RESUMEN
Response to arsenic stress in Saccharomyces cerevisiae is orchestrated by the regulatory protein Yap8, which mediates transcriptional activation of ACR2 and ACR3. This study contributes to the state of art knowledge of the molecular mechanisms underlying yeast stress response to arsenate as it provides the genetic and biochemical evidences that Yap8, through cysteine residues 132, 137, and 274, is the sensor of presence of arsenate in the cytosol. Moreover, it is here reported for the first time the essential role of the Mediator complex in the transcriptional activation of ACR2 by Yap8. Based on our data, we propose an order-of-function map to recapitulate the sequence of events taking place in cells injured with arsenate. Modification of the sulfhydryl state of these cysteines converts Yap8 in its activated form, triggering the recruitment of the Mediator complex to the ACR2/ACR3 promoter, through the interaction with the tail subunit Med2. The Mediator complex then transfers the regulatory signals conveyed by Yap8 to the core transcriptional machinery, which culminates with TBP occupancy, ACR2 upregulation and cell adaptation to arsenate stress. Additional co-factors are required for the transcriptional activation of ACR2 by Yap8, particularly the nucleosome remodeling activity of SWI/SNF and SAGA complexes.
Asunto(s)
Arseniato Reductasas/genética , Arseniatos/toxicidad , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/metabolismo , Complejo Mediador/metabolismo , Complejos Multiproteicos/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Activación Transcripcional/genética , Arseniato Reductasas/metabolismo , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/química , Cisteína/metabolismo , Regiones Promotoras Genéticas , Unión Proteica , Subunidades de Proteína/metabolismo , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/genética , Estrés Fisiológico/efectos de los fármacosRESUMEN
Accumulation of iron (Fe) is often detected in the brains of people suffering from neurodegenerative diseases. High Fe concentrations have been consistently observed in Parkinson's, Alzheimer's, and Huntington's diseases; however, it is not clear whether this Fe contributes to the progression of these diseases. Other conditions, such as Friedreich's ataxia or neuroferritinopathy are associated with genetic factors that cause Fe misregulation. Consequently, excessive intracellular Fe increases oxidative stress, which leads to neuronal dysfunction and death. The characterization of the mechanisms involved in the misregulation of Fe in the brain is crucial to understand the pathology of the neurodegenerative disorders and develop new therapeutic strategies. Saccharomyces cerevisiae, as the best understood eukaryotic organism, has already begun to play a role in the neurological disorders; thus it could perhaps become a valuable tool also to study the metalloneurobiology.
Asunto(s)
Hierro/metabolismo , Enfermedades Neurodegenerativas/metabolismo , Encéfalo/metabolismo , Homeostasis , Humanos , Modelos Biológicos , Enfermedades Neurodegenerativas/patología , Estrés Oxidativo , Especies Reactivas de Oxígeno/metabolismo , Saccharomyces cerevisiae/metabolismoRESUMEN
The budding yeast Saccharomyces cerevisiae has developed several mechanisms to avoid either the drastic consequences of iron deprivation or the toxic effects of iron excess. In this work, we analysed the global gene expression changes occurring in yeast cells undergoing iron overload. Several genes directly or indirectly involved in iron homeostasis showed altered expression and the relevance of these changes are discussed. Microarray analyses were also performed to identify new targets of the iron responsive factor Yap5. Besides the iron vacuolar transporter CCC1, Yap5 also controls the expression of glutaredoxin GRX4, previously known to be involved in the regulation of Aft1 nuclear localization. Consistently, we show that in the absence of Yap5 Aft1 nuclear exclusion is slightly impaired. These studies provide further evidence that cells control iron homeostasis by using multiple pathways.