Protective Effect of Heat Shock Protein 70 Against Oxidative Stresses in Human Corneal Fibroblasts

We evaluated DNA protection effect of heat shock protein (HSP) against cytotoxic effects of exogenous nitric oxide (NO) and reactive oxygen intermediate (ROI). Cultured human corneal fibroblasts were divided into 4 groups. Control (Group I) was not exposed to a sub-lethal heat treatment. Other 3 groups were exposed to 43℃ for 1 hr, then incubated at 37℃ during different duration (1, 6, 24 hr, Group II, III, IV, respectively). Expression pattern of HSP 70 was analyzed by Western blot. Cell viability was measured by MTT assay and the relationship between HSP 70 expression and DNA damage was examined by terminal deoxyribonucleotidyl transferase mediated dUTP-digoxigenin nick and labeling (TUNEL) stain and single cell gel electrophoresis. Expression pattern of HSP 70 was dependent on recovery times. Cell viability following heat treatment was significantly increased and the TUNEL positive cell number was decreased at 6 hr. In single cell gel electrophoresis, tail moments were increased in a dose-dependent manner by SNAP and X/XO. Following heat treatment, tail moments showed decreased significantly at 6 hr. These results suggest that induction of HSP 70 by sub-lethal heat treatment is closely related with cytoprotective effects against oxidative stresses in human corneal fibroblasts

Knock Down of Heat Shock Protein 27 (HspB1) Induces Degradation of Several Putative Client Proteins

Hsp27 belongs to the heat shock protein family and displays chaperone properties in stress conditions by holding unfolded polypeptides, hence avoiding their inclination to aggregate. Hsp27 is often referenced as an anti-cancer therapeutic target, but apart from its well-described ability to interfere with different stresses and apoptotic processes, its role in non-stressed conditions is still not well defined. In the present study we report that three polypeptides (histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3) were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. In addition, these proteins interacted with Hsp27 complexes of different native size. Altogether, these findings suggest that HDAC6, STAT2 and procaspase-3 are client proteins of Hsp27. Hence, in non stressed cancerous cells, the structural organization of Hsp27 appears to be a key parameter in the regulation by this chaperone of the level of specific polypeptides through client-chaperone type of interactions

HSP70 depletion sensitizes cells to Pter.

<p>A) Representative HSP70 and GAPDH (loading control) immunoblots of proteins extracted from indicated cells. Densitometric analysis of the immunoblots (n = 3) are shown below. B) Inhibition of HSP70 expression by siRNA. Cells were transfected with HSP70 siRNA or GAPDH SiRNA (positive control). Protein levels were measured by western blotting. C) HT29 and MCF7 cells were seeded and transfected with HSP70 siRNA 24 h later. Pter was added at 24 h post-transfection. Cell viability was performed by sulforhodamine B colorimetric assay 48 h later. The number of replicates per experiment was at least six (n = 3). The results were statistically analyzed by ANOVA and the Tukey test (*p<0.05; ***p<0.001 vs. control). D) Cysteine and aspartyl cathepsins were determined in HT29 and MCF7 cells 72 h post- HSP70 siRNA transfection and 24 h after Pter treatment (n = 6). The results were statistically analyzed by ANOVA and the Tukey test (***p<0.001 vs. Pter 50µM).</p

Pterostilbene induces lysosomal membrane permeabilization.

<p>A) Flow cytometry analysis of acridine orange staining after 24 h incubation with indicated concentrations of Pter. Increases in red fluorescence (x-axis), observed in treated cells, indicated changes at the lysosomal membrane. B) Microscopic images of Lysotracker red-stained cells untreated or treated with indicated concentrations of Pter for 24 h. C) Cytosolic cysteine cathepsin (zFRase) activity expressed as percentage of total activity (n = 7) was measured 24 h after Pter addition. D) Cytosolic aspartyl cathepsin activity expressed as percentage of total activity (n = 7) after 24 h of Pter treatment. The results were statistically analyzed by ANOVA and the Tukey test (*p<0.05; **p<0.01; ***p<0.001 vs. control). E) Cathepsins B and D inhibitors, Leupeptin and Pepstatin A, were added 1 h prior to the addition of 50 µM Pter. Cell number was analyzed 24 h later.</p

Effects of pterostilbene on autophagic flux.

<p>Proteins were detected by western blot with LC3A/B (A) or SQSTM1/p62 antibodies (B). Graphic shows the percentage of induction of eGFP-LC3 punctuation/aggregation in control and Pter (50 µM) conditions after 24 h of treatment (A). Densitometric analysis of SQSTM1/p62 correlated with GAPDH levels. The ratio in untreated control cells was set to 100% (B). MCF7-eGFP-LC3 cells were visualized by confocal and transmission electronic microscopy after treatment with 50 µM Pter for 24 h or 100 nM Rapamycin for 1 h (C).</p

Effect of pterostilbene on cell cycle distribution and DNA synthesis.

<p>A) Tumor cells were seeded in six well-plates and treated 24 h later with indicated concentrations of Pter. After 24 h, cells were fixed and stained with propidium iodide as explained under <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044524#s2" target="_blank">material and methods</a>. The DNA content of the cells was analyzed by flow cytometry (10,000 cell events were collected per sample). Representative cell cycle histograms for Control and Pter-treated cells are shown. Results are expressed as % of total cells ± SD (n = 3) (*p<0.05 Vs. Control). B) DNA synthesis was evaluated by BrdU incorporation after 4 h of incubation with Pter followed by 2 h with Pter and 10 µM BrdU.</p

Effect of pterostilbene and resveratrol on tumor cell growth <i>in vitro</i>.

<p>A375, A549, HT29 and MCF7 cells were incubated for 24, 48 or 72 h with indicated concentrations of Pter or Res. Actual cell number was analyzed using the Countess Automated Cell Counter. Results were expressed as relative proliferation index ± SD (n = 4) where control is 100% (*P<0.05).</p

Pter induces caspase-independent cell death.

<p>A) Caspase-3/7 (DEVDase) activities were evaluated 24 and 48 h after addition of Pter. Results are expressed as a relative index of fluorescence ± SD (n = 3) when compared with control (100%). The results were statistically analyzed by ANOVA and contrasted by the Tukey test (*p<0.001; **p<0.01 Vs. Control). B) Induction of apoptosis was assayed by staining with Annexin V. The total percentage of Annexin V-positive cells was determined by flow cytometry 48 h after treatment with DMSO or with increasing concentrations of Pter (*p<0.001 Vs. Control). C) Effect of Pter on tumor cell number in the presence of 20 µM pancaspase inhibitor zVAD fmk, which was added 1 h prior to the addition of 50 µM Pter or vehicle (1.5 µl/ml DMSO). Cell number was analyzed 24 and 48 h later. Results are expressed as relative proliferation index ± SD (n = 3) where control is 100%.</p