Stalling of RNA Polymerase II (RNAPII) on chromatin during transcriptional stress results in polyubiquitination and degradation of the largest subunit of RNAPII, Rpb1, by the ubiquitin proteasome ...system (UPS). Here, we report that the ATP-dependent chromatin remodeling complex INO80 is required for turnover of chromatin-bound RNAPII in yeast. INO80 interacts physically and functionally with Cdc48/p97/VCP, a component of UPS required for degradation of RNAPII. Cells lacking INO80 are defective in Rpb1 degradation and accumulate tightly bound ubiquitinated Rpb1 on chromatin. INO80 forms a ternary complex with RNAPII and Cdc48 and targets Rpb1 primed for degradation. The function of INO80 in RNAPII turnover is required for cell growth and survival during genotoxic stress. Our results identify INO80 as a bona fide component of the proteolytic pathway for RNAPII degradation and suggest that INO80 nucleosome remodeling activity promotes the dissociation of ubiquitinated Rpb1 from chromatin to protect the integrity of the genome.
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•INO80 interacts with the protein segregase Cdc48•INO80 physically associates with RNAPII in the context of the UPS•INO80 is required for degradation of RNAPII•INO80 promotes dissociation of ubiquitinated Rpb1 from chromatin
The INO80 ATP-dependent chromatin remodeling complex is implicated in transcription, DNA replication, and repair of DNA damage. Lafon et al. reveal that it also plays a role in maintaining genome integrity facilitating dissociation of ubiquitinated RNAPII from chromatin and promoting its degradation.
Chromatin-modifying enzymes and ATP-dependent remodeling complexes have been intensely studied individually, yet how these activities are coordinated to ensure essential cell functions such as ...transcription, replication, and repair of damage is not well understood. In this study, we show that the critical loss of Sas3 and Gcn5 acetyltransferases in yeast can be functionally rescued by inactivation of ISWI remodelers. This genetic interaction depends on the ATPase activities of Isw1 and Isw2, suggesting that it involves chromatin remodeling activities driven by the enzymes. Genetic dissection of the Isw1 complexes reveals that the antagonistic effects are mediated specifically by the Isw1a complex. Loss of Sas3 and Gcn5 correlates with defective RNA polymerase II (RNAPII) occupancy at actively transcribed genes, as well as a significant loss of H3K14 acetylation. Inactivation of the Isw1a complex in the acetyltransferase mutants restores RNAPII recruitment at active genes, indicating that transcriptional regulation may be the mechanism underlying suppression. Dosage studies and further genetic dissection reveal that the Isw1b complex may act in suppression through down-regulation of Isw1a. These studies highlight the importance of balanced chromatin modifying and remodeling activities for optimal transcription and cell growth.
We have carried out an in silico exploration of the genomes of
Aspergillus nidulans,
Aspergillus fumigatus, and
Aspergillus oryzae, and identified components of G-protein/cAMP-mediated signaling. ...Putative G-protein coupled receptors (GPCRs) were distributed over nine classes. The GPCRs within classes were well conserved among aspergilli but varied in other ascomycetes. As previously observed in
A. nidulans and other fungi, three Gα, one Gβ, and one Gγ subunits of G proteins were identified in
A. fumigatus, whereas an additional likely non-functional Gα subunit was present in
A. oryzae. While most fungal species had five proteins containing the regulator of G-protein signaling (RGS) domain predicted to participate in attenuation of G-protein signaling,
A. fumigatus and
A. oryzae had an additional RGS protein (RgsD) related to RgsA of
A. nidulans. Genes encoding adenylate cyclase, a regulatory subunit and two catalytic subunits of the cAMP-dependent protein kinase, were also identified in the three aspergilli. Finally, regulators of cAMP signaling including low- and high-affinity phosphodiesterases were identified. Taken together, our data indicate a striking diversity at the GPCR level, but little diversity of components at the G-protein and cAMP-signaling level. This may reflect the abilities of these fungi to adapt to various ecological niches and to integrate diverse environmental cues into highly conserved cellular processes.
CD44 is a transmembrane glycoprotein linked to various biological processes reliant on epigenetic plasticity, which include development, inflammation, immune responses, wound healing and cancer ...progression. Although it is often referred to as a cell surface marker, the functional regulatory roles of CD44 remain elusive. Here we report the discovery that CD44 mediates the endocytosis of iron-bound hyaluronates in tumorigenic cell lines, primary cancer cells and tumours. This glycan-mediated iron endocytosis mechanism is enhanced during epithelial-mesenchymal transitions, in which iron operates as a metal catalyst to demethylate repressive histone marks that govern the expression of mesenchymal genes. CD44 itself is transcriptionally regulated by nuclear iron through a positive feedback loop, which is in contrast to the negative regulation of the transferrin receptor by excess iron. Finally, we show that epigenetic plasticity can be altered by interfering with iron homeostasis using small molecules. This study reveals an alternative iron-uptake mechanism that prevails in the mesenchymal state of cells, which illuminates a central role of iron as a rate-limiting regulator of epigenetic plasticity.
Histone modifications direct chromatin-templated events in the genome and regulate access to DNA sequence information. There are multiple types of modifications, and a common feature is their dynamic ...nature. An essential step for understanding their regulation, therefore, lies in characterizing the enzymes responsible for adding and removing histone modifications. Starting with a dosage-suppressor screen in Saccharomyces cerevisiae, we have discovered a functional interaction between the acetyltransferase Gcn5 and the protein phosphatase 2A (PP2A) complex, two factors that regulate post-translational modifications. We find that RTS1, one of two genes encoding PP2A regulatory subunits, is a robust and specific high-copy suppressor of temperature sensitivity of gcn5∆ and a subset of other gcn5∆ phenotypes. Conversely, loss of both PP2A(Rts1) and Gcn5 function in the SAGA and SLIK/SALSA complexes is lethal. RTS1 does not restore global transcriptional defects in gcn5∆; however, histone gene expression is restored, suggesting that the mechanism of RTS1 rescue includes restoration of specific cell cycle transcripts. Pointing to new mechanisms of acetylation-phosphorylation cross-talk, RTS1 high-copy rescue of gcn5∆ growth requires two residues of H2B that are phosphorylated in human cells. These data highlight the potential significance of dynamic phosphorylation and dephosphorylation of these deeply conserved histone residues for cell viability.
Cancer stem cells (CSCs) have been shown to be refractory to conventional therapeutic agents, can promote metastasis, and have been linked to cancer relapse. Salinomycin can selectively kill CSCs. We ...have shown that salinomycin derivatives accumulate in lysosomes and sequester iron in this organelle. As a result, accumulation of iron leads to the production of reactive oxygen species and lysosomal membrane permeabilization, which in turn promotes cell death by ferroptosis. These findings have revealed the prevalence of iron homeostasis in CSCs and paved the way toward the development of next-generation therapeutics.
Les cellules souches cancéreuses sont réfractaires aux chimiothérapies conventionnelles, peuvent produire des métastases et être à l'origine de récurrences. La salinomycine est capable de tuer sélectivement ce type de cellules. Nous avons montré que les dérivés de la salinomycine s'accumulent dans les lysosomes et y séquestrent le fer. L'accumulation de fer conduit à la production d'espèces réactives de l'oxygène et à la perméabilisation de la membrane lysosomale, qui provoque la mort par ferroptose. Ces découvertes ont révélé la prévalence de l'homéostasie du fer dans les cellules souches cancéreuses, ouvrant des opportunités pour le développement de nouvelles générations de drogues.
The role of heterotrimeric G-proteins in cAMP-dependent germination of conidia was investigated in the filamentous ascomycete Aspergillus nidulans. We demonstrate that the G alpha-subunit GanB ...mediates a rapid and transient activation of cAMP synthesis in response to glucose during the early period of germination. Moreover, deletion of individual G-protein subunits resulted in defective trehalose mobilization and altered germination kinetics, indicating that GanB(alpha)-SfaD(beta)-GpgA(gamma) constitutes a functional heterotrimer and controls cAMP/PKA signaling in response to glucose as well as conidial germination. Further genetic analyses suggest that GanB plays a primary role in cAMP/PKA signaling, whereas the SfaD-GpgA (G betagamma) heterodimer is crucial for proper activation of GanB signaling sensitized by glucose. In addition, the RGS protein RgsA is also involved in regulation of the cAMP/PKA pathway and germination via attenuation of GanB signaling. Genetic epistatic analyses led us to conclude that all controls exerted by GanB(alpha)-SfaD(beta)-GpgA(gamma) on conidial germination are mediated through the cAMP/PKA pathway. Furthermore, GanB may function in sensing various carbon sources and subsequent activation of downstream signaling for germination.
This collection of essays seeks to challenge the notion of the supremacy of the brain as the key organ of the Enlightenment, by focusing on the workings of the bowels and viscera that so obsessed ...writers and thinkers during the long eighteenth-century. These inner organs and the digestive process acted as counterpoints to politeness and other modes of refined sociability, drawing attention to the deeper workings of the self. Moving beyond recent studies of luxury and conspicuous consumption, where dysfunctional bowels have been represented as a symptom of excess, this book seeks to explore other manifestations of the visceral and to explain how the bowels played a crucial part in eighteenth-century emotions and perceptions of the self. The collection offers an interdisciplinary and cross-cultural perspective on entrails and digestion by addressing urban history, visual studies, literature, medical history, religious history, and material culture in England, France, and Germany.
We have carried out an in silico exploration of the genomes of Aspergillus nidulans, Aspergillus fumigatus, and Aspergillus oryzae, and identified components of G-protein/cAMP-mediated signaling. ...Putative G-protein coupled receptors (GPCRs) were distributed over nine classes. The GPCRs within classes were well conserved among aspergilli but varied in other ascomycetes. As previously observed in A. nidulans and other fungi, three G alpha, one G beta, and one G gamma subunits of G proteins were identified in A. fumigatus, whereas an additional likely non-functional G alpha subunit was present in A. oryzae. While most fungal species had five proteins containing the regulator of G-protein signaling (RGS) domain predicted to participate in attenuation of G-protein signaling, A. fumigatus and A. oryzae had an additional RGS protein (RgsD) related to RgsA of A. nidulans. Genes encoding adenylate cyclase, a regulatory subunit and two catalytic subunits of the cAMP-dependent protein kinase, were also identified in the three aspergilli. Finally, regulators of cAMP signaling including low- and high-affinity phosphodiesterases were identified. Taken together, our data indicate a striking diversity at the GPCR level, but little diversity of components at the G-protein and cAMP-signaling level. This may reflect the abilities of these fungi to adapt to various ecological niches and to integrate diverse environmental cues into highly conserved cellular processes.
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