Regulation of the Fas apoptotic cell death pathway by Abl

BCR-ABL1 Tyrosine Kinase Complex Signaling Transduction: Challenges to Overcome Resistance in Chronic Myeloid Leukemia

The constitutively active BCR-ABL1 tyrosine kinase, found in t(9;22)(q34;q11) chromosomal translocation-derived leukemia, initiates an extremely complex signaling transduction cascade that induces a strong state of resistance to chemotherapy. Targeted therapies based on tyrosine kinase inhibitors (TKIs), such as imatinib, dasatinib, nilotinib, bosutinib, and ponatinib, have revolutionized the treatment of BCR-ABL1-driven leukemia, particularly chronic myeloid leukemia (CML). However, TKIs do not cure CML patients, as some develop TKI resistance and the majority relapse upon withdrawal from treatment. Importantly, although BCR-ABL1 tyrosine kinase is necessary to initiate and establish the malignant phenotype of Ph-related leukemia, in the later advanced phase of the disease, BCR-ABL1-independent mechanisms are also in place. Here, we present an overview of the signaling pathways initiated by BCR-ABL1 and discuss the major challenges regarding immunologic/pharmacologic combined therapies.

Novel Application of Radotinib for the Treatment of Solid Tumors via Natural Killer Cell Activation

Radotinib (Supect™) was developed to treat chronic myeloid leukemia (CML) as a BCR-ABL1 tyrosine kinase inhibitor (TKI). Other TKIs, including imatinib and nilotinib, were also developed for treatment of CML, and recent studies were increasing about the therapeutic effects of other TKIs on solid tumors. However, the effect of radotinib on solid tumors has not yet been investigated. In this study, radotinib killed CML cell line K562 directly; however, radotinib did not enhance NK cell cytotoxicity against K562 cells. Because K562 is known as a Fas-negative cell line, we investigated whether radotinib could regulate cell cytotoxicity against various Fas-expressing solid cancer cell lines. Radotinib dramatically increased NK cell cytotoxicity against various Fas-expressing solid cancer cells, including lung, breast, and melanoma cells. Additionally, the efficiency of radotinib-enhanced cytotoxicity was lower in Fas siRNA-transfected cells than in negative controls, suggesting that Fas signaling might be involved in the radotinib-enhanced NK cell cytotoxicity. This study provides the first evidence that radotinib could be used as an effective and strong therapeutic to treat solid tumors via upregulation of NK cell cytotoxicity, suggesting that radotinib has indirect killing mechanisms via upregulation of antitumor innate immune responses as well as direct killing activities for CML cells.

Evaluation of residual monomer release and toxicity of self-adhesive resin cements

The aim of this study was to evaluate the amount of leached residual monomers from self-adhesive resin cements and evaluate their toxicity in-vitro. A total of 60 disk-shaped specimens (5 mm in diameter and 0.5 mm in thickness) were prepared from each cement (RelyX U200, SpeedCEM, G-Cem) (n=20). Specimens were immersed in artificial saliva and the amount of released monomers [urethane dimethacrylate (UDMA) and triethyleneglycol dimethacrylate (TEGDMA)] was identified. Then, the cytotoxicity and genotoxicity effect on cells were evaluated using the defined amounts of released monomers from cements. The highest monomer release was detected in G-Cem (p<0.05). The highest cytotoxicity value was identified from SpeedCEM (p<0.01) and the highest genotoxicity values were calculated from RelyX U200 (p<0.05). Released UDMA and TEGDMA from self-adhesive resin cements induced cytotoxicity and genotoxicity effect on cells.

Regulation of apoptosis by cyclic nucleotides in human erythroleukemia (HEL) cells and human myelogenous leukemia (K-562) cells

The cyclic pyrimidine nucleotides cCMP and cUMP have been recently identified in numerous mammalian cell lines, in primary cells and in intact organs, but very little is still known about their biological function. A recent study of our group revealed that the membrane-permeable cCMP analog cCMP-acetoxymethylester (cCMP-AM) induces apoptosis in mouse lymphoma cells independent of protein kinase A via an intrinsic and mitochondria-dependent pathway. In our present study, we examined the effects of various cNMP-AMs in human tumor cell lines. In HEL cells, a human erythroleukemia cell line, cCMP-AM effectively reduced the number of viable cells, effectively induced apoptosis by altering the mitochondrial membrane potential and thereby caused changes in the cell cycle. cCMP itself was biologically inactive, indicating that membrane penetration is required to trigger intracellular effects. cCMP-AM did not induce apoptosis in K-562 cells, a human chronic myelogenous leukemia cell line, due to rapid export via multidrug resistance-associated proteins. The biological effects of cCMP-AM differed from those of other cNMP-AMs. In conclusion, cCMP effectively induces apoptosis in HEL cells, cCMP export prevents apoptosis of K-562 cells and cNMPs differentially regulate various aspects of apoptosis, cell growth and mitochondrial function. In a broader perspective, our data support the concept of distinct second messenger roles of cAMP, cGMP, cCMP and cUMP.

Single nucleotide polymorphisms in apoptosis pathway are associated with response to imatinib therapy in chronic myeloid leukemia

Background

The mechanism of action of imatinib is known to involve the Fas-mediated apoptosis pathway. Consequently inter-individual variations in this apoptosis pathway might be associated with imatinib response or resistance.

Methods

This study attempted to focus on eight genotypes in the apoptosis pathway including FAS (rs1800682, rs2229521, rs2234767 and rs2234978), FASLG (rs763110), CASP10 (rs13006529), and APAF1 (rs1439123, rs2288713) and analyzed their association with treatment outcomes including molecular response with 4.5 log reduction (MR4.5), following imatinib therapy in 187 Korean CML patients.

Results

The GG/GA genotype in FAS (rs2234767) showed a higher rate of MR4.5 than the AA genotype (at 5 years 59.7 vs 37.4 %, p = 0.013). Using a bootstrap procedure for internal validation we confirmed that FAS (rs2234767) correlates with MR4.5 (p = 0.050). Multivariate analysis confirmed that the FAS genotype (rs2234767) is an independent surrogate for MR4.5 (p = 0.019, HR 0.43, 95 % CI [0.22–0.87]).

Conclusions

The Fas/FasL signaling pathway may represent the major pathway that mediates apoptosis in CML treated with imatinib. SNP markers in the apoptosis pathway including FAS genotype (rs2234767) can be potential surrogates for predicting deeper molecular response after imatinib therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0837-5) contains supplementary material, which is available to authorized users.

Live cell evaluation of granzyme delivery and death receptor signaling in tumor cells targeted by human natural killer cells

Growing interest in natural killer (NK) cell-based therapy for treating human cancer has made it imperative to develop new tools to measure early events in cell death. We recently demonstrated that protease-cleavable luciferase biosensors detect granzyme B and pro-apoptotic caspase activation within minutes of target cell recognition by murine cytotoxic lymphocytes. Here we report successful adaptation of the biosensor technology to assess perforin-dependent and -independent induction of death pathways in tumor cells recognized by human NK cell lines and primary cells. Cell-cell signaling via both Fc receptors and NK-activating receptors led to measurable luciferase signal within 15 minutes. In addition to the previously described aspartase-cleavable biosensors, we report development of granzyme A and granzyme K biosensors, for which no other functional reporters are available. The strength of signaling for granzyme biosensors was dependent on perforin expression in IL-2-activated NK effectors. Perforin-independent induction of apoptotic caspases was mediated by death receptor ligation and was detectable after 45 minutes of conjugation. Evidence of both FasL and TRAIL-mediated signaling was seen after engagement of Jurkat cells by perforin-deficient human cytotoxic lymphocytes. Although K562 cells have been reported to be insensitive to TRAIL, robust activation of pro-apoptotic caspases by NK cell-derived TRAIL was detectable in K562 cells. These studies highlight the sensitivity of protease-cleaved luciferase biosensors to measure previously undetectable events in live cells in real time. Further development of caspase and granzyme biosensors will allow interrogation of additional features of granzyme activity in live cells including localization, timing, and specificity.

Multidrug resistance in chronic myeloid leukaemia: how much can we learn from MDR-CML cell lines?

The hallmark of CML (chronic myeloid leukaemia) is the BCR (breakpoint cluster region)-ABL fusion gene. CML evolves through three phases, based on both clinical and pathological features: a chronic phase, an accelerated phase and blast crisis. TKI (tyrosine kinase inhibitors) are the treatment modality for patients with chronic phase CML. The therapeutic potential of the TKI imatinib is affected by BCR-ABL dependent an independent mechanisms. Development of MDR (multidrug resistance) contributes to the overall clinical resistance. MDR involves overexpression of ABC -transporters (ATP-binding-cassette transporter) among other features. MDR studies include the analysis of cancer cell lines selected for resistance. CML blast crisis is accompanied by increased resistance to apoptosis. This work reviews the role played by the influx transporter OCT1 (organic cation transporter 1), by efflux ABC transporters, molecules involved in the modulation of apoptosis (p53, Bcl-2 family, CD95, IAPs (inhibitors of apoptosis protein)], Hh and Wnt/β-catenin pathways, cytoskeleton abnormalities and other features described in leukaemic cells of clinical samples and CML cell lines. An MDR cell line, Lucena-1, generated from K562 by stepwise exposure to vincristine, was used as our model and some potential anticancer drugs effective against the MDR cell line and patients' samples are presented.

TLR9-mediated signals rescue B-cells from Fas-induced apoptosis via inactivation of caspases

The death receptor, CD95/Fas, serves to eliminate potentially dangerous, self-reactive B cells. Engagement of B-cell receptors (BCR) on mature B-cells mediates the escape from cell death resulting in the activation and expansion of antigen specific clones. In addition to the antigen receptors, the receptors of B-cell activating factor belong to the tumor necrosis factor (TNF) family (BAFFR); moreover, the pattern recognition receptor, TLR9 may also deliver survival signals inhibiting Fas-mediated death of B-cells. Our aim was to compare the mechanism of BCR-induced and the BAFFR- or TLR9-stimulated rescue of B-cells from CD95/Fas-mediated apoptosis. We have found that BAFFR and TLR9 collaborate with BCR to protect B-cells from Fas-induced elimination and the rescue is independent of protein synthesis. The results revealed that the TLR9- and BCR-triggered rescue signals are transmitted through partially overlapping pathways; the protein kinase C (PKC) and the abl kinase induced phosphorylation may inactivate caspases in both CpG and anti-IgG stimulated cells. However, PI3-K activation is crucial upon the BCR driven anti-apoptotic effect, while p38 MAPK-mediated inactivation of caspases seems to play essential role in TLR9-mediated protection against Fas-induced programmed cell death.

c-Abl is an upstream regulator of acid sphingomyelinase in apoptosis induced by inhibition of integrins αvβ3 and αvβ5

Inhibition of integrins αvβ3/αvβ5 by the cyclic function-blocking peptide, RGDfV (Arg-Gly-Asp-Phe-Val) can induce apoptosis in both normal cells and tumor cells. We show that RGDfV induced apoptosis in ECV-304 carcinoma cells, increased activity and mRNA expression of acid sphingomyelinase (ASM), and increased ceramides C₁₆, C_18∶0, C_24∶0 and C_24∶1 while decreasing the corresponding sphingomyelins. siRNA to ASM decreased RGDfV-induced apoptosis as measured by TUNEL, PARP cleavage, mitochondrial depolarization, and caspase-3 and caspase-8 activities, as well as by annexinV in a 3D collagen model. These findings indicate a causal role for ASM in RGDfV-induced apoptosis in ECV-304. We have shown that c-Abl, a non-receptor tyrosine kinase, also mediates RGDfV-induced apoptosis. However, c-Abl, has not been previously linked to ASM in any system. Here we show that STI-571 (imatinib, inhibitor of c-Abl) inhibited RGDfV-induced ASM activity. Furthermore, STI-571 and c-Abl-siRNA both inhibited RGDfV-induced increase in ASM mRNA, but ASM-siRNA did not affect c-Abl phosphorylation or expression, supporting that c-Abl regulates the RGDfV-induced increase in ASM expression. These studies implicate ASM as a mediator of apoptosis induced by inhibition of integrins αvβ3/αvβ5, and for the first time place c-Abl as an upstream regulator of ASM expression and activity.

Apoptotic pathway induced by noscapine in human myelogenous leukemic cells

It has been shown that noscapine, an opium-derived phthalideisoquinoline alkaloid that is currently being used as an oral antitussive drug, induces apoptosis in myeloid leukemia cells. The molecular mechanism responsible for the anticancer effects of noscapine is poorly understood. In the current study, the apoptotic effects of noscapine on two myeloid cell lines, apoptosis-proficient HL60 cells and apoptosis-resistant K562 cells, were analyzed. An increase in the activity of caspase-2, -3, -6, -8 and -9, poly(ADP ribose) polymerase cleavage, detection of phosphatidylserine on the outer layer of the cell membrane, nucleation of chromatin, and DNA fragmentation suggested the induction of apoptosis. Noscapine increased the Bax/Bcl-2 ratio with a significant decrease of Bcl-2 expression accompanied with Bcl-2 phosphorylation. Using an inhibitory approach, the activation of the caspase cascade involved in the noscapine-induced apoptosis was analyzed. We observed no inhibitory effect of the caspase-8 inhibitor on caspase-9 activity. In view of these results and taking into consideration that K562 cells are Fas-null, we suggested that caspase-8 is activated in a Fas-independent manner downstream of caspase-9. In conclusion, noscapine can induce apoptosis in both apoptosis-proficient and apoptosis-resistant leukemic cells, and it can be a novel candidate in the treatment of hematological malignancies.

Src kinase signaling in leukaemia

Role of Src kinases in acute lymphoblastic leukaemia has been recently demonstrated in leukaemia mouse model. Retained activation of Src kinases by the BCR-ABL oncoprotein in leukaemic cells following inhibition of BCR-ABL kinase activity by imatinib indicates that Src activation by BCR-ABL is independent of BCR-ABL kinase activity and provides an explanation for reduced effectiveness of the BCR-ABL kinase activity inhibitors in Philadelphia chromosome-positive acute lymphoblastic leukaemia. Simultaneous inhibition of kinase activity of both BCR-ABL and Src kinases results in long-term survival of mice with acute lymphoblastic leukaemia. Leukaemic stem cells exist in acute lymphoblastic leukaemia, and complete eradication of this group of cells would provide a curative therapy for this disease.

Dysregulated human myeloid nuclear differentiation antigen expression in myelodysplastic syndromes: evidence for a role in apoptosis

Reduced levels of human myeloid nuclear differentiation antigen (MNDA) gene transcripts have been detected in both familial and sporadic cases of myelodysplastic syndromes (MDS). Numerous reports implicate elevated apoptosis/programmed cell death and death ligands and their receptors in the pathogenesis of MDS. MNDA and related proteins contain the pyrin domain that functions in signaling associated with programmed cell death and inflammation. We tested the hypothesis that MNDA is involved in the regulation of programmed cell death in human myeloid hematopoietic cells. Clones of K562 cells (MNDA-null) that expressed ectopic MNDA protein were established using retroviral transduction. MNDA-expressing K562 clones were resistant to tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-induced apoptosis, but were not protected from programmed cell death induced with genotoxic agents or H(2)O(2). MNDA protein expression assessed in control and intermediate and high-grade MDS marrows showed several patterns of aberrant reduced MNDA. These variable patterns of dysregulated MNDA expression may relate to the variable pathophysiology of MDS. We propose that MNDA has a role regulating programmed cell death in myeloid progenitor cells, and that its down-regulation in MDS is related to granulocyte-macrophage progenitor cell sensitivity to TRAIL-induced programmed cell death.

Src kinases as targets for B cell acute lymphoblastic leukaemia therapy

The participation of Src kinases in the induction of BCR-ABL-induced B cell acute lymphoblastic leukaemia (B-ALL), but not chronic myeloid leukaemia (CML), demonstrates cell type-specific signalling in Philadelphia chromosome-positive (Ph+) leukaemias. Different therapeutic strategies are therefore needed for B-ALL and CML. Activation of Src kinases is independent of BCR-ABL kinase activity for activation. Thus, Src kinases provide a mechanism for resistance to the BCR-ABL kinase inhibitors and potential targets for B-ALL therapy. Simultaneous targeting of both BCR-ABL and Src kinases may benefit human B-ALL patients. Leukaemic stem cells may exist in Ph+ B-ALL, and eradication of this group of cells would provide a curative method for this disease.

Synergistic apoptosis induction by proteasome and histone deacetylase inhibitors is dependent on protein synthesis

Proteasome inhibitors are able to efficiently induce apoptosis in many tumor cells while leaving quiescent, untransformed cells largely unharmed. Here we investigated the further enhancement of proteasome inhibitor-mediated apoptosis induction in Bcr-Abl positive K562 CML cells by simultaneous treatment with different histone deacetylase inhibitors (HDIs). Combining proteasome and HDIs resulted in rapid hyperacetylation of histone H3 and accumulation of polyubiquitinated proteins and the synergistic induction of apoptosis. Apoptosis induction was associated with caspase 8, 3 and 9 activation, Bid processing, destruction of the mitochondrial membrane potential, cleavage of PARP and lamin B and extensive DNA fragmentation. The pan-caspase inhibitor Z-VAD-FMK and the caspase-8 inhibitor Z-IETD-FMK could inhibit K562 cell apoptosis. Apoptosis was also delayed by overexpression of Bcl-xL, as well as by crmA, a known inhibitor of caspases 1 and 8. Caspase 8 activity could still be detected in the presence of ectopic Bcl-xL, but not in crmA transfected cells. The most striking anti-apoptotic effect though was obtained by the translational inhibitor cycloheximide, which abolished caspase 8 processing, blocked Bid cleavage and maintained the mitochondrial transmembrane potential. Apoptosis by the combination treatment occurred independently from CD95/Fas receptor stimulation. These results demonstrated that transcriptional activation by HDIs combined with proteasome inhibitor mediated posttranslational stabilization of protein(s) results in significantly enhanced CML apoptosis which was striktly dependent on uninterrupted protein synthesis.

Death receptor-mediated suicide: a novel target of autoimmune disease treatment

In the thymus, based on the reactivity of their T-cell receptor with self-MHC and antigenic peptides, developing immature T-cells undergo positive and negative selection. Cells recognising self-peptides and MHC with high affinity are considered autoreactive, and thus potentially harmful, and are eliminated by induction of apoptotic cell death. Thymic negative selection is, however, only incomplete and autoreactive T-cells escape into the periphery. It is not the presence of autoreactive mature T- and B-lymphocytes as the underlying cause of tissue destruction and development of autoimmune diseases, but their uncontrolled and excessive clonal expansion upon activation by self-antigen. Thus, potent regulatory mechanisms must keep these autoreactive cells under control to avoid their inappropriate activation. Recent evidence indicates that death receptors of the tumour necrosis factor receptor family play a central role in mediating antigen receptor-induced suicide of autoreactive T-lymphocytes. Defects in these apoptosis-inducing regulatory mechanisms may result in the development of autoimmune diseases. Therefore, enhancing the cell's own suicide program, offers a most attractive therapeutic target for the treatment of autoimmune diseases.

Prostate apoptosis response gene-4 (par-4) abrogates the survival function of p185(BCR-ABL) in hematopoietic cells

OBJECTIVE

Prostate apoptosis response gene-4 (par-4) is deregulated in acute and chronic lymphatic leukemia. Given its pro-apoptotic role in neoplastic lymphocytes and evidence that par-4 antagonizes oncogenic Ras in solid tumors, we hypothesized that par-4 may act as a tumor suppressor impairing transformation induced by p185(BCR-ABL).

MATERIALS AND METHODS

The capacity of par-4 to interfere with factor independence induced by p185(BCR-ABL) and V12ras was evaluated by analysis of factor-independent growth of p185(BCR-ABL)/ par-4 and V12ras/par-4 transduced cells. The expression of par-4 and p185(BCR-ABL) by the respective constructs was controlled by Western blot analysis. Activated Ras was detected by pull-down assay in the cell clones expressing p185(BCR-ABL) in the absence and presence of par-4.

RESULTS

Expression of p185(BCR-ABL) causes factor independence, signifying a conversion toward a transformed phenotype in hematopoietic precursors. We demonstrate that par-4 completely abolishes factor independence induced by p185(BCR-ABL) and partially abrogates factor independence caused by activated V12ras. Evaluating the underlying molecular mechanisms, we show that par-4 hinders activation of oncogenic Ras and causes concomitant disruptions of p185(BCR-ABL)-mediated signaling.

CONCLUSION

We provide the first evidence that par-4 exhibits an antitransforming capacity by antagonizing p185(BCR-ABL)-induced factor-independent proliferation in hematopoietic cells.

Bacterial N-acylhomoserine lactone-induced apoptosis in breast carcinoma cells correlated with down-modulation of STAT3

Cell growth is promoted by mitogens and survival factors, which activate intracellular signalling pathways to control cell cycle progression and cellular integrity. Proliferation signals are transmitted through Ras and Rho family small G-proteins coupled to mitogen-activated protein kinase (MAPK) cascades, while survival signals are propagated by lipid-dependent kinases such as phosphatidylinositide 3-kinases (PI3Ks) and protein kinase B (Akt/PKB). Recently, signal transducer and activator of transcription (STAT) proteins were identified as positive regulators of proliferation in a variety of cell types. Persistent activation of these pathways is associated with tumour cell growth, whereas their inhibition can halt proliferation and precipitate apoptotic cell death. The human pathogen Pseudomonas aeruginosa uses quorum-sensing signal molecules (QSSMs) to regulate virulence gene expression. QSSMs also suppress host immune responses although the mechanism of suppression is unknown. Here, we demonstrate that the QSSM N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) from P. aeruginosa blocks proliferation and induces apoptosis in human BC cell lines. Analyses of signalling events reveal that OdDHL has little or no effect on MAPK cascades, partially inhibits the Akt/PKB pathway and ablates STAT3 activity. Pharmacological inhibition of each pathway independently indicates that STAT3 activity is critical for BC cell proliferation and survival, while a constitutively active STAT3 confers resistance to OdDHL. These results support the notion of OdDHL as a bioactive molecule in eukaryotic systems and a paradigm for a novel class of antiproliferative compounds.

Caspase-dependent cleavage of c-Abl contributes to apoptosis

The nonreceptor tyrosine kinase c-Abl may contribute to the regulation of apoptosis. c-Abl activity is induced in the nucleus upon DNA damage, and its activation is required for execution of the apoptotic program. Recently, activation of nuclear c-Abl during death receptor-induced apoptosis has been reported; however, the mechanism remains largely obscure. Here we show that c-Abl is cleaved by caspases during tumor necrosis factor- and Fas receptor-induced apoptosis. Cleavage at the very C-terminal region of c-Abl occurs mainly in the cytoplasmic compartment and generates a 120-kDa fragment that lacks the nuclear export signal and the actin-binding region but retains the intact kinase domain, the three nuclear localization signals, and the DNA-binding domain. Upon caspase cleavage, the 120-kDa fragment accumulates in the nucleus. Transient-transfection experiments show that cleavage of c-Abl may affect the efficiency of Fas-induced cell death. These data reveal a novel mechanism by which caspases can recruit c-Abl to the nuclear compartment and to the mammalian apoptotic program.

Transforming pathways activated by the v-Abl tyrosine kinase

The Abelson Murine Leukemia Virus (A-MuLV) is the acute transforming retrovirus encoding the v-abl oncogene. Two isolates of the virus encoding proteins of p120 Kd and 160 Kd have been extensively studied. These viral isolates have been found to transform both hematopoietic and fibroblastic cells in vitro, while inducing predominantly pre-B cell leukemias in vivo. Both p120(v-Abl) and p160(v-Abl) are plasma membrane-associated non-receptor tyrosine kinases and the transforming activity of these proteins requires their tyrosine kinase activity. A-MuLV infection of hematopoietic cells has often been found to result in the abrogation of their cytokine-dependence for growth. In addition, v-Abl expressing hematopoietic cells often lose their ability to differentiate in response to appropriate cytokines. This review discusses some of the early transformation studies of A-MuLV, as well as some of the findings concerning the structure and biochemical activity of the v-Abl protein. Finally, we discuss the mechanisms associated with v-Abl mediated transformation through examination of the various signal transduction pathways activated by this oncogene.

Novel targeted therapies for Bcr-Abl positive acute leukemias: beyond STI571

In the pathophysiology of CML, the constitutive activity of the Bcr-Abl tyrosine kinase (TK) is, most likely, the sole molecular abnormality of the chronic phase. It also remains a critical molecular determinant of malignant behavior of the leukemic progenitors in the accelerated and blastic phase of CML. Therefore, downregulation of the levels and activity of Bcr-Abl is clearly the lynchpin of a rational therapeutic strategy against all phases of CML. Support for this has only been strengthened by the observations that resistance to imatinib mesylate (imatinib) commonly involves a breakthrough and the persistent activity of Bcr-Abl TK. This is due to either mutations that inhibit imatinib action on Bcr-Abl TK or amplification of the bcr-abl gene. Recent studies have demonstrated that other small molecule tyrosine kinase inhibitors that also inhibit Bcr-Abl TK may be highly active in inducing differentiation and apoptosis of CML progenitors, regardless of their sensitivity to imatinib. Small molecule inhibitors that downregulate the levels of Bcr-Abl by inhibiting its translation, e.g., arsenic trioxide, or promoting its proteasomal degradation, e.g., geldanamycin analogues, have also been identified. Finally the identification of other potent survival and antiapoptotic signaling pathways in imatinib-resistant CML progenitors indicates that inhibitors of these pathways will eventually be treatment strategies for advanced phases of CML.

Ionomycin-activated calpain triggers apoptosis. A probable role for Bcl-2 family members

Ubiquitous calpains (mu- and m-calpain) have been repeatedly implicated in apoptosis, but the underlying mechanism(s) remain(s) to be elucidated. We examined ionomycin-induced cell death in LCLC 103H cells, derived from a human large cell lung carcinoma. We detected hallmarks of apoptosis such as membrane blebbing, nuclear condensation, DNA ladder formation, caspase activation, and poly-(ADP-ribose)polymerase cleavage. Apoptosis was prevented by preincubation of the cells with the calpain inhibitor acetyl-calpastatin 27-peptide and the caspase inhibitor Z-DEVD-fmk, implicating both the calpains and caspases in the apoptotic process. The apoptotic events correlated in a calpastatin-inhibitable manner with Bid and Bcl-2 decrease and with activation of caspases-9, -3, and -7. In vitro both ubiquitous calpains cleaved recombinant Bcl-2, Bid, and Bcl-x(L) at single sites truncating their N-terminal regions. Binding studies revealed diminished interactions of calpain-truncated Bcl-2 and Bid with immobilized intact Bcl-2 family proteins. Moreover, calpain-cleaved Bcl-2 and Bid induced cytochrome c release from isolated mitochondria. We conclude that ionomycin-induced calpain activation promotes decrease of Bcl-2 proteins thereby triggering the intrinsic apoptotic pathway.

Hepatocyte nuclear factor (HNF)-4alpha induces expression of endothelial Fas ligand (FasL) to prevent cancer cell transmigration: a novel defense mechanism of endothelium against cancer metastasis

Endothelial Fas ligand (FasL) contributes to the "immune privilege" of tissues such as testis and eye, in which apoptosis is induced in infiltrating Fas-positive activated T cells and results in the inhibition of leukocyte extravasation. In this study, we examined the role of endothelial FasL in controlling cancer cell transmigration using rat lung endothelial (RLE) cell line bearing a doxycycline-inducible hepatocyte nuclear factor (HNF)-4alpha expression system. We showed that a detectable level of FasL was expressed in RLE cells and that this expression was markedly up-regulated and well correlated to the degree of HNF-4alpha expression in a time-dependent manner. When various cancer cells were overlaid on an RLE monolayer sheet, we examined the ability of endothelial FasL to induce massive apoptosis in Fas-expressing cancer cells and found a causal link to inhibition of the transmigration. Finally, we showed that FasL was expressed in capillaries of the rat brain by immunohistochemical staining, suggesting that FasL serves its functions not only in vitro, but also in vivo. These results raise the possibility that HNF-4alpha is involved in regulating cancer cell transmigration by modulating the Fas-FasL system.

Functional cooperation among Ras, STAT5, and phosphatidylinositol 3-kinase is required for full oncogenic activities of BCR/ABL in K562 cells

BCR/ABL tyrosine kinase generated from the chromosomal translocation t(9;22) causes chronic myelogenous leukemia and acute lymphoblastic leukemia. To examine the roles of BCR/ABL-activated individual signaling molecules and their cooperation in leukemogenesis, we inducibly expressed a dominant negative (DN) form of Ras, phosphatidylinositol 3-kinase, and STAT5 alone or in combination in p210 BCR/ABL-positive K562 cells. The inducibly expressed DN Ras (N17), STAT5 (694F), and DN phosphatidylinositol 3-kinase (Delta p85) inhibited the growth by 90, 55, and 40%, respectively. During the growth inhibition, the expression of cyclin D2 and cyclin D3 was suppressed by N17, 694F, or Delta p85; that of cyclin E by N17; and that of cyclin A by Delta p85. In addition, N17 induced apoptosis in a small proportion of K562, whereas 694F and Delta p85 were hardly effective. In contrast, coexpression of two DN mutants in any combinations induced severe apoptosis. During these cultures, the expression of Bcl-2 was suppressed by N17, 694F, or Delta p85, and that of Bcl-XL by N17. Furthermore, although K562 was resistant to interferon-alpha- and dexamethasone-induced apoptosis, disruption of one pathway by N17, 694F, or Delta p85 sensitized K562 to these reagents. These results suggested that cooperation among these molecules is required for full leukemogenic activities of BCR/ABL.

Lipoxygenase activity in altered gravity

Lipoxygenases are a family of enzymes which dioxygenate unsaturated fatty acids, thus initiating lipoperoxidation of membranes or the synthesis of signalling molecules, or inducing structural and metabolic changes in the cell. This activity is the basis for the critical role of lipoxygenases in a number of pathophysiological conditions, both in animals and plants. We review the effects of microgravity on the catalytic efficiency of purified soybean (Glycine max) lipoxygenase-1, as well as the modulation of the activity and expression of 5-lipoxygenase in human erythroleukemia K562 cells subjected to altered gravity. We also outline the molecular properties of the lipoxygenase family and discuss its possible involvement in space-related processes, such as apoptosis (programmed cell death) and immuno-depression. Finally, we discuss the modulation of cyclooxygenase activity and expression in K562 cells exposed to altered gravity, because cyclooxygenase catalyzes the oxidation of arachidonate through a pathway different from that catalyzed by lipoxygenase activity.

Protein tyrosine kinase inhibitors modulate radiosensitivity and radiation-induced apoptosis in K562 cells

We studied the modulating effect of protein tyrosine kinase inhibitors on the response of cells of the human chronic myelogenous leukemia cell line K562 to radiation. The radiosensitivity of the cells was increased by treatment with herbimycin A and decreased by treatment with genistein. This modulating effect of protein tyrosine kinase inhibitors on radiation sensitivity was associated with the alteration of the mode of radiation-induced cell death. After X irradiation, the cells arrested in the G(2) phase of the cell cycle, but these TP53(-/-) cells were unable to sustain cell cycle arrest. This G(2)-phase checkpoint deficit caused cell death. The morphological pattern of cell death was characterized by swelling of the cytoplasmic compartments, cytosolic vacuolation, disruption of the plasma membrane, less evident nuclear condensation, and faint DNA fragmentation, all of which were consistent with oncosis or cytoplasmic apoptosis. The nonreceptor protein tyrosine kinase inhibitor herbimycin A accelerated the induction of typical apoptosis by X irradiation, which was demonstrated by morphological assessments using nuclear staining and electron microscopy as well as oligonucleosomal fragmentation and caspase 3 activity. Herbimycin A is known to be a selective antagonist of the BCR/ABL kinase of Philadelphia chromosome-positive K562 cells; this kinase blocks the induction of apoptosis after X irradiation. Our results showed that the inhibition of protein tyrosine kinase by herbimycin A enhanced radiation-induced apoptosis in K562 cells. This effect was associated with the activation of caspase 3 and rapid abrogation of the G(2)-phase checkpoint with progression out of G(2) into G(1) phase. In contrast, the receptor-type protein tyrosine kinase inhibitor genistein protected K562 cells from all types of radiation-induced cell death through the inhibition of caspase 3 activity and prolonged maintenance of G(2)-phase arrest. Further investigations using this model may give valuable information about the mechanisms of radiation-induced apoptosis and about the radiosensitivity and radioresistance of chronic myelogenous leukemia cells having the Philadelphia chromosome.

Expression of apoptosis proteins in chronic myelogenous leukemia: associations and significance

BACKGROUND

The mechanisms favoring the growth advantage of Philadelphia chromosome positive cells over normal cells in chronic myelogenous leukemia (CML) are not fully elucidated but could be due partly to altered apoptosis and longer survival of CML clones. Also, little is known about the biologic characteristics of disease progression in CML. Bcl-2 expression has been demonstrated to exert an antiapoptotic effect resulting in increased cell survival. Other proteins such as Bax and Bad are proapoptotic proteins. Fas, a cell surface protein, can be triggered by an appropriate death-promoting ligand (FasL) to activate downstream caspases pivotal in initiation of programmed cell death. Although the mechanisms underlying cellular proliferative and apoptotic pathways are complex, with involvement of multiple interlocking proteins, the relative expression of pro- and antiapoptotic proteins may have an influence on disease progression. This study aimed to determine whether the changes in the cellular expression of Bcl-2, Bax, and Fas correlate with caspase-3 activity and disease progression in CML, or with response to interferon (IFN)-alpha therapy and prognosis in early chronic phase CML.

METHODS

Bcl-2, Bax, and Fas expression were measured on whole cell lysates from bone marrow mononuclear cell fractions by Western blot analysis and quantitative radioimmunoassay. Caspase-3 activity was determined using the DEVD system. Specimens from 203 patients with CML were examined. These included 130 patients in early chronic phase disease (ECP; diagnosis to therapy, < or =12 months), 33 patients in late chronic phase (diagnosis to therapy, > 12 months), 27 patients in accelerated phase, and 13 patients in blastic phase. Correlations between apoptosis proteins and CML phases, risk groups in ECP, and response to IFN-alpha therapy and survival in ECP were investigated by standard statistical methods, and positive findings were assessed by multivariate analysis.

RESULTS

Levels of Bcl-2, Fas, Bax, and caspase-3 activity did not correlate with disease progression. Among patients in ECP, higher Fas levels correlated with poorer risk groups (P = 0.05) and higher caspase-3 activity correlated with better risk groups (P = 0.048). With IFN-alpha therapy, major cytogenetic responses were noted in 30% of patients with high Fas and 53% with low Fas (P = 0.016) and failure to achieve a complete hematologic response (CHR) in 25% versus 2% (P = 0.0001). Survival was shorter with high Fas levels (5-year rates, 71% vs. 52%; P = 0.002), and the independent poor prognostic significance of high Fas levels was confirmed by multivariate analysis (P = 0.014). Response to IFN-alpha therapy and survival were not significantly different by different levels of Bcl-2, Bax, or caspase-3 activity.

CONCLUSIONS

High Fas levels were associated with intrinsically worse disease at diagnosis, whereas high caspase-3 activity was associated with good risk disease. In ECP CML, high Fas levels were associated with significantly worse response to IFN-alpha therapy and with significantly worse survival. The influence of these cellular proteins and caspase-3 activity on apoptosis in CML is complex and merits further investigation.

Presence and significance of CD-95 (Fas/APO1) expression after spinal cord injury

OBJECT

A glycoprotein, CD95 (Fas/APO1) is widely considered to be implicated in the development of apoptosis in a number of tissues. Based on the hypothesis that apoptosis is related to cell death after spinal cord injury (SCI), the authors studied the presence and distribution of CD95 (Fas/APO1)-positive cells in injured spinal cord tissue for the purpose of determining the significance of this protein during the early phases of SCI.

METHODS

The presence and distribution of cells showing positive immunostaining for CD95 (Fas/APO1) were studied 1, 4, 8, 24, 48, and 72 hours and 1, 2, and 4 weeks after induction of experimental SCI in rats. Studies were conducted using a monoclonal antibody to the CD95 (Fas/APO1) protein. Positivity for CD95 (Fas/APO1) was observed in apoptotic cells, mainly in the gray matter, 1 hour after trauma, and the number of immunostained cells increased for the first 8 hours, at which time the protein was expressed in both gray and white matter. From 24 to 72 hours postinjury, the number of immunostained cells decreased in the gray matter, but increased in the white matter. From then on, there were fewer CD95 (Fas/APO1)-positive cells, but some cells in the white matter still exhibited positive immunostaining 1 and 2 weeks after injury. At 4 weeks, there remained no CD95 (Fas/APO1)-positive cells in injured spinal cord.

CONCLUSIONS

These findings indicate that CD95 (Fas/APO1) is expressed after SCI, suggesting a role for this protein in the development of apoptosis after trauma and the possibility of a new therapeutic approach to SCI based on blocking the CD95 (Fas/APO1) system.

Synergistic activity of the new ABL-specific tyrosine kinase inhibitor STI571 and chemotherapeutic drugs on BCR-ABL-positive chronic myelogenous leukemia cells

The ABL-specific tyrosine kinase inhibitor STI571 (formerly CGP57148B) induced cytogenetic remissions in 33% of chronic myelogenous leukemia (CML) patients in a phase I trial (Druker et al 1999). Combination therapy may increase this proportion. We tested whether combinations of STI571 and cytarabine or other chemotherapeutic agents such as hydroxyurea, mafosfamide or etoposide would display synergistic activity in BCR-ABL-positive chronic myelogenous leukemia (CML) cell lines derived from patients in blast crisis. In addition, the toxicity of these combinations on BCR-ABL-negative cells was investigated. A tetrazolium-based MTT assay was used to quantity growth inhibition after 48 h of exposure to cytotoxic agents alone and in simultaneous combination with STI571. The drug interactions were analyzed using the median-effect method of Chou and Talalay. The combination index (CI) was calculated according to the classic isobologram equation. At growth inhibition levels of over 50%, STI571 + cytarabine as well as STI571 + etoposide were significantly synergistic (CI < 1, P < 0.05) in the BCR-ABL-positive cell lines evaluated. At 60% inhibition or higher, a similar synergistic pattern became apparent for STI571 + mafosfamide (P < 0.05), while STI571 + hydroxyurea showed ambiguous, cell line-dependent synergism (BV173), additivity (EM-3) or antagonism (K562) in CML cell lines. Furthermore, the BCR-ABL-negative HL-60, KG1a and normal CD34+ progenitor cells were not affected by 0.8 microM STI571, a concentration which produced more than 50% growth inhibition in all BCR-ABL-positive cells tested, and no potentiation of growth inhibition was observed in these BCR-ABL-negative cells when STI571 was combined with chemotherapeutic agents. Our in vitro data with CML blast crisis cell lines strongly suggest that combinations of STI571 with cytarabine or etoposide be rapidly considered for clinical testing.

Apoptosis: A Current Molecular Analysis

Apoptosis is a cell suicide program characterized by distinct morphological (cell shrinkage, membrane blebbing, pyknosis, chromatin margination, denser cytoplasmic images) and biochemical (e.g., DNA fragmentation into distinct ladders; degradation of apoptotic markers such as PARP and nuclear lamins) features. It is involved in multiple physiological processes examplified by involution of mammary tissues, embryonic development, homeostatic maintenance of tissues and organs, and maturation of the immune system, as well as in many pathological conditions represented by neurologic degeneration (Alzeimer's disease), autoimmune and inflammatory diseases, etiology of atherosclerosis, AIDS, and oncogenesis and tumor progression. Numerous molecular entities have been shown to regulate the apoptotic process. This review provides a concise summary of the recent data on the role of oncogenes/tumor suppressor genes, cytokines and growth factors/growth factor receptors, intracellular signal transducers, cell cycle regulators, reactive oxygen species or other free radicals, extracellular matrix regulators/cell adhesion molecules, and specific endonucleases and cytoplasmic proteases (the ICE family proteins) in regulating cell survival and apoptosis. Elucidation of the molecular mechanisms regulating apoptosis bears tremendous impact on enhancing our understanding of many diseases inflicting the human beings and undoubtedly brings us hope for the cure of these diseases.

Nucleophosmin–anaplastic lymphoma kinase associated with anaplastic large-cell lymphoma activates the phosphatidylinositol 3-kinase/Akt antiapoptotic signaling pathway

More than half of anaplastic large-cell lymphomas (ALCLs) have a chromosomal translocation t(2;5) that leads to the expression of a hybrid protein composed of the nucleolar phosphoprotein nucleophosmin (NPM) and the anaplastic lymphoma kinase (ALK) that exhibits an unregulated tyrosine kinase activity. We have previously identified PLC-γ as a crucial downstream signaling molecule of NPM-ALK that contributes to its mitogenic potential. Here, we show that NPM-ALK recruits the C-terminal SH2 domain of the phosphatidylinositol 3-kinase (PI 3kinase) p85 subunit. PI 3-kinase assays revealed that the kinase is activated by NPM-ALK in vivo, in turn activating PKB/Akt in NPM-ALK–expressing cells. The use of 2 specific PI 3-kinase inhibitors, wortmannin and LY294002, demonstrated the requirement of PI 3-kinase for the growth of NPM-ALK–transformed cell lines, as well as a cell line established from a patient with ALCL. Primary murine bone marrow retrovirally transduced with NPM-ALK showed a transformed phenotype that was reversible on treatment with PI 3-kinase inhibitors. Flow cytometric analysis revealed that wortmannin-treated NPM-ALK–transformed cell lines underwent apoptosis. Furthermore, apoptosis induced by overexpression of the proapoptotic molecule Bad could be partially blocked by the overexpression of NPM-ALK. Thus, NPM-ALK activates the antiapoptotic PI 3-kinase/Akt pathway, which likely contributes to the molecular pathogenesis of ALCL.

Nucleophosmin–anaplastic lymphoma kinase associated with anaplastic large-cell lymphoma activates the phosphatidylinositol 3-kinase/Akt antiapoptotic signaling pathway

More than half of anaplastic large-cell lymphomas (ALCLs) have a chromosomal translocation t(2;5) that leads to the expression of a hybrid protein composed of the nucleolar phosphoprotein nucleophosmin (NPM) and the anaplastic lymphoma kinase (ALK) that exhibits an unregulated tyrosine kinase activity. We have previously identified PLC-γ as a crucial downstream signaling molecule of NPM-ALK that contributes to its mitogenic potential. Here, we show that NPM-ALK recruits the C-terminal SH2 domain of the phosphatidylinositol 3-kinase (PI 3kinase) p85 subunit. PI 3-kinase assays revealed that the kinase is activated by NPM-ALK in vivo, in turn activating PKB/Akt in NPM-ALK–expressing cells. The use of 2 specific PI 3-kinase inhibitors, wortmannin and LY294002, demonstrated the requirement of PI 3-kinase for the growth of NPM-ALK–transformed cell lines, as well as a cell line established from a patient with ALCL. Primary murine bone marrow retrovirally transduced with NPM-ALK showed a transformed phenotype that was reversible on treatment with PI 3-kinase inhibitors. Flow cytometric analysis revealed that wortmannin-treated NPM-ALK–transformed cell lines underwent apoptosis. Furthermore, apoptosis induced by overexpression of the proapoptotic molecule Bad could be partially blocked by the overexpression of NPM-ALK. Thus, NPM-ALK activates the antiapoptotic PI 3-kinase/Akt pathway, which likely contributes to the molecular pathogenesis of ALCL.

Regulation of cell death by the Abl tyrosine kinase

The c-abl proto-oncogene encodes a protein tyrosine kinase that is distributed in the nucleus and the cytoplasm of proliferating cells. In the nucleus, c-Abl activity is negatively regulated by the retinoblastoma protein (RB) and positively regulated by DNA damage signals. Activation of the c-Abl kinase by DNA damage requires the function of ATM, which regulates cell cycle checkpoint, DNA repair and apoptosis in response to DNA damage. Cells lacking c-Abl can activate cell cycle checkpoints and DNA repair, but show defects in apoptosis. The apoptosis defect of c-Abl deficient cells is correlated with a defect in the induction and activation of p73, which is a functional homologue of the p53 tumor suppressor protein and has pro-apoptotic activity. The inhibition of c-Abl by RB is consistent with RB's ability to block apoptosis; while the activation of c-Abl by ATM is consistent with ATM's ability to activate cell death. The oncogenic Bcr-Abl tyrosine kinase is a potent inhibitor of apoptosis, and it is retained exclusively in the cytoplasm of transformed cells. Interestingly, when Bcr-Abl is trapped inside of the nucleus through a combined disruption of its cytoplasmic retention and its nuclear export, this oncogenic Abl kinase induces apoptosis. Taken together, the current results support a role for the nuclear c-Abl tyrosine kinase in the regulation of apoptosis. Whether the cytoplasmic c-Abl kinase can actively inhibit apoptosis remains to be determined; however, a deliberate retention of c-Abl in the cytoplasm could potentially contribute to the attenuation of apoptosis response.

Protein tyrosine kinase inhibitor, genistein, enhances apoptosis and cell cycle arrest in K562 cells treated with gamma-irradiation

Genistein, is a natural isoflavone compound with a potent activity against protein tyrosine kinases. The leukemic cell line, K562, is a bcr/abl (Philadelphia chromosome) positive cell line that is resistant to DNA-damaging agents, including gamma-irradiation. Treatment with genistein increased apoptosis and promoted G2-phase arrest in the non-apoptotic population of the gamma-irradiated K562 cells. Irradiated cells that survived 72 h after the irradiation had a normal distribution in cell cycle, whilst genistein treatment kept cells arrested in the G2-phase, decreased the S-phase fraction and suppressed DNA-synthesis. Taken together, our results show that genistein augments apoptotic cell death after gamma-irradiation in K562 cells and this result cannot be attributed to abrogation of the G2/M checkpoint.

Intracellular Fas ligand expression causes Fas-mediated apoptosis in human prostate cancer cells resistant to monoclonal antibody-induced apoptosis

Several laboratories have attempted with little success to induce Fas-mediated apoptosis in prostate cancer (PCa) cells, using different external Fas agonists, i.e., anti-Fas antibodies and membrane-bound FasL. The present study confirms these earlier results using the anti-Fas antibody CH-11 in five human PCa cell lines (PPC-1, LNCaP, PC-3, TSU-Pr1, and DU145). However, intracellular murine FasL expression induced Fas-mediated apoptosis in all CH-11-resistant cell lines. Adenovirus (AdGFPFasL(TET)) was used to deliver a Murine FasL-GFP fusion gene into human PCa cells resulting in 70-98% apoptosis at 48 h as determined by the MTS assay. DU145 and PPC-1 cells treated with AdGFPFasL(TET) stained positive for the TUNEL assay, indicating that cell death was via apoptosis. Using immunofluorescent microscopy, Fas and GFPFasL colocalized to the same intracellular compartment. The anti-Fas neutralizing antibody ZB-4 was unable to block AdGFPFasL(TET)-mediated cell death, suggesting that intracellular FasL may ligate Fas within the Golgi and/or endoplasmic reticulum. This is the first evidence suggesting that these two molecules interact prior to cell surface presentation. Collectively, these findings indicate that intracellular GFPFasL expression is superior to CH-11 at inducing Fas-mediated apoptosis in human PCa cells and may allow use of AdGFPFasL(TET) for PCa gene therapy.

Negative regulation of Fas-mediated apoptosis by FAP-1 in human cancer cells

FAP-1 (Fas-associated phosphatase-1) was previously identified as a protein that associates with a negative regulatory domain (C-terminal 15 amino acids) of Fas using the yeast 2-hybrid system. Functional analysis indicated that FAP-1 expression correlates with resistance to Fas-induced apoptosis in human cancer cells. We first generated anti-FAP-1 polyclonal antibody and confirmed the interaction of FAP-1 and Fas in vivo. FAP-1 interacted with wild-type, but not mutant, Fas (tPLV) in 293T cells after transfecting FAP-1 and Fas or its mutant. To investigate the functional role of FAP-1 in Fas-mediated signal transduction, we established stable transfectants of FAP-1 in 3 human cancer cell lines. Apoptosis assays demonstrated that cancer cells over-expressing FAP-1 increased the resistance to Fas-induced apoptosis by the anti-Fas antibody CH-11 in contrast with the wild types or the vector-transfected cells. In addition, FAP-1 regulated the activity of both caspases 3 and 8. Our data indicate a functional role for FAP-1 as a negative regulator of Fas-mediated apoptosis in human cancer cells and suggest that an additional signal-transducing molecule may be required for complete suppression of Fas-mediated apoptosis.

Activation of different lipoxygenase isozymes induces apoptosis in human erythroleukemia and neuroblastoma cells

We investigated the ability of different hydroperoxides generated by lipoxygenase isozymes to induce programmed cell death (PCD) in human cells. Erythroleukemia K562 and neuroblastoma CHP100 cells were used, because they showed high basal activity of lipoxygenase. The hydroperoxides generated by 5-, 12-, or 15-lipoxygenases from linoleate, linolenate, or arachidonate, and the corresponding hydroxides, were able to induce PCD in both cell types, in a concentration- and time-dependent manner. After 24 h, K562 and CHP100 cells showed 2.5- to 3.5-fold more apoptotic bodies than the untreated controls. PCD elicited by lipoxygenase products was independent of intracellular glutathione concentration, and did not require mRNA transcription or protein synthesis. On the other hand, lipoxygenase products evoked an immediate and sustained rise in cytoplasmic calcium (within seconds), followed by mitochondrial uncoupling (within hours). Unlike the hydro(pero)xides, the terminal products of the arachidonate cascade (i.e., leukotrienes, prostaglandins and thromboxane) were not cytotoxic.

The inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in chronic myelogenous leukemic K562 cells

In this study, the downstream signaling of Bcr-Abl tyrosine kinase responsible for apoptosis resistance was investigated. DNA fragmentation, a hallmark of apoptosis, was observed after 2 days of herbimycin A treatment with a peak on 3 day. During the apoptosis induced by the treatment of herbimycin A, stress-activated protein kinase (SAPK) and p38 kinase were activated time- and dose-dependently, while extracellular signal-regulated kinase (ERK) was inhibited. However, apoptosis was induced by the treatment of PD98059, a specific inhibitor of MEK (MAPK or ERK kinase), not by the treatment of sorbitol, a strong activator of SAPK and p38 kinase. Although K562 cells were very resistant to sorbitol-induced apoptosis, DNA fragmentation was induced rapidly in Jurkat, HL-60 and U937 cells after exposure to sorbitol, despite that these apoptosis-sensitive cells have similar or lower activities of JNK/SAPK and p38 kinase compared with K562 cells after treatment of sorbitol. K562 cells had a much higher basal activity of ERK/MAPK than other apoptosis-sensitive cell lines, which were very susceptible to apoptosis induced by low dose of PD98059 compared with K562 cells. In HL-60 cells, sorbitol-induced apoptosis was prevented by the treatment of phorbol myristate 13-acetate (PMA), which activates the ERK/MAPK pathway, and this was blocked by PD98059. From these results, it could be suggested that the inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in K562 cells.

Mobilisation of haemopoietic progenitors in CML: a second course of intensive chemotherapy does not improve Ph-negativity in stem cell harvests

We collected peripheral blood stem cells (PBSC) in 19 early chronic phase CML patients following each of two consecutive cycles of intensive chemotherapy (CT) to evaluate whether an additional cycle of CT would increase Philadelphia (Ph)-negativity of the PBSC harvest. Autologous SCT (autoSCT) was performed if a major cytogenetic response (MCR) of the PBSC harvest was obtained. CT consisted of cytarabine 200 mg/ m2/day (days 1-7)/idarubicin 12 mg/m2/day (days 1-2) (cycle one) and cytarabine 2000 mg/m2/day (days 1-6)/amsacrine 120 mg/m2/day (days 1-3) (cycle two). One patient died of fungal pneumonia after the first cycle. Stem cells were harvested in 18 patients after cycle one and in 16 patients after cycle two. After the first cycle, all patients showed a cytogenetic response of their graft (MCR in eight patients: three complete, five partial), after cycle two, seven patients obtained an MCR (one complete, six partial). Seven patients became eligible for autoSCT. All patients proceeded with IFNalpha maintenance. Currently, 16 patients are alive. At the latest cytogenetic examination of bone marrow, four patients showed an MCR and four a minor response. In conclusion, although a second cycle of CT may contribute to elimination of leukemia residing in the patient, it appeared to be ineffective in improving the Ph-negativity of the PBSC graft.

Altered mechanisms of apoptosis in colon cancer: Fas resistance and counterattack in the tumor-immune conflict

Fas (CD95/APO-1) is a cell surface "death receptor" that mediates apoptosis upon engagement by its ligand, FasL. Fas-mediated apoptosis of lymphocytes normally serves immunoregulatory roles, including tolerance acquisition, immune response termination, and maintenance of immune privilege in certain organs. Colon tumors can exploit this lymphocyte death program by expressing FasL. This may enable colon tumors to mount a "Fas counterattack" against antitumor lymphocytes, impairing antitumor immune responses. FasL-expressing colon tumor-derived cell lines can trigger Fas-mediated apoptosis of cocultured T cells in vitro. FasL expressed in esophageal cancer has been significantly associated with apoptosis and depletion of tumor-infiltrating lymphocytes (TIL) in vivo. FasL may also facilitate metastatic colonization of Fas-sensitive organs such as the liver, by inducing apoptosis of target organ cells. Normal colonic epithelial cells express Fas and are relatively sensitive to Fas-mediated apoptosis. By contrast, colon tumor-derived cell lines are usually resistant to induction of Fas-mediated apoptosis, and colon cancer cells frequently coexpress Fas and FasL. The mechanisms allowing resistance to Fas-mediated apoptosis are complex, and defects have been identified at several levels of Fas signal transduction. The "Bcl-2 rheostat" may be pitched against apoptosis in colon cancer, inasmuch as overexpression of Bcl-2, downregulation of Bak, and mutation of Bax are common defects in colon tumors. Caspase-1 is also downregulated in colon cancer. The high frequency of p53 mutations in late-stage cancers may also inhibit Fas signaling. Fundamental defects in apoptosis signaling may contribute to both immuno- and chemoresistance in colon cancer and allow expression of FasL to counterattack antitumor lymphocytes.

Molecular cloning and characterization of cynomolgus monkey Fas

The Fas-FasL system plays a crucial role in the maintenance of homeostasis in the immune system. To characterize the Fas/FasL system in macaque monkeys that are commonly used as experimental primates, we cloned and sequenced Fas cDNA derived from the cynomolgus monkey. The predicted amino acid sequence consists of 331 amino acids with a calculated molecular weight of 35,800. The extracellular cysteine-rich motif of cynomolgus Fas is highly homologous to that of humans (96%), whereas the intracellular death domain has a relatively low similarity to that of humans (86%). An agonistic Fas antibody (CH11) or cynomolgus FasL induced apoptosis in human Fas-transfected K562 cells in the presence of CHX but not in the cynomolgus Fas transfectant. CH11 and FasL failed to trigger apoptosis in the transfectant expressing human-cynomolgus chimera Fas consisting mostly of human-derived extracellular region and cynomolgus-derived intracellular portion. On the other hand, the transfectant expressing cynomolgus-human chimera Fas with human-derived intracellular region underwent apoptosis upon exposure to FasL. In addition, the virus-transformed, Fas-positive cynomolgus monkey cell line was highly sensitive to FasL. These findings suggest that the lack of apoptotic activity in the cynomolgus Fas transfectant in the human cell line might be related to the species-specific structure of Fas, especially of the death domain.

c-Myc antagonizes the effect of p53 on apoptosis and p21WAF1 transactivation in K562 leukemia cells

c-myc protooncogene positively regulates cell proliferation and overexpression of c-myc is found in many solid tumors and leukemias. In the present study we used the K562 human myeloid leukemia cell line as a model to study the functional interaction between c-Myc and p53. Using two different methods, we generated K562 transfectant cell lines with conditional expression of either c-Myc or p53. The cells expressed the p53Vall35 mutant, which adopts a wild-type conformation at 32 degrees C, while c-Myc induction was achieved with a zinc-inducible expression vector. We found that p53 in wild-type conformation induces growth arrest and apoptosis of K562. Expression of c-Myc significantly attenuated apoptosis and impaired the transcriptional activity of p53 on p21WAF1, Bax and cytomegalovirus promoters. The impairment of p21WAF1 transactivation by c-Myc was confirmed by transfection of a c-Myc-estrogen receptor fusion protein and by induction of c-myc by zinc in transfected cells. Also, p53-mediated up-regulation of p21WAF1 mRNA protein were significantly reduced by c-Myc, while Bax levels were unaffected. Consistently, c-Myc increased cyclin-dependent kinase 2 activity in K562 cells expressing p53 in wild-type conformation. These results suggest that c-Myc overexpression may antagonize the pro-apoptotic function of p53, thus providing a molecular mechanism for the frequently observed deregulation of c-myc in human cancer.

The role of FAS-mediated apoptosis in chronic myelogenous leukemia

Clinical observation and laboratory evidence suggest that immune mechanisms play an important role in the natural control of evolution of the Ph+ clone in chronic phase as well as during progression of chronic myelogenous leukemia (CML). The understanding of these mechanisms could facilitate development of innovative therapeutic approaches. Due to bcr-abl translocation, CML cells carry an intrinsic resistance to apoptotic signals. However, resistance to apoptosis is not absolute and can be overcome through enhancement of immune-mediated pathways, e.g., during graft vs. leukemia reaction after allogeneic bone marrow transplantation, or during interferon-alpha (IFN-alpha) therapy. Among the effector mechanisms, T-lymphocyte-mediated killing of target cells via Fas-receptor (Fas-R) triggering plays an important role in the elimination of malignant cells, including CML cells. Although CML Ph+ progenitor cells express Fas-R, the expression levels are variable and do not correlate with clinical parameters. In addition, CML progenitor cells also express functional Fas-ligand (Fas-L), which may be an important immune surveillance escape factor. IFN-alpha can greatly upmodulate Fas-R expression, an effect that seems to be more pronounced in CML compared to normal cells, while Fas-L expression levels are not affected by IFN-alpha, thereby improving their susceptibility to elimination by the immune system. Responsiveness to Fas-induced apoptosis following stimulation with IFN-alpha correlates with the clinical effects of IFN-alpha therapy. This effect seems to be associated with decreased bcr-abl protein levels, which are influenced by Fas via posttranscriptional modulation. In comparison to the chronic phase, CML cells derived from patients in blast crisis are refractory to Fas-mediated apoptosis, regardless of the expression levels of Fas, suggesting that an immune-mediated selection pressure could result in acquisition of Fas-resistance. In the future, enhancement of immunological recognition and elimination of CML cells may prove to be an effective therapeutic approach directed towards the cure of CML.