Augmented expression of HSP72 protein in normal human fibroblasts irradiated with ultraviolet light

Membrane-Associated Heat Shock Proteins in Oncology: From Basic Research to New Theranostic Targets

Heat shock proteins (HSPs) constitute a large family of conserved proteins acting as molecular chaperones that play a key role in intracellular protein homeostasis, regulation of apoptosis, and protection from various stress factors (including hypoxia, thermal stress, oxidative stress). Apart from their intracellular localization, members of different HSP families such as small HSPs, HSP40, HSP60, HSP70 and HSP90 have been found to be localized on the plasma membrane of malignantly transformed cells. In the current article, the role of membrane-associated molecular chaperones in normal and tumor cells is comprehensively reviewed with implications of these proteins as plausible targets for cancer therapy and diagnostics.

UV-B exposure causes DNA damage and changes in protein expression in northern pike (Esox lucius) posthatched embryos

The ongoing anthropogenically caused ozone depletion and climate change has increased the amount of biologically harmful UV-B radiation, which is detrimental to fish in embryonal stages. The effects of UV-B radiation on the levels and locations of DNA damage manifested as cyclobutane pyrimidine dimers (CPDs), heat shock protein 70 (HSP70) and p53 protein in newly hatched embryos of pike were examined. Pike larvae were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of CPDs in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in epidermis, and caused plausible p53 activation in the brain and epidermis of some individuals. Also at a fluence rate occurring in nature, the DNA damage in the brain and eyes of pike and changes in protein expression were followed by severe behavioral disorders, suggesting that neural molecular changes were associated with functional consequences.

Amniotic fluid heat shock protein 70 concentration in histologic chorioamnionitis, term and preterm parturition

OBJECTIVE

Heat shock protein (HSP) 70, a conserved member of the stress protein family, is produced in almost all cell types in response to a wide range of stressful stimuli, and its production has a survival value. Evidence suggests that extracellular HSP70 is involved in the activation of the innate and adaptive immune response. Furthermore, increased mRNA expression of HSP70 has been observed in human fetal membranes following endotoxin stimulation. This study was conducted to determine the changes in amniotic fluid HSP70 concentrations during pregnancy, term and preterm parturition, intra-amniotic infection (IAI), and histologic chorioamnionitis.

STUDY DESIGN

A cross-sectional study was conducted in 376 pregnant women in the following groups: (1) women with a normal pregnancy who were classified into the following categories: (a) women in the mid-trimester (14-18 weeks) who underwent amniocentesis for genetic indications and delivered normal infants at term (n=72); (b) women at term not in labor (n = 23); and (c) those at term in labor (n = 48). (2) Women with spontaneous preterm labor and intact membranes who were subdivided into the following categories: (a) preterm labor who delivered at term without IAI (n = 42); (b) preterm labor who delivered preterm without IAI (n = 57); and (c) preterm labor and delivery with IAI (n = 30). (3) Women with preterm prelabor rupture of membranes (PROM) with (n = 50) and without (n = 54) IAI. Among patients with preterm labor with intact membranes and preterm PROM who delivered within 72 hours of amniocentesis, placenta, umbilical cord, and chorioamniotic membranes were collected and assessed for the presence or absence of acute inflammatory lesions in the extraplacental membranes (histologic chorioamnionitis) and/or umbilical cords (funisitis). HSP70 concentrations in amniotic fluid were determined using a sensitive and specific immunoassay. Non-parametric statistics were used for analysis. A p value of <0.05 was considered statistically significant.

RESULTS

Immunoreactive HSP70 was detected in 88% (332/376) of amniotic fluid samples. The median amniotic fluid HSP70 concentration was significantly higher in women at term without labor than in those in the mid-trimester (term no labor: median 34.9 ng/mL, range 0-78.1 ng/mL vs. mid-trimester; median 6.6 ng/mL, range 0-20.8 ng/mL; p<0.001). Among patients with spontaneous preterm labor and preterm PROM, those with IAI had a significantly higher median amniotic fluid HSP70 concentration than those without IAI (preterm labor with IAI: median 82.9 ng/mL, range 0-500 ng/mL vs. preterm labor without IAI: median 41.7 ng/mL, range 0-244 ng/mL; p = 0.001; preterm PROM with IAI: median 86.5 ng/mL, range 0-428 ng/mL vs. preterm PROM without IAI: median 55.9 ng/mL, range 14.9-299.9 ng/mL; p = 0.007). There was no significant difference in the median amniotic fluid HSP70 concentration between patients with preterm labor who delivered preterm without IAI and those who delivered at term (p = 0.6). However, among patients with preterm labor without IAI, there was an inverse relationship between amniotic fluid concentration of HSP70 and the amniocentesis-to-spontaneous delivery interval (Spearman's Rho = -0.26; p = 0.02). Patients with histologic chorioamnionitis/funisitis had a significantly higher median amniotic fluid HSP70 concentration than those without inflammation (inflammation: median 108.7 ng/mL, range 0-500 ng/mL vs. without inflammation: median 67.9 ng/mL, range 7.1-299.9 ng/mL; p = 0.02). Women at term in labor had a median amniotic fluid concentration of HSP70 significantly higher than those not in labor (term in labor: median 60.7 ng/mL, range 0-359.9 ng/mL vs. term not in labor: median 34.9 ng/mL, range 0-78.1 ng/mL; p = 0.02).

CONCLUSIONS

Intra-amniotic infection, histologic chorioamnionitis, and term parturition are associated with elevated amniotic fluid HSP70 concentrations. HSP70 plays a role in the host defense mechanism by activating the innate arm of the immune response in women with intrauterine infection. The mechanisms of preterm and term parturition in humans may involve extracellular HSP70.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

The therapeutic implications of clinically applied modifiers of heat shock protein 70 (Hsp70) expression by tumor cells

Evidence that membrane-bound and extracellular heat shock proteins (HSPs) with molecular weights of 70 and 90 kDa are potent stimulators of the immune responses has accumulated over the last decade. In this review, we discuss the modulation of Hsp70 expression, a major stress-inducible member of the HSP70 family, in the cytoplasm and on the plasma membrane of tumor cells by clinically applied interventions such as radio- and chemotherapy.

Correlation of malignant phenotypes of human tumour cell lines with augmented expression of Hsp72 protein measured by laser scanning cytometry

Augmented expression of members of the heat shock protein 70 (Hsp70) family are frequently observed in various human cancers. In this study, we examined applicability of laser scanning cytometer (LSC) to evaluate the level of Hsp72, which is the member constitutively expressed and significantly induced after heat shock, in human tumour cell lines. The relative nuclear content of Hsp72 measured by LSC correlated well with the relative intracellular content determined by Western blotting (R = 0.906). Furthermore, there was a close relationship between the relative nuclear content of Hsp72 measured by LSC and the colony-forming ability in soft agar, one of the malignant characteristics of tumour cells (R = 0.880). These results indicate that LSC measurement is useful for predicting the degree of malignancy of cancer cells, as it is reliable, faster than Western blotting and more objective and quantitative than visual measurements.

Dual function of membrane-bound heat shock protein 70 (Hsp70), Bag-4, and Hsp40: protection against radiation-induced effects and target structure for natural killer cells

CX+/CX- and Colo+/Colo- tumor sublines with stable heat shock protein 70 (Hsp70) high and low membrane expression were generated by fluorescence activated cell sorting of the parental human colon (CX2) and pancreas (Colo357) carcinoma cell lines, using an Hsp70-specific antibody. Two-parameter flow cytometry revealed that Hsp70 colocalizes with Bag-4, also termed silencer of death domain, not only in the cytosol but also on the plasma membrane. After nonlethal gamma-irradiation, the percentage of membrane-positive cells and the protein density of Hsp70 and Bag-4 were found to be strongly upregulated in carcinoma sublines with initially low expression levels (CX-, Colo-). Membrane expression of Hsp70 was also elevated in Bag-4 overexpressing HeLa cervix carcinoma cells when compared to neo-transfected cells. In response to gamma-irradiation, neo-transfected HeLa cells behaved like Hsp70/Bag-4 low-expressing CX- and Colo-, and Bag-4-transfected HeLa cells like Hsp70/Bag-4 high-expressing carcinoma sublines CX+ and Colo+. Immunoprecipitation studies further confirmed colocalization of Hsp70 and Bag-4 but also point to an association of Hsp70 and Hsp40 on the plasma membrane of CX+ and Colo+ cells; on CX- and Colo- tumor sublines, Hsp40 was detectable in the absence of Hsp70 and Bag-4. Other co-chaperones including Hsp60 and Hsp90 were neither found on the cell surface of CX+/CX-, Colo+/Colo- nor on HeLa neo-/HeLa Bag-4-transfected tumor cells. Functionally, Hsp70/Bag-4 and Hsp70/Hsp40 membrane-positive tumor cells appeared to be better protected against radiation-induced effects, including G2/M arrest and growth inhibition, on the one hand. On the other hand, membrane-bound Hsp70, but neither Bag-4 nor Hsp40, served as a recognition site for the cytolytic attack mediated by natural killer cells.

Androgenic switch: an example of plant embryogenesis from the male gametophyte perspective

Embryogenesis in plants is a unique process in the sense that it can be initiated from a wide range of cells other than the zygote. Upon stress, microspores or young pollen grains can be switched from their normal pollen development towards an embryogenic pathway, a process called androgenesis. Androgenesis represents an important tool for research in plant genetics and breeding, since androgenic embryos can germinate into completely homozygous, double haploid plants. From a developmental point of view, androgenesis is a rewarding system for understanding the process of embryo formation from single, haploid microspores. Androgenic development can be divided into three main characteristic phases: acquisition of embryogenic potential, initiation of cell divisions, and pattern formation. The aim of this review is to provide an overview of the main cellular and molecular events that characterize these three commitment phases. Molecular approaches such as differential screening and cDNA array have been successfully employed in the characterization of the spatiotemporal changes in gene expression during androgenesis. These results suggest that the activation of key regulators of embryogenesis, such as the BABY BOOM transcription factor, is preceded by the stress-induced reprogramming of cellular metabolism. Reprogramming of cellular metabolism includes the repression of gene expression related to starch biosynthesis and the induction of proteolytic genes (e.g. components of the 26S proteasome, metalloprotease, cysteine, and aspartic proteases) and stress-related proteins (e.g. GST, HSP, BI-1, ADH). The combination of cell tracking systems with biochemical markers has allowed the key switches in the developmental pathway of microspores to be determined, as well as programmed cell death to be identified as a feature of successful androgenic embryo development. The mechanisms of androgenesis induction and embryo formation are discussed, in relation to other biological systems, in special zygotic and somatic embryogenesis.

Retinoid- and sodium-butyrate-induced decrease in heat shock protein 70 membrane-positive tumor cells is associated with reduced sensitivity to natural killer cell lysis, growth delay, and altered growth morphology

Human tumors frequently present heat shock protein 70 (Hsp70) on their cell membranes, whereas corresponding normal tissues fail to do so. Therefore, an Hsp70 membrane-positive phenotype provided a tumor-specific marker. Moreover, membrane-bound Hsp70 provides a target structure for the cytolytic attack mediated by natural killer (NK) cells. Vitamin A derivatives 13-cis retinoic acid (13-RA) and all-trans retinoic acid (ATRA) and sodium-butyrate (SBU) are known for their redifferentiating capacity. Therefore, we asked the question whether loss in tumorigenicity might be associated with a reduced Hsp70 membrane expression. For our studies we used epithelial colon (CX+/CX-) and thyroid (ML-1) cancer cells, with initially different Hsp70 cell surface expression pattern. After treatment up to 7 weeks with freshly prepared 13-RA, ATRA, and SBU at nonlethal concentrations of 10 microM, 1 microM, and 0.5 mM, respectively, growth morphology, Hsp70 levels, and sensitivity toward Hsp70-specific NK cells were compared with that of untreated tumor cells. Significant growth delay was determined in CX+ tumor cells after 6 weeks treatment with 13-RA. Concomitantly, growth morphology changed from spheroid cell clusters to monolayers. Despite a weak increase in cytosolic Hsp70, the percentage of Hsp70 membrane-positive cells dropped significantly after repeated treatments with 13-RA and ATRA in CX+ and ML-1 but not in CX- tumor cells. Similar results were observed with SBU. Functionally, the decrease in Hsp70 membrane-positive CX+ and ML-1 cells correlated with a reduced sensitivity to lysis mediated by NK cells. In summary, redifferentiating agents predominantly affected Hsp70 membrane-positive tumors. The decrease in Hsp70 membrane positivity correlated with a lower sensitivity to NK lysis, growth delay, and altered growth morphology.

Nuclear translocation of the Hsp70/Hsp90 organizing protein mSTI1 is regulated by cell cycle kinases

The co-chaperone murine stress-inducible protein 1 (mSTI1), an Hsp70/Hsp90 organizing protein (Hop) homologue, mediates the assembly of the Hsp70/Hsp90 chaperone heterocomplex. The mSTI1 protein can be phosphorylated in vitro by cell cycle kinases proximal to a putative nuclear localization signal (NLS), which substantiated a predicted casein kinase II (CKII)-cdc2 kinase-NLS (CcN) motif at position 180-239 and suggested that mSTI1 might move between the cytoplasm and the nucleus under certain cell cycle conditions. The mechanism responsible for the cellular localization of mSTI1 was probed using NIH3T3 fibroblasts to investigate the localization of endogenous mSTI1 and enhanced green fluorescent protein (EGFP)-tagged mSTI1 mutants. Localization studies on cell lines stably expressing NLS(mSTI1)-EGFP and EGFP demonstrated that the NLS(mSTI1) was able to promote a nuclear localization of EGFP. The mSTI1 protein was exclusively cytoplasmic in most cells under normal conditions but was present in the nucleus of a subpopulation of cells and accumulated in the nucleus following inhibition of nuclear export (leptomycin B treatment). G1/S-phase arrest (using hydroxyurea) and inhibition of cdc2 kinase (using olomoucine) but not inhibition of casein kinase II (using 5,6-dichlorobenzimidazole riboside), increased the proportion of cells with endogenous mSTI1 nuclear staining. mSTI1-EGFP behaved identically to endogenous mSTI1. The functional importance of key residues was tested using modified mSTI1-EGFP proteins. Inactivation and phosphorylation mimicking of potential phosphorylation sites in mSTI1 altered the nuclear translocation. Mimicking of phosphorylation at the mSTI1 CKII phosphorylation site (S189E) promoted nuclear localization of mSTI1-EGFP. Mimicking phosphorylation at the cdc2 kinase phosphorylation site (T198E) promoted cytoplasmic localization of mSTI1-EGFP at the G1/S-phase transition,whereas removal of this site (T198A) promoted the nuclear localization of mSTI1-EGFP under the same conditions. These data provide the first evidence of nuclear import and export of a major Hsp70/Hsp90 co-chaperone and the regulation of this nuclear-cytoplasmic shuttling by cell cycle status and cell cycle kinases.

Overexpression of inducible heat shock protein 70 in Cos-1 cells fails to protect from cytotoxicity of oxidized ldls

Oxidized low density lipoproteins (OxLDLs) are believed to play a central role in atherogenesis and to possess a wide variety of biological properties; among them, OxLDLs are cytotoxic to cultured vascular cells in that they induce necrosis and apoptosis. Moreover, OxLDLs are known to induce the expression of heat shock protein 70 (Hsp70), a protein that protects cells from several cytotoxic stimuli. To determine whether Hsp70 can protect cells against OxLDL-induced cytotoxicity, COS-1 cells were transfected with a construct containing human Hsp70. A number of cell lines permanently expressing Hsp70 were obtained, 1 of which (cos-Hsp70/10, with high Hsp70 expression) was selected for further studies. Hsp70 overexpression protected cells from toxic stimuli, such as H(2)O(2), UV irradiation, and heat shock, suggesting that the overexpressed protein was functional. When incubated with OxLDLs, however, the clone overexpressing Hsp70 showed a significant decrease in viability, as determined by the [(3)H]adenine release assay (319.8+/-3.16% of control for transfected cells versus 217.6+/-6.08% for control cells exposed to 100 microgram protein/mL of OxLDL), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (12.5+/-0.9% versus 28.9+/-1.99% of control, respectively), and LDH release (48.4+/-0.04% versus 15.2+/-0.06% of control cells). The increased expression of BAX and the decreased expression of Bcl-2 (a proapoptotic and an antiapoptotic protein, respectively) in cos-Hsp70/10 cells and in control cells on incubation with OxLDLs suggested that overexpression of Hsp70 did not confer protection against apoptosis induced by OxLDLs. The analysis of nucleosome content and the nuclear staining with Hoechst 33258 confirmed this finding. These data suggest that overexpression of Hsp70 not only fails to protect COS-1 cells against OxLDL-induced apoptosis but rather confers a higher sensitivity to the cytotoxic action of these lipoproteins. Thus, the Hsp70 response, although induced by OxLDLs, cannot protect cells from lipoprotein toxicity.

Dose-dependent biphasic accumulation of TP53 protein in normal human embryo cells after X irradiation

The effects of various doses of X radiation on the kinetics of accumulation of TP53 protein (formerly known as p53) were examined in normal human embryo cells. We found that the rate of accumulation of TP53 protein was biphasic at X-ray doses between 1 and 4 Gy, while monophasic accumulation was observed after X irradiation with doses higher than 6 Gy. The first phase of accumulation was detected within 1 h after irradiation, and a second phase of accumulation was detected between 6 and 12 h after irradiation. The induction of CDKN1A (formerly known as p21(WAF1/CIP1)) and MDM2 proteins was also biphasic after doses of 4 Gy or less, while monophasic accumulation was observed after 6 Gy or higher. We found that the proteasome inhibitor ALLN increased the constitutive level of TP53 protein, and no change was observed in the TP53 level after X irradiation when cells were treated with ALLN. These results indicate that the dose-dependent accumulation of TP53 is due to an inhibition of TP53 degradation, and that the induction of MDM2 might be responsible in part for the different kinetics of accumulation of TP53.

Effects of protein kinase inhibitors on the accumulation kinetics of p53 protein in normal human embryo cells following X-irradiation

DNA-damaging agents induce phosphorylation of the p53 protein, resulting in its accumulation in the nucleus. To clarify the signal transduction pathway(s) involved in p53 protein accumulation in normal human embryo cells following X-irradiation, the effects of three protein kinase inhibitors were examined. Quercetin, an inhibitor of heat-shock response, dose dependently suppressed the p53 accumulation induced by X-rays at more than 100 microM. No suppression, however, was observed with calphostin-C, a specific inhibitor of protein kinase C, in the range of 0.05 to 0.25 microM. Wortmannin was the most potent inhibitor of p53 accumulation. Its suppressive effect appears within a few minutes of pretreatment with a dose of 25 microM, but posttreatment was less effective. Our findings suggest that PKC is not involved in X-ray-induced p53 accumulation in normal human embryo cells and that a wortmannin-sensitive pathway acts as a sensor of DNA damage.

Detection of heat shock protein 70 (Hsp70) and anti-Hsp70 antibodies in the serum of normal individuals

Heat shock or stress proteins (Hsp) are typically regarded as being intracellular proteins that have a range of functions including the maintenance of cellular integrity. Members of the Hsp70 family of molecules have been implicated in the processing and presentation of antigen and the cross reactivity of lymphocytes specific for pathogen-derived heat shock proteins with self Hsp70 has been suggested to be an underlying cause of certain autoimmune diseases. This study reports the presence of soluble Hsp70 in the peripheral circulation of normal individuals. Concentrations of soluble Hsp70 in females were approximately twice those in males. Circulating anti-Hsp70 antibodies were detected in all individuals assessed, but there were no differences between males and females. However, there was a significant correlation between soluble Hsp70 concentration and antibody levels in males, but not females. The physiological role for circulating heat shock proteins is intriguing, but currently unknown. These findings extend our previous observations that Hsp60 is present in the peripheral circulation and support the proposition that soluble heat shock proteins may play a regulatory role in either the prevention or protection of pathophysiological processes involving inadvertent immunorecognition or cross-recognition of heat shock proteins.

Heat shock transcription factor-1 regulates heat shock protein-72 expression in human keratinocytes exposed to ultraviolet B light

In response to ultraviolet radiation (UVR), skin keratinocytes increase expression of heat shock proteins that can protect cells from stress-induced damage. This heat shock response is known to be transcriptionally regulated in eukaryotic cells exposed to certain forms of environmental stress. In the skin, absorption of ultraviolet B light occurs primarily in the epidermis, and therefore, using primary cultures of normal human epidermal keratinocytes, we have examined whether transcriptional activation of the hsp72 gene occurs following UVB irradiation. Cultured keratinocytes were exposed to UVB (290-320 nm, 300 J per m2) and then incubated at 37 degrees C for various intervals before harvesting. Immediately following UV exposure, the heat shock transcription factor 1 (HSF1) dissociated from HSP72-HSF1 complexes, underwent trimerization and phosphorylation, and demonstrated DNA binding activity to the heat shock element in the promoter region of the hsp72 gene. UVB also increased hsp72 mRNA, with peak levels observed 1-3 h post-UVR. HSP72 protein was constitutively expressed in keratinocytes, and its expression was increased by UVB, with maximum levels at 6 h post-UVR. The stress response may be extremely important in the protection of human skin from UVB radiation, and modulation of heat shock protein expression and/or function offers a potential therapeutic target in the prevention of photoaging and skin cancer.

Heat shock and proinflammatory stressors induce differential localization of heat shock proteins in human monocytes

Heat shock (HS) proteins (HSP) are a family of molecular chaperones induced by environmental stresses such as oxidative injury, and contribute to protection from and adaptation to cellular stress. We investigated in human monocytes the expression and subcellular distribution of hsp70 and hsc70 after HS and inflammation-related stresses leading to generation of reactive oxygen species by these cells, such as the phorbol ester PMA and erythrophagocytosis (E phi). By combining immunofluorescent staining and Western blot on subcellular fractions, we found that all three stress factors resulted in an increased hsp70 expression, however the subcellular distribution pattern was different depending on the type of stress. While HS induced a rapid translocation of hsp70 into the nucleus, no nuclear translocation of hsp70 was observed after PMA or E phi. Neither of the examined stresses induced membrane expression of hsp70. The observed differences in subcellular distribution pattern might relate to distinct regulation and specific functions of hsp70 in inflammation.

DNA-damaging agents induce the 72-kD heat shock protein in SV40 transformed normal human fibroblasts

In order to elucidate the involvement of DNA damage in the induction of heat shock proteins (stress proteins), we examined the induction of 72-kD heat shock protein (HSP72) in an SV40-transformed human fibroblast cell line (WI38VA13) which was exposed to various DNA-damaging agents, including 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3 -nitro-methylmethane sulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, and 4-nitroquinoline-N-oxide. Induction of HSP72 was detected by the indirect immunofluorescence method using a monoclonal antibody. All the DNA-damaging agents used in this study induced HSP72 on human fibroblasts. This result indicates that DNA damage is one trigger for the induction of HSP72.

Oxidative stress is involved in the UV activation of p53

In many vertebrate cells exposure to ultraviolet light lead to a dramatic increase in the cellular levels of the tumour suppressor protein p53, followed by a biological response of either growth arrest or programmed cell death. Ultraviolet light can be absorbed directly by cellular macromolecules, leading to photochemical modification of DNA and proteins. Additionally, it also causes free radical formation, resulting in oxidative stress. Whereas ultraviolet light and ionizing radiation both induce DNA lesions which trigger an activation of the p53 pathway, the magnitude of the p53 response elicited by ionizing radiation is comparatively low. Following irradiation with ultraviolet light two populations of p53-reactive cells are induced: a population accumulating high levels of p53 protein and a population with comparatively low levels of p53, similar in magnitude to the p53 response following ionizing radiation. Pretreatment of cells with N-acetylcysteine, an agent known to counteract oxidative stress, attenuates the cellular p53 response to ultraviolet light by reducing the number of cells with high p53 levels but does not affect the response to ionizing radiation. We demonstrate that N-acetylcysteine pretreatment does not prevent the inflicted DNA damage and therefore conclude that oxidative stress is a causative agent in the ultraviolet light activation of the p53 pathway.

Expression of heat shock proteins in the developing rat retina

Expression of three heat shock proteins (HSPs), HSP70, HSP90, and immunoglobulin heavy chain binding protein (Bip) was examined in the developing rat retina using Northern blot analysis. The expression of the inducible form of HSP70 remained uniformly low throughout the perinatal period until P5 and increased rapidly at P7. On the other hand, the constitutive form of HSP70, HSP90, and Bip were expressed constitutively in the rat retina throughout the developmental stage except P3-P5, at which a transient decrease of the expression was observed. The increase of inducible HSP70 mRNA at P7 may correspond to the functional maturation of photoreception in the visual nervous system and may be one of the stress responses to photostimulation. The potential roles of each HSP during development of the rat visual system are discussed.

Induction of the 72-kD heat shock protein in human skin melanoma and squamous cell carcinoma cell lines

Heat shock proteins (HSPs) or stress proteins comprise a characteristic group of proteins synthesized in cells exposed to heat or other environmental stimuli. Of the many HSPs, the 72-kD heat shock protein (HSP72) is the most stress-inducible one. In the present study, we examined the effects of heat, chemicals (azetidine and sodium arsenite), ultraviolet (UV) light, and gamma-ray irradiation on the induction of HSP72 in cultured human skin melanoma cell lines (P-39 and G-361), a human skin squamous cell carcinoma cell line (HSC-1), and an SV40-transformed human lung fibroblast cell line (WI38VA13) as a control. In these cell lines, heat treatment induced HSP72 more rapidly and intensely than did chemical exposure. Compared with the SCC cell line, the two melanoma cell lines produced less HSP72 with heat treatment. UVC irradiation (20 J/m2) induced HSP72 only in the WI38VA13 cells. After gamma-ray irradiation, no HSP72 induction was detected in any of the cell lines examined. These observations suggest that, in cultured cells, inducibility of HSP72 depends not only on the inducer but also on the origin of each cell line.

Cell cycle variation of Hsp70 levels in HeLa cells at 37 degrees C and after a heat shock

The expression of the 72 kD inducible heat shock protein (hsp72) has been reported to be cell cycle associated in unheated, synchronized HeLa cells. In this study, flow cytometry was used to investigate hsp72 levels through the cell cycle in HeLa cells by dual labeling with propidium iodide and antibodies against hsp72. The entire cell cycle distribution of hsp72 could be measured in a single sample of asynchronously growing cells. For unheated cells, the level of hsp72 increased about 30% from G1 to S phase, with about a 65% increase in G2/M, probably due to cell size differences. Neither mitotic selection nor serum stimulation induced a higher level of hsp72 than in the control cells. Western blot analysis of hsp72 from Hoechst-stained cells sorted from G1, mid-S, or G2/M showed that G1 cells had the lowest level of hsp72, with about a 30% increase in S phase and a 60% increase in G2/M, in good agreement with the flow cytometry results. These data conflict with previous reports by other laboratories which showed a 3-fold higher level of hsp72 in S phase than in G1 or G2. In contrast, heat shock (both acute and chronic) led to a non-uniform increase in hsp72 through the cell cycle. Most cells in mid S phase had high levels of hsp72, and a larger range in the levels of hsp72 were found in G1 and late S/G2/M phase cells.

Binding between wild-type p53 and hsp72 accumulated after UV and gamma-ray irradiation

We have investigated the increased levels of p53 and hsp72 after UV or gamma-ray irradiation and the association of these using two human glioblastoma cell lines. Human glioblastoma cell line A-172 exhibited no mutations in the p53 gene, whereas cell line T98G had a mutation in exon 7 of the p53 gene. In A-172, the level of wild-type p53 was increased by UV or gamma-ray irradiation. Although the level of mutant p53 in T98G was very high before irradiation, it was unchanged by UV or gamma-ray irradiation. Furthermore, in the A-172 cell line after UV or gamma-ray irradiation, wild-type p53 was co-immunoprecipitated with anti-hsp72/73 antibody, and accumulated hsp72 was also co-immunoprecipitated with anti-p53 antibody. These findings indicate that wild-type p53 accumulated by UV or gamma-ray irradiation is associated with hsp72 induced by these treatments.

Expression of hsp70 induced in CHO cells by 45.0 degrees C hyperthermia is cell cycle associated and DNA synthesis dependent

In response to a heat shock, the synthesis of heat shock proteins with a molecular weight of 72 kD (hsp72) is induced. To determine whether hsp72 expression in Chinese hamster ovary (CHO) cells is cell cycle associated, flow cytometry was used to measure DNA content and heat shock protein levels simultaneously. After 10 min at 45.0 degrees C and incubation at 37 degrees C for several hours, hsp72 was induced to a high level in early S phase. Inhibitors of DNA synthesis, aphidicolin, and 1-beta-D-arabinofuranosylcytosine (araC), suppressed the induction of hsp72 but did not inhibit it completely. Hsp73 (constitutive hsp70) was also induced by heat shock, but the induction was uniform through the cell cycle and it was not suppressed by araC.

Rise in heat-shock protein level confers tolerance to energy deprivation

Heat shock (44 degrees C for 10 min) or ATP depletion by an uncoupler (CCCP for 20 min) is shown to result in stimulation of hsp68/70 synthesis in Ehrlich tumor cells. After 3 h of recovery, the cells become thermotolerant. Surprisingly, repeated ATP depletion caused by CCCP or rotenone (a respiratory inhibitor) treatment, had a much lower effect on cell viability. Both induction of tolerance to energy deprivation and hsp68/70 synthesis were totally suppressed by cycloheximide, an inhibitor of cytosolic protein synthesis. In tolerant cells, rotenone still induced ATP depletion; however, protein aggregation (the rise in Triton-insoluble proteins) was inhibited in these cells. It is suggested that cellular chaperones (e.g. hsp70) are involved in the protection of ischemic cells from necrosis, preventing protein aggregation under ATP deficiency.