The Saccharomyces cerevisiae IMP2 Gene Encodes a Transcriptional Activator That Mediates Protection against DNA Damage Caused by Bleomycin and Other Oxidants

Abstract

Bleomycin belongs to a class of antitumor drugs that damage cellular DNA through the production of free radicals. The molecular basis by which eukaryotic cells provide resistance to the lethal effects of bleomycin is not clear. Using the yeast Saccharomyces cerevisiae as a model with which to study the effect of bleomycin damage on cellular DNA, we isolated several mutants that display hypersensitivity to bleomycin. A DNA clone containing the IMP2 gene that complemented the most sensitive bleomycin mutant was identified. A role for IMP2 in defense against the toxic effects of bleomycin has not been previously reported. imp2 null mutants were constructed and were found to be 15-fold more sensitive to bleomycin than wild-type strains. The imp2 null mutants were also hypersensitive to several oxidants but displayed parental resistance to UV light and methyl methane sulfonate. Exposure of mutants to either bleomycin or hydrogen peroxide resulted in the accumulation of strand breaks in the chromosomal DNA, which remained even after 6 h postchallenge, but not in the wild type. These results suggest that the oxidant hypersensitivity of the imp2 mutant results from a defect in the repair of oxidative DNA lesions. Molecular analysis of IMP2 indicates that it encodes a transcriptional activator that can activate a reporter gene via an acidic domain located at the N terminus. Imp2 lacks a DNA binding motif, but it possesses a C-terminal leucine-rich repeat. With these data taken together, we propose that Imp2 prevents oxidative damage by regulating the expression of genes that are directly required to repair DNA damage.

MIG1‐dependent and MIG1‐independent regulation of GAL gene expression in Saccharomyces cerevisiae: role of Imp2p

“…Imp2 could be an auxiliary member of the transcriptional complex. Due to the ability of Imp2 to activate a reporter gene (Masson and Ramotar, 1996;Donnini, unpublished data), we favour the second hypothesis, that Imp2 has a role downstream from Mig1 and Nrg1 in activating expression of the GAL regulon.…”

“…Two genes involved in galactose metabolism, IMP2 and GAL6/BLH1, share the ability to protect cells from the glycopeptide bleomycin (BLM) (Enenkel and Wolf, 1993;Masson and Ramotar, 1996;Zheng and Johnston, 1998). The protease bleomycin hydrolase (Gal6p/Blh1p) is believed to prevent cytotoxic effects by degrading bleomycin.…”

“…The imp2 mutant was independently isolated during screening for bleomycin-hypersensitive mutants; bleomycin is an anti-tumour drug that damages DNA by producing free radicals (Masson and Ramotar, 1996). Yeast cells deficient in Imp2 are also hypersensitive to a variety of the oxidative agents and ions Ramotar, 1996, 1998).…”

“…Indeed, Imp2 possesses an acidic domain characteristic of many transcriptional activator proteins and it is able to activate a reporter gene (Donnini et al, 1992a;Masson and Ramotar, 1996). At present, the mechanism by which Imp2 participates in the regulation of several genetic systems is unclear.…”

“…At present, the mechanism by which Imp2 participates in the regulation of several genetic systems is unclear. However, the presence of a C-terminal leucine-rich repeat (LRR) domain that could mediate protein-protein interactions (Masson and Ramotar, 1996) and the absence of an obvious DNA binding domain suggest an indirect role in transcriptional activation.…”