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Biomedical subjects

W H Ernst

Publications and source records attributed to W H Ernst.

11 recordsLinked to original sources
PubMed2001

Enhanced copper tolerance in Silene vulgaris (Moench) Garcke populations from copper mines is associated with increased transcript levels of a 2b-type metallothionein gene.

Silene vulgaris (Moench) Garcke has evolved populations with extremely high levels of copper tolerance. To evaluate the role of metallothioneins (MTs) in copper tolerance in S. vulgaris, we screened a cDNA library derived from a highly copper-tolerant population using Arabidopsis-based MT probes and identified an MT2b-like gene. When expressed in yeast, this gene, SvMT2b, restored cadmium and copper tolerance in different hypersensitive strains. Northern-blot analysis and quantitative reverse transcriptase-PCR showed that plants from the copper-tolerant S. vulgaris populations had significantly higher transcript levels of SvMT2b than plants from the copper-sensitive populations, both in roots and shoots and with and without copper exposure. Southern-blot analysis suggested that the higher expression of the latter allele was caused by gene amplification. Segregating families of crosses between copper-sensitive and copper-tolerant plants exhibited a 1 to 3 segregation for SvMT2b expression. Allele-specific PCR showed that low-expression F(3) plants were homozygous for the allele inherited from the copper-sensitive parent, whereas high-expression plants possessed at least one allele from the tolerant parent. SvMT2b expression did not cosegregate with copper tolerance in crosses between sensitive and tolerant plants. However, a significant cosegregation with copper tolerance did occur in families derived from crosses between moderately tolerant F(3) plants with different SvMT2b genotypes. Thus, overexpression of SvMT2b conferred copper tolerance although only within the genetic background of a copper tolerant plant.

Adaptation, Physiological↗
PubMed2000

Life-cycle phases of a zinc- and cadmium-resistant ecotype of Silene vulgaris in risk assessment of polymetallic mine soils.

Short-term exposure of plants to heavy metals is often used for risk assessment of metal-enriched soils (OECD guideline 208) without considering the reliability of the assessment for long-term exposure, i.e. for the completion of a plant's life-cycle. In the present study with 15 orogenic soils three phases of the life-cycle of a Zn-Cd-resistant ecotype of Silene vulgaris were studied to improve risk assessment of metal-enriched soils. The first phase, i.e. emergence of seedlings was not related to the water-soluble or total metal concentration of the soils. Seedling mortality was low as long as the water-soluble metal concentration did not surpass 0.15 micromol Zn and 0.04 micromol Cu g(-1) dry soil. Curtailment of the life-cycle prior to flowering, i.e. the vegetative growth as second phase, occurred on those soils where roots and shoots were heavily enriched by Zn already in the seedling phase. In the third phase, i.e. the generative phase, time to flowering and yield differences between orogenic soils were substantial, but soil metal concentrations could not be directly related to timing of reproduction or biomass. Ranking of data showed a high inconsistency of the responses to metal exposure during the first phases of the life-cycle. It is concluded that total plant mass and seed mass are the only realistic endpoints of life-cycle bioassays in risk assessment as long as ranks are inconsistent between two successive early phases of the life-cycle.

Journal Article↗
PubMed1998

Sulfur metabolism in higher plants: potential for phytoremediation.

Sulfur is a major nutrient for all organisms. Plant species have a high biodiversity in uptake, metabolization and accumulation of sulfur so that there are potentials to use plants for phytoremediation of sulfur-enriched sites. A survey of soils enriched with sulfur either naturally or by human activities shows that a surplus of sulfur is mostly accompanied with a surplus of other chemical elements which may limit phytoremediation because these co-occurring elements are more toxic to plants than sulfur. In addition, the accumulation of the other elements makes the plant material (phyto-extraction) less suitable for the use as fodder and for human consumption.

Biodegradation, Environmental↗
PubMed1995

SAP1a is a nuclear target of signaling cascades involving ERKs.

The Ets protein SAP1a has been shown to interact with the c-fos serum response element upon recruitment by the serum response factor. We demonstrate that SAP1a is a nuclear protein stimulating transcription via the c-fos serum response element, and additionally via an Ets binding site independently of the serum response factor. However, transactivation has only been observed under conditions leading to the activation of extracellular signal-regulated protein kinases (ERKs). The transcriptional activation domain of SAP1a resides within the C-terminal region, the function of which may be impeded by the N-terminus. Several potential ERK consensus sites within the C-terminal region of SAP1a can modulate its transactivation efficacy, implicating that SAP1a is a direct target of ERKs. Since ERKs are activated by a broad range of signals, SAP1a may play an important role in the transformation of extracellular stimuli into a nuclear response.

Amino Acid Sequence↗
PubMed1995

Transcriptional repression mediated by the serum response factor.

The serum response element (SRE) contributes to transcriptional repression of the c-fos proto-oncogene. We show that the transcription factor SRF is able to repress SRE-dependent transcription, apparently by sequestering a co-activator. Only the DNA-binding core region is required for this SRE-dependent repression. Furthermore the phosphorylation status at potential casein kinase II sites within an N-terminal repression domain affects SRE-independent transcription. SRF may thus pleiotropically influence cellular transcription, representing a novel aspect of SRF function.

3T3 Cells↗
PubMed1995

The effect of elevated UV-B (280-320 nm) radiation levels on Silene vulgaris: a comparison between a highland and a lowland population.

Highland (altitude 1600 m above sea level) and lowland (altitude -2 m below sea level) populations of the perennial herb Silene vulgaris (Moench) Garcke, were tested on their response to elevated levels of UV-B radiation. Highland populations typically receive high natural UV-B fluxes, whereas lowland populations receive a lower natural UV-B dose. Adaptation to high UV-B levels of the highland population is to be expected. Experimental comparison of growth rates, gas exchange rates, transpiration and biochemical parameters using adult plants as well as seedlings did not show a difference in the response to elevated UV-B levels between the two populations. Individuals of both populations were relatively insensitive to elevated UV-B radiation. The response of alpine and lowland populations of Silene vulgaris is discussed in relation to the dispersal of this species after the last ice age.

Journal Article↗
PubMed1994

Regulatory squelching.

An important function of transcription factors may be to sequester coactivators or corepressors of transcription. In this manner transcription factors could regulate in trans the activity of promoters to which they do not bind. This may be of widespread significance as a mechanism to control cell cycle-dependent and differentiation-specific transcriptional activity within eukaryotic cells. Therefore squelching in vivo may be important than hitherto appreciated.

Animals↗
PubMed1994

Functional dissection of the transcription factor Elk-1.

The ternary complex factor Elk-1 belongs to the Ets oncoprotein family. We demonstrate that this transcription factor is localized predominantly in the nucleus, for which at least two regions of Elk-1 are required. One of these regions is part of the N-terminal ETS-domain, while the other encompasses amino acids 137-157. In conjunction with the ETS-domain, which mediates autonomous binding of Elk-1 to some DNA target sequences, the conserved B-region is both necessary and sufficient for ternary complex formation with the c-fos serum response element and the serum response factor. However, the B-region must be linked to the ETS-domain by a spacer. Furthermore, the B-region impedes autonomous DNA-binding, possibly by masking the ETS-domain. A point mutation within the ETS-domain, homologous to the ts1.1 point mutation of v-Ets in the E26 virus, affects DNA-binding of Elk-1 in a temperature-dependent manner, which by analogy might be causative for the altered phenotype of ts1.1 E26. Finally we show that amino acids 83-428 contribute to Elk-1 mediated transactivation. In particular, the region 376-404 is indispensable for transactivation, while flanking amino acids on both sides are only required for enhancement of transcriptional efficacy.

Amino Acid Sequence↗
PubMed1993

Activation of ternary complex factor Elk-1 by MAP kinases.

Ternary complex factors (TCFs), one of which is Elk-1, have been implicated in mediation of c-fos induction. They have been shown to be phosphorylated by mitogen-activated protein kinases (MAPKs) in vitro. We demonstrate that recombinant Elk-1 is hyperphosphorylated in vivo upon joint overexpression of MAPKs and constitutively activated Raf-1 kinase, the latter serving as an indirect in vivo activator of MAPKs. This phosphorylation is accompanied by a conformational change and results in an elevated transactivation potential of Elk-1. Mutation of mapped in vivo phosphorylation sites, which are potential targets for MAPKs, reduced Elk-1-mediated transcription. Thus, MAPKs are very probably controlling Elk-1 activity by direct phosphorylation in vivo. Furthermore, Elk-1 was shown to stimulate transcription from both the c-fos serum response element and also from an Ets binding site. While binding of TCFs to the c-fos promoter is dependent on the serum response factor, TCFs can autonomously interact with Ets binding sites. This indicates that TCFs may participate in the transcriptional regulation of two different sets of genes.

Animals↗
PubMed1993

C-terminal phosphorylation of the serum-response factor.

The serum-response factor (SRF) is essential for the induction and repression of the protooncogene c-fos. Phosphorylation of SRF has been implicated to be involved in these processes and five phosphorylation sites have already been mapped within the N-terminal region. Here we show that in vivo additional phosphorylation of SRF does occur. This modification is located primarily within amino acids 206-289, which probably contain more than one phosphorylation site. Microsequencing allowed the identification of one phosphorylation site at Ser253, which is a potential target of casein kinase II. Mutational analysis revealed that, in contrast to N-terminal phosphorylation, Ser253 phosphorylation does not affect DNA-binding properties. In addition, phosphorylation at Ser253 does not seem to change transactivation activity of SRF but rather influences its contribution to transcriptional repression. Thus, C-terminal phosphorylation of SRF may modulate c-fos basal repression.

3T3 Cells↗