Multiple pathways are involved in protection of MCF-7 cells against death due to protein synthesis inhibition

Previously we have shown that IGF-1 protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). In the present study we investigated the ability of protein kinase C activator 12-0-tetradecanoyl-phorbol-13-acetate (TPA), the protein kinase A activator 8-bromoadenosine 3′5′-cyclic monophosphate (Br-cAMP), and the enzyme inhibitor aurintricarboxylic acid (ATA) to protect MCF-7 cells against death, due to a continuous presence of CHX. Cell death was evaluated after 48 h of incubation by several techniques (trypan blue staining, release of lactic dehydrogenase, cellular ATP content, transmission electron microscopy, and DNA fragmentation). Apoptosis which terminates in necrosis, characterized this mode of cell death. TPA and ATA at optimal concentrations of 40 ng/ml and 100 μg/ml, respectively, reduced cell death to the control level (without CHX), while Br-cAMP at an optimal concentration of 650 μg/ml reduced cell death only partially. IGF-1, TPA, and ATA, which stimulated protein synthesis in the control MCF-7 cells, had no effect on protein synthesis in the CHX-treated cells, indicating that the survival effect is not due to new protein synthesis. The protein kinase C inhibitor staurosporine blocked the survival effect of TPA and IGF-1 in a dose-dependent manner, however did not affect the survival effect of ATA. The tyrosine kinase inhibitor genistein blocked the survival effect of IGF-1, but not that of TPA and ATA. Our results provide evidence for several distinctive pathways, the activation of which protects MCF-7 cells against death, due to protein synthesis inhibition. © 1995 Wiley-Liss, Inc.     

Dysregulation of bcl-2, c-myc,and Fas expression during tricyclic antidepressant-induced apoptosis in human peripheral lymphocytes

Tricyclic antidepressants (TCAs) have been shown to induce apoptosis in human lymphocytes. In the present report, we investigated in parallel the regulation of the three oncogenes bcl-2, c-myc, and Fas. A reduction in c-myc and bcl-2 levels of 35–40% and 22–27%, respectively, was observed. On the other hand, Fas expression on the outer surface of the plasma membrane was increased up to 31%. In conclusion, bcl-2, c-myc, and Fas are undergoing dysregulation due to TCA-induced apoptosis. © 1997 John Wiley & Sons, Inc.     

Different patterns of apoptosis of HL-60 cells induced by cycloheximide and camptothecin

Cells of the human promyelocytic HL-60 line, when treated with a variety of antitumor agents in the presence of the protein synthesis inhibitor cycloheximide (CHX), or with CHX alone, rapidly undergo apoptosis (“active cell death”). It is presumed, therefore, that such cells are “primed” to apoptosis in that no new protein synthesis is required for induction of their death. We have studied apoptosis of HL-60 cells triggered by the DNA topoisomerase I inhibitor camptothecin (CAM) in the absence and presence of CHX and apoptosis induced by CHX alone. Two different flcw cytometric methods were used, each allowing us to relate the apoptosis-associated DNA degradation to the cell cycle position. Apoptosis induced by CAM was limited to S phase cells, e.g., at a CAM concentration of 0.15 μM, nearly 90% of the S phase cells underwent apoptosis after 4 h. In contrast, apoptosis triggered by CHX was indiscriminate, affecting all phases of the cycle: ～40% of the cells from each phase the cycle underwent apoptosis at 5 μM CHX concentration. When CAM and CHX were added together, the pattern of apoptosis resembled that of cycloheximide alone, namely, cells in all phases of the cycle in similar proportion were affected. Thus, CHX, while itself inducing apoptosis of a fraction of cells, protected the S phase cells against apoptosis triggered by CAM. Because CHX (5 μM) did not significantly affect the rate of cell progression through S phase, the observed protective effect was most likely directly related to inhibition of protein synthesis, rather than to its possible indirect effect on DNA replication. Furthermore, whereas apoptosis (DNA degradation) triggered by CAM was prevented by the serine protease inhibitor N-tosyl-L-lysylchloromethyl ketone (TLCK), this process was actually potentiated by this inhibitor when induced by CHX. The present data indicate differences in mechanism of apoptosis triggered by CAM (and perhaps other antitumor drugs) as compared with CHX. Apoptosis caused by CHX may be unique in that it may not involve new protein synthesis. These data are compatible with the assumption that the loss of a hypothetical, rapidly turning over suppressor of apoptosis may be the trigger of apoptosis of HL-60 cells treated with CHX, whereas de novo protein synthesis is required when apoptosis is triggered by other agents. © 1993 Wiley-Liss, Inc.     

Expression and biological activity of X-linked inhibitor of apoptosis (XIAP) in human malignant glioma.

The inhibitor-of-apoptosis (IAP) proteins are a novel family of antiapoptotic proteins that are thought to inhibit cell death via direct inhibition of caspases. Here, we report that human malignant glioma cell lines express XIAP, HIAP-1 and HIAP-2 mRNA and proteins. NAIP was not expressed. IAP proteins were not cleaved during CD95 ligand (CD95L)-induced apoptosis, and loss of IAP protein expression was not responsible for the potentiation of CD95L-induced apoptosis when protein synthesis was inhibited. LN-18 cells are highly sensitive to CD95-mediated apoptosis, whereas LN-229 cells require co-exposure to CD95L and a protein synthesis inhibitor, CHX, to acquire sensitivity to apoptosis. Adenoviral XIAP gene transfer blocked caspase 8 and 3 processing in both cell lines in the absence of CHX. Apoptosis was blocked in the absence and in the presence of CHX. However, XIAP failed to block caspase 8 processing in LN-229 cells in the presence of CHX. There was considerable overlap of the effects of XIAP on caspase processing with those of BCL-2 and the viral caspase inhibitor crm-A. These data define complex regulatory mechanisms for CD95-mediated apoptosis in glioma cells and indicate that there may be a distinct pathway of death receptor-mediated apoptosis that is readily activated when protein synthesis is inhibited. The constitutive expression of natural caspase inhibitors may play a role in the resistance of these cells to apoptotic stimuli that directly target caspases, including radiochemotherapy and immune-mediated tumor cell lysis.     

Comparative study of intracellular glutathione content in rat lymphocyte cultures treated with 2-mercaptoethanol and interleukin-2

The level of intracellular glutathione (GSH) in mitogen-stimulated mouse lymphocytes is increased in the presence of 2-mercaptoethanol (2-ME), an enhancer of lymphocyte activation and proliferation. Since proliferation of lymphocytes in response to mitogens involves direct activation by a mitogen followed by continued proliferation in response to interleukin-2 (IL-2), we have investigated the effect of 2-ME and exogenous IL-2 on the GSH content and cell proliferation of rat lymphocytes stimulated with phytohemagglutinin (PHA). PHA stimulation increased both GSH content and the magnitude of the proliferative response, as measured by thymidine incorporation into cellular DNA. However, incubation of stimulated lymphocytes with 2-ME or IL-2 for 72 hr produced a significant further elevation of GSH levels and thymidine incorporation. 2-ME also increased the GSH content in unstimulated cultures, but it had little effect on thymidine incorporation. IL-2 increased GSH content and decreased thymidine incorporation in unstimulated lymphocytes. Exposure of cells to DL-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH biosynthesis, significantly depleted GSH and lowered the proliferative response, suggesting a crucial role of de novo GSH synthesis for lymphocyte activation. The data suggest that both 2-ME and IL-2 promote lymphocyte proliferation, although the mechanisms by which intracellular GSH levels are increased by the agents are apparently different.Copies of articles are available through ISI Document Delivery Services c/o The Genuine Article, 3501 Market Street, Philadelphia, PA 19104.     

Superinduction of human interleukin-2 messenger RNA by inhibitors of translation

Stimulation of human lymphocytes with phytohemagglutinin results in the induction of messenger RNA encoding interleukin-2 (IL-2), a lymphokine possessing immuno-regulatory properties. We have previously demonstrated a dramatic superinduction of the formation of IL-2 and of biologically active IL-2 mRNA in the presence of cycloheximide, an inhibitor of translation. These findings suggested the involvement of a labile protein repressor in the regulation of human IL-2 gene expression. Here, we show a commensurate superinduction of IL-2 mRNA sequences by three additional inhibitors of protein synthesis with distinct modes of action: T-2 toxin, pactamycin, and sparsomycin. These results strengthen the concept that a labile protein controls the formation of mature IL-2 mRNA. They tend to eliminate the possibility that the superinduction phenomenon observed in the presence of cycloheximide is due to its action on a process other than translation.     

Caspase activity in newt spermatogonial apoptosis induced by prolactin and cycloheximide

We previously showed in vivo and in vitro, that among the spermatogenic stages of the newt, prolactin (PRL) induces apoptosis specifically in the penultimate stage of secondary spermatogonia. In the current report, we demonstrate in vitro that cycloheximide (CHX), an inhibitor of protein synthesis, induces morphological apoptotic changes similar to those caused by PRL, such as chromatin condensation and apoptotic body formation. Next, we found that Z-VAD-fmk, an inhibitor of various caspases, suppressed the apoptosis induced by PRL and CHX, but ICE inhibitor Ac-YVAD-CHO or caspase-3 inhibitor Ac-DEVD-CHO did not. As high caspase activity was present in extracts of testes treated with CHX, we suggest that an unidentified caspase induces the morphological changes of apoptosis in newt spermatogonia.     

Preferential induction of apoptosis in the rainbow trout macrophage cell line, RTS11, by actinomycin D, cycloheximide and double stranded RNA

The rainbow trout macrophage cell line RTS11 was found to be considerably more sensitive than rainbow trout fibroblast (RTG-2) and Chinook salmon epithelial (CHSE-214) cell lines to killing by macromolecular synthesis inhibitors, actinomycin D (AMD) and cycloheximide (CHX), a synthetic double stranded RNA (dsRNA), polyinosinic:polycytidylic acid (poly IC), and combinations of poly IC with AMD or CHX. Exposures of 24-30 h to AMD or CHX alone killed RTS11, but not CHSE-214 and RTG-2, in basal medium, L-15, with or without fetal bovine serum (FBS) supplementation. A two-week exposure to poly IC killed RTS11 in L-15, whereas RTG-2 and CHSE-214 remained viable. At concentrations that caused very little or no cell death, CHX or AMD pretreatments or co-treatments sensitized RTS11 to poly IC, causing death within 30 h. In all cases death was by apoptosis as judged by two criteria. H33258 staining revealed a fragmented nuclear morphology, and genomic degradation into oligonucleosomal fragments was seen with agarose gel electrophoresis. With AMD- or CHX-induced death, killing seemed caspase-independent as the pan caspase inhibitor, z-VAD-fmk, failed to block killing. By contrast, z-VAD-fmk almost completely abrogated killing by co-treatments of poly IC and low concentrations of AMD or CHX, suggesting caspase dependence. Killing by both types of treatments was blocked by 2 aminopurine (2-AP), which suggests the involvement of dsRNA-dependent protein kinase (PKR). The sensitizing of RTS11 to poly IC killing by AMD or CHX could be explained by a decrease in the level of a short-lived anti-apoptotic protein(s) and/or by the triggering of a ribotoxic stress.     

Crm-A, bcl-2 and NDGA inhibit CD95L-induced apoptosis of malignant glioma cells at the level of caspase 8 processing

Susceptibility to CD95 (Fas/APO-1)-mediated apoptosis in human glioma cells depends on CD95 expression and unknown factors that regulate signal transduction. Thus, LN-18 cells are highly sensitive to CD95 ligand (CD95L) whereas LN-229 cells require coexposure to inhibitors of RNA or protein synthesis for induction of apoptosis. Here, we report that caspase 8 and 3 activation, poly(ADP-ribose)polymerase cleavage and apoptosis are inhibited by the lipoxygenase inhibitor, nordihydroguaretic acid (NDGA), or ectopic expression of crm-A or bcl-2. CD95L-induced glioma cell apoptosis does not involve ceramide generation. Apoptosis induced by exogenous ceramide resembles CD95-mediated apoptosis in that bcl-2 is protective but differs in that NDGA and crm-A have no effect and in that cycloheximide (CHX) inhibits rather than potentiates ceramide-induced cell death. We conclude that caspase 8 and caspase 3 activation, but not ceramide generation, are required for CD95 ligand-induced apoptosis of glioma cells and that bcl-2, crm-A and NDGA all act upstream of caspases to inhibit apoptosis.     

The destabilization of IL-2 mRNA by a premature stop codon and its differential stabilization by trans-acting inhibitors of protein synthesis do not support a role for active translation in mRNA stability.

To investigate the role that translation plays in the stabilization of the IL-2 mRNA, we inhibited protein synthesis in both cis and trans. To block translation in trans, we utilized the inhibitors puromycin (PUR) and cycloheximide (CHX), which differentially effect polysome structure. We found that CHX enhances the stability of IL-2 mRNA in cells stimulated with anti-TCR Ab alone, but it inhibits CD28-induced message stabilization in costimulated cells. In contrast, PUR had a minimal effect on IL-2 mRNA stability in either the presence or absence of costimulation. The differential effects of these two inhibitors suggest that: 1) CHX is unlikely to stabilize the IL-2 mRNA by inhibiting the expression of a labile RNase; 2) CD28-mediated IL-2 mRNA stabilization does not require translation; and 3) IL-2 mRNA decay is not coupled to translation. To block translation in cis, we generated sequence-tagged IL-2 genomic reporters that contain a premature termination codon (PTC). In both the presence and absence of costimulation, these PTC-containing mRNAs exhibit drastically diminished stability. Interestingly, the addition of CHX but not PUR completely restored CD28-mediated stabilization, suggesting that CHX can block the enhanced decay induced by a PTC. Finally, CHX was able to superinduce IL-2 mRNA levels in anti-TCR Ab-stimulated cells but not in CD28-costimulated cells, suggesting that CHX may also act by other mechanisms.     

Regulation by glutathione of the effect of lymphokines on differentiation of primary activated lymphocytes. Influence of glutathione on cytotoxic activity of CD3-AK-.

By activating murine lymphocytes with anti-CD3 antibodies for 1 to 2 days, we generated a subset of activated killer cells, namely CD3-AK-. CD3-AK- mediated the slow lysis (20-h 125I-UdR release assay) of allogeneic P815 but had little effect on syngeneic HFL/b cells. Addition of IL-2 (murine or human) or an IL-2 inducer such as PMA in the assay medium induced the cytolytic activity of CD3-AK- on HFL/b. The activating effect of murine IL-2 and PMA on CD3-AK- was decreased by anti-murine IL-2 mAb. Although anti-murine IL-4 mAb alone did not show any effect, it enhanced the inhibitory effect of anti-IL-2 mAb, suggesting that IL-2 and IL-4 may have a synergistic effect on the cytolytic activity of CD3-AK-. Incubation of CD3-AK- with L-buthionine-(SR)-sulfoximine (BSO), an inhibitor of de novo glutathione (GSH) synthesis, decreased cellular GSH levels and inhibited the cytolytic activity of CD3-AK-, in a concentration-dependent manner. This inhibitory effect of BSO was not primarily due to a general cytotoxic effect and was positively correlated with the requirement for IL-2 for the CD3-AK(-)-mediated killing of the target cells. Incubation of CD3-AK- with GSH or 2-ME, which increased the level of cellular GSH, reversed the inhibitory effect of BSO. These results suggest that cellular GSH may regulate the effect of lymphokine(s) such as IL-2 and thus affect the differentiation of activated primary cytotoxic lymphocytes.