Autoregulation of the HAC1 gene is required for sustained activation of the yeast unfolded protein response.
Eukaryotic cells respond to the accumulation of unfolded proteins in the endoplasmic reticulum (ER) by activating a transcriptional induction program termed the unfolded protein response (UPR). The transcription factor Hac1p responsible for the UPR in Saccharomyces cerevisiae is tightly regulated by a post-transcriptional mechanism. HAC1 mRNA must be spliced in response to ER stress to produce Hac1p, which then activates transcription via direct binding to the cis-acting UPR element (UPRE) present in the promoter regions of its target genes. Here, we show that the HAC1 promoter itself responds to ER stress to induce transcription of its downstream gene, similarly to the KAR2 promoter; the KAR2 gene represents a major target of the UPR. Consistent with this observation, the HAC1 promoter contains an UPRE-like sequence, which is necessary and sufficient for the induction and to which Hac1p binds directly. Cells expressing the HAC1 gene from a mutant HAC1 promoter lacking the HAC1 UPRE could not maintain high levels of either unspliced or spliced HAC1 mRNA and became sensitive to ER stress when insulted for hours. Based on these results, we concluded that autoregulation of the HAC1 genes is required for sustained activation of the UPR and sustained resistance to ER stress.
Ogawa
Naoki
N
HSP Research Institute, Kyoto 600-8813, Japan.
Mori
Kazutoshi
K
D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D045304:Cytochromes c / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000235:genetics*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis / Q000235:genetics; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D017510:Protein Folding; D012326:RNA Splicing / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D020218:Response Elements; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D050976:Basic-Leucine Zipper Transcription Factors; C014059:CYC1 protein, S cerevisiae; D005656:Fungal Proteins; C091341:HAC1 protein, S cerevisiae; D018840:HSP70 Heat-Shock Proteins; C060153:KAR2 protein, yeast; D018832:Molecular Chaperones; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D045304:Cytochromes c