Potentiation of bleomycin cytotoxicity in Saccharomyces cerevisiae

Comparative roles of the cell wall and cell membrane in limiting uptake of xenobiotic molecules by Saccharomyces cerevisiae

Using reversible electropermeabilization of cells and spheroplasts, we show that the cell wall and plasma membrane partly account for bleomycin resistance by acting as two independent barriers. We also report on the presence of a membrane protein that may be responsible for bleomycin internalization and toxicity in Saccharomyces cerevisiae.

The Aspergillus nidulans GATA factor SREA is involved in regulation of siderophore biosynthesis and control of iron uptake

A gene encoding a new GATA factor from Aspergillus nidulans, sreA, was isolated and characterized. SREA displays homology to two fungal regulators of siderophore biosynthesis: about 30% overall identity to SRE from Neurospora crassa and about 50% identity to URBS1 from Ustilago maydis over a stretch of 200 amino acid residues containing two GATA-type zinc finger motifs and a cysteine-rich region. This putative DNA binding domain, expressed as a fusion protein in Escherichia coli, specifically binds to GATA sequence motifs. Deletion of sreA results in derepression of L-ornithine-N5-oxygenase activity and consequently in derepression of the biosynthesis of the hydroxamate siderophore N,N',N"-triacetyl fusarinine under sufficient iron supply in A. nidulans. Transcription of sreA is confined to high iron conditions, underscoring the function of SREA as a repressor of siderophore biosynthesis under sufficient iron supply. Nevertheless, overexpression of sreA does not result in repression of siderophore synthesis under low iron conditions, suggesting additional mechanisms involved in this regulatory circuit. Consistent with increased sensitivity to the iron-activated antibiotics phleomycin and streptonigrin, the sreA deletion mutant displays increased accumulation of 59Fe. These results demonstrate that SREA plays a central role in iron uptake in addition to siderophore biosynthesis.

Bleomycin therapy of experimental disseminated candidiasis in mice

Bleomycin, an antineoplastic agent, was found to be very effective in vitro against a variety of fungi, including Candida albicans. Mice were infected with C. albicans intravenously and then treated with various doses of bleomycin. No efficacy was shown by either prolongation of survival or reduction of tissue counts.

Oxidative cell wall damage mediated by bleomycin-Fe(II) in Saccharomyces cerevisiae

Bleomycin mediates cell wall damage in the yeast Saccharomyces cerevisiae. Bleomycin treatments in the presence of Fe(II) increased the rate of spheroplast formation by lytic enzymes by 5- to 40-fold. Neither Fe(III) nor other tested ions caused significant cell wall damage in the presence of bleomycin. The effect of bleomycin-Fe(II) on the cell wall mimicked the characteristics of bleomycin-Fe(II)-mediated DNA damage in dependence on aeration, inhibition by ascorbate, and potentiation by submillimolar concentrations of sodium phosphate. Bleomycin-mediated cell wall damage was time and dose dependent, with incubations as short as 20 min and drug concentrations as low as 3.3 x 10(-7)M causing measurable cell wall damage in strain CM1069-40. These times and concentrations are within the range of effectiveness for bleomycin-mediated DNA damage and for the cytotoxicity of the drug. Although Fe(III) was inactive with bleomycin and O2, the bleomycin-Fe(III) complex damaged walls and lysed cells in the presence of H2O2. H2O2 causes similar activation of bleomycin-Fe(III) in assays of DNA scission. These results suggest that an activated bleomycin-Fe-O2 complex disrupts essential cell wall polymers in a manner analogous to bleomycin-mediated cleavage of DNA.