Autoantigen Ku in the brain. Developmentally regulated expression and subcellular localization

A double-stranded DNA end-binding factor with high levels of expression in brain and testis of adult mice was identified as the Ku protein, earlier described as an autoantigen in connective tissue diseases and found to be essential for recombination of the immunoglobulin genes and DNA repair. High Ku levels were found in the cerebellum and pituitary gland, lower levels in the hippocampus, hypothalamus and white matter structures. Ku levels were much higher in embryonic rat brain than in the adult brain, suggesting a role of the Ku protein in brain development. In embryonic rat brain, Ku was associated with cell nuclei, but was predominantly located in the cytosol in the adult rat cerebellum and hippocampus. The abundant expression of Ku in the brain suggests the involvement of Ku autoantibodies in the pathogenesis of neuropsychiatric complications in connective tissue diseases.

Hypersensitivity of Ku80-deficient cell lines and mice to DNA damage: the effects of ionizing radiation on growth, survival, and development

We recently have shown that mice deficient for the 86-kDa component (Ku80) of the DNA-dependent protein kinase exhibit growth retardation and a profound deficiency in V(D)J (variable, diversity, and joining) recombination. These defects may be related to abnormalities in DNA metabolism that arise from the inability of Ku80 mutant cells to process DNA double-strand breaks. To further characterize the role of Ku80 in DNA double-strand break repair, we have generated embryonic stem cells and pre-B cells and examined their response to ionizing radiation. Ku80(-/-) embryonic stem cells are more sensitive than controls to gamma-irradiation, and pre-B cells derived from Ku80 mutant mice display enhanced spontaneous and gamma-ray-induced apoptosis. We then determined the effects of ionizing radiation on the survival, growth, and lymphocyte development in Ku80-deficient mice. Ku80(-/-) mice display a hypersensitivity to gamma-irradiation, characterized by loss of hair pigmentation, severe injury to the gastrointestinal tract, and enhanced mortality. Exposure of newborn Ku80(-/-) mice to sublethal doses of ionizing radiation enhances their growth retardation and results in the induction of T cell-specific differentiation. However, unlike severe combined immunodeficient mice, radiation-induced T cell development in Ku80(-/-) mice is not accompanied by extensive thymocyte proliferation. The response of Ku80-deficient cell lines and mice to DNA-damaging agents provides important insights into the role of Ku80 in growth regulation, lymphocyte development, and DNA repair.

Protein glycosylation in rat fibroblast cells expressing deletion variants of the human hsp70 gene

Elevated heat resistance is often associated with high cellular levels of hsp70. In the rat cell line, M21, increased heat resistance is associated with both the expression of an intact exogenous human hsp70 gene, and of an exogenous stress glycoprotein, GP62. In this study, we examined heat-stress induced alterations in protein glycosylation in two variant lines of M21 that contain specific deletions in the exogenous human hsp70 gene. The deletion mutant, MVH delta Sm, lacks the nucleolar localization sequence for human hsp70 gene, whereas the other mutant, MVH delta Bg, is characterized by deletion of the ATP binding domain in the human hsp70 gene. After heat induction, the MVH delta Sm mutants exhibited constitutive and heat-induced endogenous hsp70 mRNA levels, protein glycosylation, as well as hsp70 and GP62 protein levels comparable to those in the parent cell line, Rat-1. Cellular heat sensitivity of MVH delta Sm mutants was also similar to that of Rat-1 cells, although the mutant cells had a reduced capacity for thermotolerance development. On the other hand, MVH delta Bg mutants before thermotolerance induction, exhibited constitutive endogenous and human exogenous hsp70 mRNA levels similar to those in MVH delta Sm mutants. However, after thermotolerance induction, MVH delta Bg mutants showed lower levels of heat-induced endogenous hsp70 mRNA than MVH delta Sm mutants, an overall reduction in protein glycosylation, low hsp70 and GP62 levels, and increased heat sensitivity when compared to the parent Rat-1 cell line. Incorporation of D-[2-3H]mannose into oligosaccharide precursor pools and glycoproteins was consistent with protein glycosylation pattern for each cell line. Acute heat stress resulted in the selective glycosylation of the 'prompt' glycoprotein, P-SG64, in the two deletion mutants, similar to that in M21 cells expressing the intact human hsp70 gene. The data indicate that both protein glycosylation and hsp70 expression generally correlate with cellular heat resistance and thermotolerance expression. The presence of full or partially deleted copies of human hsp70 modulates thermotolerance and protein glycosylation in a complex manner that is not yet fully understood.

Ku80 gene expression is Sp1-dependent and sensitive to CpG methylation within a novel cis element

The Ku70/80 complex, known as Ku, constitutes the DNA end binding component of the DNA-dependent protein kinase (DNA-PK). We have characterized the promoter region of the mouse and human Ku80 genes to delineate transcriptional elements necessary for basal gene expression and proliferation-dependent regulation. Consensus Sp1 recognition elements were identified in both promoters, and were determined to be essential for basal expression. We further identified a near-perfect palindrome of 21 base pairs located immediately 5' to one Sp1 element. This sequence was present once within the mouse Ku80 promoter and seven times, in a head-to-tail tandem array, within the human Ku80 promoter. This sequence possessed homology with a methylation-sensitive promoter element, Enh2, present in the LTR of mouse intractisternal A-particles. Promoter deletion studies and expression analysis of in-vitro methylated reporter gene constructs provided strong evidence that, in vivo, this repeat sequence regulates Ku80 gene expression in cis, through a mechanism involving CpG methylation. Evidence is also presented, suggesting that Ku is directly involved in this regulatory process.

Ku70 is required for DNA repair but not for T cell antigen receptor gene recombination In vivo

Ku is a complex of two proteins, Ku70 and Ku80, and functions as a heterodimer to bind DNA double-strand breaks (DSB) and activate DNA-dependent protein kinase. The role of the Ku70 subunit in DNA DSB repair, hypersensitivity to ionizing radiation, and V(D)J recombination was examined in mice that lack Ku70 (Ku70(-/-)). Like Ku80(-/-) mice, Ku70(-/-) mice showed a profound deficiency in DNA DSB repair and were proportional dwarfs. Surprisingly, in contrast to Ku80(-/-) mice in which both T and B lymphocyte development were arrested at an early stage, lack of Ku70 was compatible with T cell receptor gene recombination and the development of mature CD4+CD8- and CD4-CD8+ T cells. Our data shows, for the first time, that Ku70 plays an essential role in DNA DSB repair, but is not required for TCR V(D)J recombination. These results suggest that distinct but overlapping repair pathways may mediate DNA DSB repair and V(D)J recombination.

Heat inactivation of Ku autoantigen: possible role in hyperthermic radiosensitization

Heat shock prior, during, or immediately after ionizing radiation synergistically increases cell killing, a phenomenon termed hyperthermic radiosensitization. Recently, we have shown a constitutive DNA-binding factor in rodent cells that is inactivated by heat shock to be identical to Ku autoantigen. Ku, consisting of an Mr 70,000 (Ku70) and an Mr 86,000 (Ku80) subunit, is a heterodimeric nuclear protein and is the DNA-binding regulatory component of the mammalian DNA-dependent protein kinase DNA-PK. Recent genetic and biochemical studies indicate the involvement of Ku and DNA-PK in DNA double-strand break repair and V(D)J recombination. On the basis of these findings, we propose that heat-induced loss of the DNA-binding activity of Ku may lead to hyperthermic radiosensitization. To test this hypothesis, we examined and compared the DNA-binding activity of Ku, the DNA-PK kinase activity, and hyperthermic radiosensitization in rodent cells immediately after heat shock and during post-heat shock recovery at 37 degrees C. Our results show that the heat-induced loss of Ku-DNA binding activity correlates well with an increased radiosensitivity of the heat-shocked cells, and furthermore, the loss of synergistic interaction between heat and radiation parallels the recovery of the DNA-binding activity of Ku. On the other hand, the heat-induced decrease of DNA-PK activity did not correlate with hyperthermic radiosensitization. Our data, for the first time, provide evidence for a role of Ku protein in modulating the cellular response to combined treatments of heat shock and ionizing radiation.

Protein glycosylation in a heat-resistant rat fibroblast cell model expressing human HSP70

Thermotolerance and heat resistance are frequently associated with elevated levels of heat shock proteins (HSPs). Elevated heat resistance is also found to be associated with the overexpression of high levels of HSP70, as seen in M21 cells, derived from the Rat-1 line. In the present study, we report that M21 cells also feature an increase in general protein glycosylation and specific expression of the stress glycoprotein, GP62, both of which correlate with cellular heat resistance. The expression of GP50, a major stress glycoprotein in cell lines such as CHO, however, did not correlate with cellular heat resistance in M21 cells. Protein glycosylation that occurs during acute heat stress ("prompt" glycosylation) was associated with the glycosylation of a major "prompt" stress glycoprotein, P-SG64 (M(r) of 64,000), that was identified by immunoblotting as a glycosylated form of calreticulin. The higher level of protein glycosylation in M21 cells correlated well with increased D-[2-3H]mannose incorporation into precursor pools of dolichyl phosphomannose and dolichyl pyrophosphoryl oligosaccharides and into glycoproteins. Thus, heat resistance in M21 cells is associated not only with expression of high levels of HSP70, but also with a concomitant increase in protein glycosylation. These data support the hypothesis that stress-induced protein glycosylation is a component of cellular stress response, either in association with HSPs or as an independent mechanism.

Cloning and characterization of rat Ku70: involvement of Ku autoantigen in the heat-shock response

To study the role of the Ku autoantigen in the heat-shock response, we have cloned the 70-kDa subunit (the DNA-binding component of Ku) from a rat cDNA library. The deduced amino acid sequence of rat Ku70 bears extensive homology with the human and murine counterpart (83 and 97% identity, respectively). Overexpression of Ku70 in rat fibroblasts results in the specific repression of hsp-70 upon heat shock. The inhibition of induction of hsp-70 was greatest in cells expressing the highest level of Ku70. Induction of other heat-shock proteins besides hsp-70 by hyperthermia appears normal, as does the activation of the heat-shock transcription factor, HSF-1. It is likely that other factors besides HSF-1 are involved in controlling heat-shock gene transcription. While the formation of the Ku70 and Ku80 complex is important for repair of DNA double-strand breaks our data suggest that the 70-kDa subunit of Ku plays a role in regulating hsp-70 expression.

Down-regulation of gadd153 by c-myc in rat fibroblasts and its effect on cell growth and radiation-induced apoptosis

Using differential display reverse transcription PCR (DDRT - PCR), we found that a 360 bp cDNA fragment was absent in several c-myc transfected rat fibroblasts: REC:myc, REC:myc + ras and rat1-myc. These cells also showed enhanced sensitivity to gamma ray-induced apoptosis. This cDNA fragment was present in the parental REC (Rat Embryo Cells) and rat1 cells, and in c-Ha-ras transfected REC (REC:ras), all of which were relatively resistant to gamma ray-induced apoptosis. The cDNA fragment was subsequently cloned and used as a probe to screen a rat1 cDNA library, and identified as one of the growth arrest and DNA damaging-inducible genes, gadd153. In addition to the down-regulation of rat gadd153 in all the c-myc transfectants, methyl methanesulfonate (MMS)-induced transcription of the gadd153 was attenuated. The rat1-myc cells, when successfully transfected with and stably expressing the rat gadd153, showed a significantly longer doubling time compared to the parental cells. However, overexpression of gadd153 in rat1-myc cells did not affect gamma ray-induced apoptosis. Thus, the suppression of gadd153 appears to be inversely correlated with that of myc, but not involved in the myc-dependent apoptotic pathway.

Requirement for Ku80 in growth and immunoglobulin V(D)J recombination

The DNA-dependent protein kinase (DNA-PK) is a mammalian serine/threonine kinase that is implicated in the repair of DNA double-strand breaks, DNA replication, transcription, and V(D)J recombination. To determine the role of the DNA-binding subunit of DNA-PK in vivo, we targeted Ku80 in mice. In mutant mice, T and B lymphocyte development is arrested at early progenitor stages and there is a profound deficiency in V(D)J rearrangement. Although Ku80-/- mice are viable and reproduce, they are 40-60% of the size of littermate controls. Consistent with this growth defect, fibroblasts derived from Ku80-/- embryos showed an early loss of proliferating cells, a prolonged doubling time, and intact cell-cycle checkpoints that prevented cells with damaged DNA from entering the cell-cycle. The unexpected growth phenotype suggests a new and important link between Ku80 and growth control.

Heat shock protein 70 suppresses astroglial-inducible nitric-oxide synthase expression by decreasing NFkappaB activation

In brain glial cells, expression of calcium independent nitric-oxide synthase (NOS-2) is induced following stimulation with bacterial endotoxin (lipopolysaccharide (LPS)) and/or pro-inflammatory cytokines. We have investigated the effects of heat shock (HS), which can reduce inflammatory responses in several cell types, on the induction of glial NOS-2 expression. Preincubation of cells for 20-60 min at 43 degrees C decreased subsequent levels of NOS-2 induction, with a maximal 80% reduction after 60 min of HS. Following HS, cells were refractory to NOS inducers for up to 4 h, after which time little or no suppression was observed. HS reduced cytosolic NOS-2 enzymatic activity (3-fold), steady state mRNA levels (2-3-fold), and gene promoter activity (by 50%). HS also reduced LPS-induced nuclear accumulation of transcription factor NFkappaB p65 subunit, suggesting perturbation of NFkappaB activation. A role for HS protein (HSP) 70 in NOS-2 suppression by HS is supported by the demonstration that 1) transfection with human HSP70 cDNA partially replicated HS effects; 2) antisense, but not sense, oligonucleotides directed against rat HSP70 partially blocked HS effects; and 3) rat fibroblasts stably expressing human HSP70 did not express NOS-2 in response to LPS plus cytokines. As with heat-shocked cells, HSP70-expressing cells also exhibited decreased NFkappaB p65 subunit nuclear accumulation. These results demonstrate that in glial cells, as well as other cell types, NOS-2 induction can be modulated by the HS response, mediated at least in part by HSP70 expression.

Modulation of thermal induction of hsp70 expression by Ku autoantigen or its individual subunits

Previously, we proposed a dual control mechanism for the regulation of the heat shock response in mammalian cells: a positive control mediated by the heat shock transcription factor HSF1 and a negative control mediated by the constitutive heat shock element-binding factor (CHBF). To study the physiological role of CHBF in the regulation of heat shock response, we purified CHBF to apparent homogeneity and showed it to be identical to the Ku autoantigen, a heterodimer consisting of 70-kDa (Ku-70) and 86-kDa (Ku-80) polypeptides. To study further the functional significance of Ku/CHBF in the cellular response to heat shock, we established rodent cell lines that stably and constitutively overexpressed one or both subunits of the human Ku protein, and examined the thermal induction of hsp70 and other heat shock proteins in these Ku-overexpressing ing cells. We show that expression of the human Ku-70 and Ku-80 subunits jointly or of the Ku-70 subunit alone specifically inhibits heat-induced hsp70 expression. Conversely, expression of human Ku-80 alone does not have this effect. Thermal induction of other heat shock proteins in all of the Ku-overexpressing cell lines appears not to be significantly affected, nor is the state of phosphorylation or the DNA-binding ability of HSF1 affected. These findings support a model in which hsp70 expression is controlled by a second regulatory factor in addition to the positive activation of HSF1. The Ku protein, specifically the Ku-70 subunit, is involved in the regulation of hsp70 gene expression.

Apoptosis in heat-induced cell killing: the protective role of hsp-70 and the sensitization effect of the c-myc gene

We studied heat-induced apoptosis and loss of clonogenicity in Rat-1 fibroblasts, thermotolerant Rat-1 (TT Rat-1), Rat-1 transfected with the human hsp-70 gene (M21) and Rat-1 transfected with the human c-myc proto-oncogene (Rat-1:myc). Relative to Rat-1, TT Rat-1 and M21 cells are heat-resistant, but Rat-1:myc cells are heat-sensitive, in terms of both apoptosis and clonogenic survival. The apoptotic fractions assayed 24 h after a heat treatment of 60 min at 44 degrees C, are about 20% for Rat-1, 7% for TT Rat-1, 10% for M21 and 70% for Rat-1:myc cells, respectively. Most of the apoptotic cells detach from substratum within 1 day of heat treatment and exhibit morphological changes, chromatin condensation and DNA fragmentation. The results of this study suggest that (1) apoptosis is an important mechanism of heat-induced cell killing in some cell lines, (2) apoptosis-mediated cell killing manifests rapidly (relative to clonogenic assay) after a heat treatment, and (3) overexpression of the human hsp-70 gene reduces, whereas expression of the human c-myc proto-oncogene enhances, heat-induced apoptosis. Lastly, the effects of the hsp-70 and c-myc genes on the thermosensitivity of cells are correlated with their modulation of apoptosis.

Thermotolerance and heat shock proteins: possible involvement of Ku autoantigen in regulating Hsp70 expression

Here we characterize and compare the phenomenon of thermotolerance and permanent heat resistance in mammalian cells. The biochemical and molecular mechanisms underlying the induction of thermotolerance, and the role that heat shock proteins play in its development and decay are discussed. Finally, we describe a novel constitutive HSE-binding factor (CHBF/Ku) that appears to be involved in the regulation of the heat shock response.

Heat shock proteins, thermotolerance, and their relevance to clinical hyperthermia

Mammalian cells, when exposed to a non-lethal heat shock, have the ability to acquire a transient resistance to subsequent exposures at elevated temperatures, a phenomenon termed thermotolerance. The mechanism(s) for the development of thermotolerance is not well understood, but earlier experimental evidence suggests that protein synthesis may play a role in its manifestation. On the molecular level, heat shock activates a specific set of genes, so-called heat shock genes, and results in the preferential synthesis of heat shock proteins. The heat shock response, specifically the regulation, expression and functions of heat shock proteins, has been extensively studied in the past decades and has attracted the attention of a wide spectrum of investigators ranging from molecular and cell biologists to radiation and hyperthermia oncologists. There is much data supporting the hypothesis that heat shock proteins play important roles in modulating cellular responses to heat shock, and are involved in the development of thermotolerance. This review summarizes some current knowledge on thermotolerance and the functions of heat shock proteins, especially hsp70. The relationship between thermotolerance development and hsp70 synthesis in tumours and in normal tissues is examined. The possibility of using hsp70 as an indicator for thermotolerance is discussed.

A constitutive heat shock element-binding factor is immunologically identical to the Ku autoantigen

Analysis of the heat shock element (HSE)-binding proteins in extracts of rodent cells, during heat shock and their post-heat shock recovery, indicates that the regulation of heat shock response involves a constitutive HSE-binding factor (CHBF), in addition to the heat-inducible heat shock factor HSF1. We purified the CHBF to apparent homogeneity from HeLa cells using column chromatographic techniques including an HSE oligonucleotide affinity column. The purified CHBF consists of two polypeptides with apparent molecular masses of 70 and 86 kDa. Immunoblot and gel mobility shift analysis verify that CHBF is identical or closely related to the Ku autoantigen. The DNA binding characteristics of CHBF to double-stranded or single-stranded DNA are similar to that of Ku autoantigen. In gel mobility shift analysis using purified CHBF and recombinant human HSF1, CHBF competes with HSF1 for the binding of DNA sequences containing HSEs in vitro. Furthermore, when Rat-1 cells were co-transfected with human Ku expression vectors and the hsp70-promoter-driven luciferase reporter gene, thermal induction of luciferase is significantly suppressed relative to cells transfected with only the hsp70-luciferase construct. These data suggest a role of CHBF (or Ku protein) in the regulation of heat response in vivo.

Suppression of heat-induced hsp70 expression by the 70-kDa subunit of the human Ku autoantigen

Expression of the 70-kDa polypeptide of human Ku autoantigen in rat cells is shown to suppress specifically the induction of hsp70 upon heat shock. Thermal induction of other heat shock proteins is not significantly affected, nor is the state of phosphorylation or the DNA-binding ability of the heat shock transcription factor HSF1. These findings support a model in which hsp70 gene expression is controlled by a second regulatory factor in addition to the positive activator HSF1. The Ku autoantigen, or a protein closely related to it, is likely to be involved in the regulation of hsp70 expression.

Effects of expressing human Hsp70 and its deletion derivatives on heat killing and on RNA and protein synthesis

We have established rat cell lines stably and constitutively expressing intact human heat shock protein (hsp) 70 and its deletion mutant derivatives. Using these stable cell lines, the functions of the various domains of human hsp70 were studied. An elevated level of human hsp70 or fragments containing the C-terminal portion of the protein, but not fragments containing the amino-terminal portion of the protein, is found to protect cells against thermal killing. Only the expression of intact human hsp70, however, can reduce the degree of heat-induced inhibition of translation and most effectively accelerate the recovery from heat-induced inhibition of transcription and translation. The peptide-binding domain in the carboxyl portion of hsp70 is of primary importance in protecting cells from thermal stress, probably through its binding to unfolded or partially folded polypeptides; this interaction, in turn, retards detrimental thermal denaturation or aggregation of key cellular proteins and protects cells from thermal stress. ATP binding and hydrolysis, on the other hand, are presumably necessary in the refolding and reassembly of thermally damaged proteins through multiple cycles of interactions between hsp70 and its targets.

Heat shock protein hsp70 accelerates the recovery of heat-shocked mammalian cells through its modulation of heat shock transcription factor HSF1

The role of mammalian 70-kDa heat shock protein (hsp70) in regulating cellular response to heat shock was examined by using three closely related rat cells: control Rat-1 cells, thermotolerant Rat-1 (TT Rat-1) cells, and heat-resistant M21 cells, a derivative of Rat-1 cells that constitutively overexpress human hsp70. In all these cells, after a prescribed heat shock, the level of the phosphorylated form of heat shock transcription factor HSF1 and that of HSF1 capable of binding to its cognitive DNA sequence heat shock element (HSE) exhibit similar time dependence. The amount of a constitutive HSE-binding activity (CHBA), on the other hand, inversely correlates with those of the two aforementioned forms of HSF1. The recovery kinetics from heat shock are different for the three cell lines, with the thermal-resistant TT Rat-1 and M21 cells showing faster recovery in terms of the state of phosphorylation of HSF1 and its ability to bind HSE or in terms of the reappearance of CHBA. Treatment with okadaic acid, a serine/threonine phosphatase inhibitor, delays the recovery kinetics of Rat-1 cells but not that of thermal-resistant M21 cells. These results are interpreted in terms of a role for hsp70 in the recovery of heat-shocked mammalian cells.

Interaction between heat shock factor and hsp70 is insufficient to suppress induction of DNA-binding activity in vivo

The intracellular level of free heat shock proteins, in particular the 70-kDa stress protein family, has been suggested to be the basis of an autoregulatory mechanism by which the cell measures the level of thermal stress and regulates the synthesis of heat shock proteins. It has been proposed that the DNA-binding and oligomeric state of the heat shock transcription factor (HSF) is a principal step in the induction pathway that is responsive to the level of 70-kDa stress protein. To test this hypothesis, we investigated the association between HSF and 70-kDa stress protein by means of a coimmunoprecipitation assay. We found that 70-kDa stress proteins associate to similar extents with both latent and active forms of HSF, although unlike other 70-kDa stress protein substrates, the association with HSF was not significantly disrupted in the presence of ATP. Gel mobility shift assays indicated that active HSF trimers purified from a bacterial expression system could not be substantially deactivated in vitro with purified 70-kDa stress protein and ATP. In addition, elevated concentrations of hsp70 alone could not significantly inhibit induction of the DNA-binding activity of endogenous HSF in cultured rat cells, and the induction was also not inhibited in cultured rat cells or Drosophila cells containing elevated levels of all members of the heat shock protein family. However, the deactivation of HSF to the non-DNA-binding state after prolonged heat stress or during recovery could be accelerated by increased levels of heat shock proteins. Hence, the level of heat shock proteins may affect the rate of disassembly of HSF trimers, but another mechanism, as yet undefined, appears to control the onset of the oligomeric transitions.

[Primary retroperitoneal tumor--an analysis of 303 cases]

Primary retroperitoneal tumor (PRT) is of a heterogeneous group of neoplasms of mesenchymal origin. From April 1964 through April 1992, 303 PRT cases were treated. Of the 288 cases with histological confirmation, 197 suffered from malignant tumors and 91 were benign. Since the PRT patients were usually symptomless, diagnosis was made late in the majority of patients. It resulted in low radical resection rate in both the malignant (36.9%) and the benign (84.6%) PRT owing to invasion to adjacent organs. The tumor recurrence rate was also high, being 74.2% for the malignant and 11.7% for the benign tumors. The overall 2-, 5-, and 10-year survival rates in the patients with malignant tumors were 55.3%, 19.5%, and 9.8%, respectively. The results of treatment were dependent primarily on completeness of tumor resection. Adjuvant radiotherapy could improve the survival rates but adjuvant chemotherapy did not help. In patients with tumor recurrence, operation remained to be the treatment of choice. If complete resection was impossible, the alternative was debulking operation followed by radiotherapy.

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.

Importance of the ATP-binding domain and nucleolar localization domain of HSP72 in the protection of nuclear proteins against heat-induced aggregation

Heat treatment of cells results in an increased protein content of nuclei when isolated after the heat treatment (intranuclear protein aggregation). In a previous study, the role of HSP72 was investigated using Rat-1 fibroblasts stably transfected with the human HSP72 gene. It was observed that the expression of human HSP72 in Rat-1 cells (HR cells) confers heat resistance. The initial heat-induced increase in the nuclear protein content was lower in HR cells as compared to the parent Rat-1 cells. In the present communication, the effects of overexpression of intact or mutant human HSP72 in Rat-1 cells on heat-induced increase in intranuclear protein aggregation and their relationship to cells' thermal sensitivity were examined. Four closely related cell lines were used for this study: Rat-1 cells which constitutively expressed the intact human HSP72, or mutant human HSP72 either missing its ATP-binding domain or nucleolar localization domain, and wild type Rat-1 cells. Our results show that expression of the intact human HSP72 or mutant human HSP72 missing its ATP-binding domain confers heat resistance and protects cells against heat-induced intranuclear protein aggregation. On the other hand, cells expressing mutant human HSP72 missing its nucleolar localization domain demonstrated heat shock responses similar to control Rat-1 cells.

Mammalian cell survival studies characterizing multiport negative pi-meson irradiation with the Stanford Medical Pion Generator (SMPG)

Radiobiological measurements have been made under various conditions of muliport pion irradiation using the Stanford Medical Pion Generator (SMPG). Chinese hamster cells (HA-1) were suspended in a tissue-equivalent 25% gelatin/medium solution. Hypoxic and aerobic HA-1 cells were irradiated simultaneously in a cylindrical water tank at either 4 or 16 degrees C. Irradiation at the focus of 60 converging pion beams, at a peak dose rate of 6 rads/min, gave relative biological effectiveness (RBEs) of 2.8, 1.8 and 1.4 at 50, 20 and 5% survival, respectively, and an oxygen enhancement ratio (OER) of 1.7. Plateau irradiation with crossing pion beams, at a peak dose-rate of 3 rads/min, resulted in survival values very close to those obtained with similar doses of 85 kV X-rays. Preliminary studies with large irradiation volumes in broadened pion stopping regions indicate RBEs significantly > 1 for survival > 50%. Supporting microdosimetric data with the SMPG are consistent with the radiobiological results.