Project description:How heat shock induces the heat shock response (HSR) - a gene expression program encoding chaperones and other protein homeostasis (proteostasis) factors - remains an unresolved question in eukaryotic cell biology. Here we show that subcellular localization of the conserved J-protein Sis1 is a key regulator of the HSR in yeast. Under nonstress conditions, nucleoplasmic Sis1 promotes interaction between the chaperone Hsp70 and the transcription factor Hsf1 to repress the HSR. Heat shock triggers Sis1 to localize to the periphery of the nucleolus and to condense on the ER surface. Sis1 recruits the proteasome to this spatial network along with disaggregases and the ribosome quality control complex. Through localization dynamics, Sis1 relays the condition of the proteome to Hsf1. We conclude that the activation state of the HSR is determined by the spatial organization of the proteostasis network.
Project description:How heat shock inducesthe heat shock response (HSR) – a gene expression program encoding chaperones and other protein homeostasis (proteostasis) factors –remains an unresolved question in eukaryotic cell biology. Here we show that subcellular localization of the conserved J-protein Sis1 is a key regulator of the HSRin yeast. Under nonstress conditions, nucleoplasmic Sis1 promotes interaction between the chaperone Hsp70 and the transcription factor Hsf1to repress the HSR. Heat shock triggers Sis1 to localize to the nucleolar periphery and condense on the ER surface with the ribosome quality control complex. Sis1 recruits the proteasome to this spatial network.Through localization dynamics, Sis1 relaysthe condition of the proteome to Hsf1.Thus, the activation state of the HSR is built into spatial organization of the proteostasis network.
Project description:Cells adapt to conditions that compromise protein conformational stability by activating various stress response pathways, but the mechanisms used in sensing misfolded proteins remain unclear. Moreover, aggregates of disease proteins often fail to induce a productive stress response. Here, using a yeast model of polyQ protein aggregation, we identified Sis1, an essential Hsp40 co-chaperone of Hsp70, as a critical sensor of proteotoxic stress. At elevated levels, Sis1 prevented the formation of dense polyQ inclusions and directed soluble polyQ oligomers towards the formation of permeable condensates. Hsp70 accumulated in a liquid-like state within this polyQ meshwork, resulting in a potent activation of the HSF1 dependent stress response. Sis1, and the homologous DnaJB6 in mammalian cells, also regulated the magnitude of the cellular heat stress response, suggesting a general role in sensing protein misfolding. Sis1/DnaJB6 functions as a limiting regulator to enable a dynamic stress response and avoid hypersensitivity to environmental changes.
Project description:Ribosome biogenesis is among the most resource-intensive cellular processes, with ribosomal proteins accounting for up to half of all newly synthesized proteins in eukaryotic cells. During stress, cells shut down ribosome biogenesis in part by halting rRNA synthesis, potentially leading to massive accumulation of aggregation-prone “orphan” ribosomal proteins (oRPs). Here we show that during heat shock in yeast and human cells, oRPs accumulate as reversible condensates at the nucleolar periphery recognized by the Hsp70 co-chaperone Sis1/DnaJB6. oRP condensates are liquid-like in cell-free lysate but solidify upon depletion of Sis1 or inhibition of Hsp70. When cells recover from heat shock, oRP condensates disperse in a Sis1-dependent manner, and their ribosomal protein constituents are incorporated into functional ribosomes in the cytosol, enabling cells to efficiently resume growth.
Project description:Neurovascular dysfunction in penis is a fundamental reason of erectile dysfunction. Diabetes mellitus is one of the major causes of erectile dysfunction and leads to a poor response to oral phosphodiesterase-5 inhibitors. Heat shock protein 70 (Hsp70), a ubiquitous molecular chaperone exist in all living organisms, is known to play a role in cell survival and neuroprotection. Here, we report an effectiveness of Hsp70 in mediating neurovascular regeneration in diabetic conditions. Using Hsp70-Tg mice or Hsp70 protein administration, we demonstrate that overexpression of Hsp70 in diabetic mice restores erectile function through enhanced penile angiogenesis and neural regeneration. We found that cystathionine gamma-lyase (Cse) is a novel target of Hsp70-driven penile angiogenesis and neural regeneration. Hsp70-Cse triggered SDF1/HO-1/PI3K/Akt/eNOS/NF-κB p65 pathways involved in angiogenesis and neural regeneration. Coimmunoprecipitation and His-Tag pull down assay using mouse cavernous endothelial cells treated with Hsp70 showed the physical interaction between Hsp70 and Cse, and solid-phase binding assay revealed a high-affinity Hsp70-Cse binding with an apparent dissociation constant of 1.8 nmol/L. We provide a novel and solid evidence for Cse-dependent mechanism of Hsp70, which mediates Hsp70-induced neurovascular regeneration and the restoration of erectile function under diabetic conditions.
Project description:CRISPRi screens on the repression of 129 protein kinases and 161 transcription factors in S. cerevisiae. We quantify perturbation effects on cellular fitness at 23, 30 and 38°C, expression of the SSA1 Hsp70 chaperone (as proxy for heat shock response activity) and thermotolerance. The integration of these phenotypes allowed us to identify core signaling pathways of the HSR and their contributions to temperature-associated growth and heat resistance.
Project description:From biosynthesis to assembly into nucleosomes, histones are handed through a cascade of histone chaperones, which shield histones from non-specific interactions. Whether mechanisms exist to safeguard the histone fold during histone chaperone handover events or to release trapped intermediates is unclear. Using structure-guided and functional proteomics, we identify and characterize a histone chaperone function of DNAJC9, a heat shock co-chaperone that promotes HSP70-mediated catalysis. We elucidate the structure of DNAJC9, in a histone H3-H4 co-chaperone complex with MCM2, revealing how this dual histone and heat shock co-chaperone binds histone substrates. We show that DNAJC9 recruits HSP70-type enzymes via its J domain to fold histone H3-H4 substrates: upstream in the histone supply chain, during replication- and transcription-coupled nucleosome assembly, and to clean up spurious interactions. With its dual functionality, DNAJC9 integrates ATP-resourced protein folding into the histone supply pathway to resolve aberrant intermediates throughout the dynamic lives of histones.
Project description:Correct and efficient folding of nascent proteins to their native state requires support from the protein homeostasis network. We set to examine which newly translated proteins are less thermostable to infer which polypeptides require more time to fold. More specifically, we sought to determine which newly translated proteins are more susceptible to misfolding and aggregation under heat stress using pulse SILAC. These proteins were abundant, shorter, and highly ordered, with a potentially larger hydrophobic core as suggested by their higher hydrophobicity. Notably these proteins contain more β-sheets that typically require more time for folding and were enriched for Hsp70/Ssb and TRiC/CCT binding motifs, suggesting a higher demand for chaperone-assisted folding. These polypeptides were also more often components of stable protein complexes. All evidence combined suggests that a specific subset of newly translated proteins requires more time following synthesis to reach a thermostable native state in the cell.
Project description:BACKGROUND Antithrombotic medications target coagulation factors. Their use is associated with an increased bleeding risk. Safer drugs are needed. We described that the heat shock protein 70 (Hsp70) exhibits antithrombotic properties that do not influence bleeding. OBJECTIVES By using murine models, we want to test the hypothesis that overexpressing Hsp70 with CM-695, a dual inhibitor of HDAC6 and phosphodiesterase 9, protects against thrombosis while leaves bleeding tendency unaltered. METHODS CM-695 was used to induce Hsp70 overexpression. Hsp70 overexpressing mice were submitted to three thrombosis-triggering procedures. The ferric chloride carotid artery model was used to compare the antithrombotic role of CM-695 and rivaroxaban, a direct oral anticoagulant. The mouse tail transection model was used to compare the bleeding tendency upon CM-695 or rivaroxaban administration. RESULTS Intraperitoneal (i.p.) 20 mg/kg CM-695 increased Hsp70 expression markedly in the murine aortic tissue. This treatment delayed thrombosis in the collagen/epinephrine [P=0.04 (Log-Rank test), n=10], Rose Bengal/laser [median vessel occlusion time (OT): 58.6 vs. 39.0 minutes (min) in the control group (CG), P=0.008, n≥10] and ferric chloride (OT: 14.7 vs. 9.2 min in the CG, P=0.032, n≥10) models. I.p. 80 mg/kg CM-695 (n≥9) and intravenous 3 mg/kg rivaroxaban (n≥8) significantly delayed thrombosis. CM-695 did not induce bleeding [median bleeding time (BT): 8.5 vs. 7.5 min in the CG, n≥10]. However, this was dramatically increased by rivaroxaban (BT: 30.0 vs. 13.7 min in the CG, P=0.001, n=10). CONCLUSIONS CM-695 is a new antithrombotic drug devoid of bleeding risk that may be envisioned as a useful clinical tool.