Reduced vacuolar ATPase protects mice from Friend virus infection - an unintended but instructive effect in Hif-2afl mice.

During acute viral infections, innate immune cells invade inflamed tissues and face hypoxic areas. Hypoxia-inducible factors (HIFs) adapt cellular responses towards these conditions. We wanted to investigate the effects of a loss of HIF-2α in macrophages during acute Friend murine leukemia retrovirus (FV) infection in C57BL/6 mice using a Cre/loxP system.

Chemical Inhibition of RPA by HAMNO Alters Cell Cycle Dynamics by Impeding DNA Replication and G2-to-M Transition but Has Little Effect on the Radiation-Induced DNA Damage Response.

Replication protein A (RPA) is the major single-stranded DNA (ssDNA) binding protein that is essential for DNA replication and processing of DNA double-strand breaks (DSBs) by homology-directed repair pathways. Recently, small molecule inhibitors have been developed targeting the RPA70 subunit and preventing RPA interactions with ssDNA and various DNA repair proteins. The rationale of this development is the potential utility of such compounds as cancer therapeutics, owing to their ability to inhibit DNA replication that sustains tumor growth.

Depletion of HIF-1α by Inducible Cre/loxP Increases the Sensitivity of Cultured Murine Hepatocytes to Ionizing Radiation in Hypoxia.

The transcription factor hypoxia-inducible factor (HIF) is the main oxygen sensor which regulates adaptation to cellular hypoxia. The aim of this study was to establish cultured murine hepatocyte derived cells (mHDC) as an in vitro model and to analyze the role of HIF-1α in apoptosis induction, DNA damage repair and sensitivity to ionizing radiation (IR). We have crossed C57/BL6 mice that bear loxP sites flanking exon 2 of Hif1a with mice which carry tamoxifen-inducible global Cre expression.

In oxygen-deprived tumor cells ERp57 provides radioprotection and ensures proliferation via c-Myc, PLK1 and the AKT pathway.

The disulfide isomerase ERp57, originally found in the endoplasmic reticulum, is located in multiple cellular compartments, participates in diverse cell functions and interacts with a huge network of binding partners. It was recently suggested as an attractive new target for cancer therapy due to its critical role in tumor cell proliferation. Since a major bottleneck in cancer treatment is the occurrence of hypoxic areas in solid tumors, the role of ERp57 in cell growth was tested under oxygen depletion in the colorectal cancer cell line HCT116.

Overcoming hypoxia-induced resistance of pancreatic and lung tumor cells by disrupting the PERK-NRF2-HIF-axis.

Hypoxia-induced resistance of tumor cells to therapeutic treatment is an unresolved limitation due to poor vascular accessibility and protective cell adaptations provided by a network, including PERK, NRF2, and HIF signaling. All three pathways have been shown to influence each other, but a detailed picture remains elusive. To explore this crosstalk in the context of tumor therapy, we generated human cancer cell lines of pancreatic and lung origin carrying an inducible shRNA against NRF2 and PERK.

Tumor cells rely on the thiol oxidoreductase PDI for PERK signaling in order to survive ER stress.

Upon ER stress cells activate the unfolded protein response through PERK, IRE1 and ATF6. Remarkable effort has been made to delineate the downstream signaling of these three ER stress sensors after activation, but upstream regulation at the ER luminal site still remains mostly undefined. Here we report that the thiol oxidoreductase PDI is mandatory for activation of the PERK pathway in HEK293T as well as in human pancreatic, lung and colon cancer cells.

Carotid body type I cells engage flavoprotein and Pin1 for oxygen sensing.

Carotid body (CB) type I cells sense the blood Po and generate a nervous signal for stimulating ventilation and circulation when blood oxygen levels decline. Three oxygen-sensing enzyme complexes may be used for this purpose: ) mitochondrial electron transport chain metabolism, ) heme oxygenase 2 (HO-2)-generating CO, and/or ) an NAD(P)H oxidase (NOX). We hypothesize that intracellular redox changes are the link between the sensor and nervous signals.

The presumed MTH1-inhibitor TH588 sensitizes colorectal carcinoma cells to ionizing radiation in hypoxia.

Background: The nudix family member enzyme MutT homologue-1 (MTH1) hydrolyses the oxidized nucleotides 8-oxo-dGTP and 2-hydroxy-dATP and thus prevents the incorporation of damaged nucleotides into nuclear and mitochondrial DNA. Therefore MTH1 was proposed to protect cancer cells from oxidative DNA lesions and subsequent cell death. We investigated whether the bona fide MTH1 inhibitor TH588 affects responses of cultured colorectal tumor cells to ionizing radiation (IR) in normoxia and in moderate or severe hypoxia.

Autophagy induced by ionizing radiation promotes cell death over survival in human colorectal cancer cells.

Autophagy is commonly described as a cell survival mechanism and has been implicated in chemo- and radioresistance of cancer cells. Whether ionizing radiation induced autophagy triggers tumor cell survival or cell death still remains unclear. In this study the autophagy related proteins Beclin1 and ATG7 were tested as potential targets to sensitize colorectal carcinoma cells to ionizing radiation under normoxic, hypoxic and starvation conditions.

PDI is an essential redox-sensitive activator of PERK during the unfolded protein response (UPR).

Endoplasmic reticulum (ER) stress leads to activation of the unfolded protein response (UPR) that results in transient suppression of protein translation to allow recovery but leads to cell death when stress cannot be resolved. Central to initiation of the UPR is the activation of the ER transmembrane kinase protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). Here we report that the thiol oxidoreductase ERp57 and protein disulfide isomerase-A1 (PDI), which belong to the same family of luminal ER oxidoreductases, have strikingly opposing roles in the regulation of PERK function.

Targeted Inhibition of Glutamine-Dependent Glutathione Metabolism Overcomes Death Resistance Induced by Chronic Cycling Hypoxia.

Aims: Tumor hypoxia is a major biological factor causing poor patient outcome. Evidence is increasing that improved protection against reactive oxygen species (ROS) participates in therapy resistance of chronically hypoxic cancer cells. We aimed at characterizing the relevance of improved ROS defense for radiation resistance of cancer cells with tolerance to cycling anoxia/re-oxygenation stress ("anoxia-tolerant") and at designing rational treatment strategies for overcoming the resulting therapy resistance by targeting the underlying mechanisms identified in an in vitro model.

RHAMM splice variants confer radiosensitivity in human breast cancer cell lines.

Biomarkers for prognosis in radiotherapy-treated breast cancer patients are urgently needed and important to stratify patients for adjuvant therapies. Recently, a role of the receptor of hyaluronan-mediated motility (RHAMM) has been suggested for tumor progression. Our aim was (i) to investigate the prognostic value of RHAMM in breast cancer and (ii) to unravel its potential function in the radiosusceptibility of breast cancer cells.

Depletion of the thiol oxidoreductase ERp57 in tumor cells inhibits proliferation and increases sensitivity to ionizing radiation and chemotherapeutics.

Rapidly growing tumor cells must synthesize proteins at a high rate and therefore depend on an efficient folding and quality control system for nascent secretory proteins in the endoplasmic reticulum (ER). The ER resident thiol oxidoreductase ERp57 plays an important role in disulfide bond formation. Lentiviral, doxycycline-inducible ERp57 knockdown was combined with irradiation and treatment with chemotherapeutic agents.

Measurement of ROS Levels and Membrane Potential Dynamics in the Intact Carotid Body Ex Vivo.

Reactive oxygen species (ROS) generated by the NADPH oxidase have been proposed to play an important role in the carotid body (CB) oxygen sensing process (Cross et al. 1990). Up to now it remains unclear whether hypoxia causes an increase or decrease of CB ROS levels.

Factor inhibiting HIF-1 (FIH-1) modulates protein interactions of apoptosis-stimulating p53 binding protein 2 (ASPP2).

The asparaginyl hydroxylase factor inhibiting HIF-1 (FIH-1) is an important suppressor of hypoxia-inducible factor (HIF) activity. In addition to HIF-α, FIH-1 was previously shown to hydroxylate other substrates within a highly conserved protein interaction domain, termed the ankyrin repeat domain (ARD). However, to date, the biological role of FIH-1-dependent ARD hydroxylation could not be clarified for any ARD-containing substrate.

Synergistic antitumor effects of endostar in combination with oxaliplatin via inhibition of HIF and CXCR4 in the colorectal cell line SW1116.

Combination treatment with endostar, a novel modified endostatin, and cytotoxic chemotherapies showed a survival benefit in Chinese clinical trials. However, the exact mechanism for this synergism remains unclear. In this study, we report for the first time that the chemokine receptor CXCR4 and the hypoxia-inducible transcription factors (HIF)-1α and HIF-2α are involved in these synergistic antitumor effects in human colorectal cancer SW1116 cells in vitro when endostar treatment is combined with the cytotoxic drug oxaliplatin.

New insight into the SDF-1/CXCR4 axis in a breast carcinoma model: hypoxia-induced endothelial SDF-1 and tumor cell CXCR4 are required for tumor cell intravasation.

The SDF-1/CXCR4 axis has been implicated in breast cancer metastasis. In contrast to its well-established role in organ-specific homing and colonization of tumor cells, the involvement in intravasation, especially in a hypoxic environment, is still poorly understood. Initially, we detected both, the chemokine SDF-1 and its receptor CXCR4 in microvessels in invasive ductal cancer samples.

Stabilisation and knockdown of HIF--two distinct ways comparably important in radiotherapy.

Background: Radiotherapy is one of the most widely used treatments for cancer. The benefit of radiation is known to be negatively affected by tumor hypoxia and the expression of hypoxia-inducible factors (HIF), respectively. HIF-1α/ β and HIF-2α/ β are transcriptional activators of oxygen-regulated genes.

The ATP-binding cassette transporters ABCB1 and ABCC1 are not regulated by hypoxia in immortalised human brain microvascular endothelial cells.

Background: ATP-binding cassette transporters at the blood-brain barrier are actively regulated upon ischemic stroke in a way that impedes the access of pharmacological compounds to the brain tissue. The luminal endothelial transporter ABCB1 was recently shown to be increased, whereas the abluminal transporter ABCC1 was decreased on ischemic brain capillaries. In vitro studies using epithelial cells suggested that ABCB1 is regulated during hypoxia in a hypoxia-inducible factor (HIF)-1α-dependent way.

Prolyl hydroxylase-2 (PHD2) exerts tumor-suppressive activity in pancreatic cancer.

Background: Pancreatic cancer is 1 of the most common and poorly treated tumors. In search of new therapeutic approaches, the oxygen sensors prolyl hydroxylases (PHD) are potential targets. PHD2 is considered the key oxygen sensor-regulating hypoxia-inducible factor (HIF).

The function of hypoxia-inducible factor (HIF) is independent of the endoplasmic reticulum protein OS-9.

The protein "amplified in osteosarcoma-9" (OS-9) has been shown previously to interact with the prolyl hydroxylases PHD2 and PHD3. These enzymes initiate oxygen-dependent degradation of the α-subunit of hypoxia-inducible factor (HIF), a transcription factor that adapts cells to insufficient oxygen supply (hypoxia). A new model has been proposed where OS-9 triggers PHD dependent degradation of HIF-α.

Prolyl hydroxylase PHD3 activates oxygen-dependent protein aggregation.

The HIF prolyl hydroxylases (PHDs/EGLNs) are central regulators of the molecular responses to oxygen availability. One isoform, PHD3, is expressed in response to hypoxia and causes apoptosis in oxygenated conditions in neural cells. Here we show that PHD3 forms subcellular aggregates in an oxygen-dependent manner.

Nuclear translocation of hypoxia-inducible factors (HIFs): involvement of the classical importin alpha/beta pathway.

Hypoxia-inducible factors are the key elements in the essential process of oxygen homeostasis of vertebrate cells. Stabilisation and subsequent nuclear localisation of HIF-alpha subunits results in the activation of target genes such as vegf, epo and glut1. The passage of transcription factors e.