Deletion of the BH1 domain of Bcl-2 accelerates apoptosis by acting in a dominant negative fashion

A quinolinyl resveratrol derivative alleviates acute ischemic stroke injury by promoting mitophagy for neuroprotection via targeting CK2α'

Ischemic stroke (IS) is a serious threat to human health. The naturally derived small molecule (E)-5-(2-(quinolin-4-yl) ethenyl) benzene-1,3-diol (RV01) is a quinolinyl analog of resveratrol with great potential in the treatment of IS. The aim of this study was to investigate the potential mechanisms and targets for the protective effect of the RV01 on IS. The mouse middle cerebral artery occlusion and reperfusion (MCAO/R) and oxygen-glucose deprivation and reperfusion (OGD/R) models were employed to evaluate the effects of RV01 on ischemic injury and neuroprotection. RV01 was found to significantly increase the survival of SH-SY5Y cells and prevent OGD/R-induced apoptosis in SH-SY5Y cells. Furthermore, RV01 reduced oxidative stress and mitochondrial damage by promoting mitophagy in OGD/R-exposed SH-SY5Y cells. Knockdown of CK2α' abolished the RV01-mediated promotion on mitophagy and alleviation on mitochondrial damage as well as neuronal injury after OGD/R. These results were further confirmed by molecular docking, drug affinity responsive target stability and cellular thermal shift assay analysis. Importantly, in vivo study showed that treatment with the CK2α' inhibitor CX-4945 abolished the RV01-mediated alleviation of cerebral infarct volume, brain edema, cerebral blood flow and neurological deficit in MCAO/R mice. These data suggest that RV01 effectively reduces damage caused by acute ischemic stroke by promoting mitophagy through its interaction with CK2α'. These findings offer valuable insights into the underlying mechanisms through which RV01 exerts its therapeutic effects on IS.

Nanosized Titanium Dioxide Induced Apoptosis and Abnormal Expression of Blood-Testis Barrier Junction Proteins Through JNK Signaling Pathway in TM4 Cells

Nanosized titanium dioxide (nano-TiO₂) has been widely used in consumer products. It can cross the blood-testis barrier (BTB), and it has adverse effects on the male reproductive system. However, the specific mechanism has not been fully elucidated. The purpose of this study was to understand the role of the JNK signaling pathway in the apoptosis and abnormal expression of BTB junction proteins induced by nano-TiO₂ in TM4 cells. After different concentration of nano-TiO₂ treatments, the cell viability, apoptosis, mitochondrial membrane potential (Δψm), BTB junction proteins (Claudin-11, ZO-1, β-catenin), apoptosis-related proteins (Bax, Bcl-2, cleaved caspase-9, cleaved caspase-3), and phosphorylated (p)-JNK protein were examined. The results showed that cell viability, apoptosis rates, Δψm, and apoptosis-related protein levels changed in a concentration-dependent manner. Cell viability decreased significantly from 100 μg/mL nano-TiO₂ group. Apoptosis rates increased significantly from 150 μg/mL nano-TiO₂ group, and Δψm decreased significantly from 150 μg/mL nano-TiO₂ group. The protein levels of Bax, cleaved caspase-9, and cleaved caspase-3 increased significantly from 150 μg/mL nano-TiO₂ group, and the protein level of Bcl-2 decreased significantly from 100 μg/mL nano-TiO₂ group. The protein level of p-JNK increased significantly from 100 μg/mL nano-TiO₂ group. Abnormal expression of ZO-1 and β-catenin started from 150 μg/mL nano-TiO₂ group, and abnormal expression of Claudin-11 started from 100 μg/mL nano-TiO₂ group. Cells were treated with JNK inhibitor SP100625 to determine whether the changes of the above indicators in the concentration of 150 μg/mL nano-TiO₂ group can be reversed. We found that SP100625 at 20 μM significantly reversed these effects. These results highlighted that nano-TiO₂ could activate the JNK signaling pathway to induce mitochondria-mediated apoptosis and abnormal expression of BTB junction proteins in TM4 cells.

Hypoxia-induced oxidative stress and apoptosis in gills of scaleless carp (Gymnocypris przewalskii)

Scaleless carp (Gymnocypris przewalskii) are well adapted to low oxygen environment, but their specific adaptation mechanism to hypoxic condition remains unclear. The gill is an important respiratory organ that plays a crucial role in regulating hypoxic stress. Here, we established fish hypoxic stress model, as well as investigated oxidative stress, apoptotic responses, and relative enzyme activities in the gills of scaleless carp after exposure to various levels of hypoxic stress. The results demonstrated that gill lamellar height and basal length increased significantly under severe hypoxic stress, and interval lengths between lamellae increased significantly under hypoxic stress. Furthermore, lamellar epithelial cells underwent apoptosis, cytoplasmic contraction, and mitochondrial expansion, and the number of apoptotic cells increased significantly after exposure to severe hypoxic stress for 24 h. Subsequently, Bcl-2 and Caspase 3 mRNA levels, as well as Bcl-2/Bax expression ratio were significantly increased after exposure to severe hypoxic stress for 24 h, indicating upregulation of anti-apoptotic processes. Moreover, malondialdehyde and hydrogen peroxide levels were significantly increased after exposure to hypoxic stress for 24 h. Superoxide dismutase activity increased significantly after exposure to severe hypoxia for 8 h and then decreased, while glutathione peroxidase activity and total antioxidant capacity increased significantly under hypoxic stress. Taken together, the results indicated that scaleless carp gills respond to acute hypoxic conditions by undergoing lamellar morphology remodeling, enhanced apoptosis, and increased antioxidant enzymatic activity. The study findings provided new insight into the adaptation mechanisms of scaleless carp in response to hypoxic challenge.

Excretory-secretory product of Trichinella spiralis inhibits tumor cell growth by regulating the immune response and inducing apoptosis

The excretory-secretory product (ESP) of Trichinella spiralis (T. spiralis) has been reported to inhibit the growth of various tumor cells, but the mechanism is not yet clear. To explore the effect and mechanism of ESP on liver cancer cells, tumor models were established with H22 cells and then infected with T. spiralis. The results showed that the growth of tumors in mice infected with T. spiralis was significantly inhibited. ESP from adult worms or muscle larvae were then incubated with H22 cells in vitro, and it was found that the ESP could inhibit cell proliferation and promote apoptosis. Subsequently, apoptosis-related proteins in stimulated H22 cells were evaluated, and ESP was found to induce cell apoptosis through the mitochondrial pathway. Additionally, Th-related cytokines were investigated in vivo, and the results showed that the levels of Th1 cytokines were significantly increased in the early stage of T. spiralis infection, while Th2 cytokines increased later than Th1 cytokines, implying that Th1 cytokines with antitumor effects may play a role in inhibiting tumor growth at early stage. In short, ESP can directly induce tumor cell apoptosis and indirectly inhibit tumor cell growth through the host immune system, which may be the antitumor mechanism of T. spiralis infection.

Zearalenone promotes apoptosis of mouse Leydig cells by targeting phosphatase and tensin homolog and thus inhibiting the PI3K/AKT signal pathway

Zearalenone (ZEA) is a mycotoxin with estrogenic activity whose main effect is to impair the reproductive systems of animals. It leads to reproductive disorders in livestock and thus causes serious losses to agriculture and animal husbandry. This study aims to examine whether ZEA induces toxicity in Leydig cells through the PI3K/AKT signaling pathway and also to investigate the role played by the upstream phosphatase and tensin homolog (PTEN) gene. An adenovirus vector model was constructed to interfere with the PTEN gene to investigate whether ZEA promotes the apoptosis of TM3 cells through the PI3K/AKT pathway. Apoptosis was detected cytometrically and the protein expression levels of PTEN, AKT, p-AKT, Bax, and Bcl-2 were evaluated via western blot analysis. The results show that ZEA induces apoptosis of TM3 cells. PTEN expression is significantly increased (P < 0.01), Bax expression is increased (P < 0.05), AKT and p-AKT expression of anti-apoptotic protein is significantly decreased (P < 0.01), and Bcl-2 protein expression is decreased (P < 0.05) in the ZEA group compared with the control group. In the shRNA+ZEA group, the expression levels of PTEN and Bax proteins are significantly decreased (P < 0.01), AKT protein is significantly increased (P < 0.01), and p-AKT protein is increased (P < 0.05) compared with the ZEA group. This study thus demonstrates that ZEA promotes apoptosis of TM3 cells by targeting PTEN and thus inhibiting the PI3K/AKT signal pathway.

Clinical Review: Navitoclax as a Pro-Apoptotic and Anti-Fibrotic Agent

B-cell lymphoma 2 (BCL-2) family proteins primarily work as a programmed cell death regulator, whereby multiple interactions between them determine cell survival. This explains the two major classes of BCL-2 proteins which are anti-apoptotic and pro-apoptotic proteins. The anti-apoptotic proteins are attractive targets for BCL-2 family inhibitors, which result in the augmentation of the intrinsic apoptotic pathway. BCL-2 family inhibitors have been studied extensively for novel targeted therapies in various cancer types, fibrotic diseases, aging-related as well as autoimmune diseases. Navitoclax is one of them and it has been discovered to have a high affinity toward BCL-2 anti-apoptotic proteins, including BCL-2, BCL-W and B-cell lymphoma-extra-large. Navitoclax has been demonstrated as a single agent or in combination with other drugs to successfully ameliorate tumor progression and fibrosis development. To date, navitoclax has entered phase I and phase II clinical studies. Navitoclax alone potently treats small cell lung cancer and acute lymphocytic leukemia, whilst in combination therapy for solid tumors, it enhances the therapeutic effect of other chemotherapeutic agents. A low platelet count has always associated with single navitoclax treatments, though this effect is tolerable. Moreover, the efficacy of navitoclax is determined by the expression of several BCL-2 family members. Here, we elucidate the complex mechanisms of navitoclax as a pro-apoptotic agent, and review the early and current clinical studies of navitoclax alone as well as with other drugs. Additionally, some suggestions on the development of navitoclax clinical studies are presented in the future prospects section.

The anti-apoptotic proteins Bcl-2 and Bcl-xL suppress Beclin 1/Atg6-mediated lethal autophagy in polyploid cells

Inhibition of Aurora-B kinase is a synthetic lethal therapy for tumors that overexpress the MYC oncoprotein. It is currently unclear whether co-occurring oncogenic alterations might influence this synthetic lethality by conferring more or less potency in the killing of tumor cells. To identify such modifiers, isogenic cell lines were utilized to test a variety of cancer genes that have been previously demonstrated to promote survival under conditions of cellular stress, contribute to chemoresistance and/or suppress MYC-primed apoptosis. It was found that Bcl-2 and Bcl-xL, two antiapoptotic members of the Bcl-2 family, can partially suppress the synthetic lethality, but not multinucleation, elicited by a pan-aurora kinase inhibitor, VX-680. Suppression was show to stem from the inhibition of autophagy, specifically in multinucleated cells, rather than a general inhibition of apoptosis. The anti-autophagic activity of Bcl-2 also impacted polyploid cell recovery in colony-forming assays, suggesting a route of escape from MYC-VX-680 synthetic lethality that may have clinical consequences. These findings expand on previous conclusions that autophagic death of VX-680-induced polyploid cells is mediated by Atg6. Bcl-2 and Bcl-xL negatively modulate MYC-VX-680 synthetic lethality and it is the anti-autophagic activity of these two Bcl-2 family proteins, specifically in multinucleate cells, that contributes to resistance to Aurora kinase-targeting drugs.

Ninety-Day Nephrotoxicity Evaluation of 3-MCPD 1-Monooleate and 1-Monostearate Exposures in Male Sprague Dawley Rats Using Proteomic Analysis

Fatty acid esters of 3-monochloropropane 1,2-diol (3-MCPD esters) are processing-induced food toxicants, with the kidney as their major target organ. For the first time, this study treated Sprague Dawley (SD) rats with 3-MCPD 1-monooleate at 10 and 100 mg/kg BW/day and 1-monostearate at 15 and 150 mg/kg BW/day for 90 days and examined for their potential semi-long-term nephrotoxicity and the associated molecular mechanisms. No bodyweight difference was observed between groups during the study. Both 3-MCPD 1-monooleate and 1-monostearate resulted in a dose-dependent increase of serum urea creatinine, uric acid and urea nitrogen levels, and histological renal impairment. The proteomic analysis of the kidney samples showed that the 3-MCPD esters deregulated proteins involved in the pathways for ion transportation, apoptosis, the metabolism of xenobiotics, and enzymes related to endogenous biological metabolisms of carbohydrates, amino acids, nitrogen, lipids, fatty acids, and the tricarboxylic acid (TCA) cycle, providing partial explanation for the nephrotoxicity of 3-MCPD esters.

Zearalenone induces apoptosis of rat Sertoli cells through Fas-Fas ligand and mitochondrial pathway

Zearalenone (ZEA) is an estrogen-like toxin produced by Fusarium that is widely found in cereals worldwide. In recent years, ZEA has been found to cause reproductive dysfunction in male animals, but the underlying mechanism remains unclear. This study examined the apoptosis of rat Sertoli cells induced by different concentrations (0, 5, 10, and 20 μmol/L) of ZEA via Fas-Fas ligand and mitochondrial signaling pathway in vitro. Apoptosis rate was detected by flow cytometry. The mitochondrial membrane potential was detected by immunofluorescence assay and flow cytometry. Western Blot and qRT-PCR were used to identify the signaling pathway. The results revealed that ZEA induced apoptosis of rat Sertoli cells, significantly reduced the transcription and expression of the anti-apoptotic protein Bcl-2, increased the transcription and expression of pro-apoptotic proteins Bax and tBID, and Fas, FasL, FADD, and caspase-8. ZEA also increased the activation of caspase-8 and caspase-9, and promoted the release of cytochrome C from mitochondria to cytoplasm. Moreover, addition of caspase-8 inhibitor Z-IETD-FMK led to significant decrease in the mitochondrial membrane potential and apoptosis rate of the ZEA + Z-IETD-FMK group as compared to the ZEA treatment group. The release of cytochrome C from mitochondria to cytoplasm and the activation of caspase-9 and caspase-3 were significantly decreased in the ZEA + Z-IETD-FMK group. These results suggested that ZEA can induce apoptosis of rat Sertoli cells, activate the Fas-Fas ligand signaling pathway and participate in the regulation of mitochondrial apoptosis pathway.

Ginger polysaccharides induced cell cycle arrest and apoptosis in human hepatocellular carcinoma HepG2 cells

In this study, ginger polysaccharide (GP) was obtained from ginger by enzymatic method, its chemical properties and antitumor activity were investigated. The results indicated that the composition and proportion of GP were l‑rhamnose, d‑arabinose, d‑mannose, d‑glucose and d‑galactose in a molar ratio of 3.64:5.37:3.04:61.03:26.91, GP had the characteristic absorption peak of polysaccharide. Congo red experiment showed that GP had a triple helix structure, which could have anti-tumor effect. Furthermore, MTT assay, cell morphology observation, nuclear morphology observation and reactive oxygen species observation demonstrated that GP had significant antitumor effect. Flow cytometry suggested that GP could promote apoptosis and arrest cells in G0-G1 phase. Real-time fluorescence quantification and Western blot revealed that GP could up-regulate the expression of Bax, Fas, FasL, caspase-3, p21 and p53, and down-regulate the expression of Bcl-2. These studies suggested that GP would be used as an antitumor drug in foods to promote the development of functional foods.

Bcl-2 regulates store-operated Ca2+ entry to modulate ER stress-induced apoptosis

Ca²⁺ plays a significant role in linking the induction of apoptosis. The key anti-apoptotic protein, Bcl-2, has been reported to regulate the movement of Ca²⁺ across the ER membrane, but the exact effect of Bcl-2 on Ca²⁺ levels remains controversial. Store-operated Ca²⁺ entry (SOCE), a major mode of Ca²⁺ uptake in non-excitable cells, is activated by depletion of Ca²⁺ in the ER. Depletion of Ca²⁺ in the ER causes translocation of the SOC channel activator, STIM1, to the plasma membrane. Thereafter, STIM1 binds to Orai1 or/and TRPC1 channels, forcing them to open and thereby allow Ca²⁺ entry. In addition, several anti-cancer drugs have been reported to induce apoptosis of cancer cells via the SOCE pathway. However, the detailed mechanism underlying the regulation of SOCE by Bcl-2 is not well understood. In this study, a three-amino acid mutation within the Bcl-2 BH1 domain was generated to verify the role of Bcl-2 in Ca²⁺ handling during ER stress. The subcellular localization of the Bcl-2 mutant (mt) is similar to that in the wild-type Bcl-2 (WT) in the ER and mitochondria. We found that mt enhanced thapsigargin and tunicamycin-induced apoptosis through ER stress-mediated apoptosis but not through the death receptor- and mitochondria-dependent apoptosis, while WT prevented thapsigargin- and tunicamycin-induced apoptosis. In addition, mt depleted Ca²⁺ in the ER lumen and also increased the expression of SOCE-related molecules. Therefore, a massive Ca²⁺ influx via SOCE contributed to caspase activation and apoptosis. Furthermore, inhibiting SOCE or chelating either extracellular or intracellular Ca²⁺ inhibited mt-mediated apoptosis. In brief, our results explored the critical role of Bcl-2 in Ca²⁺ homeostasis and the modulation of ER stress.

B cell lymphoma 2 (Bcl-2) residues essential for Bcl-2's apoptosis-inducing interaction with Nur77/Nor-1 orphan steroid receptors

Apoptosis is mediated through the extrinsic or intrinsic pathway. Key regulators of the intrinsic apoptotic pathway are the family of B cell lymphoma 2 (Bcl-2) proteins. The activity of the prototypical Bcl-2 protein is usually considered antiapoptotic. However, under some conditions, Bcl-2 associates with the orphan nuclear hormone receptors Nur77 and Nor-1, converting Bcl-2 into a proapoptotic molecule. Expression of Nur77 and Nor-1 is induced by a variety of signals, including those leading to apoptosis. Translocation of Nur77/Nor-1 to mitochondria results in their association with Bcl-2, exposing the Bcl-2 homology (BH) 3 domain and causing apoptosis. However, the molecular details of this interaction are incompletely understood. Here, through extensive Bcl-2 mutagenesis and functional assays, we identified residues within Bcl-2 that are essential for its interaction with Nur77/Nor-1. Although an initial report has suggested that an unstructured loop region between the Bcl-2 BH4 and BH3 domains is required for Bcl-2's interaction with Nur77/Nor-1, we found that it is dispensable for this interaction. Instead, we found important interacting residues at the BH4 domain and crucial interacting residues between the BH1 and BH2 domains. Bcl-2 alanine mutants at this region could no longer interact with Nur77/Nor-1 and could not initiate Nur77/Bcl-2-mediated cell death. However, they still retained their anti-apoptotic capability in two different death assays. These results establish crucial residues in Bcl-2 required for Nur77/Nor-1-mediated apoptosis and point to potential new strategies for manipulating Bcl-2 function.

BK Polyomavirus Infection and Renourinary Tumorigenesis

BK polyomavirus (BKPyV) infection represents a major problem in transplantation, particularly for renal recipients developing polyomavirus-associated nephropathy (PyVAN). The possibility that BKPyV may also be oncogenic is not routinely considered. Twenty high-grade renourinary tumors expressing polyomavirus large T antigen in the entirety of the neoplasm in 19 cases, including the metastases in six, have been reported in transplant recipients with a history of PyVAN or evidence of BKPyV infection. Morphological and phenotypical features consistent with inactivation of the tumor suppressors pRB and p53 were found in the bladder tumors, suggesting a carcinogenesis mechanism involving the BKPyV large tumor oncoprotein/antigen. The pathogenesis of these tumors is unclear, but given the generally long interval between transplantation and tumor development, the risk for neoplasms after BKPyV infections may well be multifactorial. Other elements potentially implicated include exposure to additional exogenous carcinogens, further viral mutations, and cell genomic instability secondary to viral integration, as occurs with the Merkel cell PyV-associated carcinoma. The still scarce but increasingly reported association between longstanding PyVAN and renourinary neoplasms requires a concerted effort from the transplant community to better understand, diagnose, and treat the putative association between the BKPyV and these neoplasms.

Bax/Bak-dependent, Drp1-independent Targeting of X-linked Inhibitor of Apoptosis Protein (XIAP) into Inner Mitochondrial Compartments Counteracts Smac/DIABLO-dependent Effector Caspase Activation

Efficient apoptosis requires Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP), which releases death-promoting proteins cytochrome c and Smac to the cytosol, which activate apoptosis and inhibit X-linked inhibitor of apoptosis protein (XIAP) suppression of executioner caspases, respectively. We recently identified that in response to Bcl-2 homology domain 3 (BH3)-only proteins and mitochondrial depolarization, XIAP can permeabilize and enter mitochondria. Consequently, XIAP E3 ligase activity recruits endolysosomes into mitochondria, resulting in Smac degradation. Here, we explored mitochondrial XIAP action within the intrinsic apoptosis signaling pathway. Mechanistically, we demonstrate that mitochondrial XIAP entry requires Bax or Bak and is antagonized by pro-survival Bcl-2 proteins. Moreover, intramitochondrial Smac degradation by XIAP occurs independently of Drp1-regulated cytochrome c release. Importantly, mitochondrial XIAP actions are activated cell-intrinsically by typical apoptosis inducers TNF and staurosporine, and XIAP overexpression reduces the lag time between the administration of an apoptotic stimuli and the onset of mitochondrial permeabilization. To elucidate the role of mitochondrial XIAP action during apoptosis, we integrated our findings within a mathematical model of intrinsic apoptosis signaling. Simulations suggest that moderate increases of XIAP, combined with mitochondrial XIAP preconditioning, would reduce MOMP signaling. To test this scenario, we pre-activated XIAP at mitochondria via mitochondrial depolarization or by artificially targeting XIAP to the intermembrane space. Both approaches resulted in suppression of TNF-mediated caspase activation. Taken together, we propose that XIAP enters mitochondria through a novel mode of mitochondrial permeabilization and through Smac degradation can compete with canonical MOMP to act as an anti-apoptotic tuning mechanism, reducing the mitochondrial contribution to the cellular apoptosis capacity.

Expression of galectin-3 correlates with apoptosis in pituitary adenoma cells

OBJECTIVE

To investigate the expressions of Galectin-3 (Gal-3), Bcl-2 and Bax in human pituitary adenomas, and to explore the interrelation among them.

METHODS

RT-PCR and immunohistochemistry were applied to detect the mRNA and protein expressions of Gal-3, Bcl-2 and Bax in surgically excised human pituitary adenoma tissues, including invasive and non-invasive pituitary adenomas, and the correlation analysis was performed.

RESULTS

The Gal-3 and Bcl-2 expressions in the invasive pituitary group were significantly higher than those in the non-invasive group, and the expression of Bax had no significant difference between the two groups. Pearsonos correlation analyses showed that the Gal-3 expression was positively correlated with Bcl-2, but was not correlated with Bax, which was inversely correlated with expression of Bcl-2.

CONCLUSION

Gal-3 may function through a cell death inhibition pathway involving Bcl-2 to enhance cell proliferation, which result in the invasive growth of pituitary adenoma. These results indicate that Gal-3 has an important role in pituitary tumor cell proliferation and may serves as a possible therapeutic target in treatment of pituitary tumors.

Involvement of BH4 domain of bcl-2 in the regulation of HIF-1-mediated VEGF expression in hypoxic tumor cells

In addition to act as an antiapoptotic protein, B-cell lymphoma (bcl)-2 can also promote tumor angiogenesis. In this context, we have previously demonstrated that under hypoxia bcl-2 promotes hypoxia-inducible factor-1 (HIF-1)-mediated vascular endothelial growth factor (VEGF) expression in melanoma and breast carcinoma. Here, we report on the role of the BH4 domain in bcl-2 functions, by showing that removal of or mutations at the BH4 domain abrogate the ability of bcl-2 to induce VEGF protein expression and transcriptional activity under hypoxia in human melanoma cells. We have also extended this observation to other human tumor histotypes, such as colon, ovarian and lung carcinomas. The involvement of BH4 on HIF-1α protein expression, stability, ubiquitination and HIF-1 transcriptional activity was also demonstrated in melanoma experimental model. Moreover, we validated the role of the BH4 domain of bcl-2 in the regulation of HIF-1/VEGF axis, demonstrating that BH4 peptide is sufficient to increase HIF-1α protein half-life impairing HIF-1α protein ubiquitination, and to enhance VEGF secretion in melanoma cells exposed to hypoxia. Finally, we found that the mechanism by which bcl-2 regulates HIF-1-mediated VEGF expression does not require BH1 and BH2 domains, and it is independent of antiapoptotic and prosurvival function of bcl-2.

Runx2-mediated bcl-2 gene expression contributes to nitric oxide protection against hydrogen peroxide-induced osteoblast apoptosis

Nitric oxide (NO) can regulate osteoblast activities. This study was aimed to evaluate the protective effects of pretreatment with sodium nitroprusside (SNP) as a source of NO on hydrogen peroxide-induced osteoblast insults and its possible mechanisms. Exposure of human osteosarcoma MG63 cells to hydrogen peroxide significantly increased cellular oxidative stress, but decreased ALP activity and cell viability, inducing cell apoptosis. Pretreatment with 0.3 mM SNP significantly lowered hydrogen peroxide-induced cell insults. Treatment of human MG63 cells with hydrogen peroxide inhibited Bcl-2 mRNA and protein production, but pretreatment with 0.3 mM SNP significantly ameliorated such inhibition. Sequentially, hydrogen peroxide decreased the mitochondrial membrane potential, but increased the levels of cytochrome c and caspase-3 activity. Pretreatment with 0.3 mM SNP significantly lowered such alterations. Exposure to hydrogen peroxide decreased Runx2 mRNA and protein syntheses. However, pretreatment with 0.3 mM SNP significantly lowered the suppressive effects. Runx2 knockdown using RNA interference inhibited Bcl-2 mRNA production in human MG63 cells. Protection of pretreatment with 0.3 mM SNP against hydrogen peroxide-induced alterations in ALP activity, caspase-3 activity, apoptotic cells, and cell viability were also alleviated after administration of Runx2 small interference RNA. Thus, this study shows that pretreatment with 0.3 mM SNP can protect human MG63 cells from hydrogen peroxide-induced apoptotic insults possibly via Runx2-involved regulation of bcl-2 gene expression.

Relevance of Bcl-x expression in different types of endometrial tissues

OBJECTIVES

To explore the roles of Bcl-xl and Bcl-xs in the development and progression of endometrial carcinoma, and to analyze the correlation between Bcl-xl and Bcl-xs.

METHODS

RT-PCR and Western-blot assay were applied to detect the expressions of Bcl-xl and Bcl-xs in endometrial tissues of various histomorphologic types.

RESULTS

The Bcl-xl expression levels of simple and atypical hyperplasia endometrial tissues were not significantly different from that of normal endometrial tissue (both P > 0.05). On contrary, Bcl-xl expression in endometrial carcinoma tissue was significantly higher than the normal endometrial tissue (P = 0.00), which was correlated with the pathological grading of endometrial carcinoma (F = 5.33, P = 0.02). In addition, Bcl-xs mRNA level in simple hyperplasia endometrial tissue had no significant difference compared to that in normal endometrial tissue (P = 0.12), while the levels of atypical hyperplasia and endometrial carcinoma endometrial tissues were significantly different from the normal endometrial tissue (both P = 0.00). Furthermore, level of Bcl-xs mRNA was correlated with the clinical staging and lymph node metastasis of the endometrial carcinoma (P < 0.05). The expressions of Bcl-xl and Bcl-xs were negatively correlated with each other (r = -0.76).

CONCLUSION

The abnormal expressions of Bcl-xs and Bcl-xl were one of the molecular mechanisms for the pathogenesis of endometrial carcinoma, and altered ratio between these two might involve in the onset of endometrial carcinoma.

Vacuolar H+-ATPase inhibitors overcome Bcl-xL-mediated chemoresistance through restoration of a caspase-independent apoptotic pathway

The anti-apoptotic oncoproteins Bcl-2 and Bcl-xL play crucial roles in tumorigenesis and chemoresistance, and are thus therapeutic cancer targets. We searched for small molecules that disturbed the anti-apoptotic function of Bcl-2 or Bcl-xL, and found vacuolar H(+)-ATPase (V-ATPase) inhibitors, such as bafilomycin A1 (BMA), that showed such activity. Bcl-xL-overexpressing Ms-1 cells displayed resistance to anticancer drugs, but underwent apoptosis following treatment with a combination of V-ATPase inhibitors at doses similar to those that caused inhibitory activities of V-ATPase. We investigated the apoptosis mechanism induced by cotreatment of Bcl-xL-overexpressing Ms-1 cells with BMA as a V-ATPase inhibitor and taxol (TXL) as an anticancer drug. With BMA, TXL triggered mitochondrial membrane potential loss and cytochrome c release, whereas downstream caspase activation was not observed. In contrast, pronounced nuclear translocation of mitochondrial apoptosis-inducing factor and endonuclease G, known as effectors of caspase-independent apoptosis, was observed with BMA and TXL cotreatment. Moreover, depletion of apoptosis-inducing factor and endonuclease G using each siRNA significantly rescued cells from BMA- and TXL-induced apoptosis. Hence, the apoptosis-inducing factor- and endonuclease G-dependent pathway was critical for apoptosis induction by BMA and TXL cotreatment. Our data suggest that V-ATPase inhibitors could not only suppress anti-apoptotic Bcl-2 nor Bcl-xL but could also facilitate the caspase-independent apoptotic pathway. V-ATPase inhibition will be a promising therapeutic approach for Bcl-2- or Bcl-xL-overexpressing malignancies.

Polo-like kinase 1 phosphorylates and regulates Bcl-x(L) during pironetin-induced apoptosis

Bcl-x(L), an anti-apoptotic Bcl-2 family member protein, contributes to the resistance against chemotherapies such as tubulin-binder treatment in many human tumors. Although Bcl-x(L) is phosphorylated after tubulin-binder treatment, the role of the phosphorylation and its responsible kinase(s) are poorly understood. Here, we identified Plk1 (polo-like kinase 1) as a Bcl-x(L) kinase. Same location of Bcl-x(L) and Plk1 was revealed by immunocytochemical analyses at M-phase in situ. Plk1 phosphorylates Bcl-x(L) in vitro, and we identified Plk1 phosphorylation sites in Bcl-x(L). When all of these phosphorylation sites were substituted to alanines, the anti-apoptotic activity of the Bcl-x(L) mutant against the apoptosis induced by pironetin, but not against ultraviolet-induced apoptosis, was increased. These observations suggest that Plk1 is a regulator of Bcl-x(L) phosphorylation and controls the anti-apoptotic activity of Bcl-x(L) during pironetin-induced apoptosis.

To trigger apoptosis, Bak exposes its BH3 domain and homodimerizes via BH3:groove interactions

The Bcl-2 relative Bak is thought to drive apoptosis by forming homo-oligomers that permeabilize mitochondria, but how it is activated and oligomerizes is unclear. To clarify these pivotal steps toward apoptosis, we have characterized multiple random loss-of-function Bak mutants and explored the mechanism of Bak conformation change during apoptosis. Single missense mutations located to the alpha helix 2-5 region of Bak, with most altering the BH3 domain or hydrophobic groove (BH1 domain). Loss of function invariably corresponded to impaired ability to oligomerize. An essential early step in Bak activation was shown to be exposure of the BH3 domain, which became reburied in dimers. We demonstrate that oligomerization involves insertion of the BH3 domain of one Bak molecule into the groove of another and may produce symmetric Bak dimers. We conclude that this BH3:groove interaction is essential to nucleate Bak oligomerization, which in turn is required for its proapoptotic function.

Oligomerization of BH4-truncated Bcl-x(L) in solution

BH4 domain is critical for the anti-apoptotic functions of Bcl-2 and Bcl-x(L) and their binding abilities with other members of the Bcl-2 family. The cleavage of the BH4 domain in Bcl-x(L) and Bcl-2 by caspase 1 or 3 converts the anti-apoptotic Bcl-x(L) and Bcl-2 into pro-apoptotic proteins that potently induce apoptosis. Herein, we report that recombinant Bcl-x(L) proteins without N-terminal 61 residues, His(6)-NDelta61-Bcl-x(L)-CDelta21 and NDelta61-Bcl-x(L)-CDelta21, form oligomers in solution, whereas Bcl-x(L)-CDelta21 exists as a monomer. The oligomerization of the truncated proteins is independent of protein-lipid interaction, protein concentration or the ion strength of the solution. Circular dichroism spectrum shows a significant decrease in the content of alpha-helices upon deletion of N-terminal residues. NDelta61-Bcl-x(L)-CDelta21 also loses its heterodimerization capability with the BH3 peptide derived from Bak. This newly acquired property might be linked to its ability to induce apoptosis in cells.