Phosphorylation of AKT induced by phosphorylated Hsp27 confers the apoptosis-resistance in t-AUCB-treated glioblastoma cells in vitro

Phosphorylated Hsp27 promotes adriamycin resistance in breast cancer cells through regulating dual phosphorylation of c-Myc

Chemotherapy resistance of breast cancer cells is one of the major factors affecting patient survival rate. Heat shock protein 27 (Hsp27) is a member of the small heat shock protein family that has been reported to be associated with chemotherapy resistance in tumor cells, but the exact mechanism is not fully understood. Here, we explored the regulation of Hsp27 in adriamycin-resistant pathological conditions of breast cancer in vitro and in vivo. We found that overexpression of Hsp27 in MCF-7 breast cancer cells reversed DNA damage induced by adriamycin, and thereby reduced subsequent cell apoptosis. Non-phosphorylated Hsp27 accelerated ubiquitin-mediated degradation of c-Myc under normal physiological conditions. After stimulation with adriamycin, Hsp27 was phosphorylated and translocated from the cytoplasm into the nucleus, where phosphorylated Hsp27 upregulated c-Myc and Nijmegen breakage syndrome 1 (NBS1) protein levels thus leading to ATM activation. We further showed that phosphorylated Hsp27 promoted c-Myc nuclear import and stabilization by regulating T58/S62 phosphorylation of c-Myc through a protein phosphatase 2A (PP2A)-dependent mechanism. Collectively, the data presented in this study demonstrate that Hsp27, in its phosphorylation state, plays a critical role in adriamycin-resistant pathological conditions of breast cancer cells.

Functional Diversity of Mammalian Small Heat Shock Proteins: A Review

The small heat shock proteins (sHSPs), whose molecular weight ranges from 12∼43 kDa, are members of the heat shock protein (HSP) family that are widely found in all organisms. As intracellular stress resistance molecules, sHSPs play an important role in maintaining the homeostasis of the intracellular environment under various stressful conditions. A total of 10 sHSPs have been identified in mammals, sharing conserved α-crystal domains combined with variable N-terminal and C-terminal regions. Unlike large-molecular-weight HSP, sHSPs prevent substrate protein aggregation through an ATP-independent mechanism. In addition to chaperone activity, sHSPs were also shown to suppress apoptosis, ferroptosis, and senescence, promote autophagy, regulate cytoskeletal dynamics, maintain membrane stability, control the direction of cellular differentiation, modulate angiogenesis, and spermatogenesis, as well as attenuate the inflammatory response and reduce oxidative damage. Phosphorylation is the most significant post-translational modification of sHSPs and is usually an indicator of their activation. Furthermore, abnormalities in sHSPs often lead to aggregation of substrate proteins and dysfunction of client proteins, resulting in disease. This paper reviews the various biological functions of sHSPs in mammals, emphasizing the roles of different sHSPs in specific cellular activities. In addition, we discuss the effect of phosphorylation on the function of sHSPs and the association between sHSPs and disease.

Effect of Diammonium Glycyrrhizinate in Improving Focal Cerebral Ischemia-Reperfusion Injury in Rats Through Multiple Mechanisms

OBJECTIVE

Acute ischemic stroke is a current major disabling and killer disease worldwide. We aimed to investigate the protective effect and mechanism of diammonium glycyrrhizinate in alleviating acute ischemic stroke.

METHODS

Ninety male Sprague Dawley (SD) rats (weighing 250-300 g) were randomly allocated into three groups: sham operation group (sham group), diammonium glycyrrhizinate group (DG group) and model group (model group) each with 30 individuals. A rat model of focal CIR injury was established by reversible middle cerebral artery occlusion.

RESULTS

Zea-Longa scores for the rats in the DG group and model group were 7-fold and 8-fold higher than those of the sham group 2 h post-surgery (2.90 ± 0.99 vs. 0.30 ± 0.53, P < .05; 2.80 ± 0.61 vs. 0.30 ± 0.53, P < .05, respectively). Three days after model establishment, the scores of DG group were 26.92% lower compared with those of the model group (1.90 ± 0.76 vs. 2.60 ± 0.62, P < .05). In addition, compared with the sham group, the number of Nissl bodies and Akt-positive cells in were 27.35% and 30.42% lower in the hippocampus of the DG group (Nissl bodies: 83.40 ± 7.01 vs. 115.60 ± 11.97, p < 0.05; Akt-positive cells: 94.70 ± 8.23 vs. 136.10 ± 10.37, P < .05) and 58.65% and 57.31% lower in the model group (Nissl bodies: 47.80 ± 4.91 vs. 115.60 ± 11.97, P < .05; Akt-positive cells: 58.10 ± 4.98 vs. 136.10 ± 10.37, P < 0.05), respectively. However, the number of Nissl bodies and Akt-positive cells in the hippocampus of DG group were 74.48% and 62.9% higher compared with the model group, respectively (Nissl bodies: 83.40 ± 7.01 vs. 47.80 ± 4, P < 0.05; Akt-positive cells: 94.70 ± 8.23 vs. 58.10 ± 4.98, P < .05). In addition, compared with the sham group, the number of caspase-3-positive cells, the expression level of p38 mitogen-activated protein kinase (MAPK) and the expression of matrix metallopeptidase 9 (MMP-9) were 2-fold, 34.38%, 64.78% higher in the DG group (caspase-3-positive cells: 78.70 ± 6.52 vs. 27.10 ±3.00, P < .05; p-38MAPK: 0.43 ± 0.15 vs. 0.32 ± 0.10, P < .05; MMP-9: 14.83 ± 1.18 vs. 9.00 ± 2.05, P < .05, respectively), and more than 3-fold, 1-fold and 1-fold higher in model group (caspase-3-positive cells: 121.10 ± 11.04 vs. 27.10 ± 3.00, P < .05; p-38MAPK: 0.70 ± 0.12 vs. 0.32 ± 0.10, P < .05; MMP-9: 19.00 ± 1.90 vs. 9.00 ± 2.05, P < .05), respectively. However, the number of caspase-3-positive cells and the expression levels of p-38MAPK and MMP-9 were 35.01%, 38.57% and 28.12% lower in DG group compared with the model group (caspase-3-positive cells: 78.70 ± 6.52 vs. 121.10 ± 11.04, P < .05; p-38MAPK: 0.43 ± 0.15 vs. 0.70 ± 0.12, P < .05; MMP-9: 14.83 ± 1.18 vs. 19.00 ± 1.90, P < .05).

CONCLUSIONS

Our study showed that diammonium glycyrrhizinate at 20 mg/kg/day had a protective effect on cerebral ischemia-reperfusion injury in rats by promoting formation of Nissl bodies and increasing protein expression of Akt while decreasing that of caspase-3, p38 MAPK and MMP-9, either directly or indirectly, by inhibiting apoptosis and reducing neuroinflammation. All these mechanisms resulted in improved overall neurological function.

Involvement of PI3K Pathway in Glioma Cell Resistance to Temozolomide Treatment

The aim of the study was to investigate the anticancer potential of LY294002 (PI3K inhibitor) and temozolomide using glioblastoma multiforme (T98G) and anaplastic astrocytoma (MOGGCCM) cells. Apoptosis, autophagy, necrosis, and granules in the cytoplasm were identified microscopically (fluorescence and electron microscopes). The mitochondrial membrane potential was studied by flow cytometry. The activity of caspases 3, 8, and 9 and Akt was evaluated fluorometrically, while the expression of Beclin 1, PI3K, Akt, mTOR, caspase 12, and Hsp27 was determined by immunoblotting. SiRNA was used to block Hsp27 and PI3K expression. Cell migration and localization of Hsp27 were tested with the wound healing assay and immunocytochemistry, respectively. LY294002 effectively diminished the migratory potential and increased programmed death of T98G and MOGGCCM. Autophagy was dominant in MOGGCCM, while apoptosis was dominant in T98G. LY294002 with temozolomide did not potentiate cell death but redirected autophagy toward apoptosis, which was correlated with ER stress. A similar effect was observed after blocking PI3K expression with siRNA. Transfection with Hsp27 siRNA significantly increased apoptosis related to ER stress. Our results indicate that inhibition of the PI3K/Akt/mTOR pathway sensitizes glioma cells to apoptosis upon temozolomide treatment, which was correlated with ER stress. Hsp27 increases the resistance of glioma cells to cell death upon temozolomide treatment.

Reduction of SCUBE3 by a new marine-derived asterosaponin leads to arrest of glioma cells in G1/S

Many saponins are characterized as exhibiting a wide spectrum of antitumor activities at low concentrations. Most of the previous studies that aimed to understand the mechanisms underlying anticancer saponins have focused on numerous classical signaling pathways. However, at the oncogene level, little is known about the action of saponins, especially asterosaponin. In this study, CN-3, a new asterosaponin isolated from the starfish Culcita novaeguineae, decreased the proliferation of U87 and U251 cells at low doses in a dose- and time-dependent manner. Microarray analysis revealed CN-3 significantly induced the differential expression of 661 genes that are related to its antiglioma effect in U251. Nine downregulated genes (SCUBE3, PSD4, PGM2L1, ACSL3, PRICKLE1, ABI3BP, STON1, EDIL3, and KCTD12) were selected, for further verification of their low expression. Then, shRNA transfection and high-content screening were performed and significantly decreased U251 cell proliferation rate was only observed for the SCUBE3 knockdown. qPCR confirmed SCUBE3 was highly expressed in U251 and U87 cells, and had medium expression levels in U373 cells. Real-time cellular analysis using iCELLigence demonstrated that SCUBE3 is an oncogene in U251 and U87 cells, with knockdown of SCUBE3 inhibiting U251 and U87 cell proliferation while, conversely, SCUBE3 overexpression promoted their proliferation. Afterward, SCUBE3 protein was found to have high expression in primary glioma specimens from patients examined by immunohistochemistry but low expression in normal brain. PathScan ELISA analysis in conjunction with TEM observation demonstrated that the effect of SCUBE3 knockdown in U251 does not appear to be related to the induction of apoptosis. Employing CCK-8, iCELLigence, flow cytometry, western blotting, and shRNA transfection (knockdown and overexpression) experiments, we reveal that the reduction of SCUBE3 expression, induced by CN-3, mediated both inhibition and G1/S arrest of U251 via the Akt/p-Akt/p53/p21/p27/E2F1 pathway.

Molecular Chaperones in Cancer Stem Cells: Determinants of Stemness and Potential Targets for Antitumor Therapy

Cancer stem cells (CSCs) are a great challenge in the fight against cancer because these self-renewing tumorigenic cell fractions are thought to be responsible for metastasis dissemination and cases of tumor recurrence. In comparison with non-stem cancer cells, CSCs are known to be more resistant to chemotherapy, radiotherapy, and immunotherapy. Elucidation of mechanisms and factors that promote the emergence and existence of CSCs and their high resistance to cytotoxic treatments would help to develop effective CSC-targeting therapeutics. The present review is dedicated to the implication of molecular chaperones (protein regulators of polypeptide chain folding) in both the formation/maintenance of the CSC phenotype and cytoprotective machinery allowing CSCs to survive after drug or radiation exposure and evade immune attack. The major cellular chaperones, namely heat shock proteins (HSP90, HSP70, HSP40, HSP27), glucose-regulated proteins (GRP94, GRP78, GRP75), tumor necrosis factor receptor-associated protein 1 (TRAP1), peptidyl-prolyl isomerases, protein disulfide isomerases, calreticulin, and also a transcription heat shock factor 1 (HSF1) initiating HSP gene expression are here considered as determinants of the cancer cell stemness and potential targets for a therapeutic attack on CSCs. Various approaches and agents are discussed that may be used for inhibiting the chaperone-dependent development/manifestations of cancer cell stemness.

Therapeutic effects of erythropoietin expressed in mesenchymal stem cells for dilated cardiomyopathy in rat

Dilated cardiomyopathy (DCM) is considered as the final common response of myocardium to diverse genetic and environmental insults and characterized mainly by left ventricular systolic dysfunction. The current therapies for the treatment of DCM are costly high and outcomes are often unsatisfactory. To date, mesenchymal stem cells (MSCs) have been thought to be an ideal stem cell to repair damaged myocardium but was still within relatively small scales and few cases have been conducted in clinical trials. The use of erythropoietin (EPO), a growth factor produced in the kidneys have been found prevent cardiomyocyte apoptosis. This study was aimed to transplant MSCs into DCM rat bone marrow to express EPO in vivo and investigate the regulation of EPO on cell signaling pathways after transfection. The results found that transplantation of MSCs carrying EPO could significantly relief the cardiac dysfunctions of the DCM rat. This underylying mechanism involved with inhibiting p-NF-κB and p-P38, regulateing and promoting the anti-inflammatory balance, thereby alleviating tissue injury in DCM rats and exhibiting a protective role. Meanwhile, the MSCs + EPO treatment in DCM rat also activated the p-Akt pathway and thus protecting the myocardium from apoptosis in DCM rats. The study revealed an potential therapeutic effect of MSCs and EPO in clinical and provided a molecular mechanism of action for treating DCM.

Multi-kinase inhibitors can associate with heat shock proteins through their NH2-termini by which they suppress chaperone function

We performed proteomic studies using the GRP78 chaperone-inhibitor drug AR-12 (OSU-03012) as bait. Multiple additional chaperone and chaperone-associated proteins were shown to interact with AR-12, including: GRP75, HSP75, BAG2; HSP27; ULK-1; and thioredoxin. AR-12 down-regulated in situ immuno-fluorescence detection of ATP binding chaperones using antibodies directed against the NH₂-termini of the proteins but only weakly reduced detection using antibodies directed against the central and COOH portions of the proteins. Traditional SDS-PAGE and western blotting assessment methods did not exhibit any alterations in chaperone detection. AR-12 altered the sub-cellular distribution of chaperone proteins, abolishing their punctate speckled patterning concomitant with changes in protein co-localization. AR-12 inhibited chaperone ATPase activity, which was enhanced by sildenafil; inhibited chaperone – chaperone and chaperone – client interactions; and docked in silico with the ATPase domains of HSP90 and of HSP70. AR-12 combined with sildenafil in a GRP78 plus HSP27 –dependent fashion to profoundly activate an eIF2α/ATF4/CHOP/Beclin1 pathway in parallel with inactivating mTOR and increasing ATG13 phosphorylation, collectively resulting in formation of punctate toxic autophagosomes. Over-expression of [GRP78 and HSP27] prevented: AR-12 –induced activation of ER stress signaling and maintained mTOR activity; AR-12 –mediated down-regulation of thioredoxin, MCL-1 and c-FLIP-s; and preserved tumor cell viability. Thus the inhibition of chaperone protein functions by AR-12 and by multi-kinase inhibitors very likely explains why these agents have anti-tumor effects in multiple genetically diverse tumor cell types.

SPARC overexpression suppresses radiation-induced HSP27 and induces the collapse of mitochondrial Δψ in neuroblastoma cells

Neuroblastoma is the cause of >15% of cancer-associated mortality in children in the USA. Despite aggressive treatment regimens, the long-term survival rate for these children remains at <40%. The current study demonstrates that secreted protein acidic and rich in cysteine (SPARC) suppresses radiation-induced expression of heat shock protein 27 (HSP27) in vivo and suppresses mitochondrial membrane potential (Δψ) in neuroblastoma cells. In the present study, the overexpression of SPARC in SK-N-BE(2) and NB1691 neuroblastoma cell lines suppresses radiation-induced G2M cell cycle arrest, proliferation, HSP27 expression (in vitro and in vivo) and induces the collapse of the mitochondrial Δψ. Gene ontology analysis demonstrated that the overexpression of SPARC combined with irradiation, induces the expression of dissimilar molecular function genes in SK-N-BE(2) and NB1691 cells, providing evidence of a dissimilar response signaling pathway. These results demonstrate that overexpression of SPARC suppresses radiation-induced HSP27 expression in neuroblastoma cells and the combination of SPARC and radiation induces the expression of protein 21, but suppresses neuroblastoma tumor density in in vivo mouse models. SPARC also induces mitochondrial Δψ collapse in SK-N-BE(2) and NB1691 neuroblastoma cells.

Heat shock protein 27 downstream of P38-PI3K/Akt signaling antagonizes melatonin-induced apoptosis of SGC-7901 gastric cancer cells

Background

Despite the fact that melatonin treatment shows some promise in gastric cancer, the molecular mechanisms of gastric cancer cells in response to melatonin remains to be determined.

Methods

The SGC-7901 gastric cancer cells were treated with different concentrations of melatonin for 24 and 48 h. Cell viability was determined by MTT assay, Hoechst 33258 staining and FACS analysis were used to detect apoptotic cells. The contents and activation of apoptosis-related proteins HSP27, Akt and P38 were evaluated by immunoblotting analysis. Then we treated SGC-7901 cells with HSP27-specific siRNA, PI3K inhibitor LY294002 or P38 inhibitor SB203580 to investigate the role of HSP27, Akt and P38 in the anti-apoptotic response of SGC-7901 cells to melatonin.

Results

Melatonin suppressed cell viability and stimulated apoptosis of gastric cancer SGC-7901 cells dose-dependently. Mechanistically, the observed apoptosis was accompanied by the melatonin-induced phosphorylation of HSP27. HSP27-specific siRNA transfection effectively reduced HSP27 phosphorylation and augmented melatonin-induced apoptosis, indicating that HSP27 is resistant to melatonin-induced apoptosis. Moreover, melatonin increased PI3K/Akt activation, LY294002 abrogated HSP27 activation and promoted cell apoptosis induced by melatonin. Furthermore, melatonin increased P38 activity, and P38 inhibitor SB203580 inhibited melatonin-induced PI3K/Akt, HSP27 activation and accelerated cell apoptosis.

Conclusion

In contrast to the well-established anti-cancer properties of melatonin, our study revealed clearly a distinguishable anti-apoptotic pathway induced by melatonin, that is, HSP27 plays a crucial role in apoptotic resistance in melatonin-treated gastric cancer cells, and its activation is most likely via the activation of P38/PI3K/Akt signaling.