Ursolic acid sensitizes prostate cancer cells to TRAIL-mediated apoptosis.

Prostate cancer is one of the most commonly occurring malignancies in men, and because existing treatments are not able to manage this neoplasm adequately, novel approaches are needed. Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has strong antitumor activity via the induction of apoptotic cell death in a wide range of tumor cell types and has negligible toxicity to most normal cells, some prostate carcinoma cells are resistant to the apoptotic effects of TRAIL. Therefore, combinatorial approaches with TRAIL and different chemotherapeutic agents have been developed to overcome the resistance of cancer cells to TRAIL. Here, we investigated the sensitizing effects of ursolic acid (UA), a pentacyclic triterpenoid found in many plants, on TRAIL-induced prostate cancer cell apoptosis. We found TRAIL-induced prostate cancer cells apoptosis was significantly enhanced by UA, and that UA induced CHOP-dependent DR5 up-regulation. This study shows the use of UA as a sensitizer for TRAIL-induced apoptotic cell death offers a promising means of enhancing the efficacy of TRAIL-based prostate cancer treatments.

Autophagy inhibition enhances ursolic acid-induced apoptosis in PC3 cells.

The phosphoinositol 3-kinase/Akt pathway plays a critical role in oncogenesis and the dysregulation of this pathway through loss of PTEN is a particularly common phenomenon in aggressive prostate cancers. Several recent studies have indicated that ursolic acid (UA), a pentacyclic triterpenoid, and its derivatives inhibit the growth of cancer cells by cell cycle arrest and the stimulation of apoptosis. In the present study, we report a novel autophagic response of UA in PTEN-deficient PC3 prostate cancer cells. As one of the major types of programmed cell death, autophagy has been observed in response to several anticancer drugs and demonstrated to be responsible for cell death. UA-induced autophagy in PC3 cells is associated with the reduced cell viability and the enhanced expression of LC3-II, an autophagosome marker in mammals, and monodansylcadaverine incorporation into autolysosomes. Furthermore, we found that UA exhibited anti-proliferative effects characterized by G1 phase arrest and autophagy at an early stage that precedes apoptosis. We also show that UA-induced autophagy in PC3 cells are mediated through the Beclin-1 and Akt/mTOR pathways. Inhibition of autophagy by either 3-methyladenine or Beclin-1/Atg5 small interfering RNA enhanced UA-induced apoptosis. Taken together, our data suggest that autophagy functions as a survival mechanism in PC3 cells against UA-induced apoptosis and a rational for the use of autophagy inhibitors in combination with UA as a novel modality of cancer therapy.

Antagonist effects of veratric acid against UVB-induced cell damages.

Ultraviolet (UV) radiation induces DNA damage, oxidative stress, and inflammatory processes in human epidermis, resulting in inflammation, photoaging, and photocarcinogenesis. Adequate protection of skin against the harmful effect of UV irradiation is essential. In recent years naturally occurring herbal compounds such as phenolic acids, flavonoids, and high molecular weight polyphenols have gained considerable attention as beneficial protective agents. The simple phenolic veratric acid (VA, 3,4-dimethoxybenzoic acid) is one of the major benzoic acid derivatives from vegetables and fruits and it also occurs naturally in medicinal mushrooms which have been reported to have anti-inflammatory and anti-oxidant activities. However, it has rarely been applied in skin care. This study, therefore, aimed to explore the possible roles of veratric acid in protection against UVB-induced damage in HaCaT cells. Results showed that veratric acid can attenuate cyclobutane pyrimidine dimers (CPDs) formation, glutathione (GSH) depletion and apoptosis induced by UVB. Furthermore, veratric acid had inhibitory effects on the UVB-induced release of the inflammatory mediators such as IL-6 and prostaglandin-E2. We also confirmed the safety and clinical efficacy of veratric acid on human skin. Overall, results demonstrated significant benefits of veratric acid on the protection of keratinocyte against UVB-induced injuries and suggested its potential use in skin photoprotection.

S-glutathionylation regulates GTP-binding of Rac2.

Phagocyte NADPH oxidase catalyzes the reduction of molecular oxygen to superoxide and is essential for defense against microbes. Rac2 is a low molecular weight GTP-binding protein that has been implicated in the regulation of phagocyte NADPH oxidase. Here we report that Cys(157) of Rac2 is a target of S-glutathionylation and that this modification is reversed by dithiothreitol as well as enzymatically by thioltransferase in the presence of GSH. S-glutathionylated Rac2 enhanced the binding of GTP, presumably due to structural alterations. These results elucidate the redox regulation of cysteine in Rac2 and a possible mechanism for regulating NADPH oxidase activation.

Regulation of brefeldin A-induced ER stress and apoptosis by mitochondrial NADP⁺-dependent isocitrate dehydrogenase.

Brefeldin A (BFA), an endoplasmic reticulum (ER)-Golgi transport inhibitor, has been shown to cause accumulation of proteins in the ER, ER stress, and ultimately apoptosis. In this paper, we demonstrate that the knockdown of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm), a mitochondrial NADPH-generating enzyme, by small interfering RNA (siRNA) enhanced BFA-induced apoptosis. However, attenuated IDPm activity results in the suppression of ER stress response, presumably, via the inhibition of the PI3K/Akt pathway. Collectively, our data suggest that the association of IDPm expression and ER stress confers a survival mechanism in A549 cells against BFA-induced apoptosis.

Regulation of heat shock-induced apoptosis by sensitive to apoptosis gene protein.

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Sensitive to apoptosis gene (SAG) protein, a novel zinc RING finger protein that protects mammalian cells from apoptosis by redox reagents, is a metal chelator and a potential reactive oxygen species scavenger, but its antioxidant properties have not been completely defined. In this report, we demonstrate that modulation of SAG expression in U937 cells regulates heat shock-induced apoptosis. When we examined the protective role of SAG against heat shock-induced apoptosis with U937 cells transfected with the cDNA for SAG, a clear inverse relationship was observed between the amount of SAG expressed in target cells and their susceptibility to apoptosis. We also observed a significant decrease in the endogenous production of reactive oxygen species and oxidative DNA damage in SAG-overexpressed cells compared to control cells on exposure to heat shock. In addition, transfection of PC3 cells with SAG small interfering RNA markedly decreased the expression of SAG, enhancing the susceptibility of heat shock-induced apoptosis. Taken together, these results indicate that SAG may play an important role in regulating the apoptosis induced by heat shock presumably through maintaining the cellular redox status.

Silencing of mitochondrial NADP+-dependent isocitrate dehydrogenase by small interfering RNA enhances heat shock-induced apoptosis.

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) produces NADPH, an essential reducing equivalent for the antioxidant system. In this report, we demonstrate that silencing of IDPm expression in HeLa cells greatly enhances apoptosis induced by heat shock. Transfection of HeLa cells with an IDPm small interfering RNA (siRNA) markedly decreased activity of IDPm, enhancing the susceptibility of heat shock-induced apoptosis reflected by morphological evidence of apoptosis, DNA fragmentation, cellular redox status, mitochondria redox status and function, and the modulation of apoptotic marker proteins. These results indicate that IDPm may play an important role in regulating the apoptosis induced by heat shock and the sensitizing effect of IDPm siRNA on the apoptotic cell death of HeLa cells offers the possibility of developing a modifier of cancer therapy.

Hypochlorous acid-induced modulation of cellular redox status in HeLa cells.

Myeloperoxidase catalyzes the formation of hypochlorous acid (HOCI) via reaction of H2O2 with CI(-) ions. Although HOCI plays a major role in the human immune system by killing bacteria and other invading pathogens, excessive generation of this oxidant causes damage to tissues. Exposure of HeLa cells to HOCI decreased viability, inactivated antioxidant enzymes, damaged mitochondria, and modulated cellular redox status. HOCI also induced significant increases in cellular oxidative damage reflected by lipid peroxidation, protein oxidation, and DNA damage. HOCI-mediated oxidative damage to HeLa cells may perturb the cellular antioxidant defense mechanisms and subsequently lead to a pro-oxidant state.

Epigallocatechin gallate, a constituent of green tea, regulates high glucose-induced apoptosis.

A high concentration of glucose has been implicated as a causal factor in initiation and progression of diabetic complications, and there is evidence to suggest that hyperglycemia increases the production of free radicals and oxidative stress. Therefore, compounds that scavenge reactive oxygen species may confer regulatory effects on high glucose-induced apoptosis. Epigallocatechin gallate (EGCG), the major polyphenolic of green tea, is reported to have an antioxidant activity. We investigated the effect of EGCG on high glucose-induced apoptosis in U937 cells. Upon exposure to 35 mM glucose for 2 days, there was a distinct difference between untreated cells and cells pre-treated with 1 microM EGCG for 2 h in regard to cellular redox status and oxidative DNA damage to cells. EGCG pre-treated cells showed significant suppression of apoptotic features such as DNA fragmentation, damage to mitochondrial function, and modulation of apoptotic marker proteins upon exposure to high glucose. This study indicates that EGCG may play an important role in regulating the apoptosis induced by high glucose presumably through scavenging of reactive oxygen species.

Protective effect of Rehmannia glutinosa on the UV-induced apoptosis in U937 cells.

Ultraviolet (UV) radiation has been shown to generate reactive oxygen species (ROS), such as singlet oxygen, superoxide radicals, hydroxyl radicals and hydrogen peroxide in a variety of cells. These ROS have the potential to damage critical cellular components such as DNA, proteins, and lipids and eventually result in physical and chemical damage to tissues that may lead to cell death. The steamed root of Rehmannia glutinosa (Saeng Jihuang, SJH) is reported to have an antioxidant activity. We investigated the effect of SJH on UV-induced apoptosis in U937 cells. Upon exposure to UV, there was a distinct difference between untreated cells and cells pre-treated with 0.5-2 mg/ml SJH for 12 hours in regard to cellular redox status and morphological change to cells. SJH pre-treated cells showed significant suppression of apoptotic features such as DNA fragmentation, damage to mitochondrial function, and modulation of apoptotic marker proteins upon exposure to UV. This study indicates that SJH may play an important role in regulating the apoptosis induced by UV presumably through scavenging of reactive oxygen species.

Zingerone protects keratinocyte stem cells from UVB-induced damage.

The epidermis, the outermost layer of the skin, is a stratified epithelium that protects the body from the external environment. Keratinocyte stem cells (KSCs) are involved in epidermis homeostasis by maintaining epidermal integrity through a process of constant regeneration. Ultraviolet B (UVB) radiation is a major inducer of cellular damage in the epidermis. In this study, we investigated the effects of zingerone (a phenolic compound derived from spices) on UVB-induced cellular damage in KSCs. We found that zingerone significantly inhibited cellular senescence of KSCs in response to UVB irradiation. These effects were confirmed by the senescence-associated ß-galactosidase and comet assays. Zingerone decreased the production of proinflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and interleukin-6 (IL-6) in UVB-irradiated KSCs. Moreover, UVB-induced expression of p21, a cell cycle arrest-related gene, was reduced by zingerone treatment, whereas zingerone upregulated the expression of proliferation-related genes such as proliferating cell nuclear antigen (PCNA) and vascular endothelial growth factor (VEGF), in addition to anti-senescence-related genes including telomerase reverse transcriptase (TERT), histone deacetylase 1 (HDAC1), and DNA (cytosine-5)-methyltransferase 1 (DNMT1). The UVB-protective effects of zingerone were mediated by inhibition of p42/44 MAPK and p38 MAPK. Therefore, zingerone could potentially be used to protect the epidermis from UVB-induced damage.

S-Nitrosylation of p47(phox) enhances phosphorylation by casein kinase 2.

OBJECTIVES: Leukocyte NADPH oxidase, which is active in neutrophils, is a membrane-bound enzyme that catalyzes the reduction of oxygen to O2(-) by using NADPH as an electron donor. Previously, we reported that casein kinase 2 (CK2), a ubiquitous and highly conserved Ser/Thr kinase, is responsible for p47(phox) phosphorylation and that phosphorylation of p47(phox) by CK2 regulates the deactivation of NADPH oxidase. METHODS: Here, we report that the residue Cys(196) of p47(phox) is a target of S-nitrosylation by S-nitrosothiol and peroxynitrite and that this modification enhanced phosphorylation of p47(phox) by CK2. RESULTS: S-Nitrosylated p47(phox) enhanced CK2 b subunit binding, presumably due to alterations in protein conformation. DISCUSSION: Taken together, we propose that S-nitrosylation of p47(phox) regulates the deactivation of NADPH oxidase via enhancement of p47(phox) phosphorylation by CK2.

Antagonizing Effects of Aspartic Acid against Ultraviolet A-Induced Downregulation of the Stemness of Human Adipose Tissue-Derived Mesenchymal Stem Cells.

Ultraviolet A (UVA) irradiation is responsible for a variety of changes in cell biology. The purpose of this study was to investigate effects of aspartic acid on UVA irradiation-induced damages in the stemness properties of human adipose tissue-derived mesenchymal stem cells (hAMSCs). Furthermore, we elucidated the UVA-antagonizing mechanisms of aspartic acid. The results of this study showed that aspartic acid attenuated the UVA-induced reduction of the proliferative potential and stemness of hAMSCs, as evidenced by increased proliferative activity in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and upregulation of stemness-related genes OCT4, NANOG, and SOX2 in response to the aspartic acid treatment. UVA-induced reduction in the mRNA level of hypoxia-inducible factor (HIF)-1α was also significantly recovered by aspartic acid. In addition, the antagonizing effects of aspartic acid against the UVA effects were found to be mediated by reduced production of PGE2 through the inhibition of JNK and p42/44 MAPK. Taken together, these findings show that aspartic acid improves reduced stemness of hAMSCs induced by UVA and its effects are mediated by upregulation of HIF-1α via the inhibition of PGE2-cAMP signaling. In addition, aspartic acid may be used as an antagonizing agent to mitigate the effects of UVA.

Antagonizing effects and mechanisms of afzelin against UVB-induced cell damage.

Ultraviolet (UV) radiation induces DNA damage, oxidative stress, and inflammatory processes in human keratinocytes, resulting in skin inflammation, photoaging, and photocarcinogenesis. Adequate protection of skin against the harmful effects of UV irradiation is essential. Therefore, in this study, we investigated the protective effects of afzelin, one of the flavonoids, against UV irradiation in human keratinocytes and epidermal equivalent models. Spectrophotometric measurements revealed that the afzelin extinction maxima were in the UVB and UVA range, and UV transmission below 376 nm was <10%, indicating UV-absorbing activity of afzelin. In the phototoxicity assay using the 3T3 NRU phototoxicity test (3T3-NRU-PT), afzelin presented a tendency to no phototoxic potential. In addition, in order to investigate cellular functions of afzelin itself, cells were treated with afzelin after UVB irradiation. In human keratinocyte, afzelin effectively inhibited the UVB-mediated increase in lipid peroxidation and the formation of cyclobutane pyrimidine dimers. Afzelin also inhibited UVB-induced cell death in human keratinocytes by inhibiting intrinsic apoptotic signaling. Furthermore, afzelin showed inhibitory effects on UVB-induced release of pro-inflammatory mediators such as interleukin-6, tumor necrosis factor-α, and prostaglandin-E2 in human keratinocytes by interfering with the p38 kinase pathway. Using an epidermal equivalent model exposed to UVB radiation, anti-apoptotic activity of afzelin was also confirmed together with a photoprotective effect at the morphological level. Taken together, our results suggest that afzelin has several cellular activities such as DNA-protective, antioxidant, and anti-inflammatory as well as UV-absorbing activity and may protect human skin from UVB-induced damage by a combination of UV-absorbing and cellular activities.

Cytosolic NADP(+)-dependent isocitrate dehydrogenase regulates cadmium-induced apoptosis.

Cadmium ions have a high affinity for thiol groups. Therefore, they may disturb many cellular functions. We recently reported that cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) functions as an antioxidant enzyme to supply NADPH, a major source of reducing equivalents to the cytosol. Cadmium decreased the activity of IDPc both as a purified enzyme and in cultured cells. In the present study, we demonstrate that the knockdown of IDPc expression in HEK293 cells greatly enhances apoptosis induced by cadmium. Transfection of HEK293 cells with an IDPc small interfering RNA significantly decreased the activity of IDPc and enhanced cellular susceptibility to cadmium-induced apoptosis as indicated by the morphological evidence of apoptosis, DNA fragmentation and condensation, cellular redox status, mitochondria redox status and function, and the modulation of apoptotic marker proteins. Taken together, our results suggest that suppressing the expression of IDPc enhances cadmium-induced apoptosis of HEK293 cells by increasing disruption of the cellular redox status.

Glutathionylation regulates cytosolic NADP+-dependent isocitrate dehydrogenase activity.

Cytosolic NADP+-dependent isocitrate dehydrogenase (IDPc) is susceptible to inactivation by numerous thiol-modifying reagents. This study now reports that Cys269 of IDPc is a target for S-glutathionylation and that this modification is reversed by dithiothreitol as well as enzymatically by cytosolic glutaredoxin in the presence of GSH. Glutathionylated IDPc was significantly less susceptible than native protein to peptide fragmentation by reactive oxygen species and proteolytic digestion. Glutathionylation may play a protective role in the degradation of protein through the structural alterations of IDPc. HEK293 cells treated with diamide displayed decreased IDPc activity and accumulated glutathionylated enzyme. Using immunoprecipitation with an anti-IDPc IgG and immunoblotting with an anti-GSH IgG, we purified and positively identified glutathionylated IDPc from the kidneys of mice subjected to ischemia/reperfusion injury and from the livers of ethanol-administered rats. These results suggest that IDPc activity is modulated through enzymatic glutathionylation and deglutathionylation during oxidative stress.

Silencing of cytosolic NADP(+)-dependent isocitrate dehydrogenase by small interfering RNA enhances the sensitivity of HeLa cells toward staurosporine.

Staurosporine induces the production of reactive oxygen species, which play an important causative role in apoptotic cell death. Recently, it was demonstrated that the control of cellular redox balance and the defense against oxidative damage is one of the primary functions of cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) by supplying NADPH for antioxidant systems. The present report shows that silencing of IDPc expression in HeLa cells greatly enhances apoptosis induced by staurosporine. Transfection of HeLa cells with an IDPc small interfering RNA (siRNA) markedly decreased activity of IDPc, enhancing the susceptibility of staurosporine-induced apoptosis reflected by DNA fragmentation, cellular redox status and the modulation of apoptotic marker proteins. These results indicate that IDPc may play an important role in regulating the apoptosis induced by staurosporine and the sensitizing effect of IDPc siRNA on the apoptotic cell death of HeLa cells offers the possibility of developing a modifier of cancer chemotherapy.

Inactivation of mitochondrial NADP+-dependent isocitrate dehydrogenase by hypochlorous acid.

Myeoloperoxidase catalyses the formation of hypochlorous acid (HOCl) via reaction of H(2)O(2) with Cl(-) ion. Although HOCl is known to play a major role in the human immune system by killing bacteria and other invading pathogens, excessive generation of this oxidant is known to cause damage to tissue. Recently, it was demonstrated that the control of mitochondrial redox balance and oxidative damage is one of the primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm) to supply NADPH for antioxidant systems. This study investigated whether the IDPm would be a vulnerable target of HOCl as a purified enzyme and in intact cells. Loss of enzyme activity was observed and the inactivation of IDPm was reversed by thiols. Transfection of HeLa cells with an IDPm small interfering RNA (siRNA) markedly enhanced HOCl-induced oxidative damage to cells. The HOCl-mediated damage to IDPm may result in the perturbation of the cellular antioxidant defense mechanisms and subsequently lead to a pro-oxidant condition.

Mitochondrial NADP+-dependent isocitrate dehydrogenase protects cadmium-induced apoptosis.

Cadmium is known to exhibit high affinity for thiol groups and may therefore severely disturb many cellular functions. We have demonstrated that the control of mitochondrial redox balance and oxidative damage is one of the primary functions of mitochondrial NADP+-dependent isocitrate dehydrogenase (IDPm). When exposed to cadmium, IDPm was susceptible to loss of enzyme activity and structural alterations. Site-directed mutagenesis confirms that binding of cadmium occurs to a Cys379 of IDPm. We examined the antioxidant mechanism-mediated protective role of IDPm against cadmium-induced apoptosis with human embryonic kidney 293 cells transfected with the IDPm cDNA in sense and antisense orientations. As a result, we observed a clear inverse relationship between the amount of IDPm expressed in target cells and their susceptibility to cadmium-induced modulation of cellular redox status and apoptosis. In addition, loss of glutaredoxin (Grx, thioltransferase) activity by cadmium was more pronounced in antisense cells compared with the sense cells. When oxalomalate, a competitive inhibitor of IDPm, was administered to mice, inhibition of IDPm and Grx and enhanced susceptibility to apoptosis were observed upon their exposure to cadmium. These results suggest that IDPm plays an important protective role in cadmium-induced apoptosis by maintaining cellular redox status and by protection of Grx activity.

N-t-Butyl hydroxylamine regulates heat shock-induced apoptosis in U937 cells.

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Therefore, compounds that scavenge reactive oxygen species may regulate heat shock-induced cell death. Recently, it has been shown that the decomposition product of the spin-trapping agent alpha-phenyl-N-t-butylnitrone, N-t-butyl hydroxylamine (NtBHA), mimics alpha-phenyl-N-t-butylnitrone and is much more potent in delaying reactive oxygen species-associated senescence. We investigated the protective role of NtBHA against heat shock-induced apoptosis in U937 cells. Upon exposure to heat shock, there was a distinct difference between the untreated cells and the cells pre-treated with 0.1 mM NtBHA for 2 h in regard to apoptotic parameters, cellular redox status, and mitochondrial function. Upon exposure to heat shock, NtBHA pre-treated cells showed significant inhibition of apoptotic features such as activation of caspase-3, up-regulation of Bax, and down-regulation of Bcl-2 compared to untreated cells. This study indicates that NtBHA may play an important role in regulating the apoptosis induced by heat shock, presumably through scavenging of reactive oxygen species.