Iron-sulphur clusters as genetic regulatory switches: the bifunctional iron regulatory protein-1

AbstractIn the eighties, iron regulatory protein-1 (IRP-1) was iDAntified as a cytoplasmic mRNA-binding protein that regulates vertebrate cell iron metabolism. More recently, IRP-1 was found to represent the functional cytoplasmic homologue of mitochondrial aconitase, a citric acid cycle enzyme. Its two functions are mutually exclusive and DApend on the status of an FeS cluster: the (cluster-less) apoIRP-1 binds to RNA, while the incorporation of a cubane 4Fe-4S cluster is required for enzymatic activity. Cellular signals including iron levels, nitric oxiDA and oxidative stress can regulate between the two activities posttranslationally and reversibly via the Fe cluster. Recent reports suggest that other regulatory proteins may be controlled by similar mechanisms

Matrix metalloproteinases 2 and 9 increase permeability of sheep pleura in vitro

Background: Matrix metalloproteinases (MMPs) 2 and 9 are two gelatinase members which have been found elevated in exudative pleural effusions. In endothelial cells these MMPs increase paracellular permeability via the disruption of tight junction (TJ) proteins occludin and claudin. In the present study it was investigated if MMP2 and MMP9 alter permeability properties of the pleura tissue by degradation of TJ proteins in pleural mesothelium. Results: In the present study the transmesothelial resistance (RTM) of sheep pleura tissue was recorded in Ussing chambers after the addition of MMP2 or MMP9. Both enzymes reduced RTM of the pleura, implying an increase in pleural permeability. The localization and expression of TJ proteins, occludin and claudin-1, were assessed after incubation with MMPs by indirect immunofluorescence and western blot analysis. Our results revealed that incubation with MMPs did not alter neither proteins localization at cell periphery nor their expression. Conclusions: MMP2 and MMP9 increase the permeability of sheep pleura and this finding suggests a role for MMPs in pleural fluid formation. Tight junction proteins remain intact after incubation with MMPs, contrary to previous studies which have shown TJ degradation by MMPs. Probably MMP2 and MMP9 augment pleural permeability via other mechanisms. Backgroun

Hypoxia-Inducible Factors and the Regulation of Lipid Metabolism

Oxygen deprivation or hypoxia characterizes a number of serious pathological conditions and elicits a number of adaptive changes that are mainly mediated at the transcriptional level by the family of hypoxia-inducible factors (HIFs). The HIF target gene repertoire includes genes responsible for the regulation of metabolism, oxygen delivery and cell survival. Although the involvement of HIFs in the regulation of carbohydrate metabolism and the switch to anaerobic glycolysis under hypoxia is well established, their role in the control of lipid anabolism and catabolism remains still relatively obscure. Recent evidence indicates that many aspects of lipid metabolism are modified during hypoxia or in tumor cells in a HIF-dependent manner, contributing significantly to the pathogenesis and/or progression of cancer and metabolic disorders. However, direct transcriptional regulation by HIFs has been only demonstrated in relatively few cases, leaving open the exact and isoform-specific mechanisms that underlie HIF-dependency. This review summarizes the evidence for both direct and indirect roles of HIFs in the regulation of genes involved in lipid metabolism as well as the involvement of HIFs in various diseases as demonstrated by studies with transgenic animal models

eIF2 alpha Kinase PKR Modulates the Hypoxic Response by Stat3-Dependent Transcriptional Suppression of HIF-1 alpha

Hypoxia within the tumor microenvironment promotes angiogenesis, metabolic reprogramming, and tumor progression. In addition to activating hypoxia-inducible factor-1 alpha (HIF-1 alpha), cells also respond to hypoxia by globally inhibiting protein synthesis via serine 51 phosphorylation of translation eukaryotic initiation factor 2 alpha (eIF2 alpha). In this study, we investigated potential roles for stress-activated eIF2 alpha kinases in regulation of HIF-1 alpha. Our investigations revealed that the double-stranded RNA-dependent protein kinase R (PKR) plays a significant role in suppressing HIF-1 alpha expression, acting specifically at the level of transcription. HIF-1 alpha transcriptional repression by PKR was sufficient to impair the hypoxia-induced accumulation of HIF-1 alpha and transcriptional induction of HIF-1 alpha-dependent target genes. Inhibition of HIF-1A transcription by PKR was independent of eIF2 alpha phosphorylation but dependent on inhibition of the signal transducer and activator of transcription 3 (Stat3). Furthermore, HIF-1A repression required the T-cell protein tyrosine phosphatase, which acts downstream of PKR, to suppress Stat3. Our findings reveal a novel tumor suppressor function for PKR, which inhibits HIF-1 alpha expression through Stat3 but is independent of eIF2 alpha phosphorylation. Cancer Res; 70(20); 7820-9. (C) 2010 AACR