Nuclear Localization of Haa1, Which Is Linked to Its Phosphorylation Status, Mediates Lactic Acid Tolerance in Saccharomyces cerevisiae

Abstract

Improvement of the lactic acid resistance of the yeast Saccharomyces cerevisiae is important for the application of the yeast in industrial production of lactic acid from renewable resources. However, we still do not know the precise mechanisms of the lactic acid adaptation response in yeast and, consequently, lack effective approaches for improving its lactic acid tolerance. To enhance our understanding of the adaptation response, we screened for S. cerevisiae genes that confer enhanced lactic acid resistance when present in multiple copies and identified the transcriptional factor Haa1 as conferring resistance to toxic levels of lactic acid when overexpressed. The enhanced tolerance probably results from increased expression of its target genes. When cells that expressed Haa1 only from the endogenous promoter were exposed to lactic acid stress, the main subcellular localization of Haa1 changed from the cytoplasm to the nucleus within 5 min. This nuclear accumulation induced upregulation of the Haa1 target genes YGP1, GPG1, and SPI1, while the degree of Haa1 phosphorylation observed under lactic acid-free conditions decreased. Disruption of the exportin gene MSN5 led to accumulation of Haa1 in the nucleus even when no lactic acid was present. Since Msn5 was reported to interact with Haa1 and preferentially exports phosphorylated cargo proteins, our results suggest that regulation of the subcellular localization of Haa1, together with alteration of its phosphorylation status, mediates the adaptation to lactic acid stress in yeast.

Promotion of Cell Viability and Histone Gene Expression by the Acetyltransferase Gcn5 and the Protein Phosphatase PP2A in Saccharomyces cerevisiae

“…When testing the panel of highly expressed GCN5-regulated genes, we found significant changes in expression, particularly of GPG1 and PHM8 (117 and 68% increases in expression, respectively). Both GPG1 and PHM8 are upregulated by the transcription factor Haa1, which relocalizes to the nucleus upon weak acid stress and in conditions of DNA replication stress (Tkach et al 2012;Sugiyama et al 2014). Coincident with Haa1 nuclear accumulation is loss of phosphorylation (Sugiyama and Nikawa 2001), but the phosphatase has not yet been identified.…”

Yeast toxicogenomics: lessons from a eukaryotic cell model and cell factory

“…The presence of acetylated polymers in lignocellulosic biomass implies that the mechanisms of acetic acid tolerance will inevitably remain a key issue in the implementation and diversification of sustainable, non-food feedstocks in industrial biotechnology. While the global mechanisms of acetic acid action and tolerance in yeast cells have been mostly elucidated [38], other toxicogenomic analyses involving the yeast response to weak acids are essential to identify their molecular targets and guide the design of more robust strains for efficient industrial production of organic acids [39].…”

Improvement of yeast tolerance to acetic acid through Haa1 transcription factor engineering: towards the underlying mechanisms

“…Haa1 seems to be also an important determinant of the yeast’s tolerance to acetic acid stress, as the deletion of a significant number of genes of the Haa1-regulon was shown to result in increased susceptibility to acetic acid [7]. Moreover, several recent studies have shown that overexpression of HAA1 improves yeast’s tolerance to high concentrations of acetic and lactic acid [14–17]. Given that the deletion of the HAA1 gene was found to lead to a higher accumulation of labeled acetic acid in stressed cells [18], the role of Haa1 is, at least partially, related with its involvement in the reduction of the intracellular acetate concentration.…”

“…In response to inhibitory concentrations of lactic acid, Haa1 was found to rapidly migrate from the cytoplasm to the nucleus suggesting that the biological activity of the transcription factor is dependent on its subcellular localization [14]. The Haa1 translocation is accompanied by a decrease in the phosphorylation level of the protein indicating that the transcription factor is activated upon dephosphorylation [14].…”

“…The Haa1 translocation is accompanied by a decrease in the phosphorylation level of the protein indicating that the transcription factor is activated upon dephosphorylation [14]. The mediated export of Haa1 by the exportin Msn5, found to directly interact with Haa1 in a large-scale yeast two-hybrid screening [25], was confirmed in msn5 Δ cells harboring GFP-fused Haa1 [14].…”