Project description:Quiescence (G0) is a reversible non-dividing state that facilitates cellular survival in adverse conditions. Here we demonstrate that the function of the HIRA histone chaperone complex is required for viability during nitrogen-starvation induced quiescence in Schizosaccharomyces pombe. G0 cells lacking the HIRA protein, Hip1 exhibit elevated levels of antisense ncRNAs and an increase in unrepaired DNA double strand breaks. Nitrogen-starved hip1∆ cells retain metabolic activity but, in contrast to wild type, rapidly lose the ability to resume proliferation. After a short period in G0 (1 day), hip1∆ mutants are able to resume cell growth in response to the restoration of a nitrogen source, but do not efficiently induce Start-specific gene expression and re-enter the cell cycle. However, hip1∆ cells rapidly progress to an unresponsive state and by 4 days in G0, the majority no longer initiate growth following nitrogen source restoration. Analysis using a conditional hip1 allele is consistent with these findings and indicates that HIRA is required for efficient exit from quiescence and prevents a permanent cell cycle arrest.
Project description:Cellular senescence, a stable proliferation arrest caused by a range of cellular stresses, is a bona fide cause of cell and tissue aging. As well as proliferation arrest, cell senescence is associated with a potent pro-inflammatory phenotype, the senescence-associated secretory phenotype (SASP). Given that SASP is regulated at various levels, gaining a comprehensive understanding of its regulation is crucial. This understanding can pave the way for potential therapeutic approaches aimed at modulating SASP, which could promote healthy aging and alleviate the burden of senescence-associated diseases and degeneration. We show here that both the Promyelocytic Leukemia (PML) protein and HIRA histone chaperone are required for SASP expression in senescent cells. PML protein is the key organizer of PML nuclear bodies, nuclear features up to 1mM in diameter, containing many proteins and previously implicated in diverse cellular processes, including control of cell senescence and cellular intrinsic anti-viral immunity. HIRA is a histone chaperone best known for its ability to incorporate histone variant H3.3 into nuclear chromatin in a DNA replication-independent manner, including in non-proliferating senescent cells. HIRA localizes to PML nuclear bodies in senescent cells. We show that both HIRA and PML are required for activation of NF-kB and SASP. We found that HIRA regulates cytoplasmic NF-kB signaling in senescent cells through CCF-cGAS-STING-TBK1 pathway and interaction with autophagy cargo receptor Sequestosome-1 (p62/SQSTM1).
Project description:Cellular senescence is a stable proliferation arrest that suppresses tumorigenesis. Histone chaperone HIRA deposits nucleosome-destabilizing histone variant H3.3 into chromatin in a DNA replication-independent manner. Histone H3.3 and a subset of other typically M-bM-^@M-^\replication-dependentM-bM-^@M-^] core histones were expressed in non-proliferating senescent cells, the latter linked to alternative mRNA splicing and polyadenylation. Senescent cells incorporated newly-synthesized histones into chromatin, partially dependent on HIRA. HIRA and newly-deposited histone H3.3 co-localized at promoters of expressed genes, and their distribution shifted between proliferating and senescent cells, paralleling changes in gene expression. In senescent cells, gene promoters showed exceptional enrichment of a histone acetylation linked to open and dynamic chromatin, H4K16ac. Abundance of H4K16ac depended on HIRA. In the mouse, inactivation of HIRA downregulated H4K16ac and dramatically enhanced oncogene-induced hyperplasia. To conclude, HIRA controls a previously undefined dynamic non-canonical H4K16ac-decorated chromatin landscape in senescence, and also plays an unanticipated role in suppression of oncogene-induced neoplasia. Examination of HIRA protein binding alongside histone modification H4K16ac and H3.3 in proliferating and senescent IMR90 cells
Project description:The assembly of nucleosomes by histone chaperones is an important component of transcriptional regulation. Here we have assessed the global roles of the S. pombe HIRA histone chaperone complex. Microarray analysis indicates that inactivation of the HIRA complex results in increased expression of at least 4% of fission yeast genes. HIRA-regulated genes overlap with those which are normally repressed in vegetatively growing cells, such as targets of the Clr6 histone deacetylase and silenced genes located in subtelomeric regions. HIRA is also required for silencing of all 13 intact copies of the Tf2 long terminal repeat (LTR) retrotransposon. However, the role of HIRA is not restricted to bona fide promoters, because it also suppresses non-coding transcripts from solo LTR elements and spurious antisense transcripts from cryptic promoters associated with transcribed regions. Furthermore, the HIRA complex is essential in the absence of the quality control provided by nuclear exosome-mediated degradation of illegitimate transcripts. This suggests that HIRA restricts genomic accessibility, and, consistent with this, the chromosomes of cells lacking HIRA are more susceptible to genotoxic agents that cause double strand breaks. Thus the HIRA histone chaperone is required to maintain the protective functions of chromatin.
Project description:Cellular senescence is a stable proliferation arrest that suppresses tumorigenesis. Histone chaperone HIRA deposits nucleosome-destabilizing histone variant H3.3 into chromatin in a DNA replication-independent manner. Histone H3.3 and a subset of other typically “replication-dependent” core histones were expressed in non-proliferating senescent cells, the latter linked to alternative mRNA splicing and polyadenylation. Senescent cells incorporated newly-synthesized histones into chromatin, partially dependent on HIRA. HIRA and newly-deposited histone H3.3 co-localized at promoters of expressed genes, and their distribution shifted between proliferating and senescent cells, paralleling changes in gene expression. In senescent cells, gene promoters showed exceptional enrichment of a histone acetylation linked to open and dynamic chromatin, H4K16ac. Abundance of H4K16ac depended on HIRA. In the mouse, inactivation of HIRA downregulated H4K16ac and dramatically enhanced oncogene-induced hyperplasia. To conclude, HIRA controls a previously undefined dynamic non-canonical H4K16ac-decorated chromatin landscape in senescence, and also plays an unanticipated role in suppression of oncogene-induced neoplasia.
Project description:The HIRA chaperone complex, comprised of HIRA, UBN1 and CABIN1, collaborates with histone-binding protein ASF1a to incorporate histone variant H3.3 into chromatin in a DNA replication-independent manner. To better understand its function and mechanism, we integrated HIRA, UBN1, ASF1a and histone H3.3 ChIP-seq and gene expression analyses. Most HIRA-binding sites co-localize with UBN1, ASF1a and H3.3 at active promoters and active and weak/poised enhancers. At promoters, binding of HIRA/UBN1/ASF1a correlates with the level of gene expression. HIRA is required for deposition of histone H3.3 at its binding sites. There are marked differences in nucleosome and co-regulator composition at different classes of HIRA-bound regulatory site. Underscoring this, we report novel physical interactions between the HIRA complex and transcription factors, a chromatin insulator and an ATP-dependent chromatin-remodelling complex. Our results map the distribution of the HIRA chaperone across the chromatin landscape and point to different interacting partners at functionally distinct regulatory sites. Examination of 3 histone chaperone proteins in HeLa cells
Project description:Cells that have been pre-exposed to mild stress (priming stress) acquire transient resistance to subsequent severe stress even under different combinations of stresses. This phenomenon is called cross-tolerance. Although it has been reported that cross-tolerance occurs in many organisms, the molecular basis is not clear yet. Here, we identified slm9+ as a responsible gene for the cross-tolerance in the fission yeast Schizosaccharomyces pombe. Slm9 is a homolog of mammalian HIRA histone chaperone. HIRA forms a conserved complex and gene disruption of other HIRA complex components, Hip1, Hip3, and Hip4, also yielded a cross-tolerance-defective phenotype, indicating that the fission yeast HIRA is involved in the cross-tolerance as a complex. We also revealed that Slm9 was recruited to the stress-responsive gene loci upon stress treatment in an Atf1-dependent manner. The expression of stress-responsive genes under stress conditions was compromised in HIRA disruptants. Consistent with this, Pol II recruitment and nucleosome eviction at these gene loci were impaired in slm9D cells. Furthermore, we found that the priming stress enhanced the expression of stress-responsive genes in wild-type cells that were exposed to the severe stress. These observations suggest that HIRA functions in stress response through transcriptional regulation. To determine whether fission yeast HIRA specifically regulates stress-responsive genes under stress condition, we performed genome-wide analysis by using Affymetrix GeneChip oligonucleotide microarrays. Fission yeast cells (WT, slm9D, hip1D) were grown in quadruplicate at 32°C to the logarithmic phase and an aliquot was collected as the unstressed control. The other three aliquots were exposed to 40°C for 1 h, 25 mM H2O2 for 1 h, or 40°C for 1 h followed by 25 mM H2O2 for 1 h, respectively. Total RNA was purified and all the 12 RNA samples were analyzed with GeneChip Yeast Genome 2.0 Array (Affymetrix).
Project description:The HIRA chaperone complex, comprised of HIRA, UBN1 and CABIN1, collaborates with histone-binding protein ASF1a to incorporate histone variant H3.3 into chromatin in a DNA replication-independent manner. To better understand its function and mechanism, we integrated HIRA, UBN1, ASF1a and histone H3.3 ChIP-seq and gene expression analyses. Most HIRA-binding sites co-localize with UBN1, ASF1a and H3.3 at active promoters and active and weak/poised enhancers. At promoters, binding of HIRA/UBN1/ASF1a correlates with the level of gene expression. HIRA is required for deposition of histone H3.3 at its binding sites. There are marked differences in nucleosome and co-regulator composition at different classes of HIRA-bound regulatory site. Underscoring this, we report novel physical interactions between the HIRA complex and transcription factors, a chromatin insulator and an ATP-dependent chromatin-remodelling complex. Our results map the distribution of the HIRA chaperone across the chromatin landscape and point to different interacting partners at functionally distinct regulatory sites. We used microarrays to detail the global programme of gene expression after knockdown of HIRA HeLa cells were nucleofacted with Dharmacon control siRNA and siRNA to HIRA and RNA was isolated 72 hours after transfection in four biological replicates
Project description:Appropriate responses to environmental challenges are imperative for the survival of all living organisms. Exposure to low-dose stresses is recognized to yield increased cellular fitness, a phenomenon termed hormesis. However, our molecular understanding of how cells respond to low-dose stress remains profoundly limited. Here we report that histone variant H3.3-specific chaperone, HIRA, is required for acquired tolerance, where low-dose heat stress exposure confers resistance to subsequent lethal heat stress. We found that human HIRA activates stress-responsive genes, including HSP70, by depositing histone H3.3 following low-dose stresses. These genes are also marked with histone H3 Lys-4 trimethylation and H3 Lys-9 acetylation, both active chromatin markers. Moreover, depletion of HIRA greatly diminished acquired tolerance, both in normal diploid fibroblasts and in HeLa cells. Collectively, our study revealed that HIRA is required for eliciting adaptive stress responses under environmental fluctuations and is a master regulator of stress tolerance.
Project description:Cells that have been pre-exposed to mild stress (priming stress) acquire transient resistance to subsequent severe stress even under different combinations of stresses. This phenomenon is called cross-tolerance. Although it has been reported that cross-tolerance occurs in many organisms, the molecular basis is not clear yet. Here, we identified slm9+ as a responsible gene for the cross-tolerance in the fission yeast Schizosaccharomyces pombe. Slm9 is a homolog of mammalian HIRA histone chaperone. HIRA forms a conserved complex and gene disruption of other HIRA complex components, Hip1, Hip3, and Hip4, also yielded a cross-tolerance-defective phenotype, indicating that the fission yeast HIRA is involved in the cross-tolerance as a complex. We also revealed that Slm9 was recruited to the stress-responsive gene loci upon stress treatment in an Atf1-dependent manner. The expression of stress-responsive genes under stress conditions was compromised in HIRA disruptants. Consistent with this, Pol II recruitment and nucleosome eviction at these gene loci were impaired in slm9D cells. Furthermore, we found that the priming stress enhanced the expression of stress-responsive genes in wild-type cells that were exposed to the severe stress. These observations suggest that HIRA functions in stress response through transcriptional regulation. To determine whether fission yeast HIRA specifically regulates stress-responsive genes under stress condition, we performed genome-wide analysis by using Affymetrix GeneChip oligonucleotide microarrays.