Association of HSP72 with the nuclear (TX-100-insoluble) fraction upon heating tolerant and non-tolerant HeLa S3 cells

ATR-FTIR spectrum analysis of plasma samples for rapid identification of recovered COVID-19 individuals

The development of fast, cheap and reliable methods to determine seroconversion against infectious agents is of great practical importance. In the context of the COVID-19 pandemic, an important issue is to study the rate of formation of the immune layer in the population of different regions, as well as the study of the formation of post-vaccination immunity in individuals after vaccination. Currently, the main method for this kind of research is enzyme immunoassay (ELISA, enzyme-linked immunosorbent assay). This technique is sufficiently sensitive and specific, but it requires significant time and material costs. We investigated the applicability of attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy associated with machine learning in blood plasma to detect seroconversion against SARS-CoV-2. The study included samples of 60 patients. Clear spectral differences in plasma samples from recovered COVID-19 patients and conditionally healthy donors were identified using multivariate and statistical analysis. The results showed that ATR-FTIR spectroscopy, combined with principal components analysis (PCA) and linear discriminant analysis (LDA) or artificial neural network (ANN), made it possible to efficiently identify specimens from recovered COVID-19 patients. We built classification models based on PCA associated with LDA and ANN. Our analysis led to 87% accuracy for PCA-LDA model and 91% accuracy for ANN, respectively. Based on this proof-of-concept study, we believe this method could offer a simple, label-free, cost-effective tool for detecting seroconversion against SARS-CoV-2. This approach could be used as an alternative to ELISA.

Distinct β-sheet structure in protein aggregates determined by ATR-FTIR spectroscopy

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the conformation of aggregated proteins in vivo and in vitro. Several different protein aggregates, including amyloid fibrils from several peptides and polypeptides, inclusion bodies, folding aggregates, soluble oligomers, and protein extracts from stressed cells, were examined in this study. All protein aggregates demonstrate a characteristic new β structure with lower-frequency band positions. All protein aggregates acquire this new β band following the aggregation process involving intermolecular interactions. The β sheets in some proteins arise from regions of the polypeptide that are helical or non β in the native conformation. For a given protein, all types of the aggregates (e.g., inclusion bodies, folding aggregates, and thermal aggregates) showed similar spectra, indicating that they arose from a common partially folded species. All of the aggregates have some nativelike secondary structure and nonperiodic structure as well as the specific new β structure. The new β could be most likely attributed to stronger hydrogen bonds in the intermolecular β-sheet structure present in the protein aggregates.

Hsp70 architecture: the formation of novel polymeric structures of Hsp70.1 and Hsc70 after proteotoxic stress

Heat induces Hsp70.1 (HSPA1) and Hsc70 (HSPA8) to form complex detergent insoluble cytoplasmic and nuclear structures that are distinct from the cytoskeleton and internal cell membranes. These novel structures have not been observed by earlier immunofluorescence studies as they are obscured by the abundance of soluble Hsp70.1/Hsc70 present in cells. While resistant to detergents, these Hsp70 structures display complex intracellular dynamics and are efficiently disaggregated by ATP, indicating that this pool of Hsp70.1/Hsc70 retains native function and regulation. Hsp70.1 promotes the repair of proteotoxic damage and cell survival after stress. In heated fibroblasts expressing Hsp70.1, Hsp70.1 and Hsc70 complexes are efficiently disaggregated before the cells undergo-heat induced apoptosis. In the absence of Hsp70.1, fibroblasts have increased rates of heat-induced apoptosis and maintain stable insoluble Hsc70 structures. The differences in the intracellular distribution of Hsp70.1 and Hsc70, combined with the ability of Hsp70.1, but not Hsc70, to promote the disaggregation of insoluble Hsp70.1/Hsc70 complexes, indicate that these two closely related proteins perform distinctly different cellular functions in heated cells.

Intracellular redistribution and modification of proteins of the Mre11/Rad50/Nbs1 DNA repair complex following irradiation and heat-shock

Mre11, Rad50, and Nbs1form a tight complex which is homogeneously distributed throughout the nuclei of mammalian cells. However, after irradiation, the Mre11/Rad50/Nbs1 (M/R/N) complex rapidly migrates to sites of double strand breaks (DSBs), forming foci which remain until DSB repair is complete. Mre11 and Rad50 play direct roles in DSB repair, while Nbs1 appears to be involved in damage signaling. Hyperthermia sensitizes mammalian cells to ionizing radiation. Radiosensitization by heat shock is believed to be mediated by an inhibition of DSB repair. While the mechanism of inhibition of repair by heat shock remains to be elucidated, recent reports suggest that the M/R/N complex may be a target for inhibition of DSB repair and radiosensitization by heat. We now demonstrate that when human U-1 melanoma cells are heated at 42.5 or 45.5 degrees C, Mre11, Rad50, and Nbs1 are rapidly translocated from the nucleus to the cytoplasm. Interestingly, when cells were exposed to ionizing radiation (12 Gy of X-rays) prior to heat treatment, the extent and kinetics of translocation were increased when nuclear and cytoplasmic fractions of protein were analyzed immediately after treatment. The kinetics of the translocation and subsequent relocalization back into the nucleus when cells were incubated at 37 degrees C from 30 min to 7 h following treatment were different for each protein, which suggests that the proteins redistribute independently. However, a significant fraction of the translocated proteins exist as a triple complex in the cytoplasm. Treatment with leptomycin B (LMB) inhibits the translocation of Mre11, Rad50, and Nbs1 to the cytoplasm, leading us to speculate that the relocalization of the proteins to the cytoplasm occurs via CRM1-mediated nuclear export. In addition, while Nbs1 is rapidly phosphorylated in the nuclei of irradiated cells and is critical for a normal DNA damage response, we have found that Nbs1 is rapidly phosphorylated in the cytoplasm, but not in the nucleus, of heated irradiated cells. The phosphorylation of cytoplasmic Nbs1, which cannot be inhibited by wortmannin, appears to be a unique post-translational modification in heated, irradiated cells, and coupled with our novel observations that Mre11, Rad50, and Nbs1 translocate to the cytoplasm, lend further support for a role of the M/R/N complex in thermal radiosensitization and inhibition of DSB repair.

The non-homologous end-joining pathway is not involved in the radiosensitization of mammalian cells by heat shock

A synergistic increase in cell killing is observed when a heat-shock is administered prior to, during, or immediately after exposure to ionizing radiation (IR). This phenomenon, known as heat-radiosensitization, is believed to be mediated by inhibition of repair of radiation-induced double strand breaks (DSB) when cells are exposed to temperatures above 42 degrees C. However, the mechanism by which heat inhibits DSB repair is unclear. The bulk of radiation-induced DSBs are repaired via the non-homologous end-joining pathway (NHEJ). Several reports indicate that the Ku70 and Ku80 subunits of the mammalian DNA-dependent protein kinase (DNA-PK), a complex involved in NHEJ, appear to be susceptible to a heat-induced loss of DNA-binding activity, with Ku80 representing the heat-sensitive component. Since the heat-induced loss and subsequent recovery of Ku-DNA binding activity correlates well with heat-radiosensitization, a role for Ku80 and NHEJ in heat-radiosensitization has been proposed. However, direct evidence implicating Ku80 (and NHEJ) in heat-radiosensitization has been indeterminate. In this study, we demonstrate that equitoxic heat treatments at 42.5-45.5 degrees C induce a similar amount of aggregation of Ku80 in human U-1 melanoma cells. These data suggest that the time-temperature-dependent relationship between heat lethality and Ku80 aggregation are similar. However, the aggregation/disaggregation of Ku80 and its transient or permanent inactivation is unrelated to heat-radiosensitization. When survival curves were obtained for irradiated or irradiated and heated Ku80(-/-) mouse embryo fibroblasts (MEFs) and compared with survival curves obtained for wild-type (WT) cells, we found that heat-radiosensitization was not reduced in the Ku80(-/-) cells, but actually increased. Thus, our findings indicate that Ku80 is not essential for heat-radiosensitization. Non-involvement of Ku-dependent or Ku-independent NHEJ pathways in heat-radiosensitization was confirmed by comparing clonogenic survival between DNA ligase IV-defective and WT human cells. Our data therefore implicate homologous recombination in inhibition of repair of radiation-induced DSBs and as a target for heat-radiosensitization.

Translocation of MRE11 from the nucleus to the cytoplasm as a mechanism of radiosensitization by heat

Zhu, W-G., Seno, J. D., Beck, B. D. and Dynlacht, J. R. Translocation of MRE11 from the Nucleus to the Cytoplasm as a Mechanism of Radiosensitization by Heat. Radiat. Res. 156, 95-102 (2001).Hyperthermia sensitizes mammalian cells to ionizing radiation, presumably by inhibiting the repair of radiation-induced double-strand breaks (DSBs). However, the mechanism by which heat inhibits DSB repair is unclear. The nuclear protein MRE11 is a component of a multi-protein complex involved in nonhomologous end joining (NHEJ) of radiation-induced DSBs. Using one-dimensional sodium dodecylsulfate polyacrylamide gel electrophoresis and Western blotting, we found that MRE11 is translocated from the nucleus to the cytoplasm when human U-1 melanoma or HeLa cells are heated for 15 min at 45.5 degrees C or when cells are heated after irradiation with 12 Gy of X rays. No such translocation is observed in unheated irradiated cells. The kinetics of migration of MRE11 to the cytoplasm was dependent upon whether the heated cells were irradiated, while the magnitude of redistribution of MRE11 was dependent upon post-treatment incubation time at 37 degrees C. Cytoplasmic MRE11 content reached a maximum 2-4 h after heating; the increase was not due to new protein synthesis. Partial recovery of nuclear MRE11 content was observed when heated cells or heated irradiated cells were incubated for up to 7 h at 37 degrees C after treatment. Western blotting results showing translocation of MRE11 from the nucleus to the cytoplasm after heating and irradiation were confirmed using confocal microscopy and immunofluorescence staining of fixed cells. Our data suggest that radiosensitization by heat may be caused, at least in part, by translocation of the DNA repair protein MRE11 from the nucleus to the cytoplasm.

Disruption of LT-antigen/p53 complex by heat treatment correlates with inhibition of DNA synthesis during transforming infection with SV40

Transforming infection of Go/G1-arrested primary mouse kidney cell cultures with simian virus 40 (SV40) induces cells to re-enter the S-phase of the cell cycle. In Go-arrested cells, no p53 is detected, whereas in cells induced to proliferate by infection, a gradual accumulation of p53 complexed to SV40 large T-antigen is observed in the nucleus. Heat treatment of actively proliferating SV40-infected cells leads to inhibition of DNA synthesis and growth arrest. To determine the fate of p53 after heat treatment, proliferating infected cells were exposed to mild heat (42.5°C) for increasing lengths of time. The results presented here show that after ninety minutes of treatment, the arrest of DNA synthesis by heat correlates with the disruption of the p53/LT-antigen complex. Longer treatments induce, in addition, a reduction in the solubility of p53, which was recovered tightly associated with the nuclear fraction. This contrasted with large T-antigen, whose solubility remained unaffected by heat treatment. Although the total amount of p53 in the nucleus remained constant, as shown by immunoblot analyses, p53 was no longer detectable after immunoprecipitation or by immunofluorescent staining techniques. These results suggest that heat treatment had either induced conformational changes in its antigenic sites, or had sequestered the sites through aggregation or binding to insoluble nuclear components.Key words: p53, heat shock, LT-antigen/p53 complex, S-phase.

Lamin B is a prompt heat shock protein

The cellular response to hyperthermia involves the increased synthesis of heat shock proteins (HSPs) within several hours after treatment. In addition, a subset of proteins has been shown to be increased immediately after heating. These "prompt" HSPs are predominantly found in the nuclear matrix-intermediate filament fraction and are not present or detectable in unheated cells. Since the nuclear matrix has been suggested to be a target for heat-induced cell killing, prompt HSPs may play a prominent role in the heat shock response. Using Western blotting and flow cytometry, we found that an increase in the synthesis of lamin B, one of the major proteins of the nuclear lamina, is induced during heating at 45.5 degrees C but not during heating at 42 degrees C. Since it is an abundant protein which is constitutively expressed in mammalian cells, lamin B appears to be a unique member of the prompt HSP family. The kinetics of induction of lamin B during 45.5 degrees C heating did not correlate with the dose-dependent reduction in cell survival. While increased levels of lamin B during 45.5 degrees C heating do not appear to confer a survival advantage directly, a possible role for lamin B in cellular recovery after heat shock cannot be discounted.

Heat shock causes protein aggregation and reduced protein solubility at the centrosome and other cytoplasmic locations

Heat shock markedly inhibited centrosome staining by antisera raised against the two centrosome-specific proteins, pericentrin and gamma tubulin. The inhibition of anti-pericentrin binding was measured by fluorescence imaging. Heat had the greatest effect on intact cells, followed in sensitivity by centrosomes attached to their companion nucleus, with purified centrosomes being least sensitive. The centrosomal content of pericentrin was measured by immunoprecipitation followed by western blotting. Heat caused the amount of pericentrin in the centrosomal fraction to increase, suggesting that pericentrin did not leave the centrosome during heat shock. Furthermore, the pericentrin of the centrosomal fraction became less soluble after heat shock, and could only be solubilized by the most denaturing condition of boiling in 0.1% SDS. Immunoelectron microscopy revealed a heat-induced increase in the electron-dense material comprising the pericentriolar material (PCM), consistent with protein aggregation. Lastly, in heated cells immunoelectron microscopy demonstrated an increase in the binding of heat shock protein 70 (HSP70) to numerous locations throughout the cytoplasm. These data suggest that heat shock reduces the solubility of centrosomal and other cytoplasmic proteins, most likely through protein aggregation.

Heat shock proteins HSP25, HSP60, HSP72, HSP73 in isoosmotic cortex and hyperosmotic medulla of rat kidney

The distribution of heat shock proteins (HSP) HSP60, HSP73, HSP72 and HSP25 in the isoosmotic cortex and the hyperosmotic medulla of the rat kidney was investigated using Western blot analysis and immunohistochemistry. HSP73 was homogeneously distributed throughout the whole kidney. The level of HSP60 was high in the renal cortex and low in the medulla. HSP25 and HSP72 were present in large amounts in the medulla. Only low levels of HSP25 and almost undetectable amounts of HSP72 were found in the cortex. HSP25 exists in one nonphosphorylated and several phosphorylated isoforms. Western blot analysis preceded by isoelectric focussing showed that HSP25 predominates in its nonphosphorylated form in the outer medulla but in its phosphorylated form in cortex and inner medulla. Although this intrarenal distribution pattern was not changed during prolonged anaesthesia (thiobutabarbital sodium), a shift from the nonphosphorylated to the phosphorylated isoforms of HSP25 occurred in the medulla. The characteristic intrarenal distribution of the constitutively expressed HSPs (HSP73, HSP60, HSP25) may reflect different states of metabolic activity in the isoosmotic (cortex) and hyperosmotic (medulla) zones of the kidney. The high content of inducible HSP72 in the medulla most likely is a consequence of the osmotic stress imposed upon the cells by the high urea and salt concentrations in the hyperosmotic medullary environment.

A stress-inducible 72-kDa heat-shock protein (HSP72) is expressed on the surface of human tumor cells, but not on normal cells

It is suggested that members of the heat-shock protein (HSP) 70 and 90 families are involved in intracellular antigen processing and the presentation of cell-membrane-anchored antigens. We show that non-lethal heat shock (41.8 degrees C) causes comparable rates of HSP72 (about 20x) and HSP73 (about 3x) synthesis in both tumor (including human Ewing's sarcoma, ES and osteosarcoma cells, HOS58) and normal cells (including EBV-transformed B-LCL, PBL and fibroblasts derived from healthy human volunteers). However, following non-lethal heat stress and a recovery period at 37 degrees C, flow cytometric analysis with a specific MAb showed HSP72 to be expressed only on the cell surface of tumor cells. The cell-surface localization of HSP72 was confirmed by Western-blot analysis of separated membranes and by immunoprecipitation with the HSP72-specific MAb. In addition, co-incubation of untreated tumor cells with supernatants from lethally heat-shocked cells, which contain HSP72, did not lead to HSP72 cell-surface expression. Thus, non-specific association of HSP72 molecules with the outer plasma membrane is unlikely. In conclusion, despite comparable cytoplasmic HSP72 induction, human tumor cells differ from normal cells in their capacity to express HSP72 on their surface. This might imply clinical application as a means to target a stress-inducible, tumor-specific immune response.

Integrity of intermediate filaments is associated with the development of acquired thermotolerance in 9L rat brain tumor cells

Withangulatin A (WA), a newly discovered withanolide isolated from an antitumor Chinese herb, has been shown to be a vimentin intermediate filament-targeting drug by using immunofluorescence microscopy. Together with cytochalasin D and colchicine, these drugs were employed to investigate the importance of vimentin intermediate filaments, actin filaments, and microtubules in the development of acquired thermotolerance in 9L rat brain tumor cells treated at 45 degrees C for 15 min (priming heat-shock). Acquired thermotolerance was abrogated in cells incubated with WA before the priming heat-shock but it could be detected in cells treated with WA after the priming heat-shock. In contrast, cytochalasin D and colchicine do not interfere with the development of thermotolerance at all. The intracellular localizations of vimentin and the constitutive heat-shock protein70 (HSC70) in treated cells were examined by using immunofluorescence microscopy and detergent-extractability studies. In cells treated with WA before the priming heat-shock, vimentin IFs were tightly aggregated around the nucleus and unable to return to their normal organization after a recovery under normal growing conditions. In contrast, the IF network in cells treated with WA after the priming heat-shock was able to reorganize into filamentous form after a recovery period, a behavior similar to that of the cells treated with heat-shock only. HSC70 was found to be co-localized with vimentin during these changes. It is suggested that the integrity of intermediate filaments is important for the development of thermotolerance and that HSC70 may be involved in this process by stabilizing the intermediate filaments through direct or indirect binding.

On the role of hsp72 in heat-induced intranuclear protein aggregation

Heat treatment of cells results in an increased protein content of nuclei and nuclear matrices when isolated after the heat treatment. This increase of TX-100 insoluble protein is interpreted as being the result of protein denaturation and subsequent aggregation. After the heat treatment cells can (partly) recover from these aggregates. Recent data suggest that heat shock proteins (hsps) might be involved in the recovery (disaggregation) from these heat-induced insoluble protein complexes. In this report, the role of hsp72 in the process of aggregation and disaggregation was investigated using: non-tolerant rat-1 cells, thermotolerant rat-1 cells (rat-1 TT), and transfected rat-1 cells constitutively expressing the human inducible hsp72 gene (HR-24 cells). After heating the various cells, it was observed that the expression of the human hsp72 confers heat resistance (43-45 degrees C). Heat-induced intranuclear protein aggregation was less in HR and rat-1 TT cells as compared to nontolerant rat-1 cells. After heat treatments leading to the same initial intranuclear protein aggregation, rat-1 TT cells recovered more rapidly from these aggregates, while HR cells recovered at the same rate as nontolerant rat-1 cells. Our data suggest that increased levels of hsp72 can confer heat resistance at the level of initial (nuclear) heat damage. Elevated levels of hsp72 alone, however, do not enable cells to recover more rapidly from heat-induced intranuclear protein aggregates.