|ognizant Communication Corporation|
VOLUME 7, NUMBER 4-6, 1998
Activation of the AP-1 Transcription Factor by Inflammatory Cytokines of the TNF Family
John M. Kyriakis
Diabetes Research Laboratory, Medical Services, Massachusetts General Hospital and Department of Medicine, Harvard Medical School, Charlestown, MA
Inflammatory cytokines of the tumor necrosis factor (TNF) family mediate a large variety of cellular and organismal inflammatory responses and are important to the pathogenesis of a number of important disease states including arthritis, septic shock, inflammatory bowel disease, and, possibly, type II diabetes. Many of the responses to these cytokines require de novo gene expression mediated by the activator protein-1 (AP-1) heterodimeric transcription factor. This review will discuss what is known of how cytokines of the TNF family, acting at the cell surface, recruit two mitogen-activated protein kinase (MAPK) subfamilies, the stress-activated protein kinases (SAPKs, also called JNKs) and the p38s, to transduce signals to AP-1.
Key words: AP-1; c-Jun; JNK; p38; SAPK; TNF; TRAF
Address correspondence to John M. Kyriakis, Diabetes Research Laboratory, Massachusetts General Hospital East, 149 13th Street, Charlestown, MA 02129. Tel: (617) 726-9451; Fax: (617) 726-9452; E-mail: email@example.com
Regulation of NF-kB by the HTLV-1 Tax Protein
Xiao Hua Li and Richard B. Gaynor
Division of Hematology-Oncology, Department of Medicine, Harold Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX 75235-8594
The Tax protein encoded by the human T-cell leukemia virus type 1 (HTLV-1) activates viral gene expression via the ATF/CREB pathway. Tax also induces a variety of cellular genes through activation of the transcription factor NF-kB. The ability of Tax to activate the NF-kB pathway plays an essential role in HTLV-1-induced cellular transformation. This review briefly summarizes the remarkable discoveries of the past several years that have greatly advanced our knowledge on signal-mediated activation of the NF-kB pathway. It highlights our current understanding of how viral agents like Tax modulate cellular signaling machinery to activate the NF-kB pathway.
Key words: HTLV-1; Tax protein; NF-kB
Address correspondence to Richard B. Gaynor, Division of Hematology-Oncology, Department of Medicine, U.T. Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-8594. Tel: (214) 648-7570; Fax: (214) 648-8862; E-mail: firstname.lastname@example.org
Nucleocytoplasmic Traffic of MAP Kinases
Vladimír Reiser, Gustav Ammerer, and Helmut Ruis
Vienna Biocenter, Institute of Biochemistry and Molecular Cell Biology, University of Vienna and Ludwig Boltzmann-Forschungstelle für Biochemie, Dr. Bohrgasse 9, A-1030, Vienna, Austria
MAPK pathways represent a unique extracellular signal response system. An important feature of such a multicomponent system appears to be the spatial intracellular organization of individual components. Recent studies demonstrate that the MAP kinases of such pathways are the molecular link between the plasma membrane sensors and the nuclear transcription factors. Stimulation of several MAPK pathways induces rapid and transient nuclear accumulation of MAP kinases. Investigations on the mode of regulation of this process using higher eukaryotes Erk2 and lower eukaryotes Hog1 and Sty1/Spc1 have revealed that at least three events contribute to signal-induced nuclear localization of these MAP kinases: activation by phosphorylation, regulated nuclear import and export, and nuclear retention.
Key words: MAPK; MEK; Nuclear import and export; Stress; Yeast
Address correspondence to Vladimír Reiser, Institute of Biochemistry and Molecular Cell Biology, University of Vienna, Dr. Bohrgasse 9, A-1030, Vienna, Austria. Tel: 00431 4277 52805; Fax: 00431 4277 9528.
Stress, Superoxide, and Signal Transduction
Pascal J. Goldschmidt-Clermont and Leni Moldovan
Heart and Lung Institute, and Division of Cardiology, The Ohio State University, Columbus, OH 43210
A variety of stressful events can trigger the production of free radicals by exposed cells. For years, the effect of such highly reactive radicals was expected to be damaging to cells, altering their biology irreversibly. However, many recent reports have shown that reactive oxygen species can have additional functions, and contribute to important signaling pathways to regulate key biological responses, including cell migration, mitosis, and apoptosis. With this review, we address the role of the small GTP binding protein, Rac, as a regulatory protein that controls superoxide production, and the effect of superoxide and derived oxidants in cell signaling.
Key words: Stress; Reactive oxygen species; Superoxide; Rac; Small GTP binding proteins; Signal transduction; Actin; Review
Address correspondence to Pascal J. Goldschmidt-Clermont, Heart and Lung Institute, Ohio State University, 420 West 12th Street, Columbus, OH 43210. Tel: (614) 688-5779; Fax: (614) 688-5778; E-mail: Goldschmidtemail@example.com
Stress and the Cell Nucleus: Dynamics of Gene Expression and Structural Reorganization
Caroline Jolly and Richard I. Morimoto
Department of Biochemistry, Molecular Biology and Cell Biology, Rice Institute for Biomedical Research, Northwestern University, Evanston, IL 60208
A growing number of experimental observations reveal that the cell nucleus is functionally compartmentalized yet organized to ensure a dynamic response to events that influence nuclear activities. The cellular and molecular response to physiological and environmental stress induces a rapid and transient change in gene expression associated with major changes in nuclear architecture that impacts on signals involved in cell growth. In this review, we will address the effects of stress on the functional compartmentation of the cell nucleus and the dynamic reorganization of nuclear stuctures and function.
Key words: Heat shock; HSFs; HSPs; Nuclear structure; Nuclear function
Address correspondence to Richard I. Morimoto, Department of Biochemistry, Molecular Biology and Cell Biology, Rice Institute for Biomedical Research, Northwestern University, 2153 North Campus Drive, Evanston, IL 60208. Phone: (847) 491-3340; Fax: (847) 491-4461; E-mail: firstname.lastname@example.org
Heat Shock Factor Function and Regulation in Response to Cellular Stress, Growth, and Differentiation Signals
Kevin A. Morano and Dennis J. Thiele
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109-0606
Heat shock factors (HSF) activate the transcription of genes encoding products required for protein folding, processing, targeting, degradation, and function. Although HSFs have been extensively studied with respect to their role in thermotolerance and the activation of gene expression in response to environmental stress, the involvement of HSFs in response to stresses associated with cell growth and differentiation, and in response to normal physiological processes is becoming increasingly clear. In this work, we review recent advances toward understanding how cells transmit growth control and developmental signals, and interdigitate cellular physiology, to regulate HSF function.
Key words: Hsp; HSF; Heat shock; Cell cycle; Stress; Growth signals
Address correspondence to Dennis J. Thiele. Tel: (734) 763-5717; Fax: (734) 763-4581; E-mail: email@example.com
A Role for RNA Metabolism in Inducing the Heat Shock Response
Tage Carlson,1 Noah Christian,2 and J. José Bonner1*
Departments of 1Biology and 2Chemistry, Indiana University, Bloomington, IN 47405
Yeast HSF is constitutively trimeric and DNA bound. Heat shock is thought to activate HSF by inducing a conformational change. We have developed an assay in which we can follow a conformational change of HSF that correlates with activity and thus appears to be the active conformation. This conformational change requires two HSF trimers bound cooperatively to DNA. The conformational change can be induced in whole cell extracts, and is thus amenable to biochemical analysis. We have purified a factor that triggers the conformational change. The factor is sensitive to dialysis, insensitive to NEM, and is not extractable by phenol. It is small, and apparently not a peptide. Mass spectroscopy identifies a novel guanine nucleotide that tracks with activity on columns. This novel nucleotide, purchased from Sigma, induces the conformational change (although this does not prove the identity of the activating factor unambiguously, because Sigma's preparation is contaminated with other compounds). What is the source of this nucleotide in cells? Activity can be generated by treating extracts with ribonuclease; this implicates RNA degradation as a source of HSF-activating activity. The heat shock response is primarily responsible for monitoring the levels of protein chaperones; how can RNA degradation be involved? Synthetic lethal interactions link HSF activity to ribosome biogenesis, suggesting a possible model. Ribosomal proteins are produced in large quantities, and in excess of rRNA; unassembled r-proteins are rapidly degraded (t1/2 = 3 min). Unassembled r-proteins aggregate readily. It is likely that unassembled r-proteins represent a major target of chaperones in vivo, and for proteasome-dependent degradation. Interference with rRNA processing (e.g., by heat shock) requires hsp70s to handle the aggregation-prone r-proteins, and proteasome proteins to help degrade the unassembled r-proteins before they aggregate. A nucleotide signal could be generated from the degradation products of the rRNA itself.
Key words: Heat shock; Conformational change; HSF; Saccharomyces cerevisiae; DNA binding protein; Transcription factor
Address correspondence to J. Jose Bonner, Department of Biology, Indiana University, 142 Jordan Hall, 1001 E. 3rd Street, Bloomington, IN 47405-3700. Tel: (812) 855-7074; Fax: (812) 855-6705; E-mail: firstname.lastname@example.org
*Current address: Parke Davis Inc., Ann Arbor, MI.
The Cellular Response to Protein Misfolding in the Endoplasmic Reticulum
Ajith A. Welihinda,1 Witoon Tirasophon,1 and Randal J. Kaufman1,2
1Department of Biological Chemistry and 2Howard Hughes Medical Institute, The University of Michigan Medical Center, 1150 W. Medical Center Drive, Ann Arbor, MI 48109-0650
In eukaryotic cells, accumulation of unfolded proteins in the lumen of the endoplasmic reticulum (ER) leads to a stress response. Cells respond to ER stress by upregulating the synthesis of ER resident protein chaperones, thus increasing the folding capacity in this organelle. In addition, this response also activates pathways to induce programmed cell death. The stress-induced chaperone synthesis is regulated at the level of transcription. In Saccharomyces cerevisiae, the transmembrane protein, Ire1p, with both serine/threonine kinase and site-specific endoribonuclease activities is implicated as the sensor of unfolded proteins in the ER that transmits the signal from the ER to activate transcription in the nucleus. Activation of the unfolded protein response (UPR) pathway also requires the bZIP transcription factor, Hac1p. Although HAC1 is transcribed constitutively, the mRNA is poorly translated. Upon accumulation of unfolded proteins, Ire1p generates a new processed form of HAC1 mRNA that is efficiently translated by removal of a 252 base sequence. Using the yeast-interaction trap system we identified additional components of the UPR. A yeast transcriptional coactivator complex, Gcn5p/Ada, which is composed of Gcn5p, Ada2p, Ada3p, and Ada5p, was identified that interacts with Ire1p and Hac1p. Deletion of GCN5, ADA2, and/or ADA3 reduces, and deletion of ADA5 completely abrogates, the transcriptional induction in response to misfolded protein in the ER. A protein phosphatase, Ptc2p, was also identified as a negative regulator of the UPR that directly interacts with and dephosphorylates activated Ire1p. Recently, two mammalian homologues of Ire1p, IRE1 and IRE2, were identified. hIre1p, is preferentially localized to the nuclear envelope and requires a functional nuclease activity to transmit the UPR. These results indicate that some features of the UPR are conserved from yeast to humans and may be composed of a multicomponent complex that is regulated by phosphorylation status and is associated with the nuclear envelope to regulate processes including transcriptional induction and mRNA processing. We propose that activation of Ire1p induces splicing of HAC1 mRNA as well as engages and targets the Gcn5/Ada/Hac1 protein complex to genes that are transcriptionally activated in response to unfolded protein in the ER. The transcriptional activation is facilitated by targeting the histone acetylase, Gcn5p in yeast, to promote histone acetylation at chromatin encoding ER stress-responsive genes. In addition, activation of Ire1p leads to increased lipid biosynthesis, thereby allowing ER expansion to accommodate increasing lumenal constituents. Under conditions of more severe stress, cells activate an Ire1p-dependent death pathway that is mediated through induction of GADD153/CHOP.
Key words: Unfolded protein response; Ire1; Gcn5/Ada complex; Ptc2; ER stress
Address correspondence to Dr. Randal J. Kaufman, Howard Hughes Medical Institute, The University of Michigan Medical Center, MSRB II Room 4570, 1150 W. Medical Center Drive, Ann Arbor, MI 48109-0650. Tel: (734) 763-9037; Fax: (734) 763-9323; E-mail: email@example.com
Induction of Metallothionein by Stress and its Molecular Mechanisms
Samson T. Jacob,1 Kalpana Ghoshal,1 and John F. Sheridan2
1 Department of Medical Biochemistry, The Ohio State University College of Medicine, 2Section of Oral Biology, The Ohio State University College of Dentistry, Columbus, OH 43210
This article describes the effect of restraint stress or social reorganization stress on the induction of metallothionein (MT) in the liver, heart, lung, and spleen. Both MT-I and MT-II mRNA were elevated as much as 30- fold following just 12 h (one cycle) of restraint stress. The amount of MT protein also increased following stress. The MT induction was the highest in the liver, followed by the lung, heart, and spleen. MT-I induction was also observed in the fore, mid, and hind regions of the brain whereas the brain-specific MT-III gene was not activated by stress. The increase in MT mRNA correlated well with the rise in stress-induced serum corticosterone. The induction occurred at the transcriptional level and was mediated essentially by the activation of glucocorticoid receptor. The MT mRNA returned to the control level after nine cycles of stress. Exposure of these habituated mice to a different type of stress (treatment with heavy metals such as cadmium or zinc sulfate) led to further MT induction. Because heavy metals induced MT via activation of the factor MTF-1, distinct molecular mechanisms should be responsible for the activation of MT promoter by different inducers.
Key words: Metallothionein; Restraint stress; Social reorganization stress; Molecular mechanisms
Address correspondence to Samson T. Jacob, 333 Hamilton Hall, 1645 Neil Avenue, Columbus, OH 43210. Tel: (614) 688-5494; Fax: (614) 688-5600.
Transcriptional Regulation of the Heat Shock Protein Genes by STAT Family Transcription Factors
Anastasis Stephanou and David S. Latchman
Department of Molecular Pathology, Windyer Institute of Medical Sciences, University College London, London W1P 6DB, UK
We have previously demonstrated that interleukin-6 (IL-6) increases the levels of the heat shock protein 90 (Hsp90) and activates the Hsp90b promoter via the IL-6-activated transcription factors NF-IL6 and STAT-3. In addition, interferon-g (IFN-g) treatment increases the levels of Hsp70 and Hsp90 and also enhances the activity of the Hsp70 and Hsp90b promoters with these effects being dependent on activation of the STAT-1 transcription factor by IFN-g. The effect of IL-6/STAT-3 and IFN-g/STAT-1 was mediated via a short region of the Hsp70/Hsp90 promoters, which also mediates the effects of NF-IL6. This region also contains a binding site for the stress-activated transcription factor HSF-1. Furthermore, STAT-1 and HSF-1 interact with one another via a protein-protein interaction and produce a strong activation of transcription. In contrast, STAT-3 and HSF-1 antagonize one another and reduce the activation of both the Hsp70 and Hsp90 promoters. Thus, STAT-1 or STAT-3 activation alone or together results in the activation of Hsp promoters. However, STAT-1 or STAT-3 interact differently with HSF-1 to regulate Hsp promoter activity. These results indicate that STATs are able to moduate the Hsp70 and Hsp90 gene promoters and that these transcription factors are likely to play a very important role in Hsp gene activation by nonstressful stimuli and the intergration of these responses with the stress response of these genes.
Key words: Heat shock protein; Transcription factors; Stress response; STAT family
Address correspondence to Anastasis Stephanou, Department of Molecular Pathology, Windyer Institute of Medical Sciences, University College London, 46 Cleveland Street, London W1P 6DB, UK. Tel: 171-59-04-9343; Fax: 171-387-3310.
ATF3 and Stress Responses
Tsonwin Hai,1,2 Curt D. Wolfgang,1 Derek K. Marsee,2 Amy E. Allen,1 and Umasundari Sivaprasad1
Department of Medical Biochemistry, Neurobiotechnology Center, 1Ohio State Biochemistry Program, and 2Molecular, Cellular and Developmental Biology Program, Ohio State University, Columbus, OH 43210
The purpose of this review is to discuss ATF3, a member of the ATF/CREB family of transcription factors, and its roles in stress responses. In the introduction, we briefly describe the ATF/CREB family, which contains more than 10 proteins with the basic region-leucine zipper (bZip) DNA binding domain. We summarize their DNA binding and heterodimer formation with other bZip proteins, and discuss the nomenclature of these proteins. Over the years, identical or homologous cDNA clones have been isolated by different laboratories and given different names. We group these proteins into subgroups according to their amino acid similarity; we also list the alternative names for each member, and clarify some potential confusion in the nomenclature of this family of proteins. We then focus on ATF3 and its potential roles in stress responses. We review the evidence that the mRNA level of ATF3 greatly increases when the cells are exposed to stress signals. In animal experiments, the signals include ischemia, ischemia coupled with reperfusion, wounding, axotomy, toxicity, and seizure; in cultured cells, the signals include serum factors, cytokines, genotoxic agents, cell death-inducing agents, and the adenoviral protein E1A. Despite the overwhelming evidence for its induction by stress signals, not much else is known about ATF3. Preliminary results suggest that the JNK/SAPK pathway is involved in the induction of ATF3 by stress signals; in addition, IL-6 and p53 have been demonstrated to be required for the induction of ATF3 under certain conditions. The consequences of inducing ATF3 during stress responses are not clear. Transient transfection and in vitro transcription assays indicate that ATF3 represses transcription as a homodimer; however, ATF3 can activate transcription when coexpressed with its heterodimeric partners or other proteins. Therefore, it is possible that, when induced during stress responses, ATF3 activates some target genes but represses others, depending on the promoter context and cellular context. Even less is understood about the physiological significance of inducing ATF3. We will discuss our preliminary results and some reports by other investigators in this regard.
Key words: ATF3; Stress responses; Transcription factors; ATF/CERB
Address correspondence to Tsonwin Hai, Room 148, Rightmire Hall, 1060 Carmack Road, Neurobiotechnology Center, Ohio State University, Columbus. OH 43210. Tel: (614) 292-2910. Fax: (614) 292-5379. E-mail: firstname.lastname@example.org
Signaling Pathways Mediating the Response to Hypertrophic Stress in the Heart
Thomas Force, Roger Hajjar, Federica del Monte, Anthony Rosenzweig, and Gabriel Choukroun
Medical Services, Massachusetts General Hospital, and Department of Medicine, Harvard Medical School, Boston, MA
Cardiac hypertrophy is an increase in the mass of the heart. It is a major risk factor for the development of myocardial infarction and congestive heart failure, diseases that afflict millions of patients worldwide. Hypertrophy can be caused by intrinsic defects of the proteins of the contractile apparatus of the heart, or by extrinsic stimuli such as hypertension. In this review, we will focus on the cytosolic signal transduction pathways that mediate the hypertrophic response to extrinsic stimuli. Although a large number of signaling molecules have been implicated in the hypertrophic response, we will review data that, we believe, suggest there may be only a few molecules that serve as signaling funnels through which many hypertrophic signals must pass on their way to the nucleus. These include the stress response protein kinases (the stress-activated protein kinases or SAPKs, and, possibly, the p38 kinases) and calcineurin. These molecules have as their primary targets transcription factors, many of which have been implicated in the complex yet stereotypic genetic response to hypertrophic stress. In most cases, it is not possible at present to complete the link from hypertrophic stimulus through a specific signaling molecule and a specific transcription factor to the induction of a specific gene that initiates a particular biologic response. We will attempt to identify some of the most important areas where major questions remain in the hopes of stimulating further research into this major cause of death and disability.
Key words: Cardiac hypertrophy; Stress-activated protein kinases; c-Jun N-terminal kinases; Heart failure
Address correspondence to Gabriel Choukroun, Massachusetts General Hospital East, Suite 4002, 149 13th St., Charlestown, MA 02129. Tel: (617) 726-9334; Fax: (617) 726-4356; E-mail: email@example.com
Influence of Phosphorylation and Oligomerization on the Protective Role of the Small Heat Shock Protein 27 in Rat Adult Cardiomyocytes
Jody L. Martin,1 Eileen Hickey,2 Lee A. Weber,2 Wolfgang H. Dillmann,3 and Ruben Mestril1
1 Department of Physiology, The Cardiovascular Institute,
Loyola University, Chicago, IL
2Department of Biology, University of Nevada, Reno, NV
3Department of Medicine, University of California, San Diego, CA
Recent reports have demonstrated that the heat shock proteins (hsp) and in particular the hsp70 confer protection against cardiac ischemic damage. More recently, we have shown that increased expression of another heat shock protein, the hsp27, through an adenovirus vector system protects adult cardiomyocytes against ischemic injury. This small heat shock protein undergoes phosphorylation when the cell is under stress. This has led many to speculate that phosphorylation of hsp27 is required for the protective role this protein plays in the cell. In order to investigate this possibility, we have mutated the serines that are the sites of phosphorylation on the hsp27, to glycines or alanines. These nonphosphorylatable mutants of hsp27 were cloned into adenoviral vectors and used to infect adult rat cardiomyocytes to assess their ability in protecting against ischemic injury. In addition, we used a specific inhibitor of p38 MAP kinase that is a key member of the kinase pathway responsible for phosphorylating the hsp27. Our present results show that the nonphosphorylated hsp27 forms larger oligomeric complexes than the phosphorylated hsp27. Interestingly, phosphorylation of hsp27 seems not to play a role in its ability to protect adult rat cardiomyocytes against ischemic damage.
Key words: Heat shock proteins; Ischemia; Cardiomyocytes; p38 MAP kinase; Cardioprotection
Address correspondence to Ruben Mestril, Ph.D., The Cardiovascular Institute, Loyola University Medical Center, 2160 South First Avenue, Bldg. 110, Room 5227, Maywood, IL 60153. Tel: (708) 327-2395; Fax: (708) 327-2849; E-mail: firstname.lastname@example.org
Calcium-Induced Stabilization of AU-Rich Short-Lived mRNAs Is a Common Default Response
Nicola Klein,* Anna Maria Curatola,** and Robert J. Schneider
Department of Biochemistry and Microbiology, Kaplan Cancer Center, NYU Medical School, New York, NY 10016
The AU-rich element (AUUUA)n, found in the 3´ noncoding region of many short-lived cytokine and proto-oncogene mRNAs, is sufficient to specifically target these mRNAs for rapid degradation in mammalian cells. The mechanism by which the AU-rich element promotes rapid mRNA decay is not known. Previous studies have shown that release of intracellular stored calcium by ionophore treatment of thymocytes and mast cells inhibits the rapid turnover of AU-rich interleukin mRNAs. Increased cytoplasmic half-life of interleukin mRNAs was linked to calcium-induced activation of the N-terminal c-Jun kinase. In this report we have characterized the calcium-induced stabilization of AU-rich mRNAs. We show that calcium induces stabilization of mRNAs with canonical AU-rich elements in all cell types tested. These results indicate that short-lived mRNA stabilization by calcium is not unique to immune cells nor interleukin mRNAs, but is a widespread default response that includes generic AU-rich mRNAs. Stabilization is shown to be rapid but transient, and to act without altering nuclear transcription or cytoplasmic translation rates. These data support the view that calcium release likely stabilizes short-lived mRNAs by altering trans-acting decay factors that promote AU-rich mRNA turnover.
Key words: Calcium-induced stabilization; AU-rich element; Short-lived mRNAs
Address correspondence to Robert J. Schneider, Department of Biochemistry and Microbiology, Kaplan Cancer Center, NYU Medical School, 550 First Avenue, New York, NY 10016. Tel: (212) 263-6006; Fax: (212) 263-8166; E-mail: email@example.com
*Present address: Department of Pediatric Medicine, Stanford University
Medical School, Stanford, CA 94305.
**Present address: Department of Medicine, NYU Medical School, New York, NY 10016.
Regulation of the Iron Regulatory Proteins by Reactive Nitrogen and Oxygen Species
Eric S. Hanson and Elizabeth A. Leibold
Eccles Program in Human Molecular Biology and Genetics and the Department of Medicine, Division of Hematology-Oncology, University of Utah, Salt Lake City, UT 84112
Iron regulatory proteins 1 and 2 (IRP1 and IRP2) are RNA binding proteins that posttranscriptionally regulate the expression of mRNAs coding for proteins involved in the maintenance of iron and energy homeostasis. The RNA binding activities of the IRPs are regulated by changes in cellular iron. Thus, the IRPs are considered iron sensors and the principle regulators of cellular iron homeostasis. The mechanisms governing iron regulation of the IRPs are well described. Recently, however, much attention has focused on the regulation of IRPs by reactive nitrogen and oxygen species (RNS, ROS). Here we focus on summarizing the iron-regulated RNA binding activities of the IRPs, as well as the recent findings of IRP regulation by RNS and ROS. The recent observations that changes in oxygen tension regulate both IRP1 and IRP2 RNA binding activities will be addressed in light of ROS regulation of the IRPs.
Key words: Iron regulatory proteins; Reactive nitrogen species; Reactive oxygen species
Address correspondence to Elizabeth A. Leibold, University of Utah, 15 N. 2030 E., Bldg. 533, Room 4220, Salt Lake City, UT 84112. Tel: (801) 585-5002; Fax: (801) 585-3501; E-mail firstname.lastname@example.org
Functional Role of p21 During the Cellular Response to Stress
Myriam Gorospe, Xiantao Wang, and Nikki J. Holbrook
Laboratory of Biological Chemistry, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
A wide range of stress stimuli, including oxidants, genotoxins, metabolic deficiencies, and irradiation, have been shown to induce expression of the cyclin-dependent kinase inhibitor p21. Among the best characterized mediators of p21 induction by stress is the tumor suppressor gene p53, which acts as a transcriptional activator to enhance the expression of the p21 gene. However, many other mechanisms involving transcriptional and posttranscriptional events have been found to participate in the elevation of p21 levels by stressful agents. The significance of the stress-mediated elevation in p21 expression is not fully understood, but it is clear that alterations in p21 expression impact on the ability of the cell to survive the insult. Although a large number of reports have demonstrated correlations between the expression of p21 and cellular outcome, this review will focus only on those reports where the role of p21 in a given stress paradigm has been investigated directly, through use of different strategies to manipulate p21 expression followed by assessment of the consequences of altered p21 expression on cell survival. The majority of such studies have revealed that p21 exerts a protective function against stress, and this property appears to rely, at least in part, on the ability of p21 to suppress cell proliferation. A few exceptions to this universal protective influence of p21 have also been observed and will be discussed.
Key words: Cip1; Waf1; Sdi1; Cyclin-dependent kinase inhibitor; Stress response; Genotoxic stress; p53; Growth arrest; Apoptosis; Gene induction
Address correspondence to Nikki J. Holbrook, Box 12, Laboratory of Biological Chemistry, GRC, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825. Tel: (410) 558-8197; Fax: (410) 558-8335; E-mail: email@example.com
The Complexity of Radiation Stress Responses: Analysis by Informatics and Functional Genomics Approaches
Albert J. Fornace, Jr.,1 Sally A. Amundson,1 Michael Bittner,2 Timothy G. Myers,2 Paul Meltzer,3 John N. Weinsten,1 and Jeffrey Trent3
1Division of Basic Science, 2Developmental Therapeutics Program, NCI, and 3NHGRI, NIH, Bethesda, MD
Molecular responses to genotoxic stress are complex and are mediated by a variety of regulatory pathways. One key element in cellular response is the stress gene transcription factor p53, which can regulate nearly 100 genes that have already been identified. Although p53 plays a central role in the cellular response to DNA-damaging agents such as ionizing radiation (IR), other pathways can also have important roles. One example is the transcriptional responses associated with IR-induced apoptosis, where induction of some genes is limited to p53 wild-type (wt) cells that also have the ability to undergo rapid apoptosis after irradiation. In contrast, other genes are triggered after IR in lines undergoing rapid apoptosis regardless of p53 status. From this and other examples, it is apparent that the pattern of stress gene expression is cell type specific in both primary and transformed lines. The premise will be developed that such differences in stress gene responsiveness can be employed as molecular markers using a combination of informatics and functional genomics approaches. An example is given using the panel of lines of the NCI anticancer drug screen where both the p53 status and sensitivity to a large collection of cytotoxic agents have been determined. The utility of cDNA microarray hybridization to measure IR-stress gene responses has recently been demonstrated and a large number of additional IR-stress genes have been identified. The responses of some of these genes to IR and other DNA-damaging agents varied widely in cell lines from different tissues of origin and different genetic backgrounds, highlighting the importance of cellular context to genotoxic stress responses; this also highlights the need for informatics approaches to discover and prioritize hypotheses regarding the importance of particular cellular factors. The aim of this review is to demonstrate the utility of combining an informatics approach with functional genomics in the study of stress responses.
Key words: Ionizing radiation; p53; Microarray; Genotoxic stress
Address correspondence to Albert J. Fornace, Jr., Building 37, Room
5C09, NCI, National Institutes of Health, 37 Convent Dr. MSC 4255, Bethesda,
MD 20892-4255. Tel: (301) 402-0744; Fax: (301) 480-1946; E-mail: firstname.lastname@example.org