Oestrogen-mediated suppression of tumour necrosis factor alpha-induced apoptosis in MCF-7 cells: subversion of Bcl-2 by anti-oestrogens

In oestrogen receptor (ER)-positive breast carcinoma cells, 17β-oestradiol suppresses a dose-dependent induction of cell death by tumour necrosis factor alpha (TNF). The ability of oestrogens to promote cell survival in ER-positive breast carcinoma cells is linked to a coordinate increase in Bcl-2 expression, an effect that is blocked with the pure anti-oestrogen ICI 182,780. The role of Bcl-2 in MCF-7 cell survival was confirmed by stable overexpression of Bcl-2 which resulted in suppression of apoptosis induced by doxorubicin (DOX), paclitaxel (TAX) and TNF as compared to vector-control cells. The pure anti-oestrogen ICI 182,780 in combination with TNF, DOX or TAX potentiated apoptosis in vector-transfected cells. Interestingly, pre-treatment with ICI 182,780 markedly enhanced chemotherapeutic drug- or TNF-induced apoptosis in Bcl-2 expressing cells, an effect that was correlated with ICI 182,780 induced activation of c-Jun N-terminal kinase. Our results suggest that the effects of oestrogens/anti-oestrogens on the regulation of apoptosis may involve coordinate activation of signalling events and Bcl-2 expression.     

Estrogen regulates cytokine production and apoptosis in PMA-differentiated,macrophage-like U937 cells

We have investigated the effects of sex steroids, estradiol (E2), and testosterone (T) on the synthesis of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) in phorbol-myristate-acetate (PMA)-differentiated human monoblastic U937 cells. The ability of both hormones to modulate the viability and programmed cell death of macrophage-like PMA-differentiated U937 cells was also inspected. E2 increased TNF-alpha synthesis, whereas T had no effect on the production of this cytokine. The combination of E2 and its antagonist tamoxifen or ICI-182,789 completely abolished the induction of TNF-alpha, while combination of T and its antagonist Casodex (CSDX) did not significantly affect TNF-alpha production by U937 cells. Exposure of cells to E2 resulted in a dose-dependent decrease of IL-10 synthesis, while again T did not show any detectable effect. In addition, E2 induced a significant increase of apoptosis in macrophage-like U937 cells and this increase was inhibited by the simultaneous addition of either tamoxifen or ICI-182. In contrast, T alone or in combination with CSDX did not modify apoptotic rates of U937 cells. This evidence, taken together, suggests that estrogens, but not androgens, exert a pro-inflammatory action through the modulation of TNF-alpha and IL-10, and regulate the immune effector cells by the induction of programmed cell death.     

Regulation of progesterone receptor isoforms content in human astrocytoma cell lines

Progesterone regulates several functions through the interaction with its intracellular receptor (PR) which expresses two isoforms with different functions and regulation: PR-A and PR-B. Both PR isoforms have been detected in human astrocytomas, the most common and aggressive primary brain tumours, but their regulation and function are unknown. We studied the effects of estradiol, progesterone and their receptor antagonists (ICI 182,780 and RU 486) on PR isoforms content in U373 and D54 human astrocytoma cell lines, respectively derived from grades III and IV astrocytomas, by Western blot analysis. In U373 cells we also evaluated the effects of PR-A overexpression on cell growth. We observed that in U373 cells estradiol increased the content of both PR isoforms whereas in D54 cells it had no effects. Estradiol effects were blocked by ICI 182,780. In both cell lines, PR isoforms content was down-regulated by progesterone after estradiol treatment. This effect was blocked by RU 486. We observed that overexpression of PR-A significantly diminished the increase in U373 cells number produced after progesterone treatment. Our results suggest a differential PR isoforms regulation depending on the evolution grade of human astrocytoma cells, and an inhibitory role of PR-A on progesterone effects on astrocytomas cell growth.     

Inhibition of estrogen receptor alpha expression and function in MCF-7 cells by kaempferol

Estrogens are mitogenic for estrogen receptor (ER)-positive breast cancer cells. Current treatment of ER-positive breast tumors is directed towards interruption of estrogen activity. We report that treatment of ER-positive breast cancer cells with kaempferol resulted in a time- and dose-dependent decrease in cell number. The concentration required to produce 50% growth inhibition at 48 h was approximately 35.0 and 70.0 microM for ER-positive and ER-negative breast cancer cells, respectively. For MCF-7 cells, a reduction in the ER-alpha mRNA equivalent to 50, 12, 10% of controls was observed 24 h after treatment with 17.5, 35.0, and 70.0 microM of kaempferol, respectively. Concomitantly, these treatments led to a 58, 80, and 85% decrease in ER-alpha protein. The inhibitory effect of kaempferol on ER-alpha levels was seen as early as 6 h post-treatment. Kaempferol treatment also led in a dose-dependent decrease in the expression of progesterone receptor (PgR), cyclin D1, and insulin receptor substrate 1 (IRS-1). Immunocytochemical study revealed that ER-alpha protein in kaempferol-treated MCF-7 cells formed an aggregation in the nuclei. Kaempferol also induced degradation of ER-alpha by a different pathway than that were observed for the antiestrogen ICI 182,780 and estradiol. Estradiol-induced MCF-7 cell proliferation and expression of the estrogen-responsive-element-reporter gene activity were abolished in cells co-treated with kaempferol. These findings suggest that modulation of ER-alpha expression and function by kaempferol may be, in part, responsible for its anti-proliferative effects seen in in vitro.     

脱氢表雄酮经不依赖于雌、雄激素受体的MAPK信号途径抑制成骨细胞凋亡

脱氢表雄酮(DHEA)已成为防治绝经后骨质疏松症(PMO)的新策略,但其调控成骨细胞(OB)凋亡的具体分子机制和信号转导途径尚不清楚。我们通过颅骨酶解法原代培养OB,体外模拟雌激素撤退现象,10-7mol/LDHEA分别作用0h、24h、48h、72h后,RT-PCR分析OB中ERα、ERβ和ARmRNA表达;原代OB去血清进一步培养24h,细胞以雌激素受体(ER)拮抗剂ICI182,780(1μmol/L)、雄激素受体(AR)拮抗剂Flutamide(10μmol/L)或U0126(100μmol/L)预处理后给予系列浓度DHEA(10-10-10-5mol/L)孵育72h,AnnexinV-FITC/PI双标记流式细胞仪分析细胞早期凋亡;原代OB以1μmol/LICI182,780或10μmol/LFlutamide预处理25min后给予不同浓度DHEA孵育10min,Westernblotting分析ERK1/2的磷酸化状态。结果表明OBs经10-7mol/LDHEA体外处理24h、48h、72h后,ERβ和ARmRNA水平升高(分别为P<0.05和P<0.01);而ERαmRNA水平无明显变化。10-9-10-6mol/LDHEA可显著抑制血清饥饿诱导的OBs早期凋亡(分别为P<0.05及P<0.01),该抑制效应可被U0126阻滞,ICI182,780或Flutamide则不能阻滞DHEA对OB的抗凋亡效应;Westernblot也显示ICI182,780或Flutamide都不能有效地阻滞DHEA对OB中ERKs磷酸化的诱导作用。因此可认为DHEA经ER或AR非依赖途径抑制OB凋亡;丝裂原活化蛋白激酶(MAPK)信号途径,磷酸化ERK1/2参与介导这一作用。     

Effects of neuroactive steroids on cochlear hair cell death induced by gentamicin

As neuroactive steroids, sex steroid hormones have non-reproductive effects. We previously reported that 17β-estradiol (βE2) had protective effects against gentamicin (GM) ototoxicity in the cochlea. In the present study, we examined whether the protective action of βE2 on GM ototoxicity is mediated by the estrogen receptor (ER) and whether other estrogens (17α-estradiol (αE2), estrone (E1), and estriol (E3)) and other neuroactive steroids, dehydroepiandrosterone (DHEA) and progesterone (P), have similar protective effects. The basal turn of the organ of Corti was dissected from Sprague-Dawley rats and cultured in a medium containing 100 μM GM for 48 h. The effects of βE2 and ICI 182,780, a selective ER antagonist, were examined. In addition, the effects of other estrogens, DHEA and P were tested using this culture system. Loss of outer hair cells induced by GM exposure was compared among groups. βE2 exhibited a protective effect against GM ototoxicity, but its protective effect was antagonized by ICI 182,780. αE2, E1, and E3 also protected hair cells against gentamicin ototoxicity. DHEA showed a protective effect; however, the addition of ICI 182,780 did not affect hair cell loss. P did not have any effect on GM-induced outer hair cell death. The present findings suggest that estrogens and DHEA are protective agents against GM ototoxicity. The results of the ER antagonist study also suggest that the protective action of βE2 is mediated via ER but that of DHEA is not related to its conversion to estrogen and binding to ER. Further studies on neuroactive steroids may lead to new insights regarding cochlear protection.     

Differential expression of VEGF-A mRNA by 17β-estradiol in breast tumor cells lacking classical ER-α may be mediated through a variant form of ER-α

Beta-estradiol (17beta-E2) augments VEGF-A expression in various estrogen targeted organs and cells including breast tumor derived cell lines, via an ER-alpha mediated pathway. Ironically, 17beta-E2 is able to regulate some genes via ER-alpha independent pathways. In the present study, we sought to determine whether 17beta-E2 can modulate VEGF-A expression in absence of ER-alpha, and therefore, three different cell lines including ER-alpha+ MCF-7, and ER-alpha SKBR-3 and HMEC were used for this study. The present study demonstrates that 17beta-E2 also induces VEGF-A mRNA expression in ER-negative SKBR-3 breast tumor cells in a manner similar to that observed in ER-positive MCF-7 cells. Blocking the induced-expression by antiestrogen ICI 182,780 indicates the induction pathway is ER dependent. While ER-alpha mRNA is absent in both HMEC and SKBR-3 cells, the impact of estrogen was found only in SKBR-3 cells, suggesting the existence of an analogue to ER-alpha or overlapping signal in these cells. Consistent with this suggestion, the present studies demonstrate the existence of an ER-alpha(var2) protein in MCF-7 and in SKBR-3 cells. This variant is predominantly localized in the nuclei of SKBR-3 cells. Importantly, specific binding of 17beta-E2 by these cells suggest the ER-alpha(var2) may act as active receptor in SKBR-3 cells.     

The effects of estradiol and selective estrogen receptor modulators on gene expression and messenger RNA stability in immortalized sheep endometrial stromal cells and human endometrial adenocarcinoma cells

The purpose of this study was to identify an endometrial cell line that maintained the E2 up-regulation of estrogen receptor (ER) mRNA by enhanced message stability and to assess its dependence on ER protein. Estradiol (E2) effects on gene expression were measured in three cell lines: one immortalized from sheep endometrial stroma (ST) and two from human endometrial adenocarcinomas (Ishikawa and ECC-1). E2 up-regulated ER mRNA levels in ST and Ishikawa cells, but down-regulated ER mRNA levels in ECC-1 cells. E2 up-regulated progesterone receptor (PR), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and transforming growth factor-alpha (TGF-alpha) in both Ishikawa and ECC-1 cells. The selective estrogen receptor modulator ICI 182,780 antagonized the E2-induced up-regulation of ER and/or PR mRNA levels in all three cells, while another, GW 5638, antagonized the up-regulation of PR mRNA in Ishikawa and ECC-1 cells. In mechanistic studies, E2 had no effect on ER mRNA stability in ST cells and it destabilized ER mRNA in ECC-1 cells. Thus, Ishikawa cells appear to be the most physiologically relevant cell line in which to study the up-regulation of ER mRNA levels by enhanced mRNA stability. Its antagonism by ICI 182,780 reveals that ER protein is involved in this E2 response.     

Stimulation of catecholamine synthesis through unique estrogen receptors in the bovine adrenomedullary plasma membrane by 17beta-estradiol

Incubation of cultured bovine adrenal medullary cells with 17beta-estradiol (E(2)) (0.3-100nM) or membrane-impermeable E(2)-bovine serum albumin (100nM) acutely increased (14)C-catecholamine synthesis from [(14)C]tyrosine. The stimulatory effect of E(2) was not inhibited by ICI182,780, a nuclear estrogen receptor inhibitor. E(2) also increased tyrosine hydroxylase activity and p44/42MAPK phosphorylation, the former of which was attenuated by U0126, an inhibitor of p44/42MAPK kinase. The plasma membrane isolated from the gland showed two classes of specific binding sites of [(3)H]E(2) with apparent K(d)s of 3.2 and 106nM, and B(max)s of 0.44 and 8.5pmol/mg protein, respectively. The high-affinity binding of [(3)H]E(2) was most strongly inhibited by E(2) and phytoestrogens, and to lesser extents by other steroid hormones, while it was enhanced by ICI182,780 and environmental estrogenic pollutants. These findings suggest that E(2) acutely stimulates catecholamine synthesis via activation of p44/42MAPK through unique estrogen receptors in the plasma membrane of bovine adrenal medulla.     

Activation of apoptosis, but not necrosis, during Mycobacterium tuberculosis infection correlated with decreased bacterial growth: role of TNF-alpha, IL-10, caspases and phospholipase A2

Monocyte/macrophage cell death is an important event during mycobacterial infection. To get insights about the influence of mononuclear phagocyte maturation in this event we compared the response to Mycobacterium tuberculosis (Mtb) infection of fresh isolated monocytes and monocyte-derived macrophages (MDM) from healthy tuberculin positive individuals. Both monocytes and MDM underwent apoptosis, however, there was a higher numbers of apoptotic macrophages with active Caspases 8 and 9. We also compared Mtb-induced cell death in U937 pro-monocytes and PMA-differentiated cells (U937D). In response to Mtb infection, U937D cells underwent apoptosis and promonocytes both apoptosis and necrosis. There were high number of U937D cells producing TNF-α and high number of IL-10⁺ promonocytes. These evidences suggest that U937 could be a valid model to study the mechanisms that rule Mtb-induced cell death. Experiments with the cell line and fresh isolated mononuclear cells with pharmacological inhibitors showed that induction of necrosis involved calcium and cAMP signals resulting in IL-10 production. Necrosis also correlated with Caspase 3, PLA2 activity and bacterial growth. In U937D cells and monocytes from healthy donors there was activation of calcium, TNF-α and Caspase 8 activation and decreased bacterial load. Understanding the mechanisms that control the dichotomy events between apoptosis and necrosis/oncosis associated with cell maturity might open new strategies to better control the course of mycobacterial infections.     

Participation of beta-adrenergic receptors on macrophages in modulation of LPS-induced cytokine release

For several years it is known that beta-adrenergic receptor agonists have anti-inflammatory effects. However, little is known about the role of beta-adrenergic receptors on macrophages in the modulation of cytokine production by beta-agonists during inflammation. In this study, the presence of beta-receptors on PMA-differentiated U937 human macrophages, and the participation of these receptors in the modulation of LPS-mediated cytokine production by beta-agonists was investigated. Total beta-receptor expression on undifferentiated (monocyte) and PMA-differentiated U937 cells was established using receptor binding studies on membrane fractions with a radio ligand. The expression of beta-receptors proved to be significantly lower on monocytes than on macrophages, additionally a predominant expression of beta 2-receptors was found. Production of the cytokines TNF-alpha, IL-6, and IL-10 by LPS-stimulated differentiated U937 cells was measured in time. Peak concentrations for TNF-alpha, IL-6 and IL-10 occurred at 3, 12 and 9 hrs, respectively. When differentiated U937 cells were incubated with both LPS and the beta-agonist clenbuterol the production of TNF-alpha and IL-6 was significantly reduced. However the production of IL-10 was increased. To study the mechanism of modulation of cytokine production in more detail, U937 macrophages were incubated with LPS/clenbuterol in combination with selective beta 1- and beta 2-antagonists. These results indicated that the beta 2- and not the beta 1-receptor is involved in the anti-inflammatory activity of clenbuterol.     

Programmed Cell Death in 2′,3′-dideoxycytidine-resistant Human Monoblastoid U937 Cells

2′,3′-Dideoxycytidine is a powerful in vitro inhibitor of human immunodeficiency virus and is currently used in the treatment of acquired immunodeficiency syndrome. A long-term exposure of U937 monoblastoid cells to dideoxycytidine induces the selection of drug-resistant cells (U937-R). In previous studies, we investigated some important biochemical properties and functional activities, such as basal respiration, protein kinase C activity, superoxide anion release, and the level of reduced glutathione, which were found to be higher in the drug-resistant cell line, compared to the parental one. In the present study, we evaluated the response of the two cell lines to the induction of apoptosis by treatment with staurosporine and okadaic acid, which interfere with the protein kinase and phosphatase pathways, respectively. Moreover, knowing that GSH plays a crucial role in the regulation of nitric oxide-dependent apoptosis, U937-R and parental lines have been treated with SIN-1, which is known to generate significant amounts of O₂ and nitric oxide. Resistant and parental cells have been analysed by light and electron microscopy and agarose gel electrophoresis of isolated DNA has been performed. The obtained results demonstrate a different susceptibility of U937-R cell line to apoptosis induced with the three triggers. U937-R cells show more advanced apoptotic features if compared with parental cells, after staurosporine treatment. Differently, the okadaic acid does not induce a different behaviour in the two models. On the contrary, the agent SIN-1 determines an increased number of apoptotic cells in the U937 line. The results suggest that a higher level of protein kinase C and glutathione could prevent programmed cell death in U937-R.     

Human monocyte differentiation stage affects response to arachidonic acid

AA-induced cell death mechanisms acting on human monocytes and monocyte-derived macrophages (MDM), U937 promonocytes and PMA-differentiated U937 cells were studied. Arachidonic acid induced apoptosis and necrosis in monocytes and U937 cells but only apoptosis in MDM and U937D cells. AA increased both types of death in Mycobacterium tuberculosis-infected cells and increased the percentage of TNFα+ cells and reduced IL-10+ cells. Experiments blocking these cytokines indicated that AA-mediated death was TNFα- and IL-10-independent. The differences in AA-mediated cell death could be explained by high ROS, calpain and sPLA-2 production and activity in monocytes. Blocking sPLA-2 in monocytes and treatment with antioxidants favored M. tuberculosis control whereas AA enhanced M. tuberculosis growth in MDM. Such evidence suggested that AA-modulated effector mechanisms depend on mononuclear phagocytes’ differentiation stage.     

Establishment of persistent infection with HIV-1 abrogates the caspase-3-dependent apoptotic signaling pathway in U937 cells

Treatment of 26L cells, a subclone obtained from U937 cells, with TNF-alpha or DNA-damaging agents such as teniposide (VM26) and camptothecin (CPT) induced morphologically and biochemically typical apoptotic changes, including the activation of procaspase-3. The cells persistently infected with HIV-1 (26L/HIV), however, showed a marked resistance to VM26 and CPT, whereas they hardly lost the sensitivity to TNF-alpha. TNF-alpha-induced apoptosis of 26L/HIV cells proceeded without the increase in caspase-3 activity, indicating that signaling for apoptosis in the infected cells proceeded through an alternative caspase-3-independent pathway which could respond to TNF-alpha but not to VM26 and CPT. The evidence that p-toluenesulfonyl-l-lysine chloromethyl ketone (a trypsin-like serine protease inhibitor) blocked VM26- and CPT-induced apoptotic changes but not TNF-alpha-induced apoptosis also supported the existence of the alternative TNF-alpha-inducible pathway. The results also suggest that a TLCK-sensitive protease is involved upstream of the procaspase-3 activation process and that the protease is essential for the progress of VM26- and CPT-induced apoptosis. The similar effect of HIV-1-productive infection on the apoptosis induced by the DNA-damaging agents was also confirmed by utilizing U1 cells, which are latently HIV-1-infected U937 cells. The cells became resistant to these agents after induction of the viral production by pretreatment with PMA. These results suggest that persistent HIV-1 infection blocks an apoptotic pathway triggered by DNA damaging agents through the inhibition of the procaspase-3 activation process.     

Estrogen preferentially promotes the differentiation of CD11c+ CD11b(intermediate) dendritic cells from bone marrow precursors

Sex biases in autoimmunity and infection suggest that steroid sex hormones directly modulate immune cells. We show in this study that 17-beta-estradiol (E2) promotes the differentiation of functional dendritic cells (DC) from murine bone marrow precursor cells. Remarkably, ex vivo DC differentiation was inhibited in steroid hormone-deficient medium, and was restored by addition of physiological amounts of E2, but not dihydrotestosterone. DC differentiation was inhibited by the estrogen receptor (ER) antagonists ICI 182,780 and tamoxifen, and from ERalpha(-/-) bone marrow cells, indicating that E2 acted via ERs. E2 addition was most effective in promoting DC differentiation immediately ex vivo, but did not increase DC proliferation. E2 treatment specifically promoted differentiation of a CD11c(+) CD11b(int) DC population that displayed high levels of cell surface MHC class II and CD86, suggesting that E2 could augment numbers of potent APC. DC that differentiated in E2-supplemented medium were fully functional in their capability to mediate presentation of self and foreign Ags and stimulate the proliferation of naive CD4(+) T cells. The requirement for estrogen during DC differentiation suggests a mechanism by which E2 levels in peripheral tissues might modulate both the number and functional capabilities of DC in vivo, thereby influencing immune responses.     

12-O-tetradecanoylphorbol-13-acetate-induced apoptosis is mediated by tumor necrosis factor alpha in human monocytic U937 cells.

12-O-tetradecanoylphorbol-13-acetate (TPA), a phorbol ester that is known as a tumor promoter, induces differentiation of myeloid cells and suppresses their proliferation. We studied the regulation of apoptosis by TPA in human monocytic cell line U937 cells that lack p53. Untreated U937 cells constitutively underwent apoptosis, and TPA enhanced apoptosis in these cells. Further studies showed that TPA increased production of tumor necrosis factor-alpha (TNFalpha) in U937 cells, and exogenously added TNFalpha induced apoptosis. Moreover, the induction of apoptosis by TPA was blocked by anti-TNFalpha antibody. Similar results were obtained in the myeloblastic cell line KY821 cells. We also found that the induction of apoptosis by TPA was increased in cells overexpressed with TNF receptor 1 but not in control cells. Furthermore, TPA failed to induce the production of TNFalpha and apoptosis in cells with either their protein kinase C or mitogen-activated protein kinase pathway blocked. Our results indicate that TPA induces apoptosis, at least in part, through a pathway that requires endogenous production of TNFalpha in U937 cells. Our data also suggest that the induction of apoptosis by TPA occurs through activation of protein kinase C and mitogen-activated protein kinase and TNFalpha is an autocrine-stimulating factor for the induction of apoptosis in these cells.     

PI3K/AKT途径在大肠埃希菌诱导U937细胞凋亡中的作用

目的探讨PI3K/AKT信号转导通路在大肠埃希菌（Escherichia coli,E.coli）诱导的人巨噬细胞系U937细胞凋亡中的作用。方法利用Western blot分析检测E.coli感染不同时间后磷酸化及非磷酸化AKT的表达;预先用不同浓度的LY294002（PI3K途径抑制剂）处理U937细胞60min,观察E.coli感染30min后U937细胞的凋亡情况。结果随着感染时间的延长,磷酸化AKT的表达逐渐下降。加入PI3K的抑制剂LY294002后,U937细胞的凋亡率逐渐升高。结论PI3K/AKT信号转导通路参与了E. coli诱导的U937细胞凋亡过程。LY294002通过特异性地抑制PI3K/AKT活性增加E.coli诱导的U937细胞凋亡率。     

Programmed cell death in 2',3'-dideoxycytidine-resistant human monoblastoid U937 cells

2,3-Dideoxycytidine is a powerful in vitro inhibitor of human immunodeficiency virus and is currently used in the treatment of acquired immunodeficiency syndrome. A long-term exposure of U937 monoblastoid cells to dideoxycytidine induces the selection of drug-resistant cells (U937-R). In previous studies, we investigated some important biochemical properties and functional activities, such as basal respiration, protein kinase C activity, superoxide anion release, and the level of reduced glutathione, which were found to be higher in the drug-resistant cell line, compared to the parental one. In the present study, we evaluated the response of the two cell lines to the induction of apoptosis by treatment with staurosporine and okadaic acid, which interfere with the protein kinase and phosphatase pathways, respectively. Moreover, knowing that GSH plays a crucial role in the regulation of nitric oxide-dependent apoptosis, U937-R and parental lines have been treated with SIN-1, which is known to generate significant amounts of O₂ and nitric oxide.Resistant and parental cells have been analysed by light and electron microscopy and agarose gel electrophoresis of isolated DNA has been performed. The obtained results demonstrate a different susceptibility of U937-R cell line to apoptosis induced with the three triggers. U937-R cells show more advanced apoptotic features if compared with parental cells, after staurosporine treatment. Differently, the okadaic acid does not induce a different behaviour in the two models. On the contrary, the agent SIN-1 determines an increased number of apoptotic cells in the U937 line. The results suggest that a higher level of protein kinase C and glutathione could prevent programmed cell death in U937-R.