Regulatory factors controlling transcription of Saccharomyces cerevisiae IXR1 by oxygen levels: a model of transcriptional adaptation from aerobiosis to hypoxia implicating ROX1 and IXR1 cross-regulation

Abstract

Ixr1p from Saccharomyces cerevisiae has been previously studied because it binds to DNA containing intrastrand cross-links formed by the anticancer drug cisplatin. Ixr1p is also a transcriptional regulator of anaerobic/hypoxic genes, such as SRP1/TIR1, which encodes a stress-response cell wall manoprotein, and COX5B, which encodes the Vb subunit of the mitochondrial complex cytochrome c oxidase. However, factors controlling IXR1 expression remained unexplored. In the present study we show that IXR1 mRNA levels are controlled by oxygen availability and increase during hypoxia. In aerobiosis, low levels of IXR1 expression are maintained by Rox1p repression through the general co-repressor complex Tup1-Ssn6. Ixr1p itself is necessary for full IXR1 expression under hypoxic conditions. Deletion analyses have identified the region in the IXR1 promoter responsible for this positive auto-control (nucleotides -557 to -376). EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation) assays show that Ixr1p binds to the IXR1 promoter both in vitro and in vivo. Ixr1p is also required for hypoxic repression of ROX1 and binds to its promoter. UPC2 deletion has opposite effects on IXR1 and ROX1 transcription during hypoxia. Ixr1p is also necessary for resistance to oxidative stress generated by H2O2. IXR1 expression is moderately activated by H2O2 and this induction is Yap1p-dependent. A model of IXR1 regulation as a relay for sensing different signals related to change in oxygen availability is proposed. In this model, transcriptional adaptation from aerobiosis to hypoxia depends on ROX1 and IXR1 cross-regulation.

Transcriptional Regulation of Yeast Oxidative Phosphorylation Hypoxic Genes by Oxidative Stress

“…The Northern blot analyses presented in Figure 1C showed that the expression of ROX1 and ORD1 in the yeast genetic background used here (W303) is not cross-regulated as previously proposed for BY4741 cells (13). This was further substantiated by quantitative polymerase chain reaction (PCR) analyses that showed that expression of ROX1 and ORD1 both in normoxia and in anoxia is independent of their respective protein products ( Supplementary Fig.…”

The Yeast Genes ROX1, IXR1, SKY1 and Their Effect upon Enzymatic Activities Related to Oxidative Stress

“…Besides, the effect of ∆ixr1 is epistatic to ∆yap1 (Bourdineaud et al, 2000). IXR1 expression is moderately activated by H 2 O 2 and this induction is Yap1-dependent (Castro-Prego et al, 2010a). In multi-cellular eukaryotes connexions between the oxidative stress response and IXR1 homologues also exist.…”

“…Structurally, both contain HMG (high-mobility group) domains, which bind to and bend DNA (Deckert et al, 1995;Deckert et al, 1999;. Functionally, both control genes that are expressed at higher levels when oxygen is low (hypoxia) or absent (anoxia) than during normoxia (Bourdineaud et al, 2000;Castro-Prego et al, 2010a, 2010bKastaniotis & Zitomer, 2000;Klinkenberg et al, 2005;Lambert et al, 1994;Zitomer & Lowry, 1992;Zitomer et al, 1997;). Moreover, a transcriptional cross-regulation between the genes ROX1 and IXR1 has been reported (Castro-Prego et al, 2010b).…”

“…We have recently found that in S. cerevisiae the transcriptional factor Ixr1 is also related to the oxidative stress response. Moreover, a cross-regulation, affecting transcription, exits between Ixr1 and Rox1, which is the aerobic transcriptional repressor of hypoxic genes (Castro-Prego et al, 2010a). Ixr1 and Sky1 are both related in mediating the cyto-toxicity of the anticancer drug cisplatin (cis-Diaminodichloroplatinum) in yeasts.…”

Ixr1p and the control of the Saccharomyces cerevisiae hypoxic response

“…Rox1p and Mot3p repress the aerobic expression of HEM13 (Klinkenberg et al 2005), while Ixr1p is a positive regulator of HEM13 transcription in hypoxia (CastroPrego et al 2010a). Besides, a transcriptional cross-regulation between the genes ROX1 and IXR1 exists (Castro-Prego et al 2010b). In aerobiosis, low levels of IXR1 expression are maintained by Rox1p repression through the general co-repressor complex Tup1-Ssn6.…”