The heat shock response in HeLa cells is accompanied by elevated expression of the c-fos proto-oncogene

Biologically sound formal model of Hsp70 heat induction

A proper response to rapid environmental changes is essential for cell survival and requires efficient modifications in the pattern of gene expression. In this respect, a prominent example is Hsp70, a chaperone protein whose synthesis is dynamically regulated in stress conditions. In this paper, we expand a formal model of Hsp70 heat induction originally proposed in previous articles. To accurately capture various modes of heat shock effects, we not only introduce temperature dependencies in transcription to Hsp70 mRNA and in dissociation of transcriptional complexes, but we also derive a new formal expression for the temperature dependence in protein denaturation. We calibrate our model using comprehensive sets of both previously published experimental data and also biologically justified constraints. Interestingly, we obtain a biologically plausible temperature dependence of the transcriptional complex dissociation, despite the lack of biological constraints imposed in the calibration process. Finally, based on a sensitivity analysis of the model carried out in both deterministic and stochastic settings, we suggest that the regulation of the binding of transcriptional complexes plays a key role in Hsp70 induction upon heat shock. In conclusion, we provide a model that is able to capture the essential dynamics of the Hsp70 heat induction whilst being biologically sound in terms of temperature dependencies, description of protein denaturation and imposed calibration constraints.

Deep transcriptome analysis of the heat shock response in an Atlantic sturgeon (Acipenser oxyrinchus) cell line

Despite efforts to restore Atlantic sturgeon in European rivers, aquaculture techniques result in animals with high post-release mortality due to, among other reasons, their low tolerance to increasing water temperature. Marker genes to monitor heat stress are needed in order to identify heat-resistant fish. Therefore, an Atlantic sturgeon cell line was exposed to different heat shock protocols (30 °C and 35 °C) and differences in gene expression were investigated. In total 3020 contigs (∼1.5%) were differentially expressed. As the core of the upregulated contigs corresponded to heat shock proteins (HSP), the heat shock factor (HSF) and the HSP gene families were annotated in Atlantic sturgeon and mapped via Illumina RNA sequencing to identify heat-inducible family members. Up to 6 hsf and 76 hsp genes were identified in the Atlantic sturgeon transcriptome resources, 16 of which were significantly responsive to the applied heat shock. The previously studied hspa1 (hsp70) gene was only significantly upregulated at the highest heat shock (35 °C), while a set of 5 genes (hspc1, hsph3a, hspb1b, hspb11a, and hspb11b) was upregulated at all conditions. Although the hspc1 (hsp90a) gene was previously used as heat shock-marker in sturgeons, we found that hspb11a is the most heat-inducible gene, with up to 3296-fold higher expression in the treated cells, constituting the candidate gene markers for in vivo trials.

Protein aggregation in cell biology: An aggregomics perspective of health and disease

Maintaining protein homeostasis (proteostasis) is essential for cellular health and is governed by a network of quality control machinery comprising over 800 genes. When proteostasis becomes imbalanced, proteins can abnormally aggregate or become mislocalized. Inappropriate protein aggregation and proteostasis imbalance are two of the central pathological features of common neurodegenerative diseases including Alzheimer, Parkinson, Huntington, and motor neuron diseases. How aggregation contributes to the pathogenic mechanisms of disease remains incompletely understood. Here, we integrate some of the key and emerging ideas as to how protein aggregation relates to imbalanced proteostasis with an emphasis on Huntington disease as our area of main expertise. We propose the term "aggregomics" be coined in reference to how aggregation of particular proteins concomitantly influences the spatial organization and protein-protein interactions of the surrounding proteome. Meta-analysis of aggregated interactomes from various published datasets reveals chaperones and RNA-binding proteins are common components across various disease contexts. We conclude with an examination of therapeutic avenues targeting proteostasis mechanisms.

Sexual Dimorphism and Aging Differentially Regulate Adaptive Homeostasis

External and internal stimuli cause modifications to gene and biochemical pathways. In turn, demonstrating that biological systems continuously make short-term adaptations both to set-points, and to the range of "normal" capacity, due to mild conditional changes, or to subtoxic, nondamaging levels of chemical agents. This is termed as "Adaptive Homeostasis," defined with the following: "The transient expansion or contraction of the homeostatic range in response to exposure to sub-toxic, nondamaging, signaling molecules or events, or the removal or cessation of such molecules or events." Research from several laboratories, including our own, found that adaptive homeostasis declines with age in organisms as diverse as worms, flies, and mammals, and decreases with senescence in mammalian cell cultures. We suggest that diminishing adaptive homeostasis may play a causal role as a factor responsible for the aging phenotype. Furthermore, although studies of humans, animals, and model organisms are often limited to a single sex, and cell culture studies may even be conducted with lines whose donor's sex was unknown, studies reveal distinct sexual dimorphism in adaptive homeostasis. Interestingly, although young males and females may exhibit dramatic differences in adaptive capacities and/or preferences, these distinctions are lost with age as adaptive homeostasis patterns converge.

Mathematical modeling of the heat-shock response in HeLa cells

The heat-shock response is a key factor in diverse stress scenarios, ranging from hyperthermia to protein folding diseases. However, the complex dynamics of this physiological response have eluded mathematical modeling efforts. Although several computational models have attempted to characterize the heat-shock response, they were unable to model its dynamics across diverse experimental datasets. To address this limitation, we mined the literature to obtain a compendium of in vitro hyperthermia experiments investigating the heat-shock response in HeLa cells. We identified mechanisms previously discussed in the experimental literature, such as temperature-dependent transcription, translation, and heat-shock factor (HSF) oligomerization, as well as the role of heat-shock protein mRNA, and constructed an expanded mathematical model to explain the temperature-varying DNA-binding dynamics, the presence of free HSF during homeostasis and the initial phase of the heat-shock response, and heat-shock protein dynamics in the long-term heat-shock response. In addition, our model was able to consistently predict the extent of damage produced by different combinations of exposure temperatures and durations, which were validated against known cellular-response patterns. Our model was also in agreement with experiments showing that the number of HSF molecules in a HeLa cell is roughly 100 times greater than the number of stress-activated heat-shock element sites, further confirming the model’s ability to reproduce experimental results not used in model calibration. Finally, a sensitivity analysis revealed that altering the homeostatic concentration of HSF can lead to large changes in the stress response without significantly impacting the homeostatic levels of other model components, making it an attractive target for intervention. Overall, this model represents a step forward in the quantitative understanding of the dynamics of the heat-shock response.

Serum cholesterol selectively regulates glucocorticoid sensitivity through activation of JNK

Glucocorticoids (Gc) are potent anti-inflammatory agents with wide clinical application. We have previously shown that increased serum concentration significantly attenuates regulation of a simple Gc-responsive reporter. We now find that glucocorticoid receptor (GR) regulation of some endogenous transactivated but not transrepressed genes is impaired, suggesting template specificity. Serum did not directly affect GR expression, activity or trafficking, implicating GR crosstalk with other signalling pathways. Indeed, a JNK inhibitor completely abolished the serum effect. We identified the Gc modulating serum component as cholesterol. Cholesterol loading mimicked the serum effect, which was readily reversed by JNK inhibition. Chelation of serum cholesterol with methyl-β-cyclodextrin or inhibition of cellular cholesterol synthesis with simvastatin potentiated the Gc response. To explore the effect in vivo we used ApoE(-/-) mice, a model of hypercholesterolaemia. Consistent with our in vitro studies, we find no impact of elevated cholesterol on the expression of GR, or on the hypothalamic-pituitary-adrenal axis, measured by dexamethasone suppression test. Instead we find selective Gc resistance on some hepatic target genes in ApoE(-/-) mice. Therefore, we have discovered an unexpected role for cholesterol as a selective modulator of Gc action in vivo. Taken together these findings reveal a new environmental constraint on Gc action with relevance to both inflammation and cancer.

PARP1 represses PAP and inhibits polyadenylation during heat shock

The 3' ends of most eukaryotic mRNAs are produced by an endonucleolytic cleavage followed by synthesis of a poly(A) tail. Poly(A) polymerase (PAP), the enzyme that catalyzes the formation of the tail, is subject to tight regulation involving several posttranslational modifications. Here we show that the enzyme poly(ADP-ribose) polymerase 1 (PARP1) modifies PAP and regulates its activity both in vitro and in vivo. PARP1 binds to and modifies PAP by poly(ADP-ribosyl)ation (PARylation) in vitro, which inhibits PAP activity. In vivo we show that PAP is PARylated during heat shock, leading to inhibition of polyadenylation in a PARP1-dependent manner. The observed inhibition reflects reduced RNA binding affinity of PARylated PAP in vitro and decreased PAP association with non-heat shock protein-encoding genes in vivo. Our results provide direct evidence that PARylation can control processing of mRNA precursors, and also identify PARP1 as a regulator of polyadenylation during thermal stress.

Passing the anaerobic threshold is associated with substantial changes in the gene expression profile in white blood cells

High and moderate intensity endurance exercise alters gene expression in human white blood cells (WBCs), but the understanding of how this effect occurs is limited. To increase our knowledge of the nature of this process, we investigated the effects of passing the anaerobic threshold (AnT) on the gene expression profile in WBCs of athletes. Nineteen highly trained skiers participated in a treadmill test with an incremental step protocol until exhaustion (ramp test to exhaustion, RTE). The average total time to exhaustion was 14:40 min and time after AnT was 4:50 min. Two weeks later, seven of these skiers participated in a moderate treadmill test (MT) at 80% peak O(2) uptake for 30 min, which was slightly below their AnTs. Blood samples were obtained before and immediately after both tests. RTE was associated with substantially greater leukocytosis and acidosis than MT. Gene expression in WBCs was measured using whole genome microarray expression analysis before and immediately after each test. A total of 310 upregulated genes were found after RTE, and 69 genes after MT of which 64 were identical to RTE. Both tests influenced a variety of known gene pathways related to inflammation, stress response, signal transduction and apoptosis. A large group of differentially expressed previously unknown small nucleolar RNA and small Cajal body RNA was found. In conclusion, a 15-min test to exhaustion was associated with substantially greater changes of gene expression than a 30-min test just below the AnT.

Turnover of AU-rich-containing mRNAs during stress: a matter of survival

Cells undergo various adaptive measures in response to stress. Among these are specific changes in the posttranscriptional regulation of various genes. In particular, the turnover of mRNA is modified to either increase or decrease the abundance of certain target messages. Some of the best-studied mRNAs that are affected by stress are those that contain adenine/uridine-rich elements (AREs) in their 3'-untranslated regions. ARE-containing mRNAs are involved in many important cellular processes and are normally labile, but in response to stress they are differentially regulated through the concerted efforts of ARE-binding proteins (AUBPs) such as HuR, AUF1, tristetraprolin, BRF1, and KSRP, along with microRNA-mediated effects. Additionally, the fate of ARE-containing mRNAs is modified by inducing their localization to stress granules or mRNA processing bodies. Coordination of these various mechanisms controls the turnover of ARE-containing mRNAs, and thereby enables proper responses to cellular stress. In this review, we discuss how AUBPs regulate their target mRNAs in response to stress, along with the involvement of cytoplasmic granules in this process.

The effects of temperature change on the circadian clock of Neurospora

The phase resetting of the circadian oscillatory system by pulses of increased temperature (zeitgebers) and the temperature compensation of its period length during longer exposures are major features of the system, but are not well understood in molecular terms. In Neurospora crassa, the effects of pulses of increased temperature on the circadian rhythm of conidiation were determined and possible inputs to the oscillatory system tested, including changes in cyclic 3',5'-adenosine monophosphate (cAMP), inositol 1,4,5-trisphosphate and H+ concentrations, as well as changes of phosphorylation, synthesis and degradation of proteins. Following the kinetics of these parameters during exposure to increased temperature showed transient changes. Experimental manipulation of cAMP, Ca2+ and H+ levels, and of the synthesis and, possibly, degradation of proteins, resulted in phase shifts of the oscillatory system. It is assumed that the temperature signal affects the oscillator(s) by multiple pathways and shifts the whole state of the oscillatory system. Second messenger levels, protein synthesis and protein degradation show adaptation to longer exposures to elevated temperature which may be involved in the temperature compensation of the period length. The temperature compensation is also proposed to involve a shift in the state of all or most oscillator variables.

Degradation of hsp70 and other mRNAs in Drosophila via the 5' 3' pathway and its regulation by heat shock

Two general pathways of mRNA decay have been characterized in yeast. Both start with deadenylation. The major pathway then proceeds via cap hydrolysis and 5'-exonucleolytic degradation whereas the minor pathway consists of 3'-exonucleolytic decay followed by hydrolysis of the remaining cap structure. In higher eukaryotes, these pathways of mRNA decay are believed to be conserved but have not been well characterized. We have investigated the decay of the hsp70 mRNA in Drosophila Schneider cells. As shown by the use of reporter constructs, rapid deadenylation of this mRNA is directed by its 3'-untranslated region. The main deadenylase is the CCR4.NOT complex; the PAN nuclease makes a lesser contribution. Heat shock prevents deadenylation not only of the hsp70 but also of bulk mRNA. A completely deadenylated capped hsp70 mRNA decay intermediate accumulates transiently and is degraded via cap hydrolysis and 5'-decay. Thus, decapping is a slow step in the degradation pathway. Cap hydrolysis is also inhibited during heat shock. Degradation of reporter RNAs from the 3'-end became detectable only upon inhibition of 5'-decay and thus represents a minor decay pathway. Because two reporter RNAs and at least two endogenous mRNAs were degraded primarily from the 5'-end with cap hydrolysis as a slow step, this pathway appears to be of general importance for mRNA decay in Drosophila.

Inhibition of the ubiquitin-proteasome system induces stress granule formation

The inhibition of the ubiquitin-dependent proteasome system (UPS) via specific drugs is one type of approach used to combat cancer. Although it has been suggested that UPS inhibition prevents the rapid decay of AU-rich element (ARE)-containing messages, very little is known about the cellular mechanisms leading to this effect. Here we establish a link between the inhibition of UPS activity, the formation of cytoplasmic stress granules (SGs), and mRNA metabolism. The assembly of the SGs requires the phosphorylation of the translation initiation factor eIF2alpha by a mechanism involving the stress kinase GCN2. On prolonged UPS inhibition and despite the maintenance of eIF2alpha phosphorylation, SGs disassemble and translation recovers in an Hsp72 protein-dependent manner. The formation of these SGs coincides with the disassembly of processing bodies (PBs), known as mRNA decay entities. As soon as the SGs assemble, they recruit ARE-containing messages such as p21(cip1) mRNA, which are stabilized under these conditions. Hence, our findings suggest that SGs could be considered as one of the players that mediate the early response of the cell to proteasome inhibitors by interfering temporarily with mRNA decay pathways.

Specific TSC22 domain transcripts are hypertonically induced and alternatively spliced to protect mouse kidney cells during osmotic stress

We recently cloned a novel osmotic stress transcription factor 1 (OSTF1) from gills of euryhaline tilapia (Oreochromis mossambicus) and demonstrated that acute hyperosmotic stress transiently increases OSTF1 mRNA and protein abundance [Fiol DF, Kültz D (2005) Proc Natl Acad Sci USA102, 927-932]. In this study, a genome-wide search was conducted to identify nine distinct mouse transforming growth factor (TGF)-beta-stimulated clone 22 domain (TSC22D) transcripts, including glucocorticoid-induced leucine zipper (GILZ), that are orthologs of OSTF1. These nine TSC22D transcripts are encoded at four loci on chromosomes 14 (TSC22D1, two splice variants), 3 (TSC22D2, four splice variants), X (TSC22D3, two splice variants), and 5 (TSC22D4). All nine mouse TSC22D transcripts are expressed in renal cortex, medulla and papilla, and in the mIMCD3 cell line. The two TSC22D3 transcripts (including GILZ) are upregulated by aldosterone but not by hyperosmolality in mIMCD3 cells. In contrast, TSC22D4 is stably upregulated by hyperosmolality in mIMCD3 cells and increased in renal papilla compared with cortex. Moreover, all four TSC22D2 transcripts are transiently upregulated by hyperosmolality and resemble tilapia OSTF1 in this regard. All TSC22D2 transcripts depend on hypertonicity as the signal for their upregulation and are unresponsive to increases in cell-permeable osmolytes. mRNA stabilization is the mechanism for TSC22D2 upregulation by hyperosmolality. Overexpression of TSC22D2-4 in mIMCD3 cells confers protection towards osmotic stress, as evidenced by a 2.7-fold increase in cell survival after 3 days at 600 mOsmol x kg(-1). Based on variable responsiveness to aldosterone and hyperosmolality in kidney cells we conclude that mouse TSC22D genes have diverse physiological functions. TSC22D2 and TSC22D4 are involved in adaptation of renal cells to hypertonicity suggesting that they represent important elements of osmosensory signal transduction in mouse kidney cells.

Lung carcinogenesis: pivotal role of metals in tobacco smoke

Although significant progress has been made in unraveling the molecular mechanisms responsible for tobacco smoke toxicity and carcinogenicity, only limited information is available concerning the mechanisms by which tar particles and the gaseous phase constituents of tobacco smoke participate and contribute to carcinogenic processes in lung cancer. The present review critically evaluates how metals contained in the tar particles and the gaseous phase of tobacco smoke play a leading role in the carcinogenic process, taking into consideration the physiology and pathophysiology of the bronchial epithelium. Overwhelmingly, the published data indicate that the bronchopulmonary epithelial cells may represent the first and most critical line of defense against cigarette smoke.

Regulation of osmotic stress transcription factor 1 (Ostf1) in tilapia(Oreochromis mossambicus) gill epithelium during salinity stress

Mechanisms of induction of osmotic stress transcription factor 1 (Ostf1)were analyzed in gill epithelium of tilapia exposed to salinity stress. Experiments with primary cultures of gill epithelial cells revealed that hyperosmotic Ostf1 induction was independent of systemic factors. In addition,the synthetic glucocorticoid receptor agonist dexamethasone did not affect Ostf1 levels, arguing against cortisol being the signal for Ostf1 induction during hyperosmotic stress. Exposure of primary gill cell cultures to a hyperosmotic agent that is cell permeable and non-hypertonic (glycerol) did not trigger Ostf1 induction. However, when gill cells were exposed to hypertonicity (either in the form of NaCl or other forms) Ostf1 was rapidly and significantly induced. Analysis of hnRNA and mRNA levels revealed that Ostf1 upregulation in gill cells of intact fish and primary cultures of gill epithelial cells was mediated by transient mRNA stabilization. In addition to the initial transient mRNA stabilization a subsequent transcriptional induction of Ostf1 was observed. In cultured gill cells increase in Ostf1 mRNA synthesis was stable and very potent, whereas in gill cells of intact fish this increase was transient. This observation suggests positive feedback by Ostf1 or one of its targets and negative feedback by systemic factors on Ostf1 transcription.

We conclude that Ostf1 induction in gill epithelial cells of tilapia exposed to salinity stress (1) is independent of cortisol or other systemic factors; (2) depends on hypertonicity as the signal; and (3) is based on transient mRNA stabilization. Moreover, our data on primary cell cultures show that systemic signals are necessary to prevent sustained transcriptional induction of Ostf1 during hyperosmotic stress, indicating feedback regulation and a high degree of complexity of osmosensing and signaling networks in euryhaline fishes.

Oxidative stress response of European flounder (Platichthys flesus) to cadmium determined by a custom cDNA microarray

The monitoring of the impact of chemical pollutants upon marine ecosystems commonly employs a multi-biomarker approach. Functional genomics, using cDNA microarrays, allows for a comprehensive view of how an organism is responding to an exposure, with respect to changes in gene expression. Differentially expressed mRNAs were first isolated from livers of European flounder by means of suppressive, subtractive hybridisation. A clone set containing a total of 284 different potentially differentially expressed mRNAs was produced, of which 84 were tentatively identified. These were combined with previously cloned known stress genes isolated by degenerate PCR to produce a custom 500-clone microarray platform with each clone arrayed to four spots. Subsequent array experiments using cadmium-treated flounder detected up-regulation of 27 transcripts, including Cu/Zn superoxide dismutase, thioredoxin, a peroxiredoxin and a glutathione-S-transferase, reflecting oxidative stress in exposed flounder, while CYP1A expression was down-regulated. These changes were confirmed by real-time PCR. The array experiment highlighted a number of candidate genes for further analysis as potential novel biomarkers of cadmium exposure and demonstrated the applicability of the custom microarray approach in the study of the effects of toxicants.

Gene expression analysis of a human lymphoblastoma cell line exposed in vitro to an intermittent 1.9 GHz pulse-modulated radiofrequency field

This study was designed to determine whether radiofrequency (RF) fields of the type used for wireless communications could elicit a cellular stress response. As general indicators of a cellular stress response, we monitored changes in proto-oncogene and heat-shock protein expression. Exponentially growing human lymphoblastoma cells (TK6) were exposed to 1.9 GHz pulse-modulated RF fields at average specific absorption rates (SARs) of 1 and 10 W/kg. Perturbations in the expression levels of the proto-oncogenes FOS, JUN and MYC after exposure to sham and RF fields were assessed by real-time RT-PCR. In addition, the transcript levels of the cellular stress proteins HSP27 and inducible HSP70 were also monitored. We demonstrated that transcript levels of these genes in RF-field-exposed cells showed no significant difference in relation to the sham treatment group. However, concurrent positive (heat-shock) control samples displayed a significant elevation in the expression of HSP27, HSP70, FOS and JUN. Conversely, the levels of MYC mRNA were found to decline in the positive (heat-shock) control. In conclusion, our study found no evidence that the 1.9 GHz RF-field exposure caused a general stress response in TK6 cells under our experimental conditions.

Activator protein-1 (AP-1) DNA binding activity is induced by hydroxyurea in organogenesis stage mouse embryos

Hydroxyurea is a potent teratogen; free radical scavengers or antioxidants reduce its teratogenicity. Activator Protein-1 (AP-1) and NF-kappaB are redox-sensitive transcription factors with important roles in normal development and the stress response. This study was designed to determine if exposure to teratogenic doses of hydroxyurea induces oxidative stress and alters gene expression by activating these transcription factors. Pregnant mice were treated with saline or hydroxyurea (400, 500, or 600 mg/kg) on gestation day 9 (GD 9) and killed either on GD 9, 0.5, 3, or 6 h after treatment, to assess oxidative stress and transcription factor activities, or on GD 18, to assess fetal development. Exposure to 400 mg/kg hydroxyurea did not affect the progeny, whereas exposure to 500 or 600 mg/kg resulted in dose-dependent increases in fetal resorptions and malformations, including curly tails, abnormal limbs (oligodactyly, hemimelia, and amelia), and short ribs. Hydroxyurea did not induce oxidative stress, as assessed by the ratio of oxidized to reduced glutathione, nor did it alter NF-kappaB DNA binding activity in the GD 9 conceptus. In contrast, exposure to hydroxyurea at any dose increased AP-1 DNA binding activity in embryos and yolk sacs 0.5 or 3 h after treatment. Hydroxyurea-induced c-Fos heterodimer activity in the embryo peaked 3-4-fold above control at 3 h and remained elevated by 6 h; in contrast, the activity of c-Jun dimers was not altered by drug exposure. A dramatic and region-specific increase in c-Fos immunoreactivity was found in hydroxyurea-treated embryos. The induction of AP-1 DNA binding activity by hydroxyurea represents an early, sensitive marker of the embryonic response to insult.

Effect of cadmium on cell cycle progression in chinese hamster ovary cells

Chinese hamster ovary K1 (CHO K1) cells are very sensitive to cadmium (Cd) toxicity. They were used to investigate the effect of Cd on cell cycle progression. Cells were cultured with 0.1, 0.4, 1 or 4 microM Cd for various time intervals. There was no difference in growth rate when less than 0.4 microM Cd was given within 24 h. A dose-dependent reduction of cell proliferation was observed when more than 0.4 microM of Cd was given. The cells were pulse-labeled with 5-bromodeoxyuridine (BrdU), and the labeled cells were cultured in the presence of increasing concentrations of Cd. Cell cycle progression was retarded as a function of Cd concentration. G2/M arrest was observed when the BrdU-labeled cells were treated with 1 microM Cd for 8h, whereas cells receiving 4 microM Cd stopped at the S phase within 4 h. Cell cycle analysis of cells treated with Cd for 24 h showed that G2/M arrest occurred only when cells received 0.8 to 2 microM Cd. Despite the occurrence of G2/M arrest in the Cd treatment, only a limited proportion of the cells were blocked in the M phase. However, the increase in M phase cells coincided with an elevation in the cyclin-dependent kinase 1 activity. To examine whether Cd acts on cells at a specific cell stage, they were synchronized at the G1 or G2/M phase then treated with 1 microM Cd for 12 h. The cells were blocked at the G2/M and G1/S phase, respectively. This finding indicates that Cd toxicity is global and not cell phase specific. We also investigated the involvement of Cd-induced reactive oxygen species (ROS) with the occurrence of G2/M block and found a lack of correlation between cell cycle arrest and ROS production. We measured the Cd content that caused G2/M arrest from a series of Cd treatments and determined the ranges of cumulative Cd concentrations that could result in cell cycle arrest.

A complex containing the CCR4 and CAF1 proteins is involved in mRNA deadenylation in Drosophila

The CCR4-NOT complex is the major enzyme catalyzing mRNA deadenylation in Saccharomyces cerevisiae. We have identified homologs for almost all subunits of this complex in the Drosophila genome. Biochemical fractionation showed that the two likely catalytic subunits, CCR4 and CAF1, were associated with each other and with a poly(A)-specific 3' exonuclease activity. In Drosophila, the CCR4 and CAF1 proteins were ubiquitously expressed and present in cytoplasmic foci. Individual knock-down of several potential subunits of the Drosophila CCR4-NOT complex by RNAi in tissue culture cells led to a lengthening of bulk mRNA poly(A) tails. Knock-down of two individual subunits also interfered with the rapid deadenylation of Hsp70 mRNA during recovery from heat shock. Similarly, ccr4 mutant flies had elongated bulk poly(A) and a defect in Hsp70 mRNA deadenylation. A minor increase in bulk poly(A) tail length was also observed in Rga mutant flies, which are affected in the NOT2 subunit. The data show that the CCR4-NOT complex is conserved in Drosophila melanogaster and plays a role in general and regulated mRNA deadenylation.

CRM1-dependent, but not ARE-mediated, nuclear export of IFN-alpha1 mRNA

While the bulk of cellular mRNA is known to be exported by the TAP pathway, export of specific subsets of cellular mRNAs may rely on chromosome region maintenance 1 (CRM1). One line of evidence supporting this hypothesis comes from the study of mRNAs of certain early response genes (ERGs) containing the adenylate uridylate-rich element (ARE) in their 3' untranslated regions (3' UTRs). It was reported that HuR-mediated nuclear export of these mRNAs was CRM1-dependent under certain stress conditions. To further examine potential CRM1 pathways for other cellular mRNAs under stress conditions, the nuclear export of human interferon-alpha1 (IFN-alpha1) mRNA, an ERG mRNA induced upon viral infection, was studied. Overproduction of human immunodeficiency virus type 1 Rev protein reduced the expression level of the co-transfected IFN-alpha1 gene. This inhibitory effect, resulting from nuclear retention of IFN-alpha1 mRNA, was reversed when rev had a point mutation that made its nuclear export signal unable to associate with CRM1. Leptomycin B sensitivity experiments revealed that the cytoplasmic expression of IFN-alpha1 mRNA was arrested upon inhibition of CRM1. This finding was further supported by overexpression of DeltaCAN, a defective form of the nucleoporin Nup214/CAN that inhibits CRM1 in a dominant-negative manner, which resulted in the effective inhibition of IFN-alpha1 gene expression. Subsequent RNA fluorescence in situ hybridisation and immunocytochemistry demonstrated that the IFN-alpha1 mRNA was colocalised with CRM1, but not with TAP, in the nucleus. These results therefore imply that the nuclear export of IFN-alpha1 mRNA is mediated by CRM1. However, truncation of the 3' UTR did not negatively affect the nuclear export of IFN-alpha1 mRNA that lacked the ARE, unexpectedly indicating that this CRM1-dependent mRNA export may not be mediated via the ARE.

Proto-oncogene amplification and overexpression in cadmium-induced cell transformation

Cadmium (Cd) is an essential material used in the battery, metal-coating, and alloy industries. In addition to these industrial uses, it is also a component of cigarette smoke. Therefore, exposure to cadmium is widespread and presents a considerable health concern. Cadmium is known to be a carcinogen; however, the possible mechanism of carcinogenesis with regards to the activation and inactivation of cancer-related genes has not yet been fully elucidated. In this study, amplification, expression, and point mutation of cancer-related genes associated with Cd-induced cell transformation in BALB/c-3T3 cells were studied. Six proto-oncogenes (K-ras, c-myc, c-fos, c-jun, c-sis, and erbB), as well as the p53 tumor suppressor, were investigated for gene amplification using differential polymerase chain reaction (PCR), while the expression of the proteins produced by these genes was evaluated by Western blot analysis. Point mutations in K-ras and p53 were studied by PCR restriction fragment length polymorphism analysis and DNA sequencing. There were no point mutations observed in codons 12, 13, and 61 of K-ras or in exons 4-10 of p53 and no observed differences in the levels of any of the proteins studied. Among 10 Cd-induced transformed cell lines, significant gene amplification was found for c-myc and c-jun in 50% and 80% of the cell lines, respectively. Chromosome painting was performed to confirm that this amplification was not simply due to additional copies of the chromosomes carrying these oncogenes. In addition, reverse-transcription PCR (RT-PCR) was performed to confirm increased expression of c-myc and c-jun. These results suggest that cell transformation induced by Cd may be attributed, at least in part, to gene amplification of c-myc and c-jun and that some of the Cd-transformed cells may possess neoplastic potential resulting from genomic instability.

Temperature effect on entrainment, phase shifting, and amplitude of circadian clocks and its molecular bases

Effects of temperature and temperature changes on circadian clocks in cyanobacteria, unicellular algae, and plants, as well as fungi, arthropods, and vertebrates are reviewed. Periodic temperature with periods around 24 h even in the low range of 1-2 degrees C (strong Zeitgeber effect) can entrain all ectothermic (poikilothermic) organisms. This is also reflected by the phase shifts-recorded by phase response curves (PRCs)-that are elicited by step- or pulsewise changes in the temperature. The amount of phase shift (weak or strong type of PRC) depends on the amplitude of the temperature change and on its duration when applied as a pulse. Form and position of the PRC to temperature pulses are similar to those of the PRC to light pulses. A combined high/low temperature and light/dark cycle leads to a stabile phase and maximal amplitude of the circadian rhythm-when applied in phase (i.e., warm/light and cold/dark). When the two Zeitgeber cycles are phase-shifted against each other the phase of the circadian rhythm is determined by either Zeitgeber or by both, depending on the relative strength (amplitude) of both Zeitgeber signals and the sensitivity of the species/individual toward them. A phase jump of the circadian rhythm has been observed in several organisms at a certain phase relationship of the two Zeitgeber cycles. Ectothermic organisms show inter- and intraspecies plus seasonal variations in the temperature limits for the expression of the clock, either of the basic molecular mechanism, and/or the dependent variables. A step-down from higher temperatures or a step-up from lower temperatures to moderate temperatures often results in initiation of oscillations from phase positions that are about 180 degrees different. This may be explained by holding the clock at different phase positions (maximum or minimum of a clock component) or by significantly different levels of clock components at the higher or lower temperatures. Different permissive temperatures result in different circadian amplitudes, that usually show a species-specific optimum. In endothermic (homeothermic) organisms periodic temperature changes of about 24 h often cause entrainment, although with considerable individual differences, only if they are of rather high amplitudes (weak Zeitgeber effects). The same applies to the phase-shifting effects of temperature pulses. Isolated bird pineals and rat suprachiasmatic nuclei tissues on the other hand, respond to medium high temperature pulses and reveal PRCs similar to that of light signals. Therefore, one may speculate that the self-selected circadian rhythm of body temperature in reptiles or the endogenously controlled body temperature in homeotherms (some of which show temperature differences of more than 2 degrees C) may, in itself, serve as an internal entraining system. The so-called heterothermic mammals (undergoing low body temperature states in a daily or seasonal pattern) may be more sensitive to temperature changes. Effects of temperature elevation on the molecular clock mechanisms have been shown in Neurospora (induction of the frequency (FRQ) protein) and in Drosophila (degradation of the period (PER) and timeless (TIM) protein) and can explain observed phase shifts of rhythms in conidiation and locomotor activity, respectively. Temperature changes probably act directly on all processes of the clock mechanism some being more sensitive than the others. Temperature changes affect membrane properties, ion homeostasis, calcium influx, and other signal cascades (cAMP, cGMP, and the protein kinases A and C) (indirect effects) and may thus influence, in particular, protein phosphorylation processes of the clock mechanism. The temperature effects resemble to some degree those induced by light or by light-transducing neurons and their transmitters. In ectothermic vertebrates temperature changes significantly affect the melatonin rhythm, which in turn exerts entraining (phase shifting) functions.

Effect of acute heat shock on gene expression by human peripheral blood mononuclear cells

We studied the effect of heat shock on gene expression by normal human cells. Peripheral blood mononuclear cells (PBMCs) were obtained from healthy adults. Paired samples from each subject were subjected to either 20 min of heat shock (43 degrees C) or control (37 degrees C) conditions and then returned to 37 degrees C. RNA was isolated 160 min later, and five representative samples were analyzed on Affymetrix gene chip arrays containing approximately 12,600 probes. A biologically meaningful effect was defined as a statistically significant, twofold or greater difference in expression of sequences that were detected in all five experiments under control (downregulated sequences) or heat shock (upregulated sequences) conditions. Changes occurred in 395 sequences (227 increased by heat shock, 168 decreased), representing 353 Unigene numbers, in every functional category previously implicated in the heat shock response. By RT-PCR, we confirmed the findings for one upregulated sequence (Rad, a G protein) and one downregulated sequence (osteopontin, a cytokine). We conclude that heat shock causes extensive gene expression changes in PBMCs, affecting all functional categories of the heat shock response.

Invited review: Effects of heat and cold stress on mammalian gene expression

This review examines the effects of thermal stress on gene expression, with special emphasis on changes in the expression of genes other than heat shock proteins (HSPs). There are approximately 50 genes not traditionally considered to be HSPs that have been shown, by conventional techniques, to change expression as a result of heat stress, and there are <20 genes (including HSPs) that have been shown to be affected by cold. These numbers will likely become much larger as gene chip array and proteomic technologies are applied to the study of the cell stress response. Several mechanisms have been identified by which gene expression may be altered by heat and cold stress. The similarities and differences between the cellular responses to heat and cold may yield key insights into how cells, and by extension tissues and organisms, survive and adapt to stress.

Structural and functional compartmentalization of the cell nucleus in supraoptic neurons

It is well-established that the neuronal cell nucleus is organized in discrete compartments involved in transcription and RNA processing. The main nuclear compartments in neurons include the chromosome territories, the nucleolus, nuclear speckles of splicing factors, Cajal bodies, and nuclear rodlets. The supraoptic nucleus (SON) neurons provide a powerful model in vivo to study the organization of these nuclear compartments in response to variations of cellular activity. The upregulation of transcription in SON neurons under chronic hyperosmolar conditions is associated with 1) nuclear and nucleolar enlargement, 2) dispersion of chromatin, 3) reduction in the size of nuclear speckles, 4) increase in the number of Cajal bodies implicated in the maturation of splicing small nuclear ribonucleoproteins, and 5) proliferation of the fibrillar centers of the nucleolus, the sites of nucleolar transcription of ribosomal genes. These changes revert after the cessation of the activation by rehydration of animals. Under conditions of neuronal stress induced by hypertonic saline injection, SON neurons exhibit an early response of downregulation of transcription. This is accompanied by chromatin condensation, redistribution of splicing factors, reduction in the number of Cajal bodies, and microsegregation of the fibrillar and granular components of the nucleolus and disruption of its fibrillar centers, all of which are associated with a transitory expression of c-Fos. These changes progressively revert and at 24 hours after the stress induction a rebound upregulation of transcription is observed. These findings illustrate the transcription-dependent organization and behavior of nuclear compartments in the neuronal model of magnocellular neurosecretory cells of the hypothalamus.

Transcription factor activation in response to cutaneous injury: role of AP-1 in reepithelialization

Reepithelialization is the process responsible for restoring an intact epidermis following cutaneous injury. A change in the activity of keratinocytes is required for reepithelialization to occur, and this is likely to be regulated by the altered expression of effector genes, mediated by transcription factors. The injury itself provides a stimulus for transcription factor activation either directly due to mechanical stress, or via paracrine mechanisms such as the release of growth factors from damaged cells. Members of the activator protein-1 family, in particular c-fos and c-jun, have been the most widely studied wound-induced transcription factors. The signal transduction pathways linking cellular injury to activator protein-1 stimulation appear to involve an increase in intracellular Ca2+ and activation of mitogen-activated protein kinases. Given that a number of genes involved in the reepithelialization of wounds are regulated by activator protein-1, a distinct role for this transcription factor in reepithelialization is beginning to emerge. This article reviews the evidence for activator protein-1 involvement in reepithelialization, with particular focus on the activation of this transcription factor in response to wounding, the second messenger/kinase pathways involved, and the modulation of downstream genes that have the capacity to regulate keratinocyte function.

Protein ligands mediate the CRM1-dependent export of HuR in response to heat shock

AU-rich elements (AREs) located in the 3' UTRs of the messenger RNAs (mRNAs) of many mammalian early response genes promote rapid mRNA turnover. HuR, an RRM-containing RNA-binding protein, specifically interacts with AREs, stabilizing these mRNAs. HuR is primarily nucleoplasmic, but shuttles between the nucleus and the cytoplasm via a domain called HNS located between RRM2 and RRM3. We recently showed that HuR interacts with two protein ligands, pp32 and APRIL, which are also shuttling proteins, but rely on NES domains recognized by CRM1 for export. Here we show that heat shock induces increased association of HuR with pp32 and APRIL through protein-protein interactions and that these ligands partially colocalize with HuR in cytoplasmic foci. HuR associations with the hnRNP complex also increase, but through RNA links. CRM1 coimmunoprecipitates with HuR only after heat shock, and nuclear export of HuR becomes sensitive to leptomycin B, an inhibitor of CRM1. Export after heat shock requires the same domains of HuR (HNS and RRM3) that are essential for binding pp32 and APRIL. In situ hybridization and coimmunoprecipitation experiments show that LMB treatment blocks both hsp70 mRNA nuclear export and its cytoplasmic interaction with HuR after heat shock. Together, our results argue that upon heat shock, HuR switches its export pathway to that of its ligands pp32 and APRIL, which involves the nuclear export factor CRM1. HuR and its ligands may be instrumental in the nuclear export of heat-shock mRNAs.

Expression of c-jun and c-fos in apoptotic cells after DNA damage

Apoptosis was induced in HeLa cells by exposure to 50 microM N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for various time intervals (up to 120 min). Apoptotic death was confirmed by the microscopic observation of cell blebbing, cell granulation, and cell aggregation. Cells also showed loss of phospholipid symmetry as judged by immunofluorescent microscopy with fluorescently labeled phosphatidyl serine-specific annexin V. In addition, staining of cells with ethidium bromide showed the presence of genomic DNA apoptotic bodies. The protein expression levels of c-jun and c-fos increased in DNA-damaged HeLa cells after MNNG treatment in a time-dependent fashion. Although the levels of c-fos increased rapidly during the first 30 min and remained high for 2 hr, the increase in c-jun expression was more gradual and slower (60-120 min) after MNNG treatment. These results are consistent with the conclusion that c-fos is important in the initial stages (commitment phase) of apoptosis and c-jun is involved in the late stages (execution phase) of apoptosis induced with alkylating agents.

Protein ligands to HuR modulate its interaction with target mRNAs in vivo

AU-rich elements (AREs) present in the 3' untranslated regions of many protooncogene, cytokine, and lymphokine messages target them for rapid degradation. HuR, a ubiquitously expressed member of the ELAV (embryonic lethal abnormal vision) family of RNA binding proteins, selectively binds AREs and stabilizes ARE-containing mRNAs in transiently transfected cells. Here, we identify four mammalian proteins that bind regions of HuR known to be essential for its ability to shuttle between the nucleus and the cytoplasm and to stabilize mRNA: SETalpha, SETbeta, pp32, and acidic protein rich in leucine (APRIL). Three have been reported to be protein phosphatase 2A inhibitors. All four ligands contain long, acidic COOH-terminal tails, while pp32 and APRIL share a second motif: rev-like leucine-rich repeats in their NH(2)-terminal regions. We show that pp32 and APRIL are nucleocytoplasmic shuttling proteins that interact with the nuclear export factor CRM1 (chromosomal region maintenance protein 1). The inhibition of CRM1 by leptomycin B leads to the nuclear retention of pp32 and APRIL, their increased association with HuR, and an increase in HuR's association with nuclear poly(A)+ RNA. Furthermore, transcripts from the ARE-containing c-fos gene are selectively retained in the nucleus, while the cytoplasmic distribution of total poly(A)+ RNA is not altered. These data provide evidence that interaction of its ligands with HuR modulate HuR's ability to bind its target mRNAs in vivo and suggest that CRM1 is instrumental in the export of at least some cellular mRNAs under certain conditions. We discuss the possible role of these ligands upstream of HuR in pathways that govern the stability of ARE-containing mRNAs.

Protooncogenes as mediators of apoptosis

Apoptosis has been well established as a vital biological phenomenon that is important in the maintenance of cellular homeostasis. Three major protooncogene families and their encoded proteins function as mediators of apoptosis in various cell types and are the subject of this chapter. Protooncogenic proteins such as c-Myc/Max, c-Fos/c-Jun, and Bcl-2/Bax utilize a synergetic effect to enhance their roles in the pro- or antiapoptotic action. These family members activate and repress the expression of their target genes, control cell cycle progression, and execute programmed cell death. Repression or overproduction of these protooncogenic proteins induces apoptosis, which may vary as a result of either cell type specificity or the nature of the apoptotic stimuli. The proapoptotic and antiapoptotic proteins exert their effects in the membrane of cellular organelles. Here they generate cell-type-specific signals that activate the caspase family of proteases and their regulators for the execution of apoptosis.

Sodium arsenite-induced dysregulation of proteins involved in proliferative signaling

It is well accepted that arsenic is a human carcinogen, yet its mechanism of action is not defined. Arsenic cannot be classified as an initiating agent or as a promoter, although altered proliferative responsiveness has been proposed as a mechanism by which arsenic exerts its carcinogenic effects. Based on the hypothesis that arsenic exposure results in modulation of both positive and negative regulators of cell proliferation, this study examined physiological and biochemical changes in the proliferative response of murine fibroblasts grown long-term in the maximum tolerated concentration of sodium arsenite. In response to EGF stimulation, DNA synthesis and the proportion of cells entering S phase of the cell cycle both were increased in cells grown long-term in arsenic compared to control cells. Analysis of positive proliferative regulators revealed an increase in the expression of c-myc and E2F-1, thereby supporting the hypothesis that arsenic increases activity of positive growth modulators. In contrast, the activity and expression of ERK-2 were unchanged, as was the expression of EGF-receptor and mSOS. When negative regulators of proliferation were examined, expression levels of MAP kinase phosphatase-1 and p27(Kip1) were found to be lower in arsenic-treated cells compared to control cells; this result supports a model in which arsenic disinhibits normal regulation of cell proliferation. Taken together, these data indicate that long-term exposure to sodium arsenite creates conditions within the cell consistent with sensitization to mitogenic stimulation. It is further postulated that the observed changes in mitogenic signaling proteins contribute to the carcinogenic property of arsenic.

Cadmium-induced apoptosis and changes in expression of p53, c-jun and MT-I genes in testes and ventral prostate of rats

Apoptosis and a change in the expression of p53, c-jun and MT-I genes occurred in rats exposed to cadmium in a way known to cause carcinogenesis in testes and ventral prostate. In situ end labelling (ISEL), DNA electrophoresis, and RT-PCR methods were used in present study. Adult male Wistar rats were given a single (s.c.) injection of 0, 5, 10, or 20 micromol/kg CdCl2. Then 12, 48 or 96 h after administration of cadmium, animals were sacrificed. It was observed that cadmium markedly induced apoptosis in the testes at the dose of 5 micromol/kg while 10 and 20 micromol/kg cadmium caused more necrosis than apoptosis. Apoptosis in the ventral prostate was markedly induced by all the doses of cadmium and there was an obvious time- and dose-dependent relationship between apoptotic index (AI) and cadmium treatment. Far fewer apoptotic cells appeared in liver, compared to the testes and ventral prostate. p53 mRNA expression was clearly enhanced in the ventral prostate but clearly suppressed in the testes by cadmium exposure, and the time- and dose-effect was very clear. The expression level of p53 in the liver was not affected by cadmium treatment. Cadmium-induced overexpression of c-jun gene appeared at 12 h in the liver, but not until 96 h in the testes and ventral prostate. Although the MT-I gene was found to be expressed in all tissues, marked induction by cadmium of the expression of MT-I gene was only observed in the liver. These results indicate: (1) that apoptosis is an early mechanism of acute tissue damage by cadmium in the testes and ventral prostate; (2) that p53 and c-jun genes may be involved in cadmium-induced cytotoxicity (apoptosis) and related carcinogenicity in male reproductive tissues; and (3) that the enhanced expression of MT-I in the liver could protect this organ from cadmium-induced cytotoxicity (apoptosis) and carcinogenicity.

c-fos gene expression in rat liver is induced by phenobarbital

In the present study we investigated c-fos expression in rat livers, that was initiated with the three arylamines, 2-acetylaminofluorene, 2-acetylaminophenanthrene and trans-4-acetylaminostilbene. The tumor promoter phenobarbital was applied chronically for 26, 52 and 100 weeks. Gene expression, determined by the mRNA level, and FOS protein were increased after 52 weeks of treatment in arylamine initiated as well as in phenobarbital only treated animals. Expression of c-fos seems to be a phenobarbital induced effect that is independent of additional initiator treatments. This finding was supported by immunohistochemical studies demonstrating increased FOS levels to be localized around the central vein. The results indicate that phenobarbital, a widely used tumor promoter, induces c-fos expression. In addition, we demonstrated enhanced FOS in GST-P-positive foci and in tumors.

c-fos induction by heat, arsenite, and cadmium is mediated by a heat shock element in its promoter

c-fos mRNA is induced by many types of noxious stimuli that are known to enhance transcription mediated by the heat shock element (HSE). Nonetheless, it has been accepted that the c-fos promoter does not contain an HSE. In this report, we revealed that the human and rodent c-fos promoters do contain HSEs which are highly responsive to heat, arsenite, and cadmium. These HSEs may play important roles in regulating c-fos expression in various pathological and physiological situations.

Heat shock factor 1 represses Ras-induced transcriptional activation of the c-fos gene

Heat shock factor 1, the critical molecular regulator of the stress response is conserved throughout eukaryotic organisms and activates the transcription of heat shock genes. We now show that heat shock factor 1 inhibits the expression of c-fos, an immediate early gene that controls responses to extracellular stimuli for growth and differentiation. Heat shock factor 1 inhibits the transcription of the c-fos gene and antagonizes the activating effects of the signal transducing protein Ras on the c-fos promoter and on the promoter of another Ras responsive gene uPA. This property was specific for heat shock factor 1; c-fos repression was not seen with the structurally related protein heat shock factor 2. Repression involved different molecular mechanisms compared with those involved in transcriptional activation by heat shock factor 1 and specifically did not require binding to the c-fos promoter. Thus, in addition to its known role as a transcriptional activator of the cellular heat shock response, heat shock factor 1 also antagonizes the expression of Fos, a key component of the ubiquitous AP-1 transcription factor complex and as such could influence multiple aspects of cell regulation.

Gene expression in liver after toxic injury: analysis of heat shock response and oxidative stress-inducible genes

In the liver, CCl4 induces cell necrosis followed by regeneration. Cell injury is caused by free radical damage and may be due, at least in part, to oxidative stress and the subsequent formation of reactive oxygen intermediates (ROIs). In a rat model of acute CCl4-induced hepatic injury, we examined the expression of genes involved in cellular response to different kinds of stress, including oxidative stress (hsp 70 family, heme oxygenase), in free radical detoxification (Mn superoxide dismutase and Cu/ Zn superoxide dismutase), in iron homeostasis (H and L ferritin subunits) and in the cell cycle (c-fos, c-jun, histone H3). As an experimental approach, we first analysed the pattern of protein synthesised by liver slices in vitro. Then we studied the mechanisms regulating the expression of different genes, by analysing both mRNA steady state levels and transcription rates. Activation of the specific heat shock transcription factor (HSF) by CCl4 was also investigated. We observed that different members of the hsp70 family (hsp70, hsc73, grp78) are activated by different kinetics and are regulated mainly at the transcriptional level. Induction of the hsp70 gene occurs rapidly and transiently and is preceded by the activation of HSF DNA-binding activity. We demonstrated an increase in the steady-state levels of mRNAs for heme oxygenase, Mn and Cu/Zn superoxide dismutases and H and L ferritin subunits. However, different kinetics and regulatory mechanisms occurred with different genes. We showed that induction of c-fos and c-jun protooncogenes is the earliest event after CCl4 administration, whereas histone H3 expression peaked at 24-48 h. The results of this study are interpreted as evidence that activation of specific stress response genes is primarily related to the defence against the rapidly occurring cell damage, but may also be related to subsequent processes of tissue inflammation and cell proliferation.

Heat-shock and cadmium chloride increase the vimentin mRNA and protein levels in U-937 human promonocytic cells

Heat-shock for 2 hours at 42 degrees C, or the administration for 3 hours of 100 or 150 microM cadmium chloride, inhibited the subsequent proliferation activity, induced the expression of functional differentiation markers, and caused an increase in the amount of the stress-responsive HSP70 protein in U-937 human promonocytic cells. In addition, both heat and cadmium produced an increase in the amount of the intermediate filament protein vimentin, as determined by immunoblot and immunofluorescence assays. By contrast, the amounts of actin and beta-tubulin were not significantly altered. The amount of vimentin mRNA was also increased during recovery from stress, indicating that vimentin expression was not exclusively regulated at the protein level. Although cadmium caused an early, transient stimulation of c-jun and c-fos expression and AP-1 binding activity, heat-shock failed to alter both protooncogene expression and transcription factor binding, indicating that the stress-induced vimentin increase was not the result of AP-1-mediated transcriptional activation. Finally, it was observed that the rate of decay of vimentin mRNA upon actinomycin D administration was decreased in heat- and cadmium-pretreated cells in comparison to untreated cells. These results indicate that stress treatments cause an increase in vimentin levels in promonocytic cells, which may be explained at least in part by transcript stabilization.

Arsenite induces apoptosis in Chinese hamster ovary cells by generation of reactive oxygen species

Arsenic, a human carcinogen, possesses a serious environmental threat but the mechanism of its toxicity remains unclear. Knowledge of how arsenic induces cell death and how cells escape the death path may help to understand arsenic carcinogenesis. We have investigated the nature of sodium arsenite-induced cell death in Chinese hamster ovary K1 cells. Following phosphate-citric acid buffer extraction, apoptotic cells with lower DNA content than the G1 cells were detected by flow cytometry. Immediately after 4 h of 40 microM arsenite treatment, no appreciable fraction of cells with sub-G1 DNA content was detected; however, the sub-G1 cell fraction increased with postarsenite incubation time, and detectable increase started at 8 h of incubation, whereas the intracellular peroxide level as measured by the fluorescent intensity of 2',7'-dichlorofluorescein increased immediately following a 4-h arsenite treatment. Simultaneous treatment with arsenite plus antioxidant (N-acetyl-cysteine, Trolox, and Tempo); copper ion chelator (neocuproine); protein kinase inhibitor (H-7) or protein synthesis inhibitor (cycloheximide) reduced the fraction of sub-G1 cell and internucleosomal DNA degradation. Trolox, neocuproine, or cycloheximide given after arsenite treatment also effectively reduced apoptosis. These results lead to a working hypothesis that arsenite-induced apoptosis in CHO-K1 cells is triggered by the generation of hydrogen peroxide, followed by a copper-mediated Fenton reaction that catalyzes the production of hydroxyl radicals, which selectively activates protein kinase through de novo synthesis of macromolecules.

Immunohistochemical evaluation of p53 and retinoblastoma proteins in relation to hyperthermia treatment: results in human urothelial carcinomas

Immunohistochemical staining of urothelial tumours using paraffin-embedded tissue blocks was performed for p53 and Retinoblastoma (RB) proteins, to characterize any correlation with sensitivity to hyperthermia treatment. Seventeen patients with primary urothelial tumours (16 of the bladder and one of the ureter) treated at our institute between July, 1987 and March, 1993 were included in this study; tissues investigated consisted of 16 transitional cell carcinomas (TCC) (6 Grade2 (G2), 6 G3, 2 G2 > G3, 1 G3 > squamous cell carcinoma (SCC), 1 undifferentiated carcinoma > G3), and 1 SCC. One case was Tis, 4, 3, 1, and 4, were T1 to T4, respectively, and 4 were post-cystectomy. Clinically, in terms of response to treatment, there were four complete response (CR) cases, four partial response (PR) cases, six no change (NC) cases, and three progressive disease (PD) cases, the total in which treatment was effective thus accounting for approximately half of those examined (CR + PR, 47%). Immunohistochemically, six of eight pre-hyperthermia lesions which demonstrated positive staining for RB were CRs or PRs, 75% of which were high-grade lesions, and 50% exhibited invasion and lymph node metastasis. Only three in total were positive for p53 staining, two of which were T4 and these both responded to treatment. The results suggested that RB gene expression may be related to heat sensitivity to some degree.

Calreticulin is transcriptionally upregulated by heat shock, calcium and heavy metals

Calreticulin is a new human rheumatic disease-associated autoantigen that plays a multifaceted role in cell biology. In earlier studies, this protein was shown to share an intimate relationship with the Ro/SS-A autoantigen complex, although the nature of this association continues to be debated. Since modulation of the Ro/SS-A autoantigen in epidermal keratinocytes has been implicated in the pathogenesis of subacute cutaneous lupus erythematosus and neonatal lupus erythematosus, we have begun to examine the transcriptional regulation of calreticulin. A 504 bp calreticulin promoter fragment was subcloned into a reporter gene plasmid containing firefly luciferase. Calcium ionophore, heat shock, and heavy metals such as zinc and cadmium were consistently found to increase calreticulin transcriptional activities in A431 cells (a human epidermoid squamous carcinoma cell line) under transient transfection conditions. These studies suggest that (a) calreticulin is regulated at the transcriptional level, and (b) calreticulin, like some other LE-related autoantigens, appears to function as a heat shock/stress-response gene.

Heat-shock induced protein modifications and modulation of enzyme activities

Upon heat stress, the cell physiology is profoundly altered. The extent of the alterations depends on the severity of the stress and may lead to cell death. The heat shock response is an array of metabolic changes characterized by the impairment of major cellular functions and by an adaptative reprogramming of the cell metabolism. The enhanced synthesis of the HSPs is a spectacular manifestation of this reprogramming. Numerous post translational modifications of proteins occur in response to heat stress and can be related to altered cellular functions. Some proteins are heat-denatured and temporarily inactivated. Heat-denaturation is reversible, chaperones may contribute to the repair. The extent of heat-denaturation depends on the cell metabolism: (a) it is attenuated in thermotolerant cells or in cells overexpressing the appropriate chaperones (b) it is enhanced in energy-deprived cells. Covalent modifications may also rapidly alter protein function. Changes in protein glycosylation, methylation, acetylation, farnesylation, ubiquitination have been found to occur during stress. But protein phosphorylation is the most studied modification. Several protein kinase cascades are activated, among which the various mitogen activated protein kinase (MAP kinase) cascades which are also triggered by a wide range of stimuli. As a possible consequence, stress modifies the phosphorylation status and the activity of components from the transcriptional and translational apparatuses. The same kinases also target key enzymes of the cellular metabolism. Protein denaturation results in constitutive hsp titration, this titration is a signal to trigger the heat-shock gene transcription and to activate some of the protein kinase cascades.

Differential gene expression in migrating renal epithelial cells after wounding

An in vitro model of wound healing was used to study cell migration that is independent of proliferation during renal regeneration after acute tubular necrosis. Monolayer cultures of high-density, quiescent renal epithelial cells of the BSC-1 line were subjected to scrape wounding and then Northern blot analysis was employed to identify genes that mediate cell migration. After wounding the monolayer, there is maximal induction of the immediate-early genes Egr-1, c-fos, NAK-1, and gro at 1 hour, followed by peak induction of connective tissue growth factor (CTGF) and c-myc at 4 hours. Message levels of urokinase-type plasminogen activator (u-PA) and its inhibitor (PAI-1) and heat shock protein (HSP)-70 are markedly raised 4-8 hours after wounding. Constitutive expression is repressed at 1 hour for transcripts that encode receptors for fibronectin (FN), epidermal growth factor, and hepatocyte growth factor (c-met), and the secreted proteins FN and osteopontin. Expression of genes encoding transforming growth factor (TGF)-beta 1 and -beta 2, retinoic acid receptor alpha, int-1, int-2, and gap junction protein which can play a role in cell movement, appeared unchanged after wounding. Differential expression of genes was a function of cell location relative to the wound; NAK-1, PAI-1, and HSP-70 were induced or stimulated only in cells at the wound edge, u-PA was stimulated in cells away from the wound, and CTGF was induced in each of these populations suggesting that cell-to-cell communication may regulate gene expression after wounding. Adenosine diphosphate, a potent stimulator of cell migration which enhances expression of u-PA and PAI-1 in nonwounded cultures, additively stimulates these genes after wounding and may thereby potentiate wound healing. Thus scrape wounding of renal epithelial cells is followed by induction, stimulation, or repression of specific genes with distinct responses in different populations of cells.

Increased c-fos expression associated with hyperthermia-induced apoptosis of a Burkitt lymphoma cell line

Hyperthermia (42 - 44 degrees C for 30 min to 1 h) can induce apoptosis in a variety of cell types and tumour cell lines. This process is usually, but not invariably unaffected by RNA and protein synthesis inhibition. C-fos expression has been implicated in the regulation of apoptosis occurring under diverse circumstances. By heating the Burkitt lymphoma cell line, BM 13674, for 43 degrees C for 30 min, approximately 60% of cells underwent apoptosis within 6h of treatment. Co-ordinate with the massive induction of apoptosis, a 10-fold increase in the steady state c-fos mRNA expression occurred.

Effect of ionizing radiation on AP-1 binding activity and basic fibroblast growth factor gene expression in drug-sensitive human breast carcinoma MCF-7 and multidrug-resistant MCF-7/ADR cells

We studied the effect of ionizing radiation on the activation of the AP-1 transcription factors and the regulation of basic fibroblast growth factor (bFGF) gene expression in drug-sensitive human breast carcinoma (MCF-7) cells and its drug-resistant variant (MCF-7/ADR) cells. Northern blot and gel mobility shift assays showed that 135 cGy of ionizing radiation induced c-jun and c-fos gene expression, AP-1 binding activity, as well as bFGF gene expression in MCF-7/ADR cells. In MCF-7 cells, however, we observed little/no induction of bFGF gene expression and AP-1 binding activity after the stress. Nevertheless, MCF-7 cells transfected with plasmids containing c-jun gene contain high levels of bFGF protein. H-7 (60 micrograms/ml), a potent protein kinase C (PKC) inhibitor, inhibited the stress-induced AP-1 binding activity and bFGF gene expression in MCF-7/ADR cells. Corroborating this observation, overexpression of PKC alpha induced bFGF gene expression in MCF-7 cells. Taken together, these results suggest that stress-induced bFGF gene expression is mediated through the activation of PKC and AP-1 transcription factors. Differences in the levels of PKC activity and AP-1 binding factors may be responsible for differential expression of bFGF among breast cancer cell lines. Although there are large differences in response to ionizing radiation between MCF-7 and MCF-7/ADR cell lines, we observed no significant differences in radiocytotoxicity between them.