptide-1-(7-36)amide like immunoreactivity (GLP-1-(7-36)NH2 IR) in rat brain was determined. Highest concentrations were found in the hypothalamus. A combination of gel chromatography and anion exchange chromatography showed that the majority of hypothalamic immunoreactivity exactly corresponded in position to synthetic GLP-1-(7-36)NH2. Chromatographic analyses of rat ileum demonstrated a similar pattern, whereas in rat pancreas mainly a large proglucagon fragment and GLP-1 were indicated. Determination of the subcellular distribution by differential centrifugation of hypothalamic tissue revealed that most of the GLP-1-(7-36)NH2 IR was present in the synaptosome fraction. GLP-1-(7-36)NH2 was released from hypothalamic tissue slices in a calcium-dependent fashion by potassium-induced depolarization. Thus GLP-1-(7-36)NH2 appears to fulfil two criteria for a neurotransmitter. No change was found in its hypothalamic content in streptozocin-induced diabetic rats compared to normal controls but a decrease was seen in hyperinsulinemic hyperglycemic KKAy mice compared to KK mice.

Isolation and characterisation of GLP-1 7-36 amide from rat intestine. Elevated levels in diabetic rats

Glucagon-like peptide-1 (GLP-1) was purified to homogeneity by HPLC and anion-exchange chromatography. A molecular mass of 3297.4 Da was obtained by FAB mass spectrometry which corresponded exactly to GLP-1 7-36 NH2, providing evidence that amidation occurs at an arginine residue during the post-translational processing of GLP-1. The distribution of GLP-1 7-36 NH2-like immunoreactivity (GLP-1 7-36 NH2 IR) was determined in the rat gastrointestinal tract. Highest concentrations were found in terminal ileum and colon. Streptozocin-induced diabetic rats, who showed a significant increase in food intake, had a significant increase of GLP-1 7-36 NH2 IR in the colon.

Differential expression of alpha-CGRP and beta-CGRP by primary sensory neurons and enteric autonomic neurons of the rat

Expression of the calcitonin gene-related peptide, alpha-calcitonin gene-related peptide (CGRP), and the homologous beta-CGRP were compared in sensory and enteric nerves of the rat. Analysis of CGRP-like immunoreactivity by cation exchange chromatography and radioimmunoassay showed that in the dorsal root ganglia, dorsal spinal cord and in those peripheral tissues where CGRP-like immunoreactivity is primarily localized to sensory fibres, alpha-CGRP concentrations were three to six times greater than beta-CGRP concentrations. In the intestine, however, beta-CGRP concentrations were up to seven times greater than alpha-CGRP concentrations. Only beta-CGRP was detected in the intestines of capsaicin-treated rats. Northern blot and in situ hybridization to alpha-CGRP- and beta-CGRP-specific probes showed that while both alpha-CGRP and beta-CGRP messenger ribonucleic acids occurred in the dorsal root ganglia, only beta-CGRP messenger ribonucleic acid occurred in the intestine, where it was localized to enteric neurons. Receptor binding sites on membranes of rat heart and colon had approximately equal affinities for alpha-CGRP and beta-CGRP. The two peptides were equipotent in increasing the rate and force of atrial contractions but alpha-CGRP was slightly (2.6 times) more potent than beta-CGRP in relaxing colonic smooth muscle. Thus, both alpha-CGRP and beta-CGRP occur in the rat nervous system and are both biologically active. Sensory neurons and enteric neurons have been identified as populations which preferentially express alpha-CGRP and beta-CGRP, respectively.