Biphasic regulation of the preproendothelin-1 gene by c-myc

Thrombospondin-1 CD47 Signalling: From Mechanisms to Medicine

Recent advances provide evidence that the cellular signalling pathway comprising the ligand-receptor duo of thrombospondin-1 (TSP1) and CD47 is involved in mediating a range of diseases affecting renal, vascular, and metabolic function, as well as cancer. In several instances, research has barely progressed past pre-clinical animal models of disease and early phase 1 clinical trials, while for cancers, anti-CD47 therapy has emerged from phase 2 clinical trials in humans as a crucial adjuvant therapeutic agent. This has important implications for interventions that seek to capitalize on targeting this pathway in diseases where TSP1 and/or CD47 play a role. Despite substantial progress made in our understanding of this pathway in malignant and cardiovascular disease, knowledge and translational gaps remain regarding the role of this pathway in kidney and metabolic diseases, limiting identification of putative drug targets and development of effective treatments. This review considers recent advances reported in the field of TSP1-CD47 signalling, focusing on several aspects including enzymatic production, receptor function, interacting partners, localization of signalling, matrix-cellular and cell-to-cell cross talk. The potential impact that these newly described mechanisms have on health, with a particular focus on renal and metabolic disease, is also discussed.

Endothelin-1 Regulation Is Entangled in a Complex Web of Epigenetic Mechanisms in Diabetes

Endothelial cells (ECs) are primary targets of glucose-induced tissue damage. As a result of hyperglycemia, endothelin-1 (ET-1) is upregulated in organs affected by chronic diabetic complications. The objective of the present study was to identify novel transcriptional mechanisms that influence ET-1 regulation in diabetes. We carried out the investigation in microvascular ECs using multiple approaches. ECs were incubated with 5 mM glucose (NG) or 25 mM glucose (HG) and analyses for DNA methylation, histone methylation, or long non-coding RNA- mediated regulation of ET-1 mRNA were then performed. DNA methylation array analyses demonstrated the presence of hypomethylation in the proximal promoter and 5’ UTR/first exon regions of EDN1 following HG culture. Further, globally blocking DNA methylation or histone methylation significantly increased ET-1 mRNA expressions in both NG and HG-treated HRECs. While, knocking down the pathogenetic lncRNAs ANRIL, MALAT1, and ZFAS1 subsequently prevented the glucose-induced upregulation of ET-1 transcripts. Based on our past and present findings, we present a novel paradigm that reveals a complex web of epigenetic mechanisms regulating glucose-induced transcription of ET-1. Improving our understanding of such processes may lead to better targeted therapies.

Vascular dysfunction by myofibroblast activation in patients with idiopathic pulmonary fibrosis and prognostic significance

In this study, we demonstrated the importance of telomerase protein expression and determined the relationships among telomerase, endothelin-1 (ET-1) and myofibroblasts during early and late remodeling of parenchymal and vascular areas in usual interstitial pneumonia (UIP) using 27 surgical lung biopsies from patients with idiopathic pulmonary fibrosis (IPF). Telomerase+, myofibroblasts α-SMA+, smooth muscle cells caldesmon+, endothelium ET-1+ cellularity, and fibrosis severity were evaluated in 30 fields covering normal lung parenchyma, minimal fibrosis (fibroblastic foci), severe (mural) fibrosis, and vascular areas of UIP by the point-counting technique and a semiquantitative score. The impact of these markers was determined in pulmonary functional tests and follow-up until death from IPF. Telomerase and ET-1 expression was significantly increased in normal and vascular areas compared to areas of fibroblast foci. Telomerase and ET-1 expression was inversely correlated with minimal fibrosis in areas of fibroblast foci and directly associated with severe fibrosis in vascular areas. Telomerase activity in minimal fibrosis areas was directly associated with diffusing capacity of the lung for oxygen/alveolar volume and ET-1 expression and indirectly associated with diffusing capacity of the lungs for carbon monoxide and severe fibrosis in vascular areas. Cox proportional hazards regression revealed a low risk of death for females with minimal fibrosis displaying high telomerase and ET-1 expression in normal areas. Vascular dysfunction by telomerase/ET-1 expression was found earlier than vascular remodeling by myofibroblast activation in UIP with impact on IPF evolution, suggesting that strategies aimed at preventing the effect of these mediators may have a greater impact on patient outcome.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.

Nitric oxide decreases endothelin-1 secretion through the activation of soluble guanylate cyclase

The use of exogenous nitric oxide (NO) has been shown to alter the regulation of other endothelially derived mediators of vascular tone, such as endothelin-1 (ET-1). However, the interaction between NO and ET-1 appears to be complex and remains incompletely understood. One of the major actions of NO is the activation of soluble guanylate cyclase (sGC) with the subsequent generation of cGMP. Therefore, we undertook this study to test the hypothesis that NO regulates ET-1 production via the activation of the sGC/cGMP pathway. The results obtained indicated that the exposure of primary cultures of 4-wk-old ovine pulmonary arterial endothelial cells (4-wk PAECs) to the long-acting NO donor DETA NONOate induced both a dose- and time-dependent decrease in secreted ET-1. This decrease in ET-1 secretion occurred in the absence of changes in endothelin-converting enzyme-1 or sGC expression but in conjunction with a decrease in prepro-ET-1 mRNA. The changes in ET-1 release were inversely proportional to the cellular cGMP content. Furthermore, the NO-independent activator of sGC, YC-1, or treatment with a cGMP analog also produced significant decreases in ET-1 secretion. Conversely, pretreatment with the sGC inhibitor ODQ blocked the NO-induced decrease in ET-1. Therefore, we conclude that exposure of 4-wk PAECs to exogenous NO decreases secreted ET-1 resulting from the activation of sGC and increased cGMP generation.

Intravenous gene therapy for familial hypercholesterolemia using ligand-facilitated transfer of a liposome:LDL receptor gene complex

Familial hypercholesterolemia (FH) is an autosomal dominant disorder because of a mutation in the low-density lipoprotein receptor (LDLR) gene. Although lowering plasma cholesterol decreases the risk of coronary artery disease, FH patients respond poorly to pharmacologic treatment. Transferrin-facilitated intravenous transfer of a cationic liposome rabbit LDLR cDNA complex alleviated hypercholesterolemia in Watanabe Heritable Hyperlipidemic Rabbits (WHHL), an animal model of FH. Intravenous treatment dose dependently decreased plasma total and LDL cholesterol levels, correlating with an increased level of LDLR mRNA transcripts in leukocytes. Transferrin-facilitated intravenous delivery of cationic liposome LDLR gene complexes could serve as an important adjunct therapy for the treatment of FH.

Defective repression of c-myc in breast cancer cells: A loss at the core of the transforming growth factor beta growth arrest program

Loss of growth inhibitory responses to the cytokine transforming growth factor beta (TGF-beta) in cancer cells may result from mutational inactivation of TGF-beta receptors or their signal transducers, the Smad transcription factors. In breast cancer, however, loss of TGF-beta growth inhibition often occurs without a loss of these signaling components. A genome-wide analysis of rapid TGF-beta gene responses in MCF-10A human mammary epithelial cells and MDA-MB-231 breast cancer cells shows that c-myc repression, a response that is key to the TGF-beta program of cell cycle arrest, is selectively lost in the cancer cell line. Transformation of MCF-10A cells with c-Ha-ras and c-erbB2 oncogenes also led to a selective loss of c-myc repression and cell cycle arrest response. TGF-beta stimulation of epithelial cells rapidly induces the formation of a Smad complex that specifically recognizes a TGF-beta inhibitory element in the c-myc promoter. Formation of this complex is deficient in the oncogenically transformed breast cells. These results suggest that a Smad complex that specifically mediates c-myc repression is a target of oncogenic signals in breast cancer.

Differential inhibitory actions by glucocorticoid and aspirin on cytokine-induced nitric oxide production in vascular smooth muscle cells

Glucocorticoids and nonsteroidal antiinflammatory drugs (NSAIDs) are widely used for the treatment of inflammatory and immune diseases. Nitric oxide (NO) has a diversity of physiological functions, but its excess production has been implicated in the inflammatory process. The present study was designed to elucidate the mechanisms by which glucocorticoids and NSAIDs affect inducible nitric oxide synthase (iNOS) expression in cultured rat vascular smooth muscle cells (VSMCs). Both interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha potently stimulated nitrite/nitrate (NOx) production with a concomitant expression of iNOS mRNA and protein as demonstrated by Northern and Western blot analysis, respectively. Both IL-1beta and TNF-alpha activated nuclear factor (NF)-kappaB as demonstrated by electrophoretic mobility shift assay. Dexamethasone, salicylate and aspirin, but not indomethacin, dose dependently inhibited cytokine-stimulated NOx production and iNOS protein expression. Dexamethasone decreased cytokine-induced NF-kappaB activation and iNOS mRNA expression, but neither salicylate nor aspirin affected NF-kappaB activation or iNOS mRNA expression. IL-1beta caused a rapid increase in phosphorylated IkappaB-alpha levels and subsequent transient decrease in IkappaB-alpha levels, an inhibitor of NF-kappaB, as revealed by Western blot analysis using specific antibodies for phosphorylated and nonphosphorylated IkappaB-alpha. These effects were blocked by pretreatment with dexamethasone. Aspirin dose dependently inhibited iNOS enzymatic activity, whereas salicylate and dexamethasone had limited effect. The present study demonstrates that 1) inhibitory effect of dexamethasone on cytokine-induced iNOS expression and NO production in rat VSMCs, although potentially acting at multiple levels, is partly mediated by inhibition of NF-kappaB activation resulting from decreased phosphorylation and degradation of IkappaB-alpha, 2) both salicylate and aspirin inhibit cytokine-stimulated NO production at translational and/or posttranslational levels without affecting NF-kappaB- mediated iNOS gene expression, and 3) aspirin directly inhibits iNOS enzyme activity. These data suggest the differential inhibitory mechanisms of iNOS-mediated NO synthesis by glucocorticoids and NSAIDs in the vasculature.