Patricio Aller

The role of intracellular oxidation in death induction (apoptosis and necrosis) in human promonocytic cells treated with stress inducers (cadmium, heat, X-rays)

Treatment of U-937 human promonocytic cells with the stress inducers cadmium chloride (2 h at 200 microM), heat (2 h at 42.5 C) or X-rays (20 Gy), followed by recovery, caused death by apoptosis and stimulated caspase-3 activity. In addition, all stress agents caused intracellular oxidation, as measured by peroxide and/or anion superoxide accumulation. However, while pre-incubation with antioxidants (N-acetyl-L-cysteine or butylated hydroxyanisole) inhibited the induction of apoptosis by cadmium and X-rays, it did not affect the induction by heat-shock. Pre-incubation for 24 h with the GSH-depleting agent L-buthionine-[S,R]-sulfoximine (BSO) switched the mode of death from apoptosis to necrosis in cadmium-treated cells. By contrast, BSO only caused minor modifacions in the rate of apoptosis without affecting the mode of death in heat- and X-rays-treated cells. BSO potentiated peroxide accumulation in cells treated with both cadmium and X-rays. However, while the accumulation of peroxides was stable in the case of cadmium, it was transient in the case of X-rays. Moreover, the administration of antioxidants during the recovery period sufficed to prevent necrosis and restore apoptosis in BSO plus cadmium-treated cells. Cadmium and X-rays caused a decrease in intracellular ATP levels, but the decrease was similar in both apoptotic and necrotic cells. Taken together, these results demonstrate that (i) stress inducers cause intracellular oxidation, but oxidation is not a general requirement for apoptosis; and (ii) the duration of the oxidant state seems to be critical in determining the mode of death.

Regulation of multidrug resistance 1 (MDR1)/P-glycoprotein gene expression and activity by heat-shock transcription factor 1 (HSF1).

Infection of HeLa cells with adenovirus-carrying HSF1+ cDNA, which encodes a mutated form of HSF1 with constitutive transactivation capacity, increased multidrug resistance 1 (MDR1) mRNA level and P-glycoprotein (P-gp) cell surface content and stimulated rhodamine 123 accumulation and vinblastine efflux activity. On the other hand, infection with adenovirus-carrying HSP70 andHSP27 cDNAs did not increase MDR1/P-gp expression. HSF1 regulates MDR1/P-gp expression at the transcriptional level, since HSF1+ bound the heat-shock consensus elements (HSEs) in the MDR1 gene promoter and also activated the expression of an MDR1 promoter-driven reporter plasmid (pMDR1(−1202)). In addition, heat-shock increased pMDR1(−1202) promoter activity but not the activity of a similar reporter plasmid with point mutations at specific HSEs, and the heat-induced increase was totally inhibited by co-transfection with an expression plasmid carrying HSF1−, a dominant negative mutant of HSF1. The stress inducers arsenite, butyrate, and etoposide also increased pMDR1(−1202) promoter activity, but the increase was not inhibited (in the case of butyrate) or was only partially inhibited (in the case of arsenite and etoposide) by HSF1−. These results demonstrate that HSF1 regulates MDR1 expression, and that the HSEs present in the −315 to −285 region mediate the heat-induced activation of the MDR1 promoter. However, other factors may also participate in MDR1 induction by stressing agents.

The selection between apoptosis and necrosis is differentially regulated in hydrogen peroxide-treated and glutathione-depleted human promonocytic cells

AbstractTreatment with 0.2 mM hydrogen peroxide (H2O2) or with 0.5 mM cisplatin caused caspase-9 and caspase-3 activation and death by apoptosis in U-937 human promonocytic cells. However, treatment with 2 mM H2O2, or incubation with the glutathione suppressor DL-buthionine-(S,R)-sulfoximine (BSO) prior to treatment with cisplatin, suppressed caspase activation and changed the mode of death to necrosis. Treatment with 2 mM H2O2 caused a great decrease in the intracellular ATP level, which was partially prevented by 3-aminobenzamide (3-ABA). Correspondingly, 3-ABA restored the activation of caspases and the execution of apoptosis. By contrast, BSO plus cisplatin did not decrease the ATP levels, and the generation of necrosis by this treatment was not affected by 3-ABA. On the other hand, while all apoptosis-inducing treatments and treatment with 2 mM H2O2 caused Bax translocation from the cytosol to mitochondria as well as cytochrome c release from mitochondria to the cytosol, treatment with BSO plus cisplatin did not. Treatment with cisplatin alone caused Bid cleavage, while BSO plus cisplatin as well as 0.2 and 2 mM H2O2 did not. Bcl-2 overexpression reduced the generation of necrosis by H2O2, but not by BSO plus cisplatin. These results indicate the existence of different apoptosis/necrosis regulatory mechanisms in promonocytic cells subjected to different forms of oxidative stress.

Quercetin decreases intracellular GSH content and potentiates the apoptotic action of the antileukemic drug arsenic trioxide in human leukemia cell lines.

Arsenic trioxide (ATO) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, but successful application of this agent may occasionally require the use of sensitizing strategies. The present work demonstrates that the flavonoids quercetin and chrysin cooperate with ATO to induce apoptosis in U937 promonocytes and other human leukemia cell lines (THP-1, HL-60). Co-treatment with ATO plus quercetin caused mitochondrial transmembrane potential dissipation, stimulated the mitochondrial apoptotic pathway, as indicated by cytochrome c and Omi/Htra2 release, XIAP and Bcl-X(L) down-regulation, and Bax activation, and caused caspase-8/Bid activation. Bcl-2 over-expression abrogated cytochrome c release and apoptosis, and also blocked caspase-8 activation. Quercetin and chrysin, alone or with ATO, decreased Akt phosphorylation as well as intracellular GSH content. GSH depletion was regulated at the level of L-buthionine-(S,R)-sulfoximine (BSO)-sensitive enzyme activity, and N-acetyl-L-cysteine failed both to restore GSH content and to prevent apoptosis. Treatment with BSO caused GSH depletion and potentiated ATO-provoked apoptosis, but did not affect apoptosis induction by ara-C and cisplatin. As an exception, ATO plus quercetin failed to elicit Akt de-phosphorylation and GSH depletion in NB4 acute promyelocytic leukemia cells, and correspondingly exhibited low cooperative effect in inducing apoptosis in this cell line. It is concluded that GSH depletion explains at least in part the selective potentiation of ATO toxicity by quercetin, and that this flavonoid might be used to increase the clinical efficacy of the antileukemic drug.

Curcumin Stimulates Reactive Oxygen Species Production and Potentiates Apoptosis Induction by the Antitumor Drugs Arsenic Trioxide and Lonidamine in Human Myeloid Leukemia Cell Lines

Arsenic trioxide (ATO, Trisenox) is an important antileukemic drug, but its efficacy is frequently low when used as a single agent. Here, we demonstrate that the apoptotic action of ATO is greatly increased when combined with subcytotoxic curcumin concentrations in U937 and HL60 human acute myeloid leukemia cells, and with lower efficacy in K562 chronic myelogenous leukemia cells. Curcumin exerts similar cooperative effect with the mitochondria-targeting drug lonidamine, whereas the response is negligible in combination with the DNA-targeting drug cisplatin. Curcumin plus ATO or lonidamine stimulates typical events of the mitochondrial executioner pathway (Bax and Bid activation, cytochrome c release, X-linked inhibitor of apoptosis down-regulation, and caspase-9/-3 activation) and causes mitochondrial transmembrane potential dissipation, which nevertheless represents a late event in the apoptotic response. Curcumin increases anion superoxide production, and its proapoptotic action in combination with ATO and lonidamine is mimicked by pro-oxidant agents (2-methoxyestradiol and H2O2) and prevented by antioxidant agents [Mn(III)tetrakis(4-benzoic acid)porphyrin chloride and N-acetyl-l-cysteine]. Within the assayed time period (16–24 h), curcumin does not significantly modify p38-mitogen-activated protein kinase and c-Jun NH2-terminal kinase phosphorylation/activation or nuclear factor-κB activity, but it greatly stimulates extracellular signal-regulated kinase (ERK) phosphorylation, and decreases Akt phosphorylation. Experiments using mitogen-activated protein kinase kinase/ERK inhibitors [2′-amino-3′-methoxyflavone (PD98059) and 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126)] and phosphatidylinositol 3-kinase inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) indicate that ERK activation does not mediate and even restrains apoptosis potentiation, whereas Akt down-regulation facilitates apoptosis generation. In summary, cotreatment with curcumin may represent a useful manner of increasing the efficacy of ATO and lonidamine as antitumor drugs in myeloid leukemia cells.

Genistein selectively potentiates arsenic trioxide-induced apoptosis in human leukemia cells via reactive oxygen species generation and activation of reactive oxygen species-inducible protein kinases (p38-MAPK, AMPK).

The observation that genistein may behave as a pro‐oxidant agent lead us to examine the capacity of this isoflavone to modulate the toxicity of the oxidation‐sensitive anti‐leukemic agent arsenic trioxide (ATO), and for comparison other anti‐tumor drugs. Co‐treatment with genistein increased ATO‐provoked apoptosis and activated apoptosis regulatory events (Bcl‐XL down‐regulation, cytochrome c and Omi/HtrA2 release from mitochondria, XIAP decrease and caspase‐8/Bid and caspase‐3 activation) in U937 promonocytes and other human leukemia cell lines (HL60, THP‐1, Jurkat, RPMI‐8866), but not in phytohemagglutinin‐stimulated non‐tumor peripheral blood lymphocytes (PBLs). Genistein, alone and with ATO, stimulated reactive oxygen species generation, and apoptosis was attenuated by N‐acetyl‐L‐cysteine and butylated hydroxyanisole. Addition of low H2O2 concentrations mimicked the capacity of genistein to increase ATO‐provoked apoptosis in leukemia cells, but not in PBLs. By contrast, co‐treatment with genistein or H2O2 failed to potentiate the toxicity of DNA‐targeting agent cisplatin, the proteasome inhibitor MG‐132 and the histone deacetylase inhibitor MS‐275. Within the here used time‐period (14 hr) genistein, alone or with ATO, did not significantly affect Akt phosphorylation and NF‐κB binding activity, nor decreased intracellular GSH content. However, it elicited N‐acetyl‐L‐cysteine‐inhibitable phosphorylation of p38‐MAPK and AMPK, and apoptosis was attenuated by pharmacologic inhibitors against these kinases. The pro‐oxidant capacity of genistein might be exploited to improve the efficacy of ATO as anti‐leukemic agent, and perhaps the efficacy of other oxidation‐based therapeutic approaches.

Regulation of apoptosis/necrosis execution in cadmium-treated human promonocytic cells under different forms of oxidative stress

Pulse-treatment of U-937 human promonocytic cells with cadmium chloride followed by recovery caused caspase-9/caspase-3-dependent, caspase-8-independent apoptosis. However, pre-incubation with the glutathione (GSH)-suppressing agent DL-buthionine-(S,R)-sulfoximine (cadmium/BSO), or co-treatment with H2O2 (cadmium/H2O2), switched the mode of death to caspase-independent necrosis. The switch from apoptosis to necrosis did not involve gross alterations in Apaf-1 and pro-caspase-9 expression, nor inhibition of cytochrome c release from mitochondria. However, cadmium/H2O2-induced necrosis involved ATP depletion and was prevented by 3-aminobenzamide, while cadmium/BSO-induced necrosis was ATP independent. Pre-incubation with BSO increased the intracellular cadmium accumulation, while co-treatment with H2O2 did not. Both treatments caused intracellular peroxide over-accumulation and disruption of mitochondrial transmembrane potential (ΔΨm). However, while post-treatment with N-acetyl-L-cysteine or butylated hydroxyanisole reduced the cadmium/BSO-mediated necrosis and ΔΨm disruption, it did not reduce the effects of cadmium/H2O2. Bcl-2 over-expression, which reduced peroxide accumulation without affecting the intracellular GSH content, attenuated necrosis generation by cadmium/H2O2 but not by cadmium/BSO. By contrast, AIF suppression, which reduced peroxide accumulation and increased the GSH content, attenuated the toxicity of both treatments. These results unravel the existence of two different oxidation-mediated necrotic pathways in cadmium-treated cells, one of them resulting from ATP-dependent apoptosis blockade, and the other involving the concurrence of multiple regulatory factors.

Pharmacologic inhibitors of extracellular signal-regulated kinase (ERKs) and c-Jun NH2-terminal kinase (JNK) decrease glutathione content and sensitize human promonocytic leukemia Cells to arsenic trioxide-induced apoptosis

Treatment with 1–4 µM As2O3 slightly induced apoptosis in U‐937 human promonocitic leukemia cells. This effect was potentiated by co‐treatment with MEK/ERK (PD98059, U0126) and JNK (SP600125, AS601245) inhibitors, but not with p38 (SB203580, SB220025) inhibitors. However, no potentiation was obtained using lonidamine, doxorubicin, or cisplatin instead of As2O3. Apoptosis potentiation by mitogen‐activated protein kinase (MAPK) inhibitors involved both the intrinsic and extrinsic executionary pathways, as demonstrated by Bax activation and cytochrome c release from mitochondria, and by caspase‐8 activation and Bid cleavage, respectively; and the activation of both pathways was prevented by Bcl‐2 over‐expression. Treatment with MEK/ERK and JNK inhibitors, but not with p38 inhibitors, caused intracellular glutathione (GSH) depletion, which was differentially regulated. Thus, while it was prevented by N‐acetyl‐L‐cysteine (NAC) in the case of U0126, it behaved as a NAC‐insensitive process, regulated at the level of DL‐buthionine‐(S,R)‐sulfoximine (BSO)‐sensitive enzyme activity, in the case of SP600125. The MEK/ERK inhibitor also potentiated apoptosis and decreased GSH content in As2O3‐treated NB4 human acute promyelocytic leukemia (APL) cells, but none of these effects were produced by the JNK inhibitor. MEK/ERK and JNK inhibitors did not apparently affect As2O3 transport activity, as measured by intracellular arsenic accumulation. SP600126 greatly induced reactive oxygen species (ROS) accumulation, while BSO and U0126 had little or null effects. These results, which indicate that glutathione is a target of MAP kinases in myeloid leukemia cells, might be exploited to improve the antitumor properties of As2O3, and provide a rationale for the use of kinase inhibitors as therapeutic agents. J. Cell. Physiol. 209: 1006–1015, 2006.

Regulation of genistein-induced differentiation in human acute myeloid leukaemia cells (HL60, NB4): Protein kinase modulation and reactive oxygen species generation

While it has been reported that genistein induces differentiation in multiple tumour cell models, the signalling and regulation of isoflavone-provoked differentiation are poorly known. We here demonstrate that genistein causes G(2)/M cycle arrest and expression of differentiation markers in human acute myeloid leukaemia cells (HL60, NB4), and cooperates with all-trans retinoic acid (ATRA) in inducing differentiation, while ATRA attenuates the isoflavone-provoked toxicity. Genistein rapidly stimulates Raf-1, MEK1/2 and ERK1/2 phosphorylation/activation, but does not stimulate and instead causes a late decrease in Akt phosphorylation/activation which is attenuated by ATRA. Both differentiation and G(2)/M arrest are attenuated by MEK/ERK inhibitors (PD98059, U0126) and ERK1-/ERK2-directed small interfering RNAs (siRNAs), and by the PI3K inhibitor LY294002, but not by the p38-MAPK inhibitor SB203580. Genistein stimulates p21(waf1/cip1) and cyclin B1 expression, phosphorylation/activation of ATM and Chk2 kinases, and Tyr15-phosphorylation/inactivation of Cdc2 (Cdk1) kinase, and these effects are attenuated by MEK/ERK inhibitors, while LY294002 also attenuates ERK and ATM phosphorylation. Caffeine abrogates the genistein-provoked G(2)/M blockade and alterations in cell cycle regulatory proteins, and also suppresses differentiation. Finally, genistein causes reactive oxygen species (ROS) over-accumulation, but the antioxidant N-acetyl-L-cysteine fails to prevent ERK activation, G(2)/M arrest, and differentiation induction. By contrast, N-acetyl-L-cysteine and p38-MAPK inhibitor attenuate the apoptosis-sensitizing (pro-apoptotic) action of genistein when combined with the antileukaemic agent arsenic trioxide. In summary, genistein-induced differentiation in acute myeloid leukaemia cells is a ROS-independent, Raf-1/MEK/ERK-mediated and PI3K-dependent response, which is coupled and co-regulated with G(2)/M arrest, but uncoupled to the pro-apoptotic action of the drug.

P38 MAPK protects against TNF-α-provoked apoptosis in LNCaP prostatic cancer cells

Purpose: One of the most relevant aspects in cell death regulation is the signalling of apoptosis by the serine/threonine kinases MAPKs. The aim of this study was to investigate the effects of TNF-α stimulation on MAPK activation, and the pro- or anti-apoptotic role of these kinases in LNCaP and PC3 cells. Material and methods: Treatments were carried out using several TNF-α concentrations, as well as specific pharmacological inhibitors of MAPKs. Apoptosis rates were evaluated by DAPI staining and flow cytometry. MAPK phosphorylation/activation was measured by Western blot. Results: TNF-α induced apoptosis in a dose-dependent manner in LNCaP but not in PC3 cells. The MAPK inhibitors revealed that the apoptotic rate in LNCaP cells increased significantly following p38 inhibition. The kinase inhibitors failed to cause changes in apoptosis in PC3 cells. Conclusions: The potentiation of apoptosis by p38 inhibition points to this kinase as a possible target for the treatment of androgen-dependent prostatic cancer.