HSP70 overexpression increases resistance of V79 cells to cytotoxicity of airborne pollutants, but does not protect the mitotic spindle against damage caused by airborne toxins

In vitro cytotoxicity testing of airborne formaldehyde collected in serum-free culture media

The purpose of this study was to identify a suitable sampling model for on-site toxicity assessment of soluble air contaminants such as formaldehyde, a well known industrial and indoor air contaminant. The in vitro cytotoxicity of formaldehyde, the selected model for soluble air contaminants, was studied using the MTS (tetrazolium salt) assay in two carcinoma cell lines, A549 epithelial lung and HepG2 hepatocarcinoma, and in skin fibroblasts. The cytotoxic effects of airborne formaldehyde were evaluated using test atmospheres in concentrations below 10 ppm (12.3 mg/m3), generated by a dynamic diffusion method and bubbled (0.3 L/min) through serum-free culture media for one or four hours. Human cells were treated with formaldehyde air samples, and cell viability was determined after four hours incubation. In parallel, the concentration of airborne formaldehyde was monitored, using the 3500 NIOSH method. Cell viability of the HepG2 cells exposed to formaldehyde air samples (8.75 ppm-4 h) was reduced to less than 50% (31.69/1.24%). The HepG2 cell lines were found to be more sensitive (IC50=103.799/23.55 mg/L) to formaldehyde than both A549 cell lines (IC50=198.369/9.54 mg/L) and skin fibroblasts (IC50=196.689/36.73 mg/L) (PB/0.01). An average of 96.8% was determined for collection efficiency of formaldehyde in serum-free culture media. The results of this study suggest that absorption of soluble air contaminants, such as formaldehyde, in serum-free culture media can be used as a suitable sampling model for on-site toxicity assessments.

Cell cycle alterations induced by urban PM2.5 in bronchial epithelial cells: characterization of the process and possible mechanisms involved

BACKGROUND

This study explores and characterizes cell cycle alterations induced by urban PM2.5 in the human epithelial cell line BEAS-2B, and elucidates possible mechanisms involved.

METHODS

The cells were exposed to a low dose (7.5 μg/cm(2)) of Milan winter PM2.5 for different time points, and the cell cycle progression was analyzed by fluorescent microscopy and flow cytometry. Activation of proteins involved in cell cycle control was investigated by Western blotting and DNA damage by (32)P-postlabelling, immunostaining and comet assay. The formation of reactive oxygen species (ROS) was quantified by flow cytometry. The role of PM organic fraction versus washed PM on the cell cycle alterations was also examined. Finally, the molecular pathways activated were further examined using specific inhibitors.

RESULTS

Winter PM2.5 induced marked cell cycle alteration already after 3 h of exposure, represented by an increased number of cells (transient arrest) in G2. This effect was associated with an increased phosphorylation of Chk2, while no changes in p53 phosphorylation were observed at this time point. The increase in G2 was followed by a transient arrest in the metaphase/anaphase transition point (10 h), which was associated with the presence of severe mitotic spindle aberrations. The metaphase/anaphase delay was apparently followed by mitotic slippage at 24 h, resulting in an increased number of tetraploid G1 cells and cells with micronuclei (MN), and by apoptosis at 40 h. Winter PM2.5 increased the level of ROS at 2 h and DNA damage (8-oxodG, single- and double stand breaks) was detected after 3 h of exposure. The PM organic fraction caused a similar G2/M arrest and augmented ROS formation, while washed PM had no such effects. DNA adducts were detected after 24 h. Both PM-induced DNA damage and G2 arrest were inhibited by the addition of antioxidants and α-naphthoflavone, suggesting the involvement of ROS and reactive electrophilic metabolites formed via a P450-dependent reaction.

CONCLUSIONS

Milan winter PM2.5 rapidly induces severe cell cycle alterations, resulting in increased frequency of cells with double nuclei and MN. This effect is related to the metabolic activation of PM2.5 organic chemicals, which cause damages to DNA and spindle apparatus.

HSPA2 overexpression protects V79 fibroblasts against bortezomib-induced apoptosis

Human HSPA2 is a member of the HSPA (HSP70) family of heat-shock proteins, encoded by the gene originally described as testis-specific. Recently, it has been reported that HSPA2 can be also expressed in human somatic tissues in a cell-type specific manner. The aim of the present study was to find out whether HSPA2 can increase the resistance of somatic cells to the toxic effect of heat shock, proteasome inhibitors, and several anticancer cytostatics. We used a Chinese hamster fibroblast V79 cell line because these cells do not express the HSPA2 and cytoprotective HSPA1 proteins under normal culture conditions and show limited ability to express HSPA1 in response to heat shock and proteasome inhibitors. We established, by retroviral gene transfer, a stable V79/HSPA2 cell line, which constitutively overexpressed HSPA2 protein. The major observation of our study was that HSPA2 increased long-term survival of cells subjected to heat shock and proteasome inhibitors. We found, that HSPA2 confers resistance to bortezomib-induced apoptosis. Thus, we showed for the first time that in somatic cells HSPA2 can be a part of a system protecting cells against cytotoxic stimuli inducing proteotoxic stress.

The HspA2 protein localizes in nucleoli and centrosomes of heat shocked cancer cells

The human HSPA2 gene, which belongs to the HSP70 family of heat shock genes, is a counterpart of rodent testis-specific HspA2 gene. Rodent genes are expressed mainly in pachytene spermatocytes, while transcripts of human HSPA2 gene have been detected in various normal somatic tissues, albeit translation of the messenger RNA into corresponding protein has not been yet unambiguously demonstrated, except for several cancer cell lines. The aim of our work, a first step in search for HspA2 function in cancer cells, was to establish its intracellular localization at physiological temperature and during heat shock. First, we used qRT-PCR and a highly specific antibody to select cell lines with the highest expression of the HspA2 protein, which turned out to be A549 and NCI-H1299 lines originating from non-small cell lung carcinoma (NSCLC). Significant expression of the HspA2 was also detected by immunohistochemistry in primary NSCLC specimens. Intracellular localization of the HspA2 was studied using both the specific anti-HspA2 polyclonal antibody and transfection of cells with fusion proteins HspA2-EGFP and mRFP-HspA2. We found that, at physiological temperature, the HspA2 was localized primarily in cytoplasm whereas, during heat shock, localization shifted to nucleus and nucleoli. Moreover, we demonstrate that in heat-shocked cells HspA2 accumulated in centrosomes. Our results suggest that the HspA2, like Hsp70 protein, can be involved in protecting nucleoli and centrosomes integrity in cancer cells subjected to heat shock and, possibly, other cellular stressors.

Toxicity Assessment of Industrial Chemicals and Airborne Contaminants: Transition fromIn VivotoIn VitroTest Methods: A Review

Exposure to occupational and environmental contaminants is a major contributor to human health problems. Inhalation of gases, vapors, aerosols, and mixtures of these can cause a wide range of adverse health effects, ranging from simple irritation to systemic diseases. Despite significant achievements in the risk assessment of chemicals, the toxicological database, particularly for industrial chemicals, remains limited. Considering there are approximately 80,000 chemicals in commerce, and an extremely large number of chemical mixtures, in vivo testing of this large number is unachievable from both economical and practical perspectives. While in vitro methods are capable of rapidly providing toxicity information, regulatory agencies in general are still cautious about the replacement of whole-animal methods with new in vitro techniques. Although studying the toxic effects of inhaled chemicals is a complex subject, recent studies demonstrate that in vitro methods may have significant potential for assessing the toxicity of airborne contaminants. In this review, current toxicity test methods for risk evaluation of industrial chemicals and airborne contaminants are presented. To evaluate the potential applications of in vitro methods for studying respiratory toxicity, more recent models developed for toxicity testing of airborne contaminants are discussed.

Inducible 70 kDa heat shock protein does not protect spermatogenic cells from damage induced by cryptorchidism

Accumulation of inducible heat shock proteins (e.g. Hsp70i) during cellular stress confers thermotolerance, reduces the consequences of damage and facilitates cellular recovery, while abrogation of Hsp70i expression renders sensitivity to apoptosis. Testis translocation into abdominal cavity, which results in temperature elevation, does not induce expression of the Hsp70i proteins. Despite constitutive expression of testis-specific Hsp70 proteins, spermatocytes are very sensitive to damage at elevated temperatures. To test whether Hsp70i protein could protect testes from heat-induced damage, we have engineered transgenic mice that over-express this protein selectively in spermatocytes and spermatids. We demonstrate that the testes of cryptorchid transgenic mice, like those of wild-type mice, exhibit reduced weight and smaller sizes of their seminiferous tubules, disorganization of their germinal epithelium structures, appearance of multinucleated giant cells, and reduced populations of germ cells. The data show that constitutive expression of Hsp70i does not protect the seminiferous epithelium against cryptorchidism-induced damage.

Interferon-gamma acts proapoptotic on hepatic stellate cells (HSC) and abrogates the antiapoptotic effect of interferon-alpha by an HSP70-dependant pathway

The activated hepatic stellate cell (HSC) is an important fibrogenic cell type of the liver. Interferon-alpha (IFN-alpha) has recently been shown to elicit an antiapoptotic effect on activated HSC by a JAK-2-dependent inhibition of caspase-8 activation. As JAK-2 has so far been shown to be a member of the IFN-gamma signal transduction pathway we studied the effect of IFN-gamma on apoptosis as well as on its signaling in primary cultured rat HSC. IFN-gamma elicited a proapoptotic effect in activated HSC. The combination of both, IFN-gamma and IFN-alpha, however, completely cancelled each other's effect. No effect of the two cytokines on major members of apoptosis-regulating systems (CD95, CD95L, bcl-2, bax, bcl-xL, p53, p21WAF1, p27, NFkappaB) could be observed. Western Blot analysis revealed that gene expression of the chaperone HSP70 was found to be downregulated by IFN-gamma but upregulated by IFN-alpha. The effect could be abrogated by administration of both. After transfection of activated HSC with a pCMV-HSP70 M expression vector the proapoptotic effect of IFN-gamma was cancelled. Using HSP70 antisense, the antiapoptotic effect of IFN-alpha was cancelled as well. However IFN-gamma had no effect on upregulation of JAK-2 and pJAK-2 by IFN-alpha. Taken together IFN-gamma and IFN-alpha exert opposite effects on apoptosis in HSC. This effect is mediated by their counteracting effect on HSP70 expression which acts antiapoptotic at the level of caspase-8.

Oligo-3-hydroxybutyrates as potential carriers for drug delivery

In the present paper we describe the synthesis and toxicity studies of well-defined tailor made oligo-[R,S]-3-hydroxybutyrates (OHBs). The results indicate potential applicability of these nano-polymers as drug delivery carriers. Several OHBs of number average molecular weight (M(n)) ranging from 800 to 2400 have been synthesized and tested on transformed hamster V79 fibroblasts and murine melanoma B16(F10) cells using the 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide (MTT) based drug resistance and clonogenic survival assays. We show that 96-h incubation of cells with 1-9 microg/ml of OHBs did not affect cell viability. Incubation of OHBs with rat hepatoma FTO-2B cells stably transfected with chloramphenicol acetyltransferase (CAT) gene ligated to heat-inducible hsp70i gene promoter demonstrated that OHBs did not induce cellular stress response. Finally, we demonstrate that doxorubicin conjugated with OHB is effectively taken up by murine melanoma B16(F10) cells in vitro and localizes in the cytoplasm. These data show for the first time that tailor-made biodegradable and biocompatible oligomers of 3-hydroxybutyric acid can be taken into consideration as effective, non-toxic vectors for delivery of drugs in a conjugated form.

Oxidative-stress potency of organic extracts of diesel exhaust and urban fine particles in rat heart microvessel endothelial cells

Exposure to fine particulate materials is associated with an increase in mortality rate of cardiovascular diseases. Particles deposited in the lung may affect the vascular system both directly (leaching of soluble components from particles) and indirectly (via cytokines and mediators). The present study addressed cytotoxicity and oxidative stress potency of organic extracts of diesel exhaust particles (OE-DEP) and urban fine particles (OE-UFP) in rat heart microvessel endothelial (RHMVE) cells. The LC(50) values of OE-DEP and OE-UFP were calculated to be 17 and 34 microg/ml, respectively, suggesting that OE-DEP was more cytotoxic than OE-UFP. The viability of OE-DEP- and OE-UFP-exposed cells was ameliorated by N-acetyl-L-cysteine (NAC). The cell monolayer was exposed to 0 (control), 1, 3, and 10 microg/ml OE-DEP for 6 h and mRNA levels of antioxidant enzymes such as heme oxygenase-1 (HO-1), thioredoxin peroxidase 2 (TRPO), glutathione S-transferase P subunit (GST-P), and NADPH dehydrogenase (NADPHD) were quantitated by northern analysis. All those mRNA levels increased dose-dependently with OE-DEP and HO-1 mRNA showed the most marked response to OE-DEP. mRNA levels of those antioxidant enzymes and heat shock protein 72 (HSP72) in OE-DEP-exposed cells were higher than those of OE-UFP-exposed cells as compared at the same concentration. The transcription levels of HO-1 and HSP72 in OE-DEP- and OE-UFP-exposed cells were also reduced by NAC. Those results suggest that the organic fraction of particulate materials in the urban air has a potency to cause oxidative stress to endothelial cells and may be implicated in cardiovascular diseases through functional changes of endothelial cells.

Effects of heat shock protein 70 (Hsp70) on arsenite-induced genotoxicity

Arsenic, a human carcinogen, is genotoxic, although its mechanism(s) of action for tumorigenesis is not well understood. Among the toxicity-related properties of this chemical are its clastogenic and aneugenic activities, as well as its capacity for inducing stress-response in the form of elevated heat shock protein (HSP) expression. In the present study, we evaluated the effects of Hsp70 expression on arsenite (As)-induced structural and numerical chromosome anomalies in human cells. Human MCF-7 Tet-off cells stably transfected with a pTRE/Hsp70-1 transgene construct were used to regulate Hsp70 levels prior to in vitro As exposures. Separate cultures of relatively high vs. low Hsp70-expressing cells were established. A cytokinesis block micronucleus assay with kinetochore immunostaining was used to detect micronuclei (MN) derived from chromosome breakage (K-MN) or loss (K+MN). These studies demonstrated significant increases in micronucleus frequencies in response to As following either a long exposure (5 or 10 microM for 46 hr), or short exposure (10 or 40 microM for 8 hr) protocol. Overall, the long protocol was more efficient in producing K+MN and cells with multiple MN. Overexpressing Hsp70 resulted in significant reductions in the percent of cells positive for MN for both the long and short As exposure protocols. Both K+ and K- types of As-induced MN were lower in cells with elevated Hsp70 as compared to cells without overexpression of Hsp70. We conclude that the dose and duration of As exposure influence the type as well as amount of chromosomal alteration produced and that inducible Hsp70 protects against both the clastogenic and aneugenic effects of this chemical.