Cloning and characterization of GETS-1, a goldfish Ets family member that functions as a transcriptional repressor in muscle

Red porgy's (Pagrus pagrus) cellular physiology and antioxidant defense in response to seasonality

Physiological stress patterns of marine organisms in their natural habitats are considerably complex in space and time. These patterns can eventually contribute in the shaping of fish' thermal limits under natural conditions. In the view of the knowledge gap regarding red porgy's thermal physiology, in combination with the characterization of the Mediterranean Sea as a climate change ''hotspot'', the aim of the present study was to investigate this species biochemical responses to constantly changing field conditions. To achieve this goal, Heat Shock Response (HSR), MAPKs pathway, autophagy, apoptosis, lipid peroxidation and antioxidant defense were estimated and exhibited a seasonal pattern. In general, all the examined biochemical indicators expressed high levels parallel to the increasing seawater temperature in spring, although several bio-indicators have shown increased levels when fish were cold-acclimatized. Similar to other sparids, the observed patterns of physiological responses in red porgy may support the concept of eurythermy.

Advances in understanding the impacts of global warming on marine fishes farmed offshore: Sparus aurata as a case study

Monitoring variations in proteins involved in metabolic processes, oxidative stress responses, cell signalling and protein homeostasis is a powerful tool for developing hypotheses of how environmental variations affect marine organisms' physiology and biology. According to the oxygen- and capacity-limited thermal tolerance hypothesis, thermal acclimation mechanisms such as adjusting the activities of enzymes of intermediary metabolism and of antioxidant defence mechanisms, inducing heat shock proteins (Hsps) or activating mitogen-activated protein kinases may all shift tolerance windows. Few studies have, however, investigated the molecular, biochemical and organismal responses by fishes to seasonal temperature variations in the field to link these to laboratory findings. Investigation of the impacts of global warming on fishes farmed offsore, in the open sea, can provide a stepping stone towards understanding effects on wild populations because they experience similar environmental fluctuations. Over the last 30 years, farming of the gilthead sea bream Sparus aurata (Linnaeus 1758) has become widespread along the Mediterranean coastline, rendering this species a useful case study. Based on available information, the prevailing seasonal temperature variations expose the species to the upper and lower limits of its thermal range. Evidence for this includes oxygen restriction, reduced feeding, reduced responsiveness to environmental stimuli, plus a range of molecular and biochemical indicators that change across the thermal range. Additionally, close relationships between biochemical pathways and seasonal patterns of metabolism indicate a connection between energy demand and metabolic processes on the one hand, and cellular stress responses such as oxidative stress, inflammation and autophagy on the other. Understanding physiological responses to temperature fluctuations in fishes farmed offshore can provide crucial background information for the conservation and successful management of aquaculture resources in the face of global change.

RAGE against the stress: Mitochondrial suppression in hypometabolic hearts

The wood frog (Rana sylvatica) can tolerate full body freezing in winter. As a protective response, wood frogs dehydrate their cells and accumulate large quantities of glucose as an intracellular cryoprotectant. Freezing causes ischemia since blood delivery to organs is interrupted. Fascinatingly, wood frogs can tolerate dehydration, extreme hyperglycemia, and anoxia independently of freezing. In response to low oxygen levels, wood frogs strategically reduce their metabolic rates and allocate the finite amount of intracellular fuel available to pro-survival processes while reducing or interrupting all others. In this study, the involvement of advanced glycation end products (AGEs) and the high mobility group box 1 (HMGB1) protein in activating RAGE (AGE receptor) were investigated. The results show that freezing, anoxia and dehydration induced the expression of total HMGB1 and its acetylation in the heart. RAGE levels were induced in response to all stress conditions, which resulted in differential regulation of the ETS1 transcription factor. While the nuclear localization of total ETS1 was not affected, the DNA binding activity of total and its active form increased in response to freezing and dehydration but not in response to anoxia. Current results indicate that ETS1 acts as a transcriptional activator for peroxiredoxin 1 in response to freezing but acts as a transcriptional repressor of several nuclear-encoded mitochondrial genes in response to all stresses. Altogether, current results show that the HMGB1/RAGE axis may activate ETS1 and that this activation could result in both transcriptional activation and/or repression in a stress-dependent manner.

Effect of water temperature on cellular stress responses in meagre (Argyrosomus regius)

Μeagre (Argyrosomus regius) is a newly introduced species in the aquaculture sector characterized by high growth rates and good nutritional value. However, the optimum conditions such as water temperature for the rearing of this species are still under research. The aim of the present study was to investigate several biochemical responses in the heart, muscle, liver, and intestine of meagre reared under different water temperatures (17, 23, and 26 °C) in comparison to the initial acclimation temperature at 20 °C. To assess its cellular stress response, the molecular markers of Hsp70 and Hsp90 induced levels, p38 MAPK and p44/42 MAPK phosphorylated levels, ubiquitin conjugates, and Bcl-2 levels were determined. Moreover, to investigate its antioxidant defense, the activities of superoxide dismutase, catalase, and glutathione reductase were measured. The obtained results in meagre showed a distinct tissue-specific response regarding the variations observed in the studied parameters under different acclimation temperatures. Specifically, most examined tissues presented a decrease in the levels of the examined markers compared to 20 °C, while in the intestine, an increase of Hsp70 and p38 MAPK levels was observed at 23 and 26 °C. However, data on the final weight and length of the fish lead to the conclusion that high water temperatures such as 26 °C might be the best for the rearing of this species. Therefore, it is assumed that the observed differential molecular responses may act in a cell-protective way at all temperatures, irrespectively of the effect of temperature on growth parameters.

Starvation and re-feeding affect Hsp expression, MAPK activation and antioxidant enzymes activity of European sea bass (Dicentrarchus labrax)

In the context of food deprivation in fish (wild and farmed), understanding of cellular responses is necessary in order to develop strategies to minimize stress caused by starvation in the aquaculture section. The present study evaluates the effects of long term starvation (1F-3S: one-month feeding-three-month starvation) and starvation/re-feeding (2S-2F: two-month starvation-two-month re-feeding) compared to the control group (4F-0S: four-month feeding-zero month starvation) on cellular stress response and antioxidant defense in organs, like the intestine, the liver, the red and white muscle of European sea bass Dicentrarchus labrax. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK) and the extracellular signal-regulated kinases (ERK-1/2). For the determination of the effect of the oxidative stress caused by food deprivation and/or re-feeding, the (maximum) activities of antioxidant enzymes such as glutathione peroxidise (GPx), catalase (CAT) and superoxide dismutase (SOD) as well as the determination of thiobarbituric acid reactive substances (TBARS) were studied. The experimental feeding trials caused a tissue distinct and differential response on the cellular and antioxidant capacity of sea bass not only during the stressful process of starvation but also in re-feeding. Specifically, the intestine phosphorylation of ERKs and antioxidant enzymatic activities increased in the 2S-2F fish group, while in the 1F-3S group an increase was detected in the levels of the same proteins except for GPx. In the liver and the red muscle of 2S-2F fish, decreased Hsp70 and phosphorylated p38 MAPK levels and increased Hsp90 levels were observed. Additionally, SOD activity decreased in the red muscle of 2S-2F and 1F-3S groups. In the liver and red muscle of 1F-3S group Hsp70 levels increased, while the activation of p38 MAPK in the liver decreased. In the white muscle, Hsp90 levels decreased and the phosphorylation of p38 MAPK increased in both feeding regimes compared to control. In the same tissue, GPx and catalase levels were decreased in 2S-2F regime, while SOD levels were decreased in 1F-3S regime.

Complexity in transcription control at the activation domain-mediator interface

Transcript elongation by polymerase II paused at the Egr1 promoter is activated by mitogen-activated protein kinase phosphorylation of the ternary complex factor (TCF) ELK1 bound at multiple upstream sites and subsequent phospho-ELK1 interaction with mediator through the MED23 subunit. Consequently, Med23 knockout (KO) nearly eliminates Egr1 (early growth response factor 1) transcription in embryonic stem (ES) cells, leaving a paused polymerase at the promoter. Med23 KO did not, however, eliminate Egr1 transcription in fibroblasts. Chromatin immunoprecipitation analysis and direct visualization of fluorescently labeled TCF derivatives and mediator subunits revealed that three closely related TCFs bound to the same control regions. The relative amounts of these TCFs, which responded differently to the loss of MED23, differed in ES cells and fibroblasts. Transcriptome analysis suggests that most genes expressed in both cell types, such as Egr1, are regulated by alternative transcription factors in the two cell types that respond differently to the same signal transduction pathways.

Modulation of ERK1/2 and p38(MAPK) by lead in the cerebellum of Brazilian catfish Rhamdia quelen

Lead (Pb2+) is a neurotoxic trace metal, widespread in aquatic environment that can change physiologic, biochemical and behavioral parameters in diverse fish species. Chemical exposure may drive modulation of mitogen-activated protein kinases (MAPKs) that are a family of highly conserved enzymes which comprise ubiquitous groups of signaling proteins playing critical regulatory roles in cell physiology. Extracellular signal-regulated kinases (ERK1/2) and p38(MAPK) control complex programs such as gene expression, embryogenesis, cell differentiation, cell proliferation, cell death and synaptic plasticity. Little information is available about MAPKs in aquatic organisms and their modulation by trace metals. The aim of this work was to determine the modulation of ERK1/2 and p38(MAPK) phosphorylation by Pb2+ in vivo and in vitro, in cerebellar slices of the catfish, Rhamdia quelen. In the in vitro model, slices were incubated for 3 h with lead acetate (1-10 microM). In the in vivo studies, the animals were exposed for 2 days to lead acetate (1 mg L(-1)). ERK1/2 and p38(MAPK) (total and phosphorylated forms) were immunodetected in cerebellar slices by Western blotting. Pb2+ added in vitro at 5 and 10 microM increased significantly the phosphorylation of both MAPKs. The in vivo exposed animals also showed a significant increase of ERK1/2 and p38(MAPK) phosphorylation without changes in the total content of the enzymes. In conclusion, the present work indicates that it is possible to evaluate the ERK1/2 and p38(MAPK) activation in the central nervous system (CNS) of a freshwater fish largely distributed in South America. Moreover, Pb2+, an important environmental pollutant may activate in vitro and in vivo ERK1/2 and p38(MAPK) enzymes. These findings are important considering the functional and ecologic implications associated to Pb2+ exposure of a freshwater fish species, such as R. quelen, and the roles of ERK1/2 and p38(MAPK) in the control of brain development, neuroplasticity and cell death.

Ets ternary complex transcription factors

The three ternary complex factors (TCFs) Elk-1, Net and Sap-1 form a subfamily of the E twenty-six (Ets) domain transcription factors. Their characteristic property is the ability to form a ternary nucleoprotein complex with the serum response factor (SRF) over the serum response element (SRE) of the c-fos promoter. The molecular mechanisms that underlie the function and regulation of these factors have been extensively studied and the TCFs are a paradigm for the study of transcriptional regulation in response to extracellular signalling through the mitogen-activated protein (MAP) kinase pathway. As final effectors of multiple signalling pathways and components of protein complexes on immediate early promoters, they represent key elements in the complex and dynamic regulation of gene expression. This review summarises the molecular, structural and biochemical studies that have led to the understanding of the functional domains of the TCFs, ternary complex formation, transcriptional regulation, protein partners and target genes in cell lines. Finally, the emerging studies of the biological roles of the TCFs in vivo will be discussed.

Ternary complex factors: prime nuclear targets for mitogen-activated protein kinases

Ternary complex factors (TCFs), a subgroup of the ETS protein family, were first described in the context of c-fos gene regulation. Subsequently, their early identification as nuclear targets for mitogen-activated protein kinases served to exemplify the fundamental links in eukaryotic cells between growth factor-mediated signalling pathways and gene control. This article provides an overview of recent work on ternary complex factors, addressing their expression and molecular structure, as well as how selective interactions with members of other protein families serve to up-1 regulate or restrict their activity. Although only one genetic study on ternary complex factors has been published to date, unravelling of the underlying molecular events provides a basis for tentative predictions about their biological roles in mammalian organisms.

Proteins of the ETS family with transcriptional repressor activity

ETS proteins form one of the largest families of signal-dependent transcriptional regulators, mediating cellular proliferation, differentiation and tumorigenesis. Most of the known ETS proteins have been shown to activate transcription. However, four ETS proteins (YAN, ERF, NET and TEL) can act as transcriptional repressors. In three cases (ERF, NET and TEL) distinct repression domains have been identified and there are indications that NET and TEL may mediate transcription via Histone Deacetylase recruitment. All four proteins appear to be regulated by MAPKs, though for YAN and ERF this regulation seems to be restricted to ERKs. YAN, ERF and TEL have been implicated in cellular proliferation although there are indications suggesting a possible involvement of YAN and TEL in differentiation as well. Other ETS-domain proteins have been shown to repress transcription in a context specific manner, and there are suggestions that the ETS DNA-binding domain may act as a transcriptional repressor. Transcriptional repression by ETS domain proteins adds an other level in the orchestrated regulation by this diverse family of transcription factors that often recognize similar if not identical binding sites on DNA and are believed to regulate critical genes in a variety of biological processes. Definitive assessment of the importance of this novel regulatory level will require the identification of ETS proteins target genes and the further analysis of transcriptional control and biological function of these proteins in defined pathways.

Critical activities of Rac1 and Cdc42Hs in skeletal myogenesis: antagonistic effects of JNK and p38 pathways

The Rho family of GTP-binding proteins plays a critical role in a variety of cellular processes, including cytoskeletal reorganization and activation of kinases such as p38 and C-jun N-terminal kinase (JNK) MAPKs. We report here that dominant negative forms of Rac1 and Cdc42Hs inhibit the expression of the muscle-specific genes myogenin, troponin T, and myosin heavy chain in L6 and C2 myoblasts. Such inhibition correlates with decreased p38 activity. Active RhoA, RhoG, Rac1, and Cdc42Hs also prevent myoblast-to-myotube transition but affect distinct stages: RhoG, Rac1, and Cdc42Hs inhibit the expression of all muscle-specific genes analyzed, whereas active RhoA potentiates their expression but prevents the myoblast fusion process. We further show by two different approaches that the inhibitory effects of active Rac1 and Cdc42Hs are independent of their morphogenic activities. Rather, myogenesis inhibition is mediated by the JNK pathway, which also leads to a cytoplasmic redistribution of Myf5. We propose that although Rho proteins are required for the commitment of myogenesis, they differentially influence this process, positively for RhoA and Rac1/Cdc42Hs through the activation of the SRF and p38 pathways, respectively, and negatively for Rac1/Cdc42Hs through the activation of the JNK pathway.

Novel negative regulatory element in the platelet-derived growth factor B chain promoter that mediates ERK-dependent transcriptional repression

Platelet-derived growth factor (PDGF), which consists of an A and/or B chain, stimulates migration and proliferation in vascular smooth muscle cells as well as a large number of other cell types. Investigations over recent years have defined roles for several positive regulatory transcription factors in the PDGF-B promoter. However, little is known about the transcriptional mechanisms that negatively regulate this gene. Here, we used transient transfection and 5' deletion analysis to define a specific region in the PDGF-B promoter-mediating repression in vascular smooth muscle cells. Gel retardation assays revealed this region is bound by nuclear protein(s) in a specific manner. Supershift assays excluded the direct association of Sp1, Sp3, and Egr-1. Mutation of the negative regulatory element no longer supported nucleoprotein complex formation and, when introduced into the PDGF-B promoter, rescued the promoter from repression. Promoter activity was also restored by transfection of oligonucleotide decoys bearing the repressor binding site. The MEK1/2 inhibitor, PD98059, and a dominant negative construct generating inactive ERK1 increased reporter expression driven by the PDGF-B promoter. In contrast, the MEK inhibitor had no effect on the activity of the mutant PDGF-B promoter. These effects were cell type-specific, since neither suppression of the PDGF-B promoter nor nucleoprotein complex formation was observed in vascular endothelial cells. These findings define a distinct negative regulatory element in the PDGF-B promoter that interacts with nuclear protein(s) and inhibits PDGF-B promoter-dependent gene expression in an ERK-dependent manner.