The FAR domain defines a new Xenopus laevis zinc finger protein subfamily with specific RNA homopolymer binding activity

Use of PMA1 as a housekeeping biomarker for assessment of toxicant-induced stress in Saccharomyces cerevisiae

The brewer's yeast Saccharomyces cerevisiae has emerged as a versatile and robust model system for laboratory use to study toxic effects of various substances. In this study, toxicant-induced stresses of pure compounds were investigated in Saccharomyces cerevisiae utilizing a destabilized version of the green fluorescent protein optimized for expression in yeast (yEGFP3) under control of the promoter of the housekeeping plasma membrane ATPase gene PMA1. The responses of the biomarker upon increasing test compound concentrations were monitored by determining the decrease in fluorescence. The reporter assay deployed a simple and robust protocol for the rapid detection of toxic effects within a 96-well microplate format. Fluorescence emissions were normalized to cell growth determined by absorption and were correlated to internal reference standards. The results were expressed as effective concentrations (EC20). Dose-response experiments were conducted in which yeast cells were exposed in minimal medium and in the presence of 20% fetal calf serum to sublethal concentrations of an array of heavy metals, salt, and a number of stress-inducing compounds (Diclofenac, Lindane, methyl-N-nitro-N-nitrosoguanidine [MNNG], hydroxyurea, and caffeine). Long-term exposure (7 h) played a considerable role in the adaptive response to intoxication compared to early responses at 4 h exposure. The data obtained after 4 h of exposure and expressed as EC20 were compared to 50% inhibitory concentration values derived from cell line and ecotoxicological tests. This study demonstrates the versatility of the novel biomarker to complement existing test batteries to assess contaminant exposure and effects.

Characterization and chondrocyte differentiation stage-specific expression of KRAB zinc-finger protein gene ZNF470

As part of a study to identify novel transcriptional regulators of chondrogenesis-related gene expression, we have cloned and characterized cDNA for zinc-finger protein 470 (ZNF470), the human ortholog of which encodes a 717 amino acid residue protein containing 17 Cys(2)His(2) zinc-finger domains, as well as KRAB-A and KRAB-B motifs. The cDNA library used to isolate the initial ZNF470 clone was prepared from human bone marrow-derived mesenchymal progenitor cells at an intermediate stage of chondrogenic differentiation. We have determined the intron-exon structure of the human ZNF470 gene, which has been mapped to a zinc-finger cluster in a known imprinted region of human chromosome 19q13.4. ZNF470 is expressed at high levels in human testis and is expressed at low or undetectible levels in other adult tissues. Human ZNF470 expressed in mammalian cells as an EGFP fusion protein localizes predominantly to the nucleus, consistent with a role in transcriptional regulation. ZNF470, analyzed by quantitative real time PCR, was transiently expressed before the maximal expression of COL2A1 during chondrogenic differentiation in vitro. We have also characterized the bovine ortholog of human ZNF470, which encodes a 508 amino acid residue protein having 10 zinc-finger domains. A bovine ZNF470 cDNA clone was used to examine expression of ZNF470 in bovine articular chondrocytes treated with retinoic acid to stimulate dedifferentiation. Bovine ZNF470 expression was undetectable in freshly isolated bovine articular chondrocytes, but was dramatically upregulated in dedifferentiated retinoic acid-treated chondrocytes. These results, in two model systems, suggest a possible role for ZNF470 in the regulation of chondrogenesis-specific gene expression.

Adaptative responses in yeast to the herbicide 2-methyl-4-chlorophenoxyacetic acid at the level of intracellular pH homeostasis

AIMS

The objective of this work was to examine adaptative responses occurring in Saccharomyces cerevisiae following exposure to the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA).

METHODS AND RESULTS

The exposure of a yeast cell population to MCPA concentrations of moderate toxicity led to a period of latency before eventual resumption of inhibited growth. During this period of adaptation, the plasma membrane (PM) H+-ATPase was activated, in coordination with the decrease of intracellular pH (pHi), cell viability and average cell volume. The in vivo activation of this ATPase was demonstrated either by assaying PM-ATPase activity in membrane suspensions extracted from cells grown in the presence or absence of MCPA or by measuring the in vivo H+-pumping activity in the same cells. The PM-H+-ATPase activation could not be attributed to transcriptional activation of the encoding genes PMA1 and PMA2.

CONCLUSIONS

The activity of PM-H+-ATPase was stimulated and the internal cell volume decreased during yeast adaptation to growth under MCPA stress. Based on the values estimated for the pHi, we hypothesize that these cell responses may contribute to the restoration of pHi homeostasis during recovery from MCPA stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is a contribution to the understanding of the toxic effects of the herbicide MCPA and of physiological mechanisms underlying adaptation to MCPA, in the eukaryotic model S. cerevisiae. Results may be useful to elucidate the adaptation mechanisms to this xenobiotic compound in more complex and experimentally less-accessible eukaryotes. They also provide indications to assist the use of yeast cells as a bioassay system to assess the toxicity of phenoxyacetic acid herbicides and of other lipophilic xenobiotics, aiming at reducing the use of animals in toxicity testing.

Mutations in erg4 affect the sensitivity of Saccharomyces cerevisiae to medium-chain fatty acids

We have found that the medium-chain fatty acids (MCFAs) undecanoic acid (11:0), 10-undecenoic acid (11:1 Delta 10), and lauric acid (12:0) can affect the growth of Saccharomyces cerevisiae in a dose-dependent manner. The principal effect was a longer lag phase in MCFA-containing medium, although higher concentrations of 11:1 Delta 10 inhibited growth. Their relative order of inhibitory action was 11:1 Delta 10>11:0>12:0. Cellular content with MCFA supplementation was dependent on the concentration and the particular species of fatty acid, with 12:0 showing the highest relative accumulation and 11:1 Delta 10 the lowest at all concentrations. We have isolated and characterized a mutant that is hypersensitive to MCFA supplementation and is unable to grow at the normally permissive condition of 1 mM 11:1 Delta 10. However, it does not appear to accumulate higher relative levels of the fed MCFA compared to wild-type cells. Complementation of the mutant revealed that the ERG4 gene, encoding the enzyme that catalyzes the last step in ergosterol biosynthesis, had been mutated. The fatty acid composition of the erg4 Delta mutant differs only slightly from wild-type cells, mainly involving an increase in the relative amount of 12:0. These results indicate that yeast require ergosterol for optimal growth on certain MCFAs. We discuss the role ergosterol may have in cells responding to exogenous MCFAs and in supporting optimal cell growth.

Cloning and characterization of a novel human gene encoding a zinc finger protein with 25 fingers

This study reports cloning and characterization of a human cDNA encoding a novel human zinc finger protein, ZFD25. ZFD25 cDNA is 6118 bp long and has an open reading frame of 2352 bp that encodes a 783 amino acid protein with 25 C2H2-type zinc fingers. The ZFD25 cDNA also contains a region with high sequence similarity to the Krüppel-associated box A and B domain in the 5'-untranslated region, suggesting that ZFD25 belongs to the Krüppel-associated box zinc finger protein family. The ZFD25 gene was localized to chromosome 7q11.2. Northern blot analysis showed that ZFD25 was expressed in a wide range of human organs. In cultured endothelial cells, the mRNA level was decreased upon serum starvation.

FLR1 gene (ORF YBR008c) is required for benomyl and methotrexate resistance in Saccharomyces cerevisiae and its benomyl-induced expression is dependent on pdr3 transcriptional regulator

In this work we report the disruption of a Saccharomyces cerevisiae ORF YBR008c (FLR1 gene) within the context of EUROFAN (EUROpean Functional Analysis Network) six-pack programme, using a PCR-mediated gene replacement protocol as well as the results of the basic phenotypic analysis of a deletant strain and the construction of a disruption cassette for inactivation of this gene in any yeast strain. We also show results extending the knowledge of the range of compounds to which FLR1 gene confers resistance to the antimitotic systemic benzimidazole fungicide benomyl and the antitumor agent methotrexate, reinforcing the concept that the FLR1 gene is a multidrug resistance (MDR) determinant. Our conclusions were based on the higher susceptibility to these compounds of flr1Delta compared with wild-type and on the increased resistance of both flr1Delta and wild-type strains upon increased expression of FLR1 gene from a centromeric plasmid clone. The present study also provides, for the first time, evidence that the adaptation of yeast cells to growth in the presence of benomyl involves the dramatic activation of FLR1 gene expression during benomyl-induced latency (up to 400-fold). Results obtained using a FLR1-lacZ fusion in a plasmid indicate that the activation of FLR1 expression in benomyl-stressed cells is under the control of the transcriptional regulator Pdr3p. Indeed, PDR3 deletion severely reduces benomyl-induced activation of FLR1 gene expression (by 85%), while the homologous Pdr1p transcription factor is apparently not involved in this activation.

Kzf1 - a novel KRAB zinc finger protein encoding gene expressed during rat spermatogenesis

Two novel KRAB (Krüppel associated box) type zinc finger protein encoding cDNAs, named Kzf1 and Kzf2 (Kzf for KRAB zinc finger), were identified by screening of a rat embryonic brain cDNA library with a human ZNF91 KRAB probe. Kzf1 and Kzf2 encode proteins with an amino-terminal KRAB domain and a carboxy-terminal zinc finger cluster containing 9 and 13 zinc finger units, respectively. While Kzf2 appears to be ubiquitously expressed, Kzf1 is preferentially expressed in the testis. Within the testis, Kzf1 mRNA is restricted to germ cells. The Kzf1 protein exhibits DNA binding activity and its KRAB domain can function as a repressor module in transcription. Using somatic cell hybrid analysis, the Kzf1 gene was mapped to chromosome 6.

The C-terminus of yeast plasma membrane H+-ATPase is essential for the regulation of this enzyme by heat shock protein Hsp30, but not for stress activation

Several stresses cause additional activation to the glucose-stimulated plasma membrane H+-ATPase activity of yeast, but it is not clear how this is achieved. We recently reported that cells lacking the integral plasma membrane heat shock protein Hsp30 display enhanced increases in plasma membrane H+-ATPase activity with either heat shock or weak organic acid stress (Piper, P.W., Ortiz-Calderon, C., Holyoak, C., Coote, P. and Cole, M. (1997) Cell Stress and Chaperones 2, 12-24), indicating that the stress induction of Hsp30 acts to reduce stress stimulation of the H+-ATPase. In this study it is shown that Hsp30 acts to reduce the Vmax of H+-ATPase in heat shocked cells. Its action is lost with deletion of the C-terminal 11 amino acids of the H+-ATPase, a deletion that does not abolish the stress stimulation of this enzyme. Mutation of the Thr-912 residue within the C-terminal domain of H+-ATPase, a potential site of phosphorylation by the Ca2+-calmodulin-dependent protein kinase, also abolishes any effect of Hsp30. Hsp30 may therefore be acting on a Thr-912 phosphorylated form of the H+-ATPase.

Effect of extracellular acidification on the activity of plasma membrane ATPase and on the cytosolic and vacuolar pH of Saccharomyces cerevisiae

The rapid in vivo activation of Saccharomyces cerevisiae plasma membrane H+-ATPase that has been attributed to medium acidification from pH 6.5 to pH 3.5 is not caused by the low pH itself but is induced by the weak organic acid (succinic) used as the acidulant. The activation induced by 50 mM succinic acid at pH 3.5 occurred in both the presence or absence of glucose. Activation at pH 3.5 was also induced by acetic acid and it was maximal at 50 mM concentration. To investigate the role of plasma membrane ATPase activation in pH homeostasis, the internal pH (cytosolic and vacuolar) of yeast cells incubated in media at pH 6.5 or at pH 3.5, acidified either with HCl or acetic acid, were compared by using in vivo (31)P-NMR. Despite plasma membrane ATPase activation by acetic acid, the decrease in cytosolic pH caused by external acidification was much more important when the permeant acetic acid was used instead of HCl as the acidulant. The supplementation of the incubation medium at pH 3.5 with glucose led to higher cytosolic pH values, consistent with the observed in vivo activation of plasma membrane ATPase by glucose. At the external pH value of 6.5 the vacuole was maintained at a mildly acidic pH (around 6) while the cytosol was at about neutral pH; however, when cytoplasmic pH decreased due to external acidification, vacuolar pH accompanied that decrease. Vacuolar pH reached 5.4-5.5 during incubation with HCI and dropped sharply to values below 4.4 in cells incubated with acetic acid. These results indicate that the vacuole also plays a role in homeostasis of the intracellular pH.

A search for a mammalian homologue of the Drosophila photoreceptor development gene glass yields Zfp64, a zinc finger encoding gene which maps to the distal end of mouse chromosome 2

Whilst searching for a mammalian homologue of the Drosophila glass gene we cloned a mouse cDNA whose deduced sequence encodes a 614 amino acid (aa) protein with ten Cys2-His2 (C2H2) zinc finger (Zf) motifs. Zfp64 is expressed in all developing and mature mouse tissues examined, except the mouse erythroleukemia (MEL) cell line. Zfp64 maps to the distal region of mouse chromosome 2 close to lens opacity 4 (Lop4), a semidominant cataract mutation. Sequence analysis shows that Zfp64 has multiple potential phosphorylation sites for casein kinase II (CK II), protein kinase C (PKC), tyrosine kinase (TK) and c-AMP- and c-GMP-dependent protein kinase (cA/GMPDPK).

The in vivo activation of Saccharomyces cerevisiae plasma membrane H(+)-ATPase by ethanol depends on the expression of the PMA1 gene, but not of the PMA2 gene

The expression of the PMA1 and PMA2 genes during Saccharomyces cerevisiae growth in medium with glucose plus increasing concentrations of ethanol was monitored by using PMA1-lacZ and PMA2-lacZ fusions and Northern blot hybridizations of total RNA probed with PMA1 gene. The presence of sub-lethal concentrations of ethanol enhanced the expression of PMA2 whereas it reduced the expression of PMA1. The inhibition of PMA1 expression by ethanol corresponded to a decrease in the content of plasma membrane ATPase as quantified by immunoassays. Although an apparent correspondence could exist between the increase of plasma membrane ATPase activity and the level of PMA2 expression, the maximal level of PMA2 expression remained about 200 times lower than PMA1. On the other hand, ethanol activated the plasma membrane H(+)-ATPase activity from a strain expressing only the PMA1 ATPase but did not activate that from a strain expressing only the PMA2 ATPase. These results provide evidence that in the presence of ethanol it is the PMA1 ATPase which is activated, probably by a post-translational mechanism and that the PMA2 ATPase is not involved.