101
|
Chen LM, Choi I, Haddad GG, Boron WF. Chronic continuous hypoxia decreases the expression of SLC4A7 (NBCn1) and SLC4A10 (NCBE) in mouse brain. Am J Physiol Regul Integr Comp Physiol 2007; 293:R2412-20. [PMID: 17928512 DOI: 10.1152/ajpregu.00497.2007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
In the mammalian CNS, hypoxia causes a wide range of physiological effects, and these effects often depend on the stage of development. Among the effects are alterations in pH homeostasis. Na+-coupled HCO3(-) transporters can play critical roles in intracellular pH regulation and several, such as NCBE and NBCn1, are expressed abundantly in the central nervous system. In the present study, we examined the effect of chronic continuous hypoxia on the expression of two electroneutral Na-coupled HCO3(-) transporters, SLC4a7 (NBCn1) and SLC4a10 (NCBE), in mouse brain, the first such study on any acid-base transporter. We placed the mice in normobaric chambers and either maintained normoxia (21% inspired O2) or imposed continuous chronic hypoxia (11% O2) for a duration of either 14 days or 28 days, starting from ages of either postnatal age 2 days (P2) or P90. We assessed protein abundance by Western blot analysis, loading equal amounts of total protein for each condition. In most cases, hypoxia reduced NBCn1 levels by 20-50%, and NCBE levels by 15-40% in cerebral cortex, subcortex, cerebellum, and hippocampus, both after 14 and 28 days, and in both pups and adults. We hypothesize that these decreases, which are out of proportion to the expected overall decreases in brain protein levels, may especially be important for reducing energy consumption.
Collapse
Affiliation(s)
- Li-Ming Chen
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA.
| | | | | | | |
Collapse
|
102
|
Chachami G, Hatziefthimiou A, Liakos P, Ioannou MG, Koukoulis GK, Bonanou S, Molyvdas PA, Simos G, Paraskeva E. Exposure of differentiated airway smooth muscle cells to serum stimulates both induction of hypoxia-inducible factor-1α and airway responsiveness to ACh. Am J Physiol Lung Cell Mol Physiol 2007; 293:L913-22. [PMID: 17660326 DOI: 10.1152/ajplung.00459.2006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Airway smooth muscle (ASM) cells are characterized by phenotypic plasticity and can switch between differentiated and proliferative phenotypes. In rabbit tracheal ASM cells that had been differentiated in vitro by serum starvation, readdition of FBS caused initiation of proliferation and induction of nuclear and transcriptionally active hypoxia-inducible factor (HIF)-1α. In addition, FBS stimulated the induction of HIF-1α by the hypoxia mimetic cobalt. Treatment with actinomycin D, cycloheximide, the phosphatidylinositol 3-kinase inhibitors LY-294002 and wortmannin or the reactive oxygen species scavenger diphenyleneiodonium inhibited the FBS-dependent induction of HIF-1α. These data indicate that, in differentiated ASM cells, FBS upregulates HIF-1α by a transcription-, translation-, phosphatidylinositol 3-kinase-, and reactive oxygen species-dependent mechanism. Interestingly, addition of FBS and cobalt also induced HIF-1α in organ cultures of rabbit trachea strips and synergistically increased their contractile response to ACh, suggesting that HIF-1α might be implicated in airway hypercontractility.
Collapse
Affiliation(s)
- Georgia Chachami
- Department of Physiology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Thessaly, Greece
| | | | | | | | | | | | | | | | | |
Collapse
|
103
|
Gaube F, Wolfl S, Pusch L, Kroll TC, Hamburger M. Gene expression profiling reveals effects of Cimicifuga racemosa (L.) NUTT. (black cohosh) on the estrogen receptor positive human breast cancer cell line MCF-7. BMC Pharmacol 2007; 7:11. [PMID: 17880733 PMCID: PMC2194763 DOI: 10.1186/1471-2210-7-11] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2007] [Accepted: 09/20/2007] [Indexed: 01/03/2023] Open
Abstract
BACKGROUND Extracts from the rhizome of Cimicifuga racemosa (black cohosh) are increasingly popular as herbal alternative to hormone replacement therapy (HRT) for the alleviation of postmenopausal disorders. However, the molecular mode of action and the active principles are presently not clear. Previously published data have been largely contradictory. We, therefore, investigated the effects of a lipophilic black cohosh rhizome extract and cycloartane-type triterpenoids on the estrogen receptor positive human breast cancer cell line MCF-7. RESULTS Both extract and purified compounds clearly inhibited cellular proliferation. Gene expression profiling with the extract allowed us to identify 431 regulated genes with high significance. The extract induced expression pattern differed from those of 17beta-estradiol or the estrogen receptor antagonist tamoxifen. We observed a significant enrichment of genes in an anti-proliferative and apoptosis-sensitizing manner, as well as an increase of mRNAs coding for gene products involved in several stress response pathways. These functional groups were highly overrepresented among all regulated genes. Also several transcripts coding for oxidoreductases were induced, as for example the cytochrome P450 family members 1A1 and 1B1. In addition, some transcripts associated with antitumor but also tumor-promoting activity were regulated. Real-Time RT-PCR analysis of 13 selected genes was conducted after treatment with purified compounds - the cycloartane-type triterpene glycoside actein and triterpene aglycons - showing similar expression levels compared to the extract. CONCLUSION No estrogenic but antiproliferative and proapoptotic gene expression was shown for black cohosh in MCF-7 cells at the transcriptional level. The effects may be results of the activation of different pathways. The cycloartane glycosides and - for the first time - their aglycons could be identified as an active principle in black cohosh.
Collapse
Affiliation(s)
- Friedemann Gaube
- Institute of Pharmacy, Department of Pharmaceutical Biology, University of Jena, Semmelweisstr. 10, 07743 Jena, Germany
| | - Stefan Wolfl
- Clinic of Internal Medicine II, University of Jena, Erlanger Allee 101, 07747 Jena, Germany
- Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Im Neuenheimerfeld 364, 69120 Heidelberg, Germany
| | - Larissa Pusch
- Clinic of Internal Medicine II, University of Jena, Erlanger Allee 101, 07747 Jena, Germany
| | - Torsten C Kroll
- Clinic of Internal Medicine II, University of Jena, Erlanger Allee 101, 07747 Jena, Germany
| | - Matthias Hamburger
- Institute of Pharmacy, Department of Pharmaceutical Biology, University of Jena, Semmelweisstr. 10, 07743 Jena, Germany
- Department of Pharmaceutical Sciences, Institute of Pharmaceutical Biology, University of Basel, Klingelbergstr. 50, CH-4053 Basel, Switzerland
| |
Collapse
|
104
|
Moore MN, Viarengo A, Donkin P, Hawkins AJS. Autophagic and lysosomal reactions to stress in the hepatopancreas of blue mussels. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2007; 84:80-91. [PMID: 17659356 DOI: 10.1016/j.aquatox.2007.06.007] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 06/05/2007] [Accepted: 06/05/2007] [Indexed: 05/16/2023]
Abstract
The aim of this investigation was to test the reactions of the hepatopancreatic digestive cells of blue mussels (Mytilus edulis and Mytilus galloprovincialis) to a variety of environmental stressors. These stressors included anoxia, hyperthermia, polycyclic aromatic hydrocarbons, copper and a combination of copper+nutritional deprivation. Paraquat was used as an experimental generator of reactive oxygen species (ROS). All of these stressors induced adverse reactions in the lysosomal system of the digestive cells and many also induced autophagy. Changes induced by anoxia and hyperthermia were reversible, whereas autophagic reactions caused by PAHs were incomplete resulting in swelling and accumulation of lipid and phospholipid in the autolysosomes. The lysosomotropic drug chloroquine, an inducer of incomplete autophagy, enhanced the toxicity of phenanthrene but was not itself toxic at the experimental concentration used. Nutritional deprivation-induced autophagy had a protective effect on lysosomal stability in mussels exposed to copper. These findings complement previous findings and support a mechanistic model for lysosomal responses to free radicals and reactive oxygen (ROS, reactive oxygen species) which are generated by normal metabolism and often enhanced by stress and toxic xenobiotics and metals. The protective role of autophagy induced by nutritional deprivation against oxidative stress can be explained by this model, where autophagy boosts "cellular housekeeping" through enhanced removal of ROS-damaged proteins and organelles minimising formation of harmful stress/age pigment (lipofuscin). Finally, we discuss the possibility of low level triggering of autophagy in mussels by fluctuating environmental regimes providing a mechanism for tolerance to environmental stress.
Collapse
Affiliation(s)
- Michael N Moore
- Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK.
| | | | | | | |
Collapse
|
105
|
Rocha S. Gene regulation under low oxygen: holding your breath for transcription. Trends Biochem Sci 2007; 32:389-97. [PMID: 17624786 DOI: 10.1016/j.tibs.2007.06.005] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2006] [Revised: 05/08/2007] [Accepted: 06/20/2007] [Indexed: 01/21/2023]
Abstract
Oxygen is both an environmental and developmental signal that governs important cellular pathways. Therefore, hypoxia (or low oxygen tensions) is part of both physiological and pathological processes. To deal with hypoxic conditions, cells and organisms have evolved exquisite mechanisms for adaptation and survival. The cellular responses are reliant on controlled transcriptional and post-transcriptional events, where certain genes are positively regulated and others either remain inactive or are actively repressed. It has been known for some time that, during hypoxia, transcription is mainly regulated by the hypoxia inducible factor (HIF). However, recently it has been demonstrated that additional transcription factors are also activated and that non-HIF-dependent processes are involved in the hypoxic stress response. Therefore, gene expression following hypoxia is the result of combined effects on transcription, translation and adjustment mechanisms such as the induction of microRNAs and changes in chromatin.
Collapse
Affiliation(s)
- Sonia Rocha
- College of Life Sciences, Division of Gene Regulation and Expression MSI/WTB/JBC Complex, Dow Street, University of Dundee, Dundee, DD1 5EH, UK.
| |
Collapse
|
106
|
Thomas JD, Johannes GJ. Identification of mRNAs that continue to associate with polysomes during hypoxia. RNA (NEW YORK, N.Y.) 2007; 13:1116-31. [PMID: 17488873 PMCID: PMC1894931 DOI: 10.1261/rna.534807] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Tumors must adapt to the hypoxic environment in order to grow beyond a benign microscopic mass. In addition to transcriptional activation mediated by HIF-1alpha, hypoxia has also been reported to inhibit translation. The degree of translational inhibition is dependent on the duration as well as the severity of the hypoxic insult. Anoxia (<0.02% O(2)) seems to have a more rapid and dramatic effect on translation as compared to hypoxia. We show here that prolonged hypoxia dramatically and reversibly inhibits translation in PC-3 cells. We also found that mTOR is inactivated and eIF-2alpha is phosphorylated during hypoxic treatment but only the eIF-2alpha phosphorylation correlates with the translational repression. We further used polysome analysis and microarray technology to analyze the impact of this translational repression on gene expression. We found that 33 mRNAs were refractory to this translational repression and that there was no correlation between mRNA induction and the ability to recruit ribosomes during hypoxia. We also found that ribosomal protein encoding mRNAs are more sensitive to this translational repression as compared to the majority of mRNAs. Although other reports have analyzed the effect of translation inhibition on gene expression under anoxic conditions, we believe that this is the first report in hypoxic cells. Our results show that the translational repression that occurs during hypoxia does impact gene expression in the highly transformed prostate cancer cell line, PC-3.
Collapse
Affiliation(s)
- Jeff D Thomas
- Department of Pathology and Laboratory Medicine, Drexel University College of Medicine, Philadelphia, PA 19341, USA
| | | |
Collapse
|
107
|
Chan N, Milosevic M, Bristow RG. Tumor hypoxia, DNA repair and prostate cancer progression: new targets and new therapies. Future Oncol 2007; 3:329-41. [PMID: 17547528 DOI: 10.2217/14796694.3.3.329] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Increasingly, the tumor microenvironment and hypoxia are being studied as potential prognostic factors in prostate cancer given their effects on the hypoxia inducible factor-1α and vascular endothelial growth factor signaling pathways. Based on immunohistochemical studies using hypoxic cell markers and direct oxygen-electrode measurements, clinically relevant levels of hypoxia are detected in 30–90% of prostate cancers. Exciting new data suggest that hypoxia can alter cell-cycle checkpoints and DNA repair within the prostate epithelium, thereby driving genetic instability and tumor aggression. Novel therapies designed to target the hypoxic response and resulting defective DNA repair may therefore be effective as chemoprevention agents or as adjuncts to surgery, radiotherapy and chemotherapy to improve clinical outcome.
Collapse
Affiliation(s)
- Norman Chan
- Departments of Medical Biophysics & Radiation Oncology, University of Toronto, Princess Margaret Hospital (University Health Network), Toronto, Ontario, Canada.
| | | | | |
Collapse
|
108
|
van den Beucken T, Magagnin MG, Savelkouls K, Lambin P, Koritzinsky M, Wouters BG. Regulation of Cited2 expression provides a functional link between translational and transcriptional responses during hypoxia. Radiother Oncol 2007; 83:346-52. [PMID: 17499866 DOI: 10.1016/j.radonc.2007.04.026] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Revised: 04/28/2007] [Accepted: 04/29/2007] [Indexed: 01/25/2023]
Abstract
BACKGROUND AND PURPOSE Protein synthesis rates are greatly reduced under hypoxic conditions as a consequence of an overall inhibition of mRNA translation. Certain specific mRNA species have the ability to escape this general translational repression. At the cellular level this results in differential protein expression during hypoxic conditions. The objective of this study was to characterize the translational regulation of the postulated HIF-1alpha antagonist Cited2. MATERIALS AND METHODS DU145 prostate carcinoma cells and mouse embryonic fibroblasts with a homozygous knock-in mutation for eIF2alpha (S51A) or wild-type eIF2alpha were exposed to severe hypoxia after which both total mRNA and efficiently translated mRNA were isolated. Quantitative RT-PCR was used to measure and compare changes in transcription (total mRNA) with changes in translation (efficiently translated mRNA fraction). RESULTS We show using HIF-1alpha null MEF cells that transcriptional induction of Cited2 during hypoxia is dependent on HIF-1alpha. Although global mRNA translation is inhibited during hypoxia Cited2 mRNA remains efficiently translated. An evolutionary conserved upstream open reading frame (uORF) in the 5'UTR of Cited2 did not stimulate translation in an eIF2alpha dependent manner during hypoxia. CONCLUSIONS Selective translation Cited2 by an eIF2alpha independent mechanism establishes a link between translation and HIF-1 dependent transcription during hypoxia.
Collapse
Affiliation(s)
- Twan van den Beucken
- Department of Radiation Oncology, Maastricht University, Maastricht, The Netherlands
| | | | | | | | | | | |
Collapse
|
109
|
Fish JE, Matouk CC, Yeboah E, Bevan SC, Khan M, Patil K, Ohh M, Marsden PA. Hypoxia-inducible expression of a natural cis-antisense transcript inhibits endothelial nitric-oxide synthase. J Biol Chem 2007; 282:15652-66. [PMID: 17403686 DOI: 10.1074/jbc.m608318200] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The destabilization of endothelial nitric-oxide synthase (eNOS) mRNA in hypoxic endothelial cells may be important in the etiology of vascular diseases, such as pulmonary hypertension. Recently, an overlapping antisense transcript to eNOS/NOS3 was implicated in the post-transcriptional regulation of eNOS. We demonstrate here that expression of sONE, also known as eNOS antisense (NOS3AS) or autophagy 9-like 2 (APG9L2), is robustly induced by hypoxia or functional deficiency of von Hippel-Lindau protein. sONE is also up-regulated in the aortas of hypoxic rats. In hypoxic endothelial cells, sONE expression negatively correlates with eNOS expression. Blocking the hypoxic induction of sONE by RNA interference attenuates the fall in both eNOS RNA and protein. We provide evidence that the induction of sONE primarily involves transcript stabilization rather than increased transcriptional activity and is von Hippel-Lindaubut not hypoxia-inducible factor 2alpha-dependent. We also demonstrate that sONE transcripts are enriched in the nucleus of normoxic cells and that hypoxia promotes an increase in the level of cytoplasmic and polyribosome-associated, sONE mRNA. The finding that eNOS expression can be regulated by an overlapping cis-antisense transcript in a stimulus-dependent fashion provides evidence that sense/antisense interactions may play a previously unappreciated role in vascular disease pathogenesis.
Collapse
Affiliation(s)
- Jason E Fish
- Department of Medical Biophysics, St. Michael's Hospital, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | | | | | | | |
Collapse
|
110
|
De Palma S, Ripamonti M, Vigano A, Moriggi M, Capitanio D, Samaja M, Milano G, Cerretelli P, Wait R, Gelfi C. Metabolic modulation induced by chronic hypoxia in rats using a comparative proteomic analysis of skeletal muscle tissue. J Proteome Res 2007; 6:1974-84. [PMID: 17391017 DOI: 10.1021/pr060614o] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hypoxia-induced changes of rat skeletal muscle were investigated by two-dimensional difference in-gel electrophoresis (2D-DIGE) and mass spectrometry. The results indicated that proteins involved in the TCA cycle, ATP production, and electron transport are down-regulated, whereas glycolytic enzymes and deaminases involved in ATP and AMP production were up-regulated. Up-regulation of the hypoxia markers hypoxia inducible factor 1 (HIF-1alpha) and pyruvate dehydrogenase kinase 1 (PDK1) was also observed, suggesting that in vivo adaptation to hypoxia requires an active metabolic switch. The kinase protein, mammalian target of rapamycin (mTOR), which has been implicated in the regulation of protein synthesis in hypoxia, appears unchanged, suggesting that its activity, in this system, is not controlled by oxygen partial pressure.
Collapse
Affiliation(s)
- S De Palma
- Department of Surgical Sciences, University of Milano, Bicocca, Italy
| | | | | | | | | | | | | | | | | | | |
Collapse
|
111
|
del Prete MJ, Vernal R, Dolznig H, Müllner EW, Garcia-Sanz JA. Isolation of polysome-bound mRNA from solid tissues amenable for RT-PCR and profiling experiments. RNA (NEW YORK, N.Y.) 2007; 13:414-21. [PMID: 17237355 PMCID: PMC1800518 DOI: 10.1261/rna.79407] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Using cell lines and primary cells, it has been shown that translation control plays a key role regulating gene expression during physiological and pathological conditions. The relevance of this type of regulation in vivo (tissues, organs) remains to be elucidated, due to the lack of an efficient method for polysome-bound fractionation of solid tissue RNA samples. A simple and efficient method is described, in which tissue samples were pulverized in liquid nitrogen and lysed with NP40-lysis buffer in the presence of the RNAse inhibitors RNAsin and vanadyl-ribonucleoside complex. After cell lysis, the cytoplasmic extract was loaded into sucrose gradients, fractionated, and RNA prepared from each fraction. The obtained RNA was reverse transcribed with a low efficiency, a problem that was overcome by purifying polyA+ RNA. Aiming to use small quantities of solid tissue samples (10-20 mg/sample), polyA+ RNA purification was discarded, and the different components were individually screened for a negative effect on reverse transcription. The polysaccharide heparin, which is present as a nonspecific RNAse inhibitor, inhibits reverse transcriptase activity, and must be removed from RNA samples for an efficient reaction. Heparin was successfully removed by precipitation of the RNA with lithium chloride, as demonstrated by the reversal of the inhibition on RT-PCR reactions. In summary, we present a reliable method allowing us to prepare high-quality polysome-bound mRNA from small quantities of liquid-nitrogen-frozen solid tissue samples from both human and mouse origin, amenable for Northern blotting, RT-PCR reactions, and expression profiling analyses.
Collapse
Affiliation(s)
- M Julieta del Prete
- Department of Immunology, Centro de Investigaciones Biológicas, Madrid, Spain
| | | | | | | | | |
Collapse
|
112
|
Abstract
Tumor hypoxia refers to the development of regions within solid tumors in which the oxygen concentration is lower (0-3%) compared to that in most normal tissues (4-9%) (Vaupel and Hockel, 2000). Considerable experimental and clinical evidence exists supporting the notion that hypoxia fundamentally alters the physiology of the tumor towards a more aggressive phenotype (Hockel and Vaupel, 2001). Therefore, delineating the mechanisms by which hypoxia affects tumor physiology at the cellular and molecular levels will be crucial for a better understanding of tumor development and metastasis and for designing better antitumor modalities.
Collapse
Affiliation(s)
- Constantinos Koumenis
- Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
| | | | | | | | | |
Collapse
|
113
|
Fähling M, Mrowka R, Steege A, Nebrich G, Perlewitz A, Persson PB, Thiele BJ. Translational control of collagen prolyl 4-hydroxylase-alpha(I) gene expression under hypoxia. J Biol Chem 2006; 281:26089-101. [PMID: 16837461 DOI: 10.1074/jbc.m604939200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Hypoxia is a pro-fibrotic stimulus, which is associated with enhanced collagen synthesis, as well as with augmented collagen prolyl 4-hydroxylase (C-P4H) activity. C-P4H activity is controlled mainly by regulated expression of the alpha C-P4H subunit. In this study we demonstrate that the increased synthesis of C-P4H-alpha(I) protein in human HT1080 fibroblasts under long term hypoxia (36 h, 1% oxygen) is controlled at the translational level. This is mediated by an interaction of RNA-binding protein nucleolin (approximately 64 kDa form) at the 5'- and 3'-untranslated regions (UTR) of the mRNA. The 5'/3'-UTR-dependent mechanism elevates the C-P4H-alpha(I) expression rate 2.3-fold, and participates in a 5.3-fold increased protein level under long term hypoxia. The interaction of nucleolin at the 5'-UTR occurs directly and depends on the existence of an AU-rich element. Statistical evaluation of the approximately 64-kDa nucleolin/RNA interaction studies revealed a core binding sequence, corresponding to UAAAUC or AAAUCU. At the 3'-UTR, nucleolin assembles indirectly via protein/protein interaction, with the help of another 3'-UTR-binding protein, presumably annexin A2. The increased protein level of the approximately 64-kDa nucleolin under hypoxia can be attributed to an autocatalytic cleavage of a high molecular weight nucleolin form, without alterations in nucleolin mRNA concentration. Thus, the alteration of translational efficiency by nucleolin, which occurs through a hypoxia inducible factor independent pathway, is an important step in C-P4H-alpha(I) regulation under hypoxia.
Collapse
Affiliation(s)
- Michael Fähling
- Charité, Universitätsmedizin Berlin, Institut für Vegetative Physiologie, D-10117 Berlin, Germany.
| | | | | | | | | | | | | |
Collapse
|
114
|
Pore N, Jiang Z, Shu HK, Bernhard E, Kao GD, Maity A. Akt1 activation can augment hypoxia-inducible factor-1alpha expression by increasing protein translation through a mammalian target of rapamycin-independent pathway. Mol Cancer Res 2006; 4:471-9. [PMID: 16849522 DOI: 10.1158/1541-7786.mcr-05-0234] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The phosphoinositide 3-kinase (PI3K)/Akt pathway is commonly activated in cancer; therefore, we investigated its role in hypoxia-inducible factor-1alpha (HIF-1alpha) regulation. Inhibition of PI3K in U87MG glioblastoma cells, which have activated PI3K/Akt activity secondary to phosphatase and tensin homologue deleted on chromosome 10 (PTEN) mutation, with LY294002 blunted the induction of HIF-1alpha protein and its targets vascular endothelial growth factor and glut1 mRNA in response to hypoxia. Introduction of wild-type PTEN into these cells also blunted HIF-1alpha induction in response to hypoxia and decreased HIF-1alpha accumulation in the presence of the proteasomal inhibitor MG132. Akt small interfering RNA (siRNA) also decreased HIF-1alpha induction under hypoxia and its accumulation in normoxia in the presence of dimethyloxallyl glycine, a prolyl hydroxylase inhibitor that prevents HIF-1alpha degradation. Metabolic labeling studies showed that Akt siRNA decreased HIF-1alpha translation in normoxia in the presence of dimethyloxallyl glycine and in hypoxia. Inhibition of mammalian target of rapamycin (mTOR) with rapamycin (10-100 nmol/L) had no significant effect on HIF-1alpha induction in a variety of cell lines, a finding that was confirmed using mTOR siRNA. Furthermore, neither mTOR siRNA nor rapamycin decreased HIF-1alpha translation as determined by metabolic labeling studies. Therefore, our results indicate that Akt can augment HIF-1alpha expression by increasing its translation under both normoxic and hypoxic conditions; however, the pathway we are investigating seems to be rapamycin insensitive and mTOR independent. These observations, which were made on cells grown in standard tissue culture medium (10% serum), were confirmed in PC3 prostate carcinoma cells. We did find that rapamycin could decrease HIF-1alpha expression when cells were cultured in low serum, but this seems to represent a different pathway.
Collapse
Affiliation(s)
- Nabendu Pore
- Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia, 19104, USA
| | | | | | | | | | | |
Collapse
|
115
|
Abstract
PURPOSE OF REVIEW Tumor hypoxia induces cancer cell treatment resistance, angiogenesis, invasiveness, and overall poor clinical outcome. Cellular adaptations to hypoxia are largely driven by hypoxia-induced alterations in gene transcription, mRNA translation, and protein stability. This review will summarize recent advances in the understanding of mammalian oxygen-sensing mechanisms in normal and cancerous cells. RECENT FINDINGS Specific molecular candidates have been identified that are involved in the primary sensing of hypoxia or its secondary consequences. Chief amongst these are the iron and 2-oxoglutarate-dependent dioxygenases that hydroxylate the alpha subunits of hypoxia-inducible transcription factors. This oxygen-dependent reaction, which prevents the transcription of many genes, is relieved under hypoxia. Evidence for the regulated expression and decay of the hypoxia-inducible transcription factor hydroxylating enzymes suggests that the sensitivity of transcriptional responses to hypoxia can be dynamically adjusted. Recent results also argue that these hydroxylating enzymes may be able to sense not only oxygen availability, but also the accumulation of bioenergetic intermediates and reactive oxygen species. In cancer cells, changes in these metabolites may accompany hypoxia or may occur independently. Several organellar compartments including plasma membrane, mitochondria and endoplasmic reticulum also appear to contribute to oxygen sensing through the generation of metabolites or through regulation of protein translation. SUMMARY Oxygen-sensing mechanisms induce prominent clinically relevant changes in cancer cells and tumor biology through the control of gene expression. Significant overlap exists between oxygen-sensing mechanisms and other metabolic and cell stress sensing pathways, which allows nonhypoxic cell stresses to activate hypoxia-inducible responses.
Collapse
Affiliation(s)
- Ajay Verma
- Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
| |
Collapse
|
116
|
Abstract
Hypoxia-inducible factor-1 (HIF-1) plays important roles in regulating radiosensitivity, making it a potentially promising target for tumour radiosensitisation. Here, we discuss the rationale for, and the potential pitfalls of, combining HIF-1 blockade with radiotherapy. In doing so, we describe clinical scenarios in which HIF-1 inhibition might optimise tumour radiosensitivity.
Collapse
Affiliation(s)
- B J Moeller
- Department of Radiation Oncology, Duke University Medical Center, Box 3455, Room 201 MSRB, Research Drive, Durham, NC 27710, UK
| | - M W Dewhirst
- Department of Radiation Oncology, Duke University Medical Center, Box 3455, Room 201 MSRB, Research Drive, Durham, NC 27710, UK
- E-mail:
| |
Collapse
|
117
|
Shojaiefard M, Lang F. Stimulation of the intestinal phosphate transporter SLC34A2 by the protein kinase mTOR. Biochem Biophys Res Commun 2006; 345:1611-4. [PMID: 16730658 DOI: 10.1016/j.bbrc.2006.05.067] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Accepted: 05/12/2006] [Indexed: 01/27/2023]
Abstract
Adequate phosphate homeostasis is of critical importance for a wide variety of functions including bone mineralization and energy metabolism. Phosphate balance is a function of intestinal absorption and renal elimination, which are both under tight hormonal control. Intestinal phosphate absorption is accomplished by the Na(+), phosphate cotransporter NaPi IIb (SLC34A2). Signaling mechanisms mediating hormonal regulation of SLC34A2 are incompletely understood. The mammalian target of rapamycin (mTOR) is a kinase regulating a variety of nutrient transporters. The present experiments explored whether mTOR regulates the activity of SLC34A2. In Xenopus oocytes expressing SLC34A2 but not in water injected oocytes phosphate (1 mM) induced a current (Ip) which was significantly enhanced by coexpression of mTOR. Preincubation of the oocytes for 24 h with rapamycin (50 nM) did not significantly affect Ip in the absence of mTOR but virtually abolished the increase of Ip following coexpression of mTOR. The wild type serum and glucocorticoid inducible kinase SGK1 and the constitutively active (S422D)SGK1 similarly stimulated Ip, an effect again reversed by rapamycin. Coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K119N)SGK1 significantly decreased Ip and abrogated the stimulating effect of mTOR on Ip. In conclusion, mTOR and SGK1 cooperate in the stimulation of the intestinal phosphate transporter SLC34A2.
Collapse
|
118
|
Liu L, Cash TP, Jones RG, Keith B, Thompson CB, Simon MC. Hypoxia-induced energy stress regulates mRNA translation and cell growth. Mol Cell 2006; 21:521-31. [PMID: 16483933 PMCID: PMC3153113 DOI: 10.1016/j.molcel.2006.01.010] [Citation(s) in RCA: 466] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2005] [Revised: 11/01/2005] [Accepted: 01/06/2006] [Indexed: 01/19/2023]
Abstract
Oxygen (O2) deprivation, or hypoxia, has profound effects on cell metabolism and growth. Cells can adapt to low O2 in part through activation of hypoxia-inducible factor (HIF). We report here that hypoxia inhibits mRNA translation by suppressing multiple key regulators, including eIF2alpha, eEF2, and the mammalian target of rapamycin (mTOR) effectors 4EBP1, p70S6K, and rpS6, independent of HIF. Hypoxia results in energy starvation and activation of the AMPK/TSC2/Rheb/mTOR pathway. Hypoxic AMP-activated protein kinase (AMPK) activation also leads to eEF2 inhibition. Moreover, hypoxic effects on cellular bioenergetics and mTOR inhibition increase over time. Mutation of the TSC2 tumor suppressor gene confers a growth advantage to cells by repressing hypoxic mTOR inhibition and hypoxia-induced G1 arrest. Together, eIF2alpha, eEF2, and mTOR inhibition represent important HIF-independent mechanisms of energy conservation that promote survival under low O2 conditions.
Collapse
Affiliation(s)
- Liping Liu
- Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
| | - Timothy P. Cash
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
| | - Russell G. Jones
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
| | - Brian Keith
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
| | - Craig B. Thompson
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
| | - M. Celeste Simon
- Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
- Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104, USA
- Corresponding author: M. Celeste Simon, Ph.D. 451 BRBII/III, 421 Curie Blvd. Philadelphia, PA 19104, Phone: (215) 746-5532, Fax:(215)746-5511,
| |
Collapse
|
119
|
Abstract
Recent insight into how mammalian cells adapt their translational machinery to hypoxic conditions raises the possibility of targeting components of the regulatory networks involved to selectively inhibit metabolically compromised tumor cells and possibly manipulate a broad range of other physiological processes.
Collapse
Affiliation(s)
- David Ron
- Skirball Institute of Biomolecular Medicine and the Department of Medicine, New York University School of Medicine, New York, New York 10016, USA.
| | | |
Collapse
|
120
|
Xi Y, Nakajima G, Schmitz JC, Chu E, Ju J. Multi-level gene expression profiles affected by thymidylate synthase and 5-fluorouracil in colon cancer. BMC Genomics 2006; 7:68. [PMID: 16584549 PMCID: PMC1448211 DOI: 10.1186/1471-2164-7-68] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2005] [Accepted: 04/03/2006] [Indexed: 11/24/2022] Open
Abstract
Background Thymidylate synthase (TS) is a critical target for cancer chemotherapy and is one of the most extensively studied biomarkers for fluoropyrimidine-based chemotherapy. In addition to its critical role in enzyme catalysis, TS functions as an RNA binding protein to regulate the expression of its own mRNA translation and other cellular mRNAs, such as p53, at the translational level. In this study, a comprehensive gene expression analysis at the levels of both transcriptional and post-transcriptional regulation was conducted to identify response markers using human genome array with TS-depleted human colon cancer HCT-C18 (TS-) cells and HCT-C18 (TS+) cells stably transfected with the human TS cDNA expression plasmid. Results A total of 38 genes were found to be significantly affected by TS based on the expression profiles of steady state mRNA transcripts. However, based on the expression profiles of polysome associated mRNA transcripts, over 149 genes were affected by TS overexpression. This indicates that additional post-transcriptionally controlled genes can be captured with profiling polysome associated mRNA population. This unique approach provides a comprehensive overview of genes affected by TS. Additional novel post-transcriptionally regulated genes affected by 5-fluorouracil (5-FU) treatment were also discovered via similar approach. Conclusion To our knowledge, this is the first time that a comprehensive gene expression profile regulated by TS and 5-FU was analyzed at the multiple steps of gene regulation. This study will provide candidate markers that can be potentially used for predicting therapeutic outcomes for fluoropyrimidine-based cancer chemotherapy.
Collapse
Affiliation(s)
- Yaguang Xi
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36688, USA
| | - Go Nakajima
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36688, USA
| | - John C Schmitz
- Yale Cancer Center, Yale University School of Medicine, New Haven, CT 06501, USA
| | - Edward Chu
- Yale Cancer Center, Yale University School of Medicine, New Haven, CT 06501, USA
| | - Jingfang Ju
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36688, USA
| |
Collapse
|
121
|
Koritzinsky M, Magagnin MG, van den Beucken T, Seigneuric R, Savelkouls K, Dostie J, Pyronnet S, Kaufman RJ, Weppler SA, Voncken JW, Lambin P, Koumenis C, Sonenberg N, Wouters BG. Gene expression during acute and prolonged hypoxia is regulated by distinct mechanisms of translational control. EMBO J 2006; 25:1114-25. [PMID: 16467844 PMCID: PMC1409715 DOI: 10.1038/sj.emboj.7600998] [Citation(s) in RCA: 273] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Accepted: 01/18/2006] [Indexed: 12/13/2022] Open
Abstract
Hypoxia has recently been shown to activate the endoplasmic reticulum kinase PERK, leading to phosphorylation of eIF2alpha and inhibition of mRNA translation initiation. Using a quantitative assay, we show that this inhibition exhibits a biphasic response mediated through two distinct pathways. The first occurs rapidly, reaching a maximum at 1-2 h and is due to phosphorylation of eIF2alpha. Continued hypoxic exposure activates a second, eIF2alpha-independent pathway that maintains repression of translation. This phase is characterized by disruption of eIF4F and sequestration of eIF4E by its inhibitor 4E-BP1 and transporter 4E-T. Quantitative RT-PCR analysis of polysomal RNA indicates that the translation efficiency of individual genes varies widely during hypoxia. Furthermore, the translation efficiency of individual genes is dynamic, changing dramatically during hypoxic exposure due to the initial phosphorylation and subsequent dephosphorylation of eIF2alpha. Together, our data indicate that acute and prolonged hypoxia regulates mRNA translation through distinct mechanisms, each with important contributions to hypoxic gene expression.
Collapse
Affiliation(s)
- Marianne Koritzinsky
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Michaël G Magagnin
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Twan van den Beucken
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Renaud Seigneuric
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Kim Savelkouls
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Josée Dostie
- Department of Biochemistry, McGill Cancer Centre, McGill University, Canada
| | - Stéphane Pyronnet
- Department of Biochemistry, McGill Cancer Centre, McGill University, Canada
| | - Randal J Kaufman
- Howard Hughes Medical Institute, University of Michigan Medical Center, USA
| | - Sherry A Weppler
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Jan Willem Voncken
- Department of Molecular Genetics, University of Maastricht, The Netherlands
| | - Philippe Lambin
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
| | - Constantinos Koumenis
- Departments of Radiation Oncology and Cancer Biology, Wake Forest University School of Medicine, USA
| | - Nahum Sonenberg
- Department of Biochemistry, McGill Cancer Centre, McGill University, Canada
| | - Bradly G Wouters
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, The Netherlands
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, UNS50/23 Postbus 616, 6200 MD Maastricht, The Netherlands. Tel.: +31 43 388 2912; Fax: +31 43 388 4540; E-mail:
| |
Collapse
|
122
|
Williams JM, White CR, Chang MM, Injeti ER, Zhang L, Pearce WJ. Chronic hypoxic decreases in soluble guanylate cyclase protein and enzyme activity are age dependent in fetal and adult ovine carotid arteries. J Appl Physiol (1985) 2006; 100:1857-66. [PMID: 16469937 DOI: 10.1152/japplphysiol.00662.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study tests the hypothesis that chronic hypoxia enhances reactivity to nitric oxide (NO) through age-dependent increases in soluble guanylate cyclase (sGC) and protein kinase G (PKG) activity. In term fetal and adult ovine carotids, chronic hypoxia had no significant effect on mRNA levels for the beta1-subunit of sGC, but depressed sGC abundance by 16% in fetal and 50% in adult arteries, through possible depression of rates of mRNA translation (15% in fetal and 50% in adult) and/or increased protein turnover. Chronic hypoxia also depressed the catalytic activity of sGC, but only in fetal arteries (63%). Total sGC activity was reduced by chronic hypoxia in both fetal (69%) and adult (37%) carotid homogenates, but this effect was not observed in intact arteries when sGC activity was measured by timed accumulation of cGMP. In intact arteries treated with 300 microM 3-isobutyl-1-methylxanthine (IBMX), chronic hypoxia dramatically enhanced sGC activity in fetal (186%) but not adult (89%) arteries. This latter observation suggests that homogenization either removed an sGC activator, released an sGC inhibitor, or altered the phosphorylation state of the enzyme, resulting in reduced activity. In the absence of IBMX, chronic hypoxia had no significant effect on rates of cGMP accumulation. Chronic hypoxia also depressed the ability of the cGMP analog, 8-(p-chlorophenylthio)-cGMP, to promote vasorelaxation in both fetal (8%) and adult (12%) arteries. Together, these results emphasize the fact that intact and homogenized artery studies of sGC activity do not always yield equivalent results. The results further suggest that enhancement of reactivity to NO by chronic hypoxia must occur upstream of PKG and can only be possible if changes in cGMP occurred in functional compartments that afforded either temporal or chemical protection to the actions of phosphodiesterase. The range and age dependence of hypoxic effects observed also suggest that some responses to hypoxia must be compensatory and homeostatic, with reactivity to NO as the primary regulated variable.
Collapse
Affiliation(s)
- James M Williams
- Department of Physiology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA
| | | | | | | | | | | |
Collapse
|
123
|
Koritzinsky M, Seigneuric R, Magagnin MG, van den Beucken T, Lambin P, Wouters BG. The hypoxic proteome is influenced by gene-specific changes in mRNA translation. Radiother Oncol 2006; 76:177-86. [PMID: 16098621 DOI: 10.1016/j.radonc.2005.06.036] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 05/24/2005] [Accepted: 06/21/2005] [Indexed: 10/25/2022]
Abstract
BACKGROUND AND PURPOSE Hypoxia causes a rapid reduction in mRNA translation efficiency. This inhibition does not affect all mRNA species to the same extent and can therefore contribute significantly to hypoxia-induced differential protein expression. Our aim in this study was to characterize changes in gene expression during acute hypoxia and evaluate the contribution of regulation via mRNA translation on these changes. For each gene, the contribution of changes in mRNA abundance versus mRNA translation was determined. MATERIALS AND METHODS DU145 prostate carcinoma cells were exposed to 4h of hypoxia (<0.02% O2). Efficiently translated mRNAs were isolated by sedimentation through a sucrose gradient. Affymetrix microarray technology was used to evaluate both the transcriptional and translational contribution to gene expression. Results were validated by quantitative PCR. RESULTS One hundred and twenty genes were more than 4-fold upregulated by hypoxia in the efficiently translated fraction of mRNA, in comparison to only 76 genes at the level of transcription. Of the 50 genes demonstrating the largest changes in translation, 11 were found to be more than 2-fold over represented in the translated fraction in comparison to their overall transcriptional level. The gene with the highest translational contribution to its induction was CITED-2, which is a negative regulator of HIF-1 transcriptional activity. CONCLUSIONS Gene-specific regulation of mRNA translation contributes significantly to differential gene expression during hypoxia.
Collapse
Affiliation(s)
- Marianne Koritzinsky
- Department of Radiation Oncology (MAASTRO Lab), Research Institute Growth and Development, Maastricht, The Netherlands
| | | | | | | | | | | |
Collapse
|
124
|
Shojaiefard M, Christie DL, Lang F. Stimulation of the creatine transporter SLC6A8 by the protein kinase mTOR. Biochem Biophys Res Commun 2006; 341:945-9. [PMID: 16466692 DOI: 10.1016/j.bbrc.2006.01.055] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Accepted: 01/17/2006] [Indexed: 12/20/2022]
Abstract
Cellular accumulation of creatine is accomplished by the Na(+), Cl(-), and creatine transporter CreaT (SLC6A8). The mammalian target of rapamycin (mTOR) is a kinase stimulating cellular nutrient uptake. The present experiments explored whether SLC6A8 is regulated by mTOR. In Xenopus oocytes expressing SLC6A8 but not in water injected oocytes, creatine-induced a current which was significantly enhanced by coexpression of mTOR. Kinetic analysis revealed that mTOR enhanced maximal current without significantly altering affinity. Preincubation of the oocytes for 32 h with rapamycin (50 nM) decreased the creatine-induced current and abrogated its stimulation by mTOR. The effect of mTOR on CreaT was blunted by additional coexpression of the inactive mutant of the serum and glucocorticoid-inducible kinase (K119N)SGK1 and mimicked by coexpression of wild type SGK1. In conclusion, mTOR stimulates the creatine transporter SLC6A8 through mechanisms at least partially shared by the serum and glucocorticoid-inducible kinase SGK1.
Collapse
|
125
|
Le Bouffant R, Cormier P, Mulner-Lorillon O, Bellé R. Hypoxia and DNA-damaging agent bleomycin both increase the cellular level of the protein 4E-BP. J Cell Biochem 2006; 99:126-32. [PMID: 16598776 DOI: 10.1002/jcb.20856] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The 4E-binding proteins (4E-BPs) regulate the cap-dependent eukaryotic initiation factor 4E (eIF4E). The level of 4E-BP protein is regulated during early development of sea urchin embryos. Fertilization leads to the rapid disappearance of the protein that reappears later in development. We show that two important cellular stresses, hypoxia and bleomycin prolonged checkpoint mobilization provoked the overexpression of the protein 4E-BP in developing sea urchin embryos. Hypoxia resulted after 1 h in a reversible gradual increase in the protein 4E-BP level. At 20 h, the protein 4E-BP had reached the level existing in the unfertilized eggs. Bleomycin used as a DNA-damaging agent for checkpoint activation, provoked cell cycle inhibition and after prolonged exposure (20 h), induced the expression of the protein 4E-BP. The effect of bleomycin on 4E-BP protein overexpression was dose-dependent between 0.4 and 1.2 mM. The role of the overexpression of the protein 4E-BP is discussed in relation with cellular stress responses.
Collapse
Affiliation(s)
- Ronan Le Bouffant
- Equipe Cycle Cellulaire et Développement, Unité de Recherche Mer & Santé, UMR 7150, Centre National de la Recherche Scientifique (CNRS) and Université Pierre et Marie Curie (UPMC), Station Biologique de Roscoff 29682 Roscoff Cedex France
| | | | | | | |
Collapse
|
126
|
Bedogni B, Welford SM, Cassarino DS, Nickoloff BJ, Giaccia AJ, Powell MB. The hypoxic microenvironment of the skin contributes to Akt-mediated melanocyte transformation. Cancer Cell 2005; 8:443-54. [PMID: 16338658 DOI: 10.1016/j.ccr.2005.11.005] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Revised: 10/25/2005] [Accepted: 11/16/2005] [Indexed: 12/21/2022]
Abstract
Constitutive activation of Akt characterizes a high percentage of human melanomas and represents a poor prognostic factor of the disease. We show that Akt transforms melanocytes only in a hypoxic environment, which is found in normal skin. The synergy between Akt and hypoxia is HIF1alpha mediated. Inhibition of HIF1alpha decreases Akt transformation capacity in hypoxia and tumor growth in vivo, while overexpression of HIF1alpha allows anchorage-independent growth in normoxia and development of more aggressive tumors. Finally, we show that mTOR activity is necessary to maintain the transformed phenotype by sustaining HIF1alpha activity. Taken together, these findings demonstrate that Akt hyperactivation and HIF1alpha induction by normally occurring hypoxia in the skin significantly contribute to melanoma development.
Collapse
Affiliation(s)
- Barbara Bedogni
- Division of Radiation and Cancer Biology, Stanford University, Stanford, California 94305, USA
| | | | | | | | | | | |
Collapse
|
127
|
Otulakowski G, Rafii B, Harris M, O'Brodovich H. Oxygen and glucocorticoids modulate alphaENaC mRNA translation in fetal distal lung epithelium. Am J Respir Cell Mol Biol 2005; 34:204-12. [PMID: 16210692 DOI: 10.1165/rcmb.2005-0273oc] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Glucocorticoid hormones play an important role in fetal lung maturation. It is unknown how they interact with changes in O2 tension, which play an important role in converting the lung from a fluid-secreting to a fluid-absorbing organ at birth. Airspace fluid absorption arises from active transepithelial Na+ transport with the amiloride-sensitive epithelial Na channel (ENaC), consisting of alpha, beta, and gamma subunits, representing the rate-limiting step under nonpathologic conditions. We investigated the individual and combined effects of dexamethasone (DEX) and PO2 on alphaENaC mRNA levels, rate of alphaENaC protein synthesis, and amiloride-sensitive short-circuit current in primary cultures of rat fetal distal lung epithelial cells. DEX significantly induced alphaENaC mRNA in fetal (3%) and postnatal (21%) O2, but increases in alphaENaC protein synthesis and function occurred only when epithelia were grown under a postnatal PO2. Sucrose density gradient analyses showed that DEX treatment of cells cultured at 3% O2 decreased the association of alphaENaC mRNA with large polysomes and enhanced the association with small polysomes. Conversely, incubation of DEX-treated cells in 21% O2 restored alphaENaC mRNA association with large polysomes. No significant changes were seen in the overall polyribosome profiles or in the distribution of mRNAs encoding beta and gamma subunits of ENaC or cytokeratin 18, indicating specific modulation of alphaENaC mRNA translation. These data suggest that postnatal O2 exposure may be important for efficient translation of the alphaENaC mRNA.
Collapse
Affiliation(s)
- Gail Otulakowski
- Programme in Lung Biology Research, Hospital for Sick Children Research Institute, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8.
| | | | | | | |
Collapse
|