Genetic background of lead and mercury metabolism in a group of medical students in Austria.

BACKGROUND: Information on the impact of genetic predisposition on metal toxicokinetics in the human body is limited. There is increasing evidence that certain genetic polymorphisms modify lead and mercury toxicokinetics. This called for analysis of further candidate genes. OBJECTIVES: Medical students (N=324) were examined in order to detect potential associations between lead exposure and polymorphisms in HFE, VDR, ALAD, and MT genes, as well as between mercury exposure and GSTT1, GSTM1, GSTA1, GSTP1, GCLC, and MT polymorphisms. METHODS: The levels of lead and mercury exposure of students were determined by blood, urine, and hair analyses (ICP-MS, CV-AAS). Genotyping of common polymorphisms was examined by MALDI-TOF MS and the TaqMan methodology. Associations between lead and mercury exposures and genetic background were examined by bivariate analysis, and by categorical regression analysis (CATREG) controlled by metal- and matrix-specific variables. RESULTS: Lead and mercury levels in urine, blood, and hair indicated low exposures. VDR polymorphism and joint presence of VDR/ALAD polymorphisms were significantly and independently associated with urine lead concentrations (CATREG P<0.05). Polymorphisms in GSTP1-114 and MT4 genes as well as dual gene combinations including GSTP1, GCLC, GSTT1, and GSTM1 polymorphisms were independent variables related to mercury body burdens (CATREG P<0.05). GSTP1-114/GSTT1 and GSTP1-105/GCLC combinations showed synergistic effects on hair mercury levels compared to single-gene variants. CONCLUSIONS: We found evidence that certain genetic backgrounds were associated with lead and mercury metabolism, suggesting gene-environment and gene-gene-environment interactions. The modes of interaction remain to be evaluated.

RPD3 and ROM2 are required for multidrug resistance in Saccharomyces cerevisiae.

The PDR5 gene encodes the major multidrug resistance efflux pump in Saccharomyces cerevisiae. In drug-resistant cells, the hyperactive Pdr1p or Pdr3p transcriptional activators are responsible for the PDR5 upregulation. In this work, it is shown that the RPD3 gene encoding the histone deacetylase that functions as a transcriptional corepressor at many promoters and the ROM2 gene coding for the GDP/GTP exchange protein for Rho1p and Rho2p participating in signal transduction pathways are required for PDR5 transcription under cycloheximide-induced and noninduced conditions. Transposon insertion mutations in ROM2, RPD3 and some other genes encoding specific subunits of the large Rpd3L protein complex resulted in enhanced susceptibility of mutant cells to antifungals. In the rpd3 Delta and rom2 Delta mutants, the level of PDR5 mRNA and the rate of rhodamine 6G efflux were reduced. Unlike rpd3 Delta, in rom2 Delta mutant cells the drug hypersensitivity and the defect in PDR5 expression were suppressed by PDR1 or PDR3 overexpressed from heterologous promoters and by the hyperactive pdr3-9 mutant allele. The results indicate that Rpd3p histone deacetylase participating in chromatin remodeling and Rom2p participating in the cell integrity pathway are involved in the control of PDR5 expression and modulation of multidrug resistance in yeast.

Loss-of-function pdr3 mutations convert the Pdr3p transcription activator to a protein suppressing multidrug resistance in Saccharomyces cerevisiae.

The PDR1 and PDR3 genes encode the main transcription activators involved in the control of multidrug resistance in Saccharomyces cerevisiae. To identify the amino acids essential for Pdr3p function, the loss-of-function pdr3 mutants were isolated and characterized. Two plasmid-borne pdr3 alleles, pdr3-E902Ter and pdr3-D853Y, which failed to complement drug hypersensitivity in the Deltapdr1Deltapdr3 mutant strain, were isolated. The E902Ter mutation resulted in a truncated protein lacking the C-terminal activation domain. The D853Y mutation allowed the expression of entire Pdr3p, but its transactivation function was lost. When overexpressed from the P(GAL1) promoter, the two mutant alleles increased the sensitivity of wild-type cells to cycloheximide and fluconazole and suppressed drug resistance in gain-of-function pdr1 and pdr3 mutant strains. The drug-sensitizing effect of overexpressed loss-of-function pdr3 mutant alleles correlated with their ability to suppress PDR5 transcription and rhodamine 6G accumulation in transformants of the wild-type and Deltapdr1 mutant strains. These results demonstrate that amino acid residue Asp853 is essential for Pdr3p function, and indicate that specific loss-of-function pdr3 mutations can convert the Pdr3p transcription activator to a multicopy suppressor of multidrug resistance.

Yeast strains designed for screening of reversal agents and genetic suppressors of multidrug resistance.

Multidrug resistance in yeast results from over-expression of drug efflux transporter genes due to gain-of-function mutations in transcription factors. To suppress multidrug resistance at the level of gene expression, we have developed a yeast-based screening system for the detection of compounds down-regulating the major multidrug ABC transporter Pdr5p expressed under the control of Pdr3p transcription factor. Here, we report the construction and properties of the improved set of yeast strains designed along with such screening also for a global analysis of genetic suppressors of multidrug resistance. The basic components of this system, the P(GAL1)-PDR3 and P(PDR5)-pma1(D378N) fusion genes, were individually or simultaneously integrated into corresponding chromosomes of a hypersensitive S. cerevisiae strain deleted in the PDR1 and PDR3 genes. This resulted in increased mitotic stability of a set of new test strains compared with the original prototrophic strain ZK11-1 developed previously. In addition, some of the strains designed are auxotrophic for leucine, uracil and histidine allowing them to be used in genetic screens for positive selection of multicopy or loss-of-function genetic suppressors of multidrug resistance.

A general strategy to uncover transcription factor properties identifies a new regulator of drug resistance in yeast.

We demonstrate a genomewide approach to determine the physiological role of a putative transcription factor, Ylr266, identified through yeast genome sequencing program. We constructed activated forms of the zinc finger (Zn(2)Cys(6)) protein Ylr266, and we analyzed the corresponding transcriptomes with DNA microarrays to characterize the up-regulated genes. The direct target genes of Ylr266 were further identified by in vivo chromatin immunoprecipitation procedure. The functions of the genes directly controlled by YLR266c are in agreement with the observed drug-resistance phenotype of the cell expressing an activated form of Ylr266. These target genes code for ATP-binding cassette or major facilitator superfamily transporters such as PDR15, YOR1, or AZR1 or for other proteins such as SNG1, YJL216c, or YLL056c which are already known to be involved in the yeast pleiotropic drug resistance (PDR) phenomenon. YLR266c could thus be named PDR8. Overlaps with the other PDR networks argue in favor of a new specific role for PDR8 in connection with the well known PDR regulators PDR1/PDR3 and YRR1. This strategy to identify the regulatory properties of an anonymous transcription factor is likely to be generalized to all the Zn(2)Cys(6) transcription factors from Saccharomyces cerevisiae and related yeasts.