Charalampos Angelidis

Hsp70 translocates to the nuclei and nucleoli, binds to XRCC1 and PARP-1, and protects HeLa cells from single-strand DNA breaks

For many years, there has been uncertainty concerning the reason for Hsp70 translocation to the nucleus and nucleolus. Herein, we propose that Hsp70 translocates to the nucleus and nucleoli in order to participate in pathways related to the protection of the nucleoplasmic DNA or ribosomal DNA from single-strand breaks. The absence of Hsp70 in HeLa cells, via Hsp70 gene silencing (knockdown), indicated the essential role of Hsp70 in DNA integrity. Therefore, HeLa Hsp70 depleted cells were very sensitive in heat treatment and their DNA breaks were multiple compared to that of control HeLa cells. The molecular mechanism with which Hsp70 performs its role at the level of nucleus and nucleolus during stress was examined. Hsp70 co-localizes with PARP1 in the nucleus/nucleoli as was observed in confocal studies and binds to the BCRT domain of PARP1 as was revealed with protein–protein interaction assays. It was also found that Hsp70 binds simultaneously to XRCC1 and PARP-1, indicating that Hsp70 function takes place at the level of DNA repair and possibly at the base excision repair system. Making a hypothetical model, we have suggested that Hsp70 is the molecule that binds and interrelates with PARP1 creating the repair proteins simultaneously, such as XRCC1, at the single-strand DNA breaks. Our data partially clarify a previously unrecognized cellular response to heat stress. Finally, we can speculate that Hsp70 plays a role in the quality and integrity of DNA.

Loss of p14ARF confers resistance to heat shock- and oxidative stress-mediated cell death by upregulating β-catenin

The p14ARF is a key tumor suppressor induced mainly by oncogenic stimuli. Although p14ARF does not seem to respond to DNA damage, there are very few data regarding its role in other forms of stress, such as heat shock (HS) and oxidative stress (OS). Here, we report that suppression of p14ARF increased resistance to cell death when cells were treated with H2O2 or subjected to HS. In this setting, protection from cell death was mediated by elevated levels and activity of β‐catenin, as downregulation of β‐catenin alleviated the protective role of p14ARF silencing. Moreover, Hsp70 was shown to regulate β‐catenin protein levels by interacting with p14ARF, suggesting that Hsp70, p14ARF and β‐catenin form a regulatory network. This novel pathway triggers cell death signals when cells are exposed to HS and OS.

Emotional and learning behaviour in mice overexpressing heat shock protein 70.

The effects of inducible heat shock protein 70 (HSP70) on emotional and learning behaviour as well as hippocampal long-term potentiation was investigated in transgenic HSP70 overexpressing mice. In active two-way avoidance learning (shuttle box) as well as spatial 8-arm radial maze learning, the HSP70 overexpressing mice showed diminished learning performance. In several tests there was no indication of differences in anxiety behaviour between transgenic mice and wild-type mice. This suggests that impairment in learning behaviour is unrelated to the learning task and motivational aspects of behaviour. To investigate the neurophysiological correlate of learning, long-term potentiation experiments were performed. In transversal hippocampal slices, an enhanced amplitude of the population spike was found in HSP70 overexpressing mice. It was hypothesised that enhanced potentiation in conjunction with potentiation effects due to learning led to learning impairment.

Arsenic induces VL30 retrotransposition: the involvement of oxidative stress and heat-shock protein 70.

Arsenic is an environmental contaminant with known cytotoxic and carcinogenic properties, but the cellular mechanisms of its action are not fully known. As retrotransposition consists a potent mutagenic factor affecting genome stability, we investigated the effect of arsenic on retrotransposition of an enhanced green fluorescent protein (EGFP)-tagged nonautonomous long terminal repeat (LTR)-retrotransposon viral-like 30 (VL30) in a mouse NIH3T3 cell culture-retrotransposition assay. Flow cytometry analysis of assay cells treated with 2.5-20μM sodium arsenite revealed induction of retrotransposition events in a dose- and time-dependent manner, which was further confirmed as genomic integrations by PCR analysis and appearance of EGFP-positive cells by UV microscopy. Specifically, 20μM sodium arsenite strongly induced the VL30 retrotransposition frequency, which was ~90,000-fold higher than the natural one and also VL30 RNA expression was ~6.6-fold. Inhibition of the activity of endogenous reverse transcriptases by efavirenz at 15μM or nevirapine at 375μM suppressed the arsenite-induced VL30 retrotransposition by 71.16 or 79.88%, respectively. In addition, the antioxidant N-acetyl-cysteine reduced the level of arsenite-induced retrotransposition, which correlated with the rescue of arsenite-induced G2/M cell cycle arrest and cell toxicity. Treatment of assay cells ectopically overexpressing the human heat-shock protein 70 (Hsp70) with 15μM sodium arsenite resulted in an additional ~4.5-fold induction of retrotransposition compared with normal assay cells, whereas treatment with 20μM produced a massive cell death. Our results show for the first time that arsenic both as an oxidative and heat-shock mimicking agent is a potent inducer of VL30 retrotransposition in mouse cells. The impact of arsenic-induced retrotransposition, as a cellular response, on contribution to or explanation of the arsenic-associated toxicity and carcinogenicity is discussed.

Spinal Cord Early Ischemic Preconditioning Activates the Stabilized Fraction of β-Catenin After Thoracoabdominal Aortic Occlusion in Pigs

BACKGROUND Paraplegia after thoracoabdominal aortic surgery is a devastating complication attributed to motor neurons loss and dysfunction, due to spinal cord ischemia. β-Catenin is a protein that has been associated with cell survival and healing and many studies have correlated this protein with late ischemic preconditioning (IPC). Herein we investigate the potential contribution of β-catenin in an early IPC animal model, and its relationship with heat shock protein 70 (Hsp70), suggesting a possible role of this protein as a first window of protection. METHODS A total of 42 pigs were used in an experimental thoracoabdominal aortic occlusion model. Twelve animals were used for neurologic evaluation and were randomly assigned to 2 groups (A and B). The remaining 30 animals were used in experiments for biologic measurements and innunohistochemical studies, and were randomly assigned to 5 groups (1-5). Western blotting analysis and immunoprecipitations were performed to study the levels of β-catenin and its binding relationship with Hsp70. The cellular distribution of β-catenin at various time-points was investigated by immunohistochemical studies. RESULTS According to neurologic evaluation, the animals in the IPC+ischemia group had significantly better neurologic scores compared with those in the ischemia group, indicating a protective role for IPC. The biologic measurements demonstrated a significant (P=0.03) increase in β-catenin levels and translocation of the protein in the nucleus at the end of ischemic preconditioning. CONCLUSIONS Our results suggest a significant role of β-catenin in early IPC protection of spinal cord after thoracoabdominal occlusion, as IPC seems to trigger the activation of the β-catenin stabilized fraction and, thus, its survival pathway.

Increased expression level of Hsp70 in the inner ears of mice by exposure to low frequency noise

&NA; Previous studies showed that people in urban areas are possibly exposed to 60–110 dB of low frequency noise (LFN) defined as noise of ≤100 Hz in their daily life. Previous studies also showed increased health risks by exposure to high levels (130–140 dB) of LFN in animals. However, little is known about the health effects of exposure to an ordinary level of LFN. We biochemically and immunohistochemically assessed the effects of exposure to inaudible LFN for mice (12 h/day of 100 Hz LFN at 95 dB for 5 days), at a level to which people are possibly exposed in daily life, on a murine inner ear by targeting 9 stress‐reactive molecules. There was more than a 5‐fold increased transcript level of heat shock protein 70 (Hsp70) in the whole inner ear exposed to LFN. However, the transcript levels of the other 8 stress‐reactive molecules including Hsp27 and Hsp90 were comparable in LFN‐exposed and unexposed murine inner ears. Only the transcript level of Cebp&bgr; among the previously reported 4 transcriptional activators for Hsp70 expression was more than 3‐fold increased by LFN exposure. Hsp70 transcript expression levels in the inner ears 3 days after LFN exposure were comparable to those in unexposed inner ears. The protein level of Hsp70, but not the levels of Hsp27 and Hsp90, was also increased in the vestibule by LFN exposure. However, hearing levels as well as expression levels of Hsp70 protein in the cochleae were comparable in LFN‐exposed mice and unexposed mice. Our results demonstrated that the inner ear might be one of the organs that is negatively affected by stress from inaudible LFN exposure. Moreover, LFN exposure might increase Hsp70 expression level via Cebp&bgr; in the inner ear. Thus, Hsp70 and Cebp&bgr; levels could be candidates of biomarkers for response to LFN exposure. HighlightsEffects of exposure to an ordinary level of low frequency noise (LFN) were examined.Hsp70 level in the whole inner ear exposed to LFN was increased >5‐fold.The increased Hsp70 had returned to the basal level 3 days after LFN exposure.Effects of LFN on hearing and Hsp70 expression in cochleae are limited.Hsp70 and Cebp&bgr; levels may be biomarkers for response to LFN exposure.