As2O3联合Aspirin对诱导肝癌细胞凋亡的影响

目的:观察As2O3与Aspirin联合应用对肝癌细胞Bel-7402的影响,并探讨其作用机制.方法:体外培养肝癌Bel-7402细胞,Aspirin、As2O3不同浓度孵育细胞.倒置显微镜观察细胞形态学改变,四甲基偶氮唑蓝(MTT)法检测As2O3和Aspirin单独及联合应用对Bel-7402细胞增殖情况的影响,流式细胞术观察细胞凋亡情况,并通过流式软件分析细胞周期变化.结果:As2O3及Aspirin对肝癌Bel-7402细胞生长均呈不同程度的抑制,且呈浓度依赖性.二者联合具有协同作用,药物联用组抑制率均显著高于单独应用同等剂量As2O3组和Aspirin组(P<0.05).2.0μmol/LAs2O3与0.2mmol/LAspirin联用组与2.0μmol/LAs2O3单药组相比,凋亡率从5.64%±0.56%提高到7.35%±0.62%,差异具有统计学意义(P<0.05).且通过对两组细胞周期检测发现,G1期细胞从40.52%±0.64%下降到32.03%±0.97%,G2期及S期细胞分别从9.57%±0.82%、50.41%±0.32%上升到13.66%±0.82%、54.37%±0.69%,Aspirin能显著增强As2O3诱导细胞集中于S及G2期的作用,从而增强其促凋亡作用.结论:Aspirin能增强As2O3诱导细胞凋亡的作用,该作用可能与影响细胞周期有关.     

Melatonin induces mitochondrial-mediated apoptosis in human myeloid HL-60 cells

Abstract:  The role of melatonin in the mediation of apoptotic events has recently gained attention, especially after recent studies have reported that melatonin exerts antiapoptotic actions in normal cells but may activate proapoptotic pathways in some tumor cells. Here, we have evaluated the effect of melatonin on apoptosis in the human leukemia cell line HL-60. Melatonin treatment (1 m m ) induced a significant increase in caspase-3 and -9 activities. The effect of melatonin on the activation of caspases was time dependent, reaching a maximum after 12 hr of stimulation, and then decreasing to a minimum after 72 hr. Treatment with melatonin also evoked mitochondrial membrane depolarization and permeability transition pore induction, which caused loss of mitochondrial staining by calcein, and increased cell death by apoptosis/necrosis as demonstrated by propidium iodide positive-staining of cells after 72 hr of stimulation. In addition, the exposure of cells to melatonin resulted in an activation and association of the proapoptotic proteins Bax and Bid, as well as promoting detectable increases in the expression of both proteins. We conclude that melatonin has proapoptotic and/or oncostatic effects in the human myeloid cell line HL-60.     

1,25-Dihydroxyvitamin D3 enhances cytosolic free calcium in HL-60 cells

1,25-Dihydroxyvitamin D3 (1,25[OH]2D3) caused a rise in the concentration of intracellular free calcium ions ([Ca2+]i) in HL-60 cells. This effect of 1,25(OH)2D3 parallels its suppression of cell proliferation and its induction of cell differentiation into monocyte-like cells. The changes in [Ca2+]i are dose and time dependent. The concentration of 1,25(OH)2D3 (10(-7) M) that induced maximal differentiation also caused the maximal increase in intracellular Ca2+. The rise in cytoplasmic free Ca2+ concentration was not immediate and reached statistical significance only after 24 h. The [Ca2+]i reached its peak at 48 h (134 +/- 4 nM vs 101 +/- 3 nM in controls) and remained stable at this level. The increase in intracellular Ca2+ was found to be related to new protein synthesis, because it was inhibited in the presence of specific RNA and protein synthesis inhibitors. The rise in [Ca2+]i was not observed during incubation of HL-60 cells with 24,25-dihydroxyvitamin D3 (24,25[OH]2D3), a vitamin D metabolite that does not induce the differentiation of HL-60 cells. In contrast, 25-hydroxyvitamin D3 (25-OH-D3) and phorbol 12-myristate 13-acetate (TPA), both of which induce differentiation in this cell line, also increase [Ca2+]i. In conclusion, the present study emphasizes that a significant increase in intracellular free Ca2+ occurs in the effect of 1,25(OH)2D3 on HL-60 cells.     

ROS在齐墩果酸诱导HL-60细胞凋亡中的作用

目的 观察ROS在齐墩果酸(OA)诱导HL-60细胞凋亡中的作用.方法 分瓶培养细胞,实验设空白对照组和12、24、48 h的OA用药组.收集细胞,提取细胞总蛋白,制备去线粒体细胞浆蛋白,Western印迹法检测caspase-9表达.流式细胞术检测ROS水平.结果 OA处理HL-60细胞后,ROS含量增加,并引起caspase-9的激活.结论 OA使ROS量增加,通过线粒体凋亡信号通路诱导HL-60细胞凋亡.     

Ascorbic acid enhances arsenic trioxide-induced cytotoxicity in multiple myeloma cells

Multiple myeloma (MM) is a clonal B-cell malignancy characterized by slow-growing plasma cells in the bone marrow (BM). Patients with MM typically respond to initial chemotherapies; however, essentially all progress to a chemoresistant state. Factors that contribute to the chemorefractory phenotype include modulation of free radical scavenging, increased expression of drug efflux pumps, and changes in gene expression that allow escape from apoptotic signaling. Recent data indicate that arsenic trioxide (As(2)O(3)) induces remission of refractory acute promyelocytic leukemia and apoptosis of cell lines overexpressing Bcl-2 family members; therefore, it was hypothesized that chemorefractory MM cells would be sensitive to As(2)O(3). As(2)O(3) induced apoptosis in 4 human MM cell lines: 8226/S, 8226/Dox40, U266, and U266/Bcl-x(L). The addition of interleukin-6 had no effect on cell death. Glutathione (GSH) has been implicated as an inhibitor of As(2)O(3)-induced cell death either through conjugating As(2)O(3) or by sequestering reactive oxygen induced by As(2)O(3). Consistent with this possibility, increasing GSH levels with N-acetylcysteine attenuated As(2)O(3) cytotoxicity. Decreases in GSH have been associated with ascorbic acid (AA) metabolism. Clinically relevant doses of AA decreased GSH levels and potentiated As(2)O(3)-mediated cell death of all 4 MM cell lines. Similar results were obtained in freshly isolated human MM cells. In contrast, normal BM cells displayed little sensitivity to As(2)O(3) alone or in combination with AA. Together, these data suggest that As(2)O(3) and AA may be effective antineoplastic agents in refractory MM and that AA might be a useful adjuvant in GSH-sensitive therapies. (Blood. 2001;98:805-813)     

The effect of pyrimidine nucleosides on adenosine-induced apoptosis in HL-60 cells

Among several nucleosides, adenosine is the only one to induce typical apoptotic cell death in human promyelocytic leukemia HL-60 cells. Intracellularly transported adenosine seemed to be required for the induction of apoptosis, since dipyridamole, which inhibits the transport of adenosine, strongly suppressed apoptosis, and 8-phenyltheophylline, a receptor antagonist, did not affect the adenosine-induced effect. The viability of adenosine-treated HL-60 cells was partially recovered by supplementation with a pyrimidine nucleoside, uridine or thymidine. Cytidine or deoxycytidine had no effect on the growth and survival of adenosine-treated cells, while uridine or thymidine inhibited adenosine-induced intracellular DNA fragmentation. These results suggest that the quantitative adjustment of purine and pyrimidine nucleosides might play an important role in the adenosine-induced apoptosis of HL-60 cells. The reduction of c-Myc expression in adenosine-treated cells was prevented by uridine or thymidine. These observations suggest that the expression of c-Myc might be related to an intracellular sensing system for the quantitative balance of nucleosides or nucleotides. Received: 14 January 1998 / Accepted: 11 May 1998     

Sodium salicylate-triggered apoptosis in HL-60 cells depends on caspase-8 activation

For investigation of the killing and proapoptotic effects of sodium salicylate (Na-Sal) on HL-60 cells, the cytotoxic activity of Na-Sal was measured by means of MTT assay. Apoptosis was identified and analyzed with the help of transmission electron microscopy, annexin V staining, and DNA gel electrophoresis, and the association of caspase-8 activation with apoptosis was determined with the specific protease inhibitor IETD-fmk. After exposure of HL-60 cells to increasing concentrations of Na-Sal (0.5, 1, 3, 5, and 7 mmol/L) for 24 hours, the mean cell viability gradually dropped to 92%, 83%, 68%, 50%, and 42%. With treatment of target cells with 5-mmol/L (IC50) Na-Sal for 6, 12, 24, or 36 hours, the mean cell survival tapered to 91%, 81%, 48% (P <.05 versus control), and 14% (P <.05 versus control). Again incubated with 5-mmol/L Na-Sal for 12 or 24 hours, HL-60 cells displayed clear early or late signs of apoptosis, including (1) notable enhancement of phosphatidylserine externalization, (2) cell shrinkage, membrane blebbing, and eventual disintegration into numerous apoptotic bodies, and (3) formation of ladder DNA. The viability of HL-60 cells increased significantly during 24 or 36 hours of coculture with 100-micromol/L IETD-fmk in combination with 5-mmol/L Na-Sal compared with the viability when 5-mmol/L Na-Sal was used alone (P < .05). Moreover, the target cells showed a considerable decrease in phosphatidylserine exposure and DNA fragmentation after coincubation for 12 or 24 hours performed as described above. The findings presented herein strongly suggest that Na-Sal can exert potent killing and proapoptotic activity against HL-60 cells, and this effect appears to depend on caspase-8 activation.     

Butyric acid and pivaloyloxymethyl butyrate, AN-9, a novel butyric acid derivative, induce apoptosis in HL-60 cells

A novel butyric acid derivative, pivaloyloxymethyl butyrate, AN-9, was previously shown to be a potent differentiating agent. AN-9 exerts a significant anticancer activity in vitro and in vivo. In all the activities examined, AN-9 was more potent than butyric acid. Here we show that AN-9 and butyric acid induce cell death by apoptosis. Exposure of HL-60 cells to butyric acid and AN-9 decreased cell numbers and induced cell differentiation and the appearance of typical apoptotic features. Induction of apoptosis and/or differentiation by AN-9 and butyric acid was dependent on the concentration and the time of exposure to the drugs. The advantage of AN-9 over butyric acid was further confirmed. Apoptosis induced by AN-9 occurred after a shorter exposure and at lower drug concentrations than that induced by butyric acid. Apoptosis by AN-9 was accompanied by reduction in Bcl-2 expression. Preincubation with antioxidants did not protect HL-60 cells from apoptosis induced by AN-9. HL-60 cells that were induced to differentiate by preincubation with retinoic acid or low AN-9 concentrations were more resistant to apoptosis, induced later by high concentrations of AN-9, than were undifferentiated cells.Abbreviation AN-9 pivaloyloxymethylbutyrate This work is part of the Ph.D. thesis of Yael Zimra of the Sackler School of Medicine, Tel Aviv University     

Deguelin blocks cells survival signal pathways and induces apoptosis of HL-60 cells in vitro

To investigate the anti-cancer effects and molecular mechanism of deguelin on the human leukemia HL-60 cells, to explore the expression and clinical significance of p-AKT, survivin and Bcl-2 in leukemia cell line HL-60 cell. Cell growth rate was assessed by MTT assay. Apoptotic index was evaluated by TUNEL staining. Apoptosis was detected by Annexin V-FITC Apoptosis Detection Kit and transmission electron microscopy (TEM), expression of p-Akt, Bcl-2 and surviving in HL-60 cells was checked by Western blot. Deguelin presented striking proliferation inhibition potency on HL-60 cells in vitro, with the I_C50 value for 48 h being 20.14 nM, and induced apoptosis in HL-60 in a concentration–time-dependent manner. Apoptotic bodies and cell shrinkage and fragmentation were observed by TUNEL and TEM. Deguelin-induced cells morphological changes and degraded several kinase proteins, including Bcl-2 and survivin (members of lap). The degradation of these kinases blocked PI3K/Akt survival signal pathways, inducing apoptosis. Deguelin may induce HL-60 cell apoptosis through depletion of multiple kinase proteins and blockage of survival signal pathways of HL-60 cells.     

New [1,2,4]triazolo[4,3-c]quinazoline enhances cisplatin- and temozolomide-induced growth inhibition and apoptosis in HL-60 cells

The purpose of this study was to investigate the therapeutic potential of a newly synthesized [1,2,4]triazolo[4,3-c]quinazoline (NTCHMTQ) alone and in combination with two anticancer drugs (cisplatin and temozolomide) against HL-60 leukemia cell line. The IC50 value of NTCHMTQ toward HL-60 cells was 19.7 microM. No apoptosis and cell cycle changes were observed in cells treated with 5 microM NTCHMTQ alone. Combination of non-toxic concentrations of NTCHMTQ (1-5 microM) with cisplatin or temozolomide sensitized HL-60 cells to these two drugs and significantly enhanced their efficacies, that is illustrated by combination indexes, sub-G0 cell fraction, apoptotic DNA fragmentation and caspase-3 activity. The results suggest that combined therapy of non-toxic concentrations of NTCHMTQ with chemotherapeutics may provide synergistic regimen for treatment of leukemia. However, further in vitro and in vivo experimental drug-cell and drug-drug studies are warranted.     

Effect of retinoic acid on the actin cytoskeleton in HL-60 cells

The cytoskeleton, in addition to its structural and kinetic functions, is also involved in modulating signal transfer in cell proliferation, differentiation and death. In some myeloid leukemic cell lines, the process of cell differentiation accompanied by apoptosis, can be induced by all-trans retinoic acid (ATRA). In this report, we describe the morphological changes in actin cytoskeleton, taking place during apoptosis in cells of the human leukemic HL-60 cell line. By using fluorescent microscopy, the morphology of microfilaments and the proportion of apoptotic cells in the cell populations untreated or treated with 10(-6) M ATRA were detected. Interphase HL-60 cells showed aggregations of short, thick microfilament bundles in the region between the plasma membrane and the nucleus. In comparison with both interphase and mitotic cells, the cells with apoptotic nuclear fragmentation showed a different organisation of the actin cytoskeleton. The following types of F-actin structures were observed: (i) Cells with a high number of large dots/patches of F-actin under the plasma membrane. These dots might be localised only in the part of the cell or occurred under the whole plasma membrane. This arrangement was often associated with a diffuse signal for F-actin. (ii) Cells with 3D-network of F-actin fibres through the cytoplasm between remnants of the cell nucleus. This 3D-structure probably played an important active role in the process of apoptotic bodies formation. (iii) Cells without any detectable signal for F-actin or cells with only a very low F-actin signal. Both of these showed typical apoptotic collapse of chromatin. It is concluded that the actin cytoskeleton is a dynamic structure actively involved in the executive phase of the process of apoptosis. It is suggested that the rearrangement of the microfilament network and its subsequent degradation are necessary for the main morphological changes of apoptotic cells, i.e., plasma membrane blebbing and apoptotic bodies formation.     

Retinoic acid-resistant HL-60 cells exclusively contain mutant retinoic acid receptor-alpha

Sequence analysis of the retinoic acid receptor-alpha (RAR alpha) gene from a subline of HL-60 cells (RA-res) stably resistant to all-trans retinoic acid (RA) disclosed a single-base change in codon number 411, the same C to T transition previously reported in an independently selected HL-60 RA resistant clone by Robertson et al (Blood 80:1885, 1992). This mutation eliminates a FokI restriction endonuclease site. Using primers framing this mutation in exon 9 of the RAR alpha gene, we showed that polymerase chain reaction products amplified from either mRNA or genomic DNA templates from the RA-res subline were completely resistant to FokI digestion whereas those from wild-type (wt) HL-60 cells could be digested to completion. The lack of a normal allele in the RA-res cells was confirmed by mixing experiments and hybridization analyses. Southern blot analysis of DNA from the RA-res and wt cells versus control placental DNA indicated that the RAR alpha gene is not haploid. The independent isolation of the same RAR alpha mutation in different laboratories suggests either that the mutation exits in a small subpopulation in the wt line or that this is a mutational "hot spot." Furthermore, the results indicate that if a dominant negative mode of resistance is involved in the RA-res subline, this must involve interference with the function of heterologous receptor proteins such as the retinoid X receptors. The lack of any normal RAR alpha in this subline may facilitate studies of the mode of action of retinoids.     

Thymidine-dependent attenuation of the mitochondrial apoptotic pathway in adenosine-induced apoptosis of HL-60 cells

OBJECTIVE: We previously reported that adenosine-induced apoptosis in HL-60 cells was attenuated by cotreating the cells with pyrimidine nucleosides. The mechanism involved in this adenosine-induced apoptosis by the differential supply of nucleosides is studied here with a particular focus on the regulation of apoptosis-associated mitochondrial events. METHODS: Time-dependent changes in the mitochondrial membrane potential (MMP) after treatment with adenosine and/or thymidine were monitored. RESULTS: The cells did not show any decrease of MMP level up to 2.5 h after 1 mM adenosine exposure, whereas cytochrome c release, caspase-9 and caspase-3 activity, and DNA fragmentation were already activated, suggesting that mitochondrial depolarization is not a prerequisite of other apoptosis-related mitochondrial events. In contrast, the translocation of Bax to mitochondria and the release of cytochrome c began within the first hour of adenosine treatment. CONCLUSION: Thus, it is believed that adenosine-induced apoptosis is mediated by the activation of the caspase cascade by cytochrome c release with concomitant increase of Bax in the mitochondria, which implies that the translocation of Bax might be a leading event in the adenosine-induced apoptosis. Moreover, we found that most of the apoptotic parameters in adenosine-induced cellular changes, such as translocation of Bax, the release of cytochrome c, and the consequent activation of caspase-9 and caspase-3, were attenuated by thymidine supplement, thus indicating that the sensing of a nucleoside or nucleotide balance might be an upstream event of cytochrome c release. Therefore, it can be concluded that thymidine can attenuate adenosine-induced apoptosis by modulating the earliest stage of the mitochondrial apoptotic pathway.     

Comparative responsiveness of HL-60, HL-60R, and HL-60R+ (LRARSN) cells to retinoic acid, calcitriol, 9 cis-retinoic acid, and sodium butyrate

In HL-60 cells, retinoic acid (RA) and 9 cis-RA induce granulocytic differentiation, and calcitriol and sodium butyrate induce monocytic differentiation. To study the role of retinoid resistance on the response to these agents, we investigated their effects in HL-60 cells, retinoid-resistant HL-60R cells, and HL-60R+ cells in which retinoid sensitivity has been restored. In HL-60 cells, cathepsin D (ctsd) mRNA levels are increased by these agents and by cholera toxin after pretreatment with each agent. Calcitriol, 9 cis-RA, and sodium butyrate increase interleukin-8 (IL-8) mRNA expression, and pretreatment with these agents or RA potentiates the stimulation of IL-8 by phorbol ester (TPA). Pretreatment of HL-60 cells with all of the agents confers inducibility of cathepsin L (ctsl) mRNA by TPA in previously unresponsive cells. In HL-60R cells, none of the agents alone or in combination significantly enhances the expression of the ctsd, IL-8, or ctsl mRNAs. Retinoid stimulation (either alone or in combination with the other agents) of the three mRNAs is partially restored in the HL- 60R+ cells. Calcitriol does not alter the expression of any of these mRNAs, and only the stimulation of IL-8 mRNA by sodium butyrate is recovered. Treatment with all of the agents inhibits proliferation and stimulates differentiation of the HL-60 cells. RA and calcitriol are unable to inhibit proliferation of the HL-60R cells, whereas only calcitriol fails to inhibit proliferation of the HL-60R+ cells. None of the agents induces differentiation in either the HL-60R or HL-60R+ cells. Therefore, the mutation of the RA receptor alpha is insufficient to account for the altered responses of the HL-60R cells, and there are likely defects in other signaling pathways in these cells. These cells may prove useful in examining the mechanism of cross-resistance between various differentiating agents.     

琼枝麒麟菜多糖对白血病细胞株HL-60凋亡的影响

目的观察琼枝麒麟菜多糖(EGP)对白血病细胞株HL-60凋亡的影响。方法分别采用100、200、400 mg/L的EGP处理HL-60细胞。采用荧光显微镜观察HL-60细胞形态、MTT法测定细胞株的增殖抑制情况,流式细胞仪测定细胞凋亡率,逆转录—聚合酶链反应(RT-PCR)检测凋亡相关基因Bcl-2、Fas表达情况。结果200、400 mg/kg的EGP作用后HL-60细胞出现典型的凋亡形态学变化,HL-60细胞抑制率增加;凋亡抑制基因Bcl-2表达下调,促凋亡基因Fas表达上调。结论琼枝麒麟菜多糖能诱导HL-60细胞发生典型凋亡。     

Hyposialylation of differentiation-inducer-resistant HL-60 cells

The total sialic acid concent of retinoic acid (RA)-resistant or 6- thioguanine (6TG)-resistant HL-60 cells was more than tenfold lower and of dimethylsulfoxide (DMSO)-resistant HL-60 cells was approximately twofold lower than that of parental, wild-type (wt) HL-60 cells. Neuraminidase-inaccessible, ie residual cell-associated sialic acid after neuraminidase treatment, was four- to twelvefold lower in the three differentiation-inducer-resistant sublines than in the parent line. Neuraminidase treatment of 125I-labeled surface membrane glycoproteins (SMGs) from wt HL-60 cells converted the two-dimensional gel electrophoretic pattern to one having features in common with RA- and 6TG-resistant cells. However, neuraminidase treatment did not alter the sensitivity of wt HL-60 cells to differentiation induction by RA, hypoxanthine (purine base), or DMSO. These results indicate that differences in peripheral, neuraminidase-accessible sialic acids are important determinants of the gel electrophoretic mobility of the SMGs of the HL-60 line and sublines but are not likely related to the differentiation-resistance mechanism. Further studies are required to determine if hyposialylation of cryptic, neuraminidase-inaccessible sites has functional significance.     

Inhibition of proliferation and induction of apoptosis by melatonin in human myeloid HL-60 cells

Melatonin is an indoleamine that is synthesized in the pineal gland and has an extensive repertoire of biological activities. In the present study, we found that melatonin reduced the growth of the human myeloid leukemia cells HL-60, inhibiting progression from G(1) to S phase of the cell cycle and increasing apoptotic cell death. Furthermore, melatonin treatment elevated cytochrome c release from mitochondria and augmented caspase-3 and caspase-9 activities. Upregulation of Bax and downregulation of Bcl-2 was also observed upon melatonin treatment. The effects of melatonin were found not to be mediated by membrane receptors for the indoleamine. Together, our results suggest that melatonin reduces the viability of HL-60 cells via induction of apoptosis primarily through regulation of Bax/Bcl-2 expression.     

Bcl2 inhibits apoptosis associated with terminal differentiation of HL- 60 myeloid leukemia cells

The Bcl2 protein inhibits apoptosis (programmed cell death) induced by a variety of noxious stimuli. However, relatively little is known about its effect on apoptosis that occurs after terminal differentiation. Bcl2 protein levels decrease during differentiation of myeloid cells into granulocytes that subsequently undergo apoptosis, but the potential role of Bcl2 in coupling survival and differentiation remains undefined. To ascertain the relationship between decreasing Bcl2 levels and the onset of apoptosis in differentiating myeloid cells, Bcl2 was hyperexpressed in the HL-60 cell line after retroviral gene transfer. After treatment of HL-60/BCL2 cells with all-trans retinoic acid or phorbol myristic acid, Bcl2 levels did not decrease as in normal HL-60 cells but, rather, increased because of activation of the viral promoter. Differentiation of the Bcl2-overexpressing cells was similar to that of normal HL-60 cells, but they showed little evidence for apoptosis and had a prolonged survival. These studies show that the survival-enhancing properties of Bcl2 counteract programmed cell death that accompanies terminal differentiation; however, Bcl2 has no significant effect on differentiation itself, suggesting that apoptosis and differentiation are regulated independently in myeloid cells.     

Melatonin prevents apoptosis and enhances HSP27 mRNA expression induced by heat shock in HL-60 cells: possible involvement of the MT2 receptor

Previous studies have reported that melatonin protects cells and tissues against stressful stimuli. In the present study using HL-60 cells, we show that cells acquire increased resistance to apoptosis normally induced by heat shock when they are incubated with melatonin. This effect of melatonin is saturable at nanomolar concentrations and appears to be mediated by the MT2 subtype melatonin receptor. The high affinity melatonin receptor agonist, 2-iodomelatonin, reproduced the melatonin effect while it was fully blocked by the selective MT2 antagonist 4-phenyl-2-propionamidotetraline. The melatonin response to heat shock-induced apoptosis was pertussis toxin sensitive and, interestingly, the non-selective MT1/MT2 melatonin receptor ligand luzindole was found to display agonistic activity. Furthermore, we provide evidence that melatonin enhanced HSP27 mRNA expression as a result of heat shock - HSP27, is known to play an important role in the defense of cells against apoptosis induced by stressful agents. Together, these results demonstrate that melatonin, likely via receptor mechanisms, interferes with the apoptotic pathway activated by heat shock.