ATP-binding domain of heat shock protein 70 is essential for its effects on the inhibition of the release of the second mitochondria-derived activator of caspase and apoptosis in C2C12 cells

Computational and experimental characterization of isomers of escin-induced renal cytotoxicity by inhibiting heat shock proteins

Escin is a natural mixture of triterpene saponins, exhibits anti-oedematous properties and promotes venous drainage by oral administration or injection. Upon clinical application of escin, adverse kidney reactions have been reported and the nephrotoxic mechanism responsible for this reaction remains elusive. In the present study, four isomeric escins (β-form: escin Ia and escin Ib; α-form: isoescin Ia and isoescin Ib) were found severely decreasing the cell viability of human kidney (HK-2) cells. A decline in HK-2 cell viability caused by sodium aescinate (a mixture of four isomers) was reduced after β-glucuronidase hydrolysis. In addition, sodium aescinate concentration-dependently inhibited the expression level of heat shock proteins (HSPs) in the Madin-Darby Canine Kidney (MDCK) cells. Moreover, with molecular docking and molecular dynamics simulation, these four isomeric escins could directly bind to the ATP-binding domain of HSP70 and HSP90, thus competitively inhibiting the function of HSPs. Escin Ia is bound to HSPs with the lowest binding free energy, which is consistent with the observation that escin Ia most severely decreases HK-2 cell viability. Thus, we demonstrate a heretofore unknown molecular mechanism of escin-induced renal cytotoxicity as well as identify HSPs as potential targets for the renal cytotoxic effect of escin.

Nucleolin regulates the proliferation of vascular smooth muscle cells in atherosclerotic via Aurora B

Vascular smooth muscle cells (VSMCs) play a significant role in atherosclerosis. As a multifunctional protein, nucleolin (NCL) is involved in many important physiological and pathological processes. In this study, we aimed to investigate the role of nucleolin in VSMCs proliferation and cell cycle. The expression of nucleolin increased in VSMCs of mice with aortas advanced plaques. With the left common carotid-artery ligation-injury model, immunofluorescence staining revealed that nucleolin and Ki67 expression increased in VSMCs in mice left carotid artery compared with right carotid artery after surgery. POVPC or ox-LDL up-regulated nucleolin mRNA and protein expression in a dose- and time-dependent manner in HAVSMCs. POVPC (5μg/ml) or ox-LDL (50μg/ml) promoted the proliferation of HAVSMCs. Nucleolin ablation relieved the pro-proliferation role of VSMCs. The cell cycle assay and cell ability results showing that POVPC or ox-LDL increased the proliferation, but nucleolin ablation inhibited the proliferation of HAVSMCs. And nucleolin ablation can prevent DNA replication at S phase and induce cell cycle arrest in S phase. The bioinformatics database predicts protein-protein interactions with nucleolin and aurora B. Nucleolin overexpression and ablation affected the expression of aurora B. These findings indicate for the first time that nucleolin actively involved the proliferation of VSMCs via aurora B.

LncRNA H19 is involved in myocardial ischemic preconditioning via increasing the stability of nucleolin protein

Myocardial ischemic preconditioning (IP) is defined as a brief period of myocardial ischemia/reperfusion (I/R) that significantly reduces injury during the subsequent exposure to long-term I/R. However, the underlying mechanisms of myocardial IP are yet to be elucidated. This study investigated the expression and roles of long noncoding RNA (lncRNA) H19 in myocardial IP in vitro and in vivo. LncRNA H19 expression levels were analyzed by quantitative reverse-transcription polymerase chain reaction, cell viability was determined by the Cell Counting Kit-8 assay, apoptosis was evaluated based on the caspase 3 activity, and RNA immunoprecipitation was performed to examine the interaction between lncRNA H19 and nucleolin. The results of this study showed that lncRNA H19 expression was significantly upregulated in mouse hearts subjected to myocardial IP, in rat H9C2 cells exposed to H2 O2 preconditioning (H2 O2 -PC), and in neonatal rat cardiomyocytes subjected to hypoxia preconditioning. H19 knockdown abrogated the H2 O2 -PC-mediated protection in cardiomyocytes evidenced by the decreased cell viability and increased caspase-3 activity. Conversely, H19 overexpression enhanced the protective role of H2 O2 -PC in cardiomyocytes. In addition, H19 overexpression increased the expression of nucleolin, whereas H19 ablation abrogated H2 O2 -PC-induced upregulation of nucleolin in cardiomyocytes. Furthermore, H19 overexpression increased the stabilization of nucleolin; an interaction between H19 and nucleolin was identified using the RNA-protein interaction studies. Furthermore, nucleolin small interfering RNA relieved the protective role of lncRNA H19. These findings demonstrated that the lncRNA H19 is involved in myocardial IP via increasing the stability of nucleolin protein and lncRNA H19 may represent a potential therapeutic target for the treatment of the myocardial injury.

Muscle Injury Associated Elevated Oxidative Stress and Abnormal Myogenesis in Patients with Idiopathic Scoliosis

Idiopathic scoliosis (IS) is a disease with unknown etiology characterized by spinal rotation asymmetry. Reports describing the histochemical and pathological analyses of IS patients have shown that necrosis, fibrosis and fatty involution occurred on the apex paraspinal muscles. However, research on the changes in the paraspinal muscles of IS patients compared with those in matched controls is rare; thus, the basic mechanism of how paraspinal muscles are injured in IS patients is still unclear. In this study, we investigated the morphological changes of paraspinal muscles in the control group and IS patients, and the possible mechanisms were examined in vivo and in vitro. Increased myofiber necrosis was found on both sides of the apex paraspinal muscles of IS patients compared with those of the control group, and the number of TUNEL-positive apoptotic cells was also increased. Apoptosis signaling pathways, including pro-apoptosis proteins such as cleaved-caspase 3 and cytochrome c, were markedly upregulated, whereas the anti-apoptotic Bcl-2/Bax was significantly downregulated in IS patients compared with the control group. Moreover, PGC-1α and SOD1 were upregulated in accordance with the increased ROS production in IS patients. The distribution of myofiber types, as well as the mRNA levels of type IIa myofiber marker MYH2 and the important myogenesis regulator MYOG were remarkably changed in IS patients. In addition, C2C12 or human skeletal muscle mesenchymal progenitor cells treated with antimycin A in glucose-free and serum-free culture medium, which can activate oxidative stress and induce apoptosis, showed similar patterns of the changed distribution of myofiber types and downregulation of MYH2 and MYOG. Altogether, our study suggested that the extents of severe muscle injury and accumulated oxidative stress were increased in IS patients compared with the control group, and the abnormal myogenesis was also observed in IS patients. Since elevated oxidative stress can lead to apoptosis and the dysregulation of myogenesis in muscle cells, it may be associated with the pathological changes observed in IS patients and contribute to the development and progression of IS.

Phosphorylation of nucleolin is indispensable to upregulate miR-21 and inhibit apoptosis in cardiomyocytes

Nucleolin is a multifunctional phosphoprotein and is involved in protecting from myocardial ischemia/reperfusion (I/R) injury. The function of nucleolin is regulated by posttranslational modifications, including phosphorylation and glycosylation. To study whether phosphorylation of nucleolin (P-nucleolin) was involved in the protection from myocardial I/R injury. We investigated the expression pattern of P-nucleolin (Thr-76 and 84) in hearts subjected to I/R injury, or rat cardiac myoblast cells (H9C2) subjected to hydrogen peroxide (H 2 O 2 ). The results showed that the expression of P-nucleolin and the ratio of P-nucleolin/nucleolin were significantly increased both in vivo and in vitro. Mutant nucleolin was obtained by site directed mutagenesis in vitro: threonine at 76 and 84 was replaced by alanine, and we found that the protective effect of nucleolin on apoptosis induced by oxidative stress was dependent on its phosphorylation at 76 and 84 in H9C2 cells. Furthermore, the cardio-protective roles of P-nucleolin (Thr-76 and 84) in H9C2 cardiomyocytes, were attributable to the upregulation of microRNA (miR)-21. Further analysis found that P-nucleolin (Thr-76 and 84) could bind to miR-21, and P-nucleolin colocalized with argonaute 2 (Ago2) in cytoplasm and could interact with Ago2 in a RNA-independent manner under cell oxidative stress. The current study revealed that P-nucleolin (Thr-76 and 84) increased in I/R injury myocardium, P-nucleolin was indispensable to upregulate miR-21 and inhibited apoptosis induced by H 2 O 2 in H9C2 cardiomyocytes. These findings provided new insight into the molecular mechanisms of nucleolin in myocardial I/R injury and oxidative stress cells.

Nucleolin protects against doxorubicin-induced cardiotoxicity via upregulating microRNA-21

Nucleolin is a multifunctional protein and participates in many important biological processes. Our previous study found that nucleolin protects the heart against myocardial ischemia-reperfusion injury. In this study, we aimed to investigate the role of nucleolin in doxorubicin (DOX)-induced cardiotoxicity. The expression pattern of nucleolin in hearts subjected to DOX injury was investigated, and we found that administration of DOX induced nucleolin expression significantly in vivo and in vitro. Gene transfection and RNA interference approaches were used in cardiomyocytes to investigate the function of nucleolin. Nucleolin overexpression protects cardiomyocytes against DOX-induced injury. Nucleolin-ablated cardiomyocytes become susceptible to the injury induced by DOX. The hearts of cardiac-myocyte-specific nucleolin transgenic mice are more resistant to DOX injury. Furthermore, nucleolin upregulates microRNA(miRNA)-21 expression in vivo and in vitro, and the miRNA-21 inhibitor negates the protective effect of nucleolin against injury induced by DOX. These results have demonstrated that nucleolin is involved in the regulation of DOX-induced cardiac injury and dysfunction via the regulation of miRNA-21 expression, and may be a novel therapeutic target for DOX-induced cardiotoxicity.

Oxidative and nitrosative stress pathways in the brain of socially isolated adult male rats demonstrating depressive- and anxiety-like symptoms

Various stressors may disrupt the redox homeostasis of an organism by causing oxidative and nitrosative stress that may activate stressor-specific pathways and provoke specific responses. Chronic social isolation (CSIS) represents a mild chronic stress that evokes a variety of neurobehavioral changes in rats similar to those observed in people with psychiatric disorders, including depression. Most rodent studies have focused on the effect of social isolation during weaning or adolescence, while its effect in adult rats has not been extensively examined. In this review, we discuss the current knowledge regarding the involvement of oxidative/nitrosative stress pathways in the prefrontal cortex and hippocampus of adult male rats exposed to CSIS, focusing on hypothalamic-pituitary-adrenocortical (HPA) axis activity, behavior parameters, antioxidative defense systems, stress signaling mediated by nuclear factor-kappa B (NF-κB), and mitochondria-related proapoptotic signaling. Although increased concentrations of corticosterone (CORT) have been shown to induce oxidative and nitrosative stress, we suggest a mechanism underlying the glucocorticoid paradox whereby a state of oxidative/nitrosative stress may exist under basal CORT levels. This review also highlights the differential susceptibility of prefrontal cortex and hippocampus to oxidative stress following CSIS and suggests a possible cellular pathway of stress tolerance that preserves the hippocampus from molecular damage and apoptosis. The differential regulation of the transcriptional factor NF-κB, and the enzymes inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) following CSIS may be one functional difference between the response of the prefrontal cortex and hippocampus, thus identifying potentially relevant targets for antidepressant treatment.

The cooperation between the autophagy machinery and the inflammasome to implement an appropriate innate immune response: do they regulate each other?

Autophagy is originally described as the main catabolic pathway responsible for maintaining intracellular nutritional homeostasis that involves the formation of a unique vacuole, the autophagosome, and the interaction with the endosome-lysosome pathways. This conserved machinery plays a key role in immune-protection against different invaders, including pathogenic bacteria, intracellular parasites, and some viruses like herpes simplex and hepatitis C virus. Importantly, autophagy is linked to a number of human diseases and disorders including neurodegenerative disease, Crohn's disease, type II diabetes, tumorigenesis, cardiomyopathy, and fatty liver disease. On the other hand, inflammasomes are multiprotein platforms stimulated upon several environmental conditions and microbial infection. Once assembled, the inflammasomes mediate the maturation of pro-inflammatory cytokines and promote phagosome-lysosome fusion to sustain an innate immune response. The intersections between autophagy and inflammasome have been observed in various diseases and microbial infections. This review highlights the molecular aspects involved in autophagy and inflammasome interactions during different medical conditions and microbial infections.

Russell's viper venom affects regulation of small GTPases and causes nuclear damage

Russell's viper with its five sub-species is found throughout the Indian subcontinent. Its venom is primarily hemotoxic. However, its envenomation causes damage to several physiological systems. The present work was aimed to study the dose and time dependent cytotoxic effects of Russell's viper venom (RVV) on human A549 cells grown in vitro. Time dependent changes have been observed in cellular morphology following exposure to RVV. Presence of stress granules, rounding-off of the cells, and formation of punctate structure and loss of cell-cell contact characterized the cellular effects. Fluorescence microscopic studies revealed that apoptotic cell population increased on exposure to RVV. Further to understand the mechanism of these effects, status of small GTPase (smGTPases) expression were studied by Western blot and RT-PCR; as smGTPases play pivotal roles in deciding the cellular morphology, polarity, cell movement and overall signaling cascade. It was shown for the first time that expression patterns of Rac, Rho and CDC42 genes are altered on exposure to RVV. Similarly, significant difference in the expression pattern of HSP70 and p53 at the mRNA levels were noted. Our results confirmed that RVV induces apoptosis in A549 cells; this was further confirmed by AO/EtBr staining as well as caspase-3 assay. All experiments were compared using RVV unexposed cells. We propose for the first time that RVV induces morphological changes in human A549 cells through modulation of smGTPase expression and affects the cellular-nuclear architecture which in turn interferes in proliferation and migration of these cells along with apoptosis.

Protective effect of geranylgeranylacetone against hydrogen peroxide-induced oxidative stress in human neuroblastoma cells

AIMS

Heat shock protein 70 (HSP70), one of the major HSPs, has been reported to suppress apoptosis and formation of pathogenic proteins in neurodegenerative disorders. Geranylgeranylacetone (GGA), an anti-ulcer drug, induces HSP70 and thereby protects against cellular damage in various diseases. We investigated the effect of GGA on hydrogen peroxide (H2O2)-induced neurotoxicity in human neuroblastoma SH-SY5Y cells.

MAIN METHODS

H2O2-induced neuronal toxicity was measured by a CCK-8 assay and Hoechst 33342 staining. We also assessed oxidative stress and apoptosis by measuring reactive oxygen species (ROS) generation with 2′,7′-dichlorofluorescein diacetate (DCFH-DA), caspase-3 activity, and mitogen-activated protein kinase (MAPK) pathway.

KEY FINDINGS

GGA showed a concentration-dependent inhibition on H2O2-induced apoptotic cell death. H2O2-induced induction of HSP70 was enhanced by GGA pretreatment. GGA effectively suppressed the up-regulation of Bax and down-regulation of Bcl-2. GGA also blocked the H2O2-induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). In addition, GGA attenuated H2O2-induced ROS generation and caspase-3 activity.

SIGNIFICANCE

These results demonstrate that GGA protects SH-SY5Y cells from H2O2-induced apoptosis, at least in part by enhancing HSP70 production. Neuroprotective properties of GGA indicate that this compound may be a potential therapeutic agent for the treatment and prevention of neurodegenerative diseases.

Heat shock protein-mediated protection against Cisplatin-induced hair cell death

Cisplatin is a highly successful and widely used chemotherapy for the treatment of various solid malignancies in both adult and pediatric patients. Side effects of cisplatin treatment include nephrotoxicity and ototoxicity. Cisplatin ototoxicity results from damage to and death of cells in the inner ear, including sensory hair cells. We showed previously that heat shock inhibits cisplatin-induced hair cell death in whole-organ cultures of utricles from adult mice. Since heat shock protein 70 (HSP70) is the most upregulated HSP in response to heat shock, we investigated the role of HSP70 as a potential protectant against cisplatin-induced hair cell death. Our data using utricles from HSP70 (-/-) mice indicate that HSP70 is necessary for the protective effect of heat shock against cisplatin-induced hair cell death. In addition, constitutive expression of inducible HSP70 offered modest protection against cisplatin-induced hair cell death. We also examined a second heat-inducible protein, heme oxygenase-1 (HO-1, also called HSP32). HO-1 is an enzyme responsible for the catabolism of free heme. We previously showed that induction of HO-1 using cobalt protoporphyrin IX (CoPPIX) inhibits aminoglycoside-induced hair cell death. Here, we show that HO-1 also offers significant protection against cisplatin-induced hair cell death. HO-1 induction occurred primarily in resident macrophages, with no detectable expression in hair cells or supporting cells. Depletion of macrophages from utricles abolished the protective effect of HO-1 induction. Together, our data indicate that HSP induction protects against cisplatin-induced hair cell death, and they suggest that resident macrophages mediate the protective effect of HO-1 induction.

Nucleolin involved in myocardial ischaemic preconditioning via post-transcriptional control of HSPA1A expression

AIMS

Recent studies have identified the critical roles of nucleolin in a variety of cellular processes, including regulation of viral replication and tumour formation. However, the possible roles of nucleolin in myocardial preconditioning remain undefined.

METHODS AND RESULTS

We used an in vivo rat myocardial ischaemic preconditioning (IP) model (four cycles of 5 min ischaemia and 10 min reperfusion) and cellular hydrogen peroxide preconditioning (H2O2-PC) models. We found that nucleolin mRNA and protein expression showed a time-dependent increase during the recovery of myocardial ischaemic preconditioning in rats and H2O2-PC in neonatal rat cardiomyocytes. Nucleolin overexpression enhanced the protective effects of H2O2-PC, whereas nucleolin ablation abrogated the H2O2-PC-mediated protection in cardiomyocytes. On the other hand, nucleolin overexpression increased the stabilization of the HSPA1A mRNA and the expression of HSPA1A protein in cardiomyocytes, whereas nucleolin ablation abrogated the up-regulation of HSPA1A induced by H2O2-PC in cardiomyocytes. An interaction between nucleolin and HSPA1A mRNA was further identified using the RNA-protein interaction studies. Reporter gene assays, which depended on the untranslated regions (UTR) of HSPA1A mRNA, revealed that the post-transcriptional regulation was mainly attributed to the 3' UTR. Finally, HSPA1A anti-sense oligonucleotides (asODNs) attenuated the protective effect of nucleolin in cardiomyocytes.

CONCLUSION

These results indicate that nucleolin is up-regulated and involved in myocardial protection of ischaemic preconditioning via a post-transcriptional control of HSPA1A expression.

Nucleolin protects the heart from ischaemia-reperfusion injury by up-regulating heat shock protein 32

AIMS

Nucleolin plays important roles in a variety of cellular processes. In this study, we aimed to investigate the role of nucleolin in cardiac ischaemia-reperfusion (I-R) injury.

METHODS AND RESULTS

We investigated the expression pattern of nucleolin in hearts subjected to I-R, or neonatal rat cardiomyocytes subjected to hypoxia-re-oxygenation. We found that nucleolin expression was significantly down-regulated and the cleaved protein was present, both in vivo and in vitro. Gene transfection and RNA interference approaches were employed in cardiomyocytes to investigate the function of nucleolin. Over-expression of nucleolin was cytoprotective, whereas nucleolin ablation enhanced both hypoxia- and H₂O₂-induced cardiomyocyte death. Furthermore, transgenic mice with cardiac-specific over-expression of nucleolin were resistant to I-R injury as indicated by decreased cellular necrosis and decreased infarct size. The cardio-protective roles of nucleolin in cardiomyocytes, are attributable to the interaction of nucleolin with the mRNA of heat shock protein 32 (Hsp32), resulting in an increase of Hsp32 mRNA stability, and subsequent up-regulation of Hsp32 expression. The selective Hsp32 inhibitor, zinc protoporphyrin-IX, abrograted the cardiac protection mediated by nucleolin.

CONCLUSION

This study has demonstrated that nucleolin is involved in the regulation of I-R-induced cardiac injury and dysfunction via the regulation of Hsp32, and may be a novel therapeutic target for ischaemic heart diseases.

Blockade of PI3K/AKT pathway enhances sensitivity of Raji cells to chemotherapy through down-regulation of HSP70

Up-regulation of heat shock protein 70 (HSP70) could be elicited primarily by heat in former studies, and this was proved to be associated with cancer progression. Burkitt's lymphoma is one of highly aggressive B-cell non-Hodgkin’s lymphoma and is one of the fastest growing human tumors. To investigate the effect of HSP70 expression on the sensitivity of human Burkitt lymphoma cells (Raji cells) to chemotherapy and its role in the involvement of PI3K/AKT pathway, we evaluated the effects of LY294002, a PI3K inhibitor, on the expression of HSP70 and cell sensitivity to adriamycin (ADM) or cisplatin (DDP). In present study, expressions of HSP70, AKT and phosphorylated AKT (p-AKT) in Raji cells were measured by Western-Blot. Apoptosis index of Raji cells was examined by flow cytometry. Cytotoxicities of adriamycin (ADM) and cisplatin (DDP) were determined by WST-8 assay. We found that hyperthermia (42 degrees for 1 hour) up-regulated the expression of HSP70 expression and blockade of PI3K/AKT pathway down-regulated HSP70 expression in Raji cells. Compared to cells treated with ADM or DDP alone, hyperthermia protected cells from chemotherapy while LY294002 enhanced sensitivity of Raji cells to chemotherapy. Our results suggested down-regulation of HSP70 expression by blockade of PI3K/AKT pathway maybe responsible for the increased sensitivity of Raji cells to chemotherapy. Targeting PI3K/AKT pathway or inhibiting HSP70 expression may be beneficial for chemotherapy treatment of Burkitt lymphoma patients.

Intracellular heat shock protein-70 negatively regulates TLR4 signaling in the newborn intestinal epithelium

Necrotizing enterocolitis (NEC) is the leading cause of gastrointestinal-related mortality in premature infants, and it develops under conditions of exaggerated TLR4 signaling in the newborn intestinal epithelium. Because NEC does not develop spontaneously, despite the presence of seemingly tonic stimulation of intestinal TLR4, we hypothesized that mechanisms must exist to constrain TLR4 signaling that become diminished during NEC pathogenesis and focused on the intracellular stress response protein and chaperone heat shock protein-70 (Hsp70). We demonstrate that the induction of intracellular Hsp70 in enterocytes dramatically reduced TLR4 signaling, as assessed by LPS-induced NF-κB translocation, cytokine expression, and apoptosis. These findings were confirmed in vivo, using mice that either globally lacked Hsp70 or overexpressed Hsp70 within the intestinal epithelium. TLR4 activation itself significantly increased Hsp70 expression in enterocytes, which provided a mechanism of autoinhibition of TLR4 signaling in enterocytes. In seeking to define the mechanisms involved, intracellular Hsp70-mediated inhibition of TLR4 signaling required both its substrate-binding EEVD domain and association with the cochaperone CHIP, resulting in ubiquitination and proteasomal degradation of TLR4. The expression of Hsp70 in the intestinal epithelium was significantly decreased in murine and human NEC compared with healthy controls, suggesting that loss of Hsp70 protection from TLR4 could lead to NEC. In support of this, intestinal Hsp70 overexpression in mice and pharmacologic upregulation of Hsp70 reversed TLR4-induced cytokines and enterocyte apoptosis, as well as prevented and treated experimental NEC. Thus, a novel TLR4 regulatory pathway exists within the newborn gut involving Hsp70 that may be pharmacologically activated to limit NEC severity.

Increased stability of Bcl-2 in HSP70-mediated protection against apoptosis induced by oxidative stress

We have previously shown that heat shock protein 70 (HSP70) markedly inhibits H(2)O(2)-induced apoptosis in mouse C2C12 myogenic cells by reducing the release of Smac. However, the molecular mechanism by which HSP70 interferes with Smac release during oxidative stress-induced apoptosis is not understood. In the current study, we showed that HSP70 increased the stability of Bcl-2 during oxidative stress. An antisense phosphorothioate oligonucleotide against Bcl-2 caused selective inhibition of Bcl-2 protein expression induced by HSP70 and significantly attenuated HSP70-mediated cell protection against H(2)O(2)-induced release of Smac and apoptosis. Taken together, our results indicate that there are important relationships among HSP70, Bcl-2, release of Smac, and induction of apoptosis by oxidative stress.

Prolonged moderate-intensity aerobic exercise does not alter apoptotic signaling and DNA fragmentation in human skeletal muscle

Apoptosis in skeletal muscle plays an important role in age- and disease-related tissue dysfunction. Physical activity can influence apoptotic signaling; however, this process has not been well studied in human skeletal muscle. The purpose of this study was to perform a comprehensive analysis of apoptosis-related proteins/enzymes, DNA fragmentation, and oxidative stress in skeletal muscle of humans during an acute bout of prolonged moderate-intensity exercise. Eight healthy, recreationally active individuals (age 20.8 +/- 0.5 yr, Vo(2peak) 51.2 +/- 0.9 ml . kg(-1) . min(-1), BMI 21.5 +/- 0.8 kg/m(2)) exercised on a cycle ergometer at approximately 60% Vo(2peak) for 2 h. Muscle biopsies were obtained at rest as well as at 60 and 120 min of exercise. Although exercise was associated with a significant whole body and muscle metabolic response, there were no significant changes in the content of antiapoptotic (ARC, Bcl-2, Hsp70, XIAP) and proapoptotic (AIF, Bax, Smac) proteins, activity of proteolytic enzymes (caspase-3, caspase-8, caspase-9), DNA fragmentation, or TUNEL-positive nuclei in skeletal muscle. Furthermore, the protein levels of several antioxidant enzymes (catalase, CuZnSOD, MnSOD), concentrations of GSH and GSSG, and degree of ROS generation in skeletal muscle were not altered by exercise. Fiber type-specific analysis also revealed that ARC (P < 0.001) and Hsp70 (P < 0.05) protein were significantly higher in type I compared with type IIA and type IIAX/X fibers; however, protein levels were not affected by exercise. These findings suggest that a single bout of prolonged moderate-intensity aerobic exercise is not sufficient to alter apoptotic signaling in skeletal muscle of healthy humans.

Nucleolin/C23 mediates the antiapoptotic effect of heat shock protein 70 during oxidative stress

Although heat shock protein 70 (Hsp70) has been shown to markedly inhibit H(2)O(2)-induced apoptosis in C2C12 cells, and nucleolin/C23 has also been implicated in apoptosis, the relationship of these two molecules is still largely unknown. The aim of the current study was to investigate the potential involvement of nucleolin/C23 in the antiapoptotic mechanism of Hsp70. We found that primary cultures of neonatal rat cardiomyocytes underwent apoptosis upon H(2)O(2) treatment, and in these cells nucleolin/C23 protein was highly unstable and had a half-life of less than 4 h. However, transfection with Hsp70 greatly stabilized nucleolin/C23 and also protected the cells from H(2)O(2)-induced apoptosis. When nucleolin/C23 was knocked down with an antisense oligomer, H(2)O(2)-induced apoptosis became more severe, even in Hsp70-overexpressed cells, demonstrating an essential role of nucleolin/C23 in the antiapoptotic effects of Hsp70. Similar results were obtained by both nuclear morphology observation and caspase-3 activity assay. Therefore, these data provide evidence that nucleolin/C23 is an essential downstream effecter of Hsp70 in the protection of cardiomyocytes against oxidative stress-induced apoptosis.

Facilitating Akt clearance via manipulation of Hsp70 activity and levels

Members of the 70-kDa heat shock family can control and manipulate a host of oncogenic client proteins. This role of Hsp70 in both the folding and degradation of these client proteins makes it a potential drug target for certain forms of cancer. The phenothiazine family of compounds, as well as the flavonoid myricetin, was recently shown to inhibit Hsp70-ATPase activity, whereas members of the dihydropyrimidine family stimulated ATPase function. Akt, a major survival kinase, was found to be under the regulation of Hsp70, and when the ATPase activity of Hsp70 was increased or decreased by these compounds, Akt levels were also increased or decreased. Also, increasing Hsp70 levels concurrent with inhibition of its ATPase function synergistically reduced Akt levels to a greater extent than either manipulation alone, providing new insights about client fate decisions. Akt reductions mediated by Hsp70 inhibitors were prevented when Hsp70 expression was silenced with small interfering RNA. Inhibiting Hsp70 ATPase function produced cytotoxic events only in breast cancer cell lines where Akt dysfunction was previously shown, suggesting therapeutic specificity depending on the Hsp70 client profile. Thus, increasing Hsp70 levels combined with inhibiting its ATPase function may serve to dramatically reduce Akt levels and facilitate cell death in certain types of cancer.