Skp2 and Slug Are Coexpressed in Aggressive Prostate Cancer and Inhibited by Neddylation Blockade

Prostate cancer (PCa) is the second leading cause of cancer-related deaths in men in Western countries, and there is still an urgent need for a better understanding of PCa progression to inspire new treatment strategies. Skp2 is a substrate-recruiting component of the E3 ubiquitin ligase complex, whose activity is regulated through neddylation. Slug is a transcriptional repressor involved in the epithelial-to-mesenchymal transition, which may contribute to therapy resistance. Although Skp2 has previously been associated with a mesenchymal phenotype and prostate cancer progression, the relationship with Slug deserves further elucidation. We have previously shown that a high Gleason score (≥8) is associated with higher Skp2 and lower E-cadherin expression. In this study, significantly increased expression of Skp2, AR, and Slug, along with E-cadherin downregulation, was observed in primary prostate cancer in patients who already had lymph node metastases. Skp2 was slightly correlated with Slug and AR in the whole cohort (Rs 0.32 and 0.37, respectively), which was enhanced for both proteins in patients with high Gleason scores (Rs 0.56 and 0.53, respectively) and, in the case of Slug, also in patients with metastasis to lymph nodes (Rs 0.56). Coexpression of Skp2 and Slug was confirmed in prostate cancer tissues by multiplex immunohistochemistry and confocal microscopy. The same relationship between these two proteins was observed in three sets of prostate epithelial cell lines (PC3, DU145, and E2) and their mesenchymal counterparts. Chemical inhibition of Skp2, but not RNA interference, modestly decreased Slug protein in PC3 and its docetaxel-resistant subline PC3 DR12. Importantly, chemical inhibition of Skp2 by MLN4924 upregulated p27 and decreased Slug expression in PC3, PC3 DR12, and LAPC4 cells. Novel treatment strategies targeting Skp2 and Slug by the neddylation blockade may be promising in advanced prostate cancer, as recently documented for other aggressive solid tumors.

3D Cell Culture Models Demonstrate a Role for FGF and WNT Signaling in Regulation of Lung Epithelial Cell Fate and Morphogenesis

FGF signaling plays an essential role in lung development, homeostasis, and regeneration. We employed mouse 3D cell culture models and imaging to study ex vivo the role of FGF ligands and the interplay of FGF signaling with epithelial growth factor (EGF) and WNT signaling pathways in lung epithelial morphogenesis and differentiation. In non-adherent conditions, FGF signaling promoted formation of lungospheres from lung epithelial stem/progenitor cells (LSPCs). Ultrastructural and immunohistochemical analyses showed that LSPCs produced more differentiated lung cell progeny. In a 3D extracellular matrix, FGF2, FGF7, FGF9, and FGF10 promoted lung organoid formation. FGF9 showed reduced capacity to promote lung organoid formation, suggesting that FGF9 has a reduced ability to sustain LSPC survival and/or initial divisions. FGF7 and FGF10 produced bigger organoids and induced organoid branching with higher frequency than FGF2 or FGF9. Higher FGF concentration and/or the use of FGF2 with increased stability and affinity to FGF receptors both increased lung organoid and lungosphere formation efficiency, respectively, suggesting that the level of FGF signaling is a crucial driver of LSPC survival and differentiation, and also lung epithelial morphogenesis. EGF signaling played a supportive but non-essential role in FGF-induced lung organoid formation. Analysis of tissue architecture and cell type composition confirmed that the lung organoids contained alveolar-like regions with cells expressing alveolar type I and type II cell markers, as well as airway-like structures with club cells and ciliated cells. FGF ligands showed differences in promoting distinct lung epithelial cell types. FGF9 was a potent inducer of more proximal cell types, including ciliated and basal cells. FGF7 and FGF10 directed the differentiation toward distal lung lineages. WNT signaling enhanced the efficiency of lung organoid formation, but in the absence of FGF10 signaling, the organoids displayed limited branching and less differentiated phenotype. In summary, we present lung 3D cell culture models as useful tools to study the role and interplay of signaling pathways in postnatal lung development and homeostasis, and we reveal distinct roles for FGF ligands in regulation of mouse lung morphogenesis and differentiation ex vivo.

Trop-2 plasticity is controlled by epithelial-to-mesenchymal transition

The cell surface glycoprotein Trop-2 is commonly overexpressed in carcinomas and represents an exceptional antigen for targeted therapy. Here, we provide evidence that surface Trop-2 expression is functionally connected with an epithelial phenotype in breast and prostate cell lines and in patient tumor samples. We further show that Trop-2 expression is suppressed epigenetically or through the action of epithelial-to-mesenchymal transition transcription factors and that deregulation of Trop-2 expression is linked with cancer progression and poor patient prognosis. Moreover, our data suggest that the cancer plasticity-driven intratumoral heterogeneity in Trop-2 expression may significantly contribute to response and resistance to therapies targeting Trop-2-expressing cells.

Novel CHK1 inhibitor MU380 exhibits significant single-agent activity in TP53-mutated chronic lymphocytic leukemia cells

Introduction of small-molecule inhibitors of B-cell receptor signaling and BCL2 protein significantly improves therapeutic options in chronic lymphocytic leukemia. However, some patients suffer from adverse effects mandating treatment discontinuation, and cases with TP53 defects more frequently experience early progression of the disease. Development of alternative therapeutic approaches is, therefore, of critical importance. Here we report details of the anti-chronic lymphocytic leukemia single-agent activity of MU380, our recently identified potent, selective, and metabolically robust inhibitor of checkpoint kinase 1. We also describe a newly developed enantioselective synthesis of MU380, which allows preparation of gram quantities of the substance. Checkpoint kinase 1 is a master regulator of replication operating primarily in intra-S and G₂/M cell cycle checkpoints. Initially tested in leukemia and lymphoma cell lines, MU380 significantly potentiated efficacy of gemcitabine, a clinically used inducer of replication stress. Moreover, MU380 manifested substantial single-agent activity in both TP53-wild type and TP53-mutated leukemia and lymphoma cell lines. In chronic lymphocytic leukemia-derived cell lines MEC-1, MEC-2 (both TP53-mut), and OSU-CLL (TP53-wt) the inhibitor impaired cell cycle progression and induced apoptosis. In primary clinical samples, MU380 used as a single-agent noticeably reduced the viability of unstimulated chronic lymphocytic leukemia cells as well as those induced to proliferate by anti-CD40/IL-4 stimuli. In both cases, effects were comparable in samples harboring p53 pathway dysfunction (TP53 mutations or ATM mutations) and TP53-wt/ATM-wt cells. Lastly, MU380 also exhibited significant in vivo activity in a xenotransplant mouse model (immunodeficient strain NOD-scid IL2Rγ^null) where it efficiently suppressed growth of subcutaneous tumors generated from MEC-1 cells.

Abstract B084: Trop-2 plasticity is driven by epithelial-to-mesenchymal transition in prostate cancer cells

Dissemination of cancer cells to distant organs has fatal consequences to most of the patients with malignant tumors. Patients with prostate and breast cancer show apparent overlap of the most common sites of cancer metastasis, suggesting that breast and prostate tumor cells share common mechanisms of dissemination and colonization. During each step of prostate and breast cancer metastasis, malignant cells display phenotypic plasticity that is associated with the manifestation of epithelial and mesenchymal properties or an epithelial-to-mesenchymal transition (EMT).

One of the molecules that most likely interlink processes of pathologic plasticity of cancer cells, their dissemination capability, and response to microenvironmental factors is Tumor-Associated Calcium Signal TransDucer 2 (Trop-2, TACSTD2). Trop-2 is a type-I transmembrane glycoprotein encoded by TACSTD2 gene often associated with tumorigenesis and cancer progression, but the data remain controversial. Trop-2 deregulation has been repeatedly proposed as an event associated with cancer progression and poor patient prognosis. Instead of this simplistic view, our results showed Trop-2 level change as a context-dependent, dynamic event associated with cancer plasticity and dissemination.

Using antibody-based surface profiling of selected cancer stem-like cell markers in human and mouse prostate and breast cancer cell lines, we identified subpopulation of Trop-2+ cells within culture of metastatic prostate cell line DU-145 and similarly Trop-2+ subpopulation within mouse mammary cancer cell line 4T1. Gene expression analysis of sorted subpopulations showed significant correlation of Trop-2 with epithelial phenotype, and this finding was further validated in wide panel of human and murine cell lines and independent patient datasets. We further proved that expression of Trop-2 is regulated by EMT transcription factors and DNA methylation. Moreover, immunohistochemical analysis of Trop-2 in pairs of primary prostate tumors and lymph node metastasis showed strong association with E-cadherin and epithelial-mesenchymal plasticity in patient samples.

In conclusion, we showed that Trop-2 expression associates with epithelial phenotype and can be suppressed either epigenetically or through the action of EMT master regulators.

Acknowledgments: This work was supported by Ministry of Health of the Czech Republic, grant no. 15-33999A and 15-28628A, and by GAČR 15-11707S, HistoPARK (CZ.1.07/2.3.00/20.0185), and by project FNUSA-ICRC (no. CZ.1.05/1.1.00/02.0123) and ICRC-ERA-HumanBridge a.k.a. REGPOT (Grant agreement no. 316 345) from the European Regional Development Fund.

Citation Format: Ján Remšík, Lucia Binó, Zuzana Kahounová, Gvantsa Kharaishvili, Sarka Simeckova, Radek Fedr, Tereza Nehybova, Eva Slabáková, Lucia Knopfová, Jan Bouchal, Milan Kral, Petr Benes, Karel Soucek. Trop-2 plasticity is driven by epithelial-to-mesenchymal transition in prostate cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B084.

The dual role of asporin in breast cancer progression

Asporin has been reported as a tumor suppressor in breast cancer, while asporin-activated invasion has been described in gastric cancer. According to our in silico search, high asporin expresion associates with significantly better relapse free survival (RFS) in patients with low-grade tumors but RFS is significantly worse in patients with grade 3 tumors. In line with other studies, we have confirmed asporin expression by RNA scope in situ hybridization in cancer associated fibroblasts. We have also found asporin expression in the Hs578T breast cancer cell line which we confirmed by quantitative RT-PCR and western blotting. From multiple testing, we found that asporin can be downregulated by bone morphogenetic protein 4 while upregulation may be facilited by serum-free cultivation or by three dimensional growth in stiff Alvetex scaffold. Downregulation by shRNA inhibited invasion of Hs578T as well as of CAFs and T47D cells. Invasion of asporin-negative MDA-MB-231 and BT549 breast cancer cells through collagen type I was enhanced by recombinant asporin. Besides other investigations, large scale analysis of aspartic acid repeat polymorphism will be needed for clarification of the asporin dual role in progression of breast cancer.

Effect of Apple Extracts on NF-κB Activation in Human Umbilical Vein Endothelial Cells

The mechanisms by which foods, such as fruit, are able to reduce the risk of chronic disease are still unclear. Several fruit products, including apples and apple juice, that are flavonoid-rich are reported to increase antioxidant levels in human subjects. This is supported by the finding from our previous studies that the chronic consumption of apple juice by human subjects reduced ex vivo low-density lipoprotein (LDL) oxidation; we hypothesized that this was due to the flavonoid in the apple juice, which, as we reported earlier, reduced in vitro LDL oxidation. To further explore whether the mixture of flavonoids and other phytochemicals in apples are biologically relevant antioxidants, we tested the effects of this flavonoid-rich apple extract (AE) on oxidant-related pathways in a model of the endothelium: human umbilical vascular endothelial cells (HUVECs). The effects of AE on oxidant-responsive (i.e., tumor necrosis factor [TNF]-α-induced) nuclear factor (NF)-κB signaling in cell culture were assessed in transfected HUVECs by using a construct that expressed luciferase under the control of NF-κB. Incubation of HUVEC for 24 hrs with up to 10 mM (as gallic acid equivalents) of AE demonstrated no cytotoxicity, as determined by lactate dehydrogenase release, caspase 3 activation, and apoptosis marker–based FACS analysis. AE after a 24-hr incubation period at either 200 or 2000 nM showed a complex pattern of decreased basal and TNF-α-stimulated NF-κB signaling (63% maximal decrease) as assessed by luciferase activity in the transfected HUVECs, as well as by reduced levels of IκBα protein phosphorylation detected by Western blot analysis. We suggest that AE downregulates NF-κB signaling and that this is indicative of an antioxidant effect of the flavonoids present in AE.

Exacerbation of substrate toxicity by IPTG in Escherichia coli BL21(DE3) carrying a synthetic metabolic pathway

BACKGROUND

Heterologous expression systems based on promoters inducible with isopropyl-β-D-1-thiogalactopyranoside (IPTG), e.g., Escherichia coli BL21(DE3) and cognate LacI(Q)/P(lacUV5)-T7 vectors, are commonly used for production of recombinant proteins and metabolic pathways. The applicability of such cell factories is limited by the complex physiological burden imposed by overexpression of the exogenous genes during a bioprocess. This burden originates from a combination of stresses that may include competition for the expression machinery, side-reactions due to the activity of the recombinant proteins, or the toxicity of their substrates, products and intermediates. However, the physiological impact of IPTG-induced conditional expression on the recombinant host under such harsh conditions is often overlooked.

RESULTS

The physiological responses to IPTG of the E. coli BL21(DE3) strain and three different recombinants carrying a synthetic metabolic pathway for biodegradation of the toxic anthropogenic pollutant 1,2,3-trichloropropane (TCP) were investigated using plating, flow cytometry, and electron microscopy. Collected data revealed unexpected negative synergistic effect of inducer of the expression system and toxic substrate resulting in pronounced physiological stress. Replacing IPTG with the natural sugar effector lactose greatly reduced such stress, demonstrating that the effect was due to the original inducer's chemical properties.

CONCLUSIONS

IPTG is not an innocuous inducer; instead, it exacerbates the toxicity of haloalkane substrate and causes appreciable damage to the E. coli BL21(DE3) host, which is already bearing a metabolic burden due to its content of plasmids carrying the genes of the synthetic metabolic pathway. The concentration of IPTG can be effectively tuned to mitigate this negative effect. Importantly, we show that induction with lactose, the natural inducer of P lac , dramatically lightens the burden without reducing the efficiency of the synthetic TCP degradation pathway. This suggests that lactose may be a better inducer than IPTG for the expression of heterologous pathways in E. coli BL21(DE3).

Growth/differentiation factor-15 is an abundant cytokine in human seminal plasma

BACKGROUND

Transforming growth factor-β cytokines have various biological effects in female reproductive tissue, including modulation of inflammatory response and induction of immune tolerance to seminal antigens in the reproductive tract. However, no studies have analyzed the presence of growth/differentiation factor-15 (GDF-15/macrophage inhibitory cytokine-1) in seminal fluid or demonstrated the quantity and form of GDF-15, its possible role or the relationship between its concentration and semen quality.

METHODS

The form and the concentration of GDF-15 were determined in 53 seminal plasma samples of both fertile and infertile men by ELISA and western blot. The sperm cells of three volunteers were treated with recombinant GDF-15, and cell viability and apoptosis were assessed by flow cytometry. The effect of GDF-15 on vaginal epithelial cells and peripheral blood mononuclear cells (PBMCs) was analyzed by quantitative RT-PCR.

RESULTS

The GDF-15 concentration in seminal plasma ranged from 0.2 to 6.6 μg/ml as determined by ELISA. Western blot analysis revealed that GDF-15 is present in the active form. In vitro cultivation of sperm cells with GDF-15 did not affect their viability or rates of apoptosis; however, it did inhibit proliferation of PBMCs and induce expression of FOXP3 in CD4+CD25+ cells.

CONCLUSIONS

To the best of our knowledge, this is the first demonstration that GDF-15 is an abundant cytokine in seminal plasma, although its concentration is not associated with semen quality or the fertility/infertility status of the donors. Moreover, our data show that GDF-15 displays immunosuppressive characteristics.

TGF-beta1 suppresses IL-6-induced STAT3 activation through regulation of Jak2 expression in prostate epithelial cells

Chronic inflammation plays an important role in the initiation and progression of various human diseases including benign prostatic hyperplasia or prostate cancer. Here we show that the proinflammatory cytokine interleukin-6 (IL-6) has prosurvival effects and chronically activates the Jak2/STAT3 signalling pathway in a model of benign prostatic hyperplasia (BPH-1). We demonstrate that the antiinflammatory cytokine transforming growth factor-beta1 (TGF-beta1), which also permanently activates its canonical signalling pathway through SMAD proteins in BPH-1 cells, modifies the effects of IL-6 on cell proliferation. Importantly, TGF-beta1 inhibits IL-6 signal transduction by decreasing the phosphorylation levels of STAT3. This effect is associated with decreased expression of Jak2 at both mRNA and protein levels. Moreover, we showed that TGF-beta1 inhibits IL-6-induced expression of the cancer-associated gene MUC1. These observations demonstrated a novel interaction between TGF-beta1 and IL-6 signalling and suggested another mechanism of how defects in TGF-beta signalling, frequently associated with prostate pathologies, can contribute to the disruption of tissue homeostasis.

LA-12 overcomes confluence-dependent resistance of HT-29 colon cancer cells to Pt (II) compounds

BACKGROUND

LA-12 is a new platinum (IV) drug with promising cytotoxic effects in a wide range of cancer cell lines. Its confluence-dependent effects were compared with cisplatin (CDDP) and oxaliplatin (L-OHP) in HT-29 cells.

MATERIALS AND METHODS

Cytotoxicity was determined by MTT test, eosin exclusion assay, and cell number quantification. The cell cycle was analysed using propidium iodide DNA staining (flow cytometry), apoptosis by phosphatidylserine externalisation (annexin-V assay), mitochondrial membrane potential by flow cytometry, nuclear morphology by means of fluorescence microscopy, and PARP cleavage by Western blotting.

RESULTS

While L-OHP and CDDP were practically inactive in the subconfluent cell population, LA-12 showed a similar toxicity in both subconfluent and growing populations. All compounds induced apoptosis, although with different potentials.

CONCLUSION

LA-12 was able to overcome confluence-dependent resistance of HT-29 cells observed for other platinum compounds, which may have potential therapeutic use in slowly growing tumours.

Drug efflux transporters, MRP1 and BCRP, affect the outcome of hypericin-mediated photodynamic therapy in HT-29 adenocarcinoma cells

Photodynamic therapy (PDT) is a flexible multi-target therapeutic approach. One of the main requirements of successful PDT is sufficient intracellular concentration of an applicable photosensitizer. Mechanisms of anticancer drug elimination by tumour cells are mostly linked to the elevated expression and activity of P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), breast cancer resistance protein (BCRP) and P450 monooxygenases. The interaction of hypericin with this cell drug-defence system is still unclear. We report here for the first time increased activity of MRP1 and BCRP in HT-29 colon cancer cells treated with hypericin per se. On the contrary, pre-treatment with proadifen (SKF525A) affected the function of MRP1 and BCRP leading to increased hypericin content, which might indicate a possible link between proadifen and these ABC transporter proteins. Subsequent enhanced intracellular oxidative stress was accompanied by loss of mitochondrial membrane potential, activation of caspase-9 and -3, PARP cleavage and onset of apoptosis. In conclusion, our study suggests that drug efflux transporters MRP1 and BCRP affect the pharmacokinetics of hypericin in HT-29 colon adenocarcinoma cells, and the action of hypericin-mediated PDT (HY-PDT) should be modulated by pre-treatment with their specific inhibitors.

Multiple defects in negative regulation of the PKB/Akt pathway sensitise human cancer cells to the antiproliferative effect of non-steroidal anti-inflammatory drugs

Antitumorigenic effects of non-steroidal anti-inflammatory drugs (NSAIDs) are well established in several types of cancer disease. However, the mechanisms driving these processes are not understood in all details. In our study, we observed significant differences in sensitivity of cancer epithelial cell lines to COX-independent antiproliferative effects of NSAIDs. The prostate cancer cell line LNCaP, lacking both critical enzymes in the negative control of PKB/Akt activation, PTEN and SHIP2, was the most sensitive to these effects, as assessed by analysing the cell cycle profile and expression of cell cycle regulating proteins. We found that p53 protein and its signalling pathway is not involved in early antiproliferative action of the selected NSAID-indomethacin. RNAi provided evidence for the involvement of p21(Cip1/Waf1), but not GDF-15, in antiproliferative effects of indomethacin in LNCaP cells. Interestingly, we also found that indomethacin activated PKB/Akt and induced nuclear localisation of p21(Cip1/Waf1) and Akt2 isoform. Our results are in agreement with other studies and suggest that maintaining of the p21(Cip1/Waf1) level and its intracellular localisation might be influenced by Akt2. Knock-down of SHIP2 by RNAi in PTEN negative prostate and colon cancer cell lines resulted in higher sensitivity to antiproliferative effects of indomethacin. Our data suggest novel mechanisms of NSAIDs antiproliferative action in cancer epithelial cells, which depends on the status of negative regulation of the PKB/Akt pathway and the isoform-specific action of Akt2. Thus, unexpectedly, multiple defects in negative regulation of the PKB/Akt pathway may contribute to increased sensitivity to chemopreventive effects of these widely used drugs.

Monocytic differentiation of leukemic HL-60 cells induced by co-treatment with TNF-alpha and MK886 requires activation of pro-apoptotic machinery

The block of hematopoietic differentiation program in acute myeloid leukemia cells can be overcome by differentiating agent like retinoic acid, but it has several side effects. A study of other differentiation signaling pathways is therefore useful to predict potential targets of anti-leukemic therapy. We demonstrated previously that the co-treatment of HL-60 cells with Tumor necrosis factor-alpha (TNF-alpha) (1 ng/mL) and inhibitor of 5-lipoxygenase MK886 (5 microm) potentiated both monocytic differentiation and apoptosis. In this study, we detected enhanced activation of three main types of mitogen-activated protein kinases (MAPKs) (p38, c-Jun amino-terminal kinase [JNK], extracellular signal-regulated kinase [ERK]), so we assessed their role in differentiation using appropriate pharmacologic inhibitors. The inhibition of pro-apoptotic MAPKs (p38 and JNK) suppressed the effect of MK886 + TNF-alpha co-treatment. On the other hand, down-regulation of pro-survival ERK pathway led to increased differentiation. Those effects were accompanied by increased activation of caspases in cells treated by MK886 + TNF-alpha. Pan-caspase inhibitor ZVAD-fmk significantly decreased both number of apoptotic and differentiated cells. The same effect was observed after inhibition of caspase 9, but not caspase 3 and 8. To conclude, we evidenced that the activation of apoptotic processes and pathways supporting apoptosis (p38 and JNK MAPKs) is required for the monocytic differentiation of HL-60 cells.

The comparison of impedance-based method of cell proliferation monitoring with commonly used metabolic-based techniques

OBJECTIVES

Determination of cell numbers is a crucial step in studies focused on cytokinetics and cell toxicity. The impedance-based analysis employing electronic sensor array system xCELLigence System allowing label-free dynamic monitoring of relative viable adherent cell amounts was compared with the most utilized methods for relative quantification of viable cell numbers based on a determination of cellular metabolism.

DESIGN

Colorimetric assay based on reduction of tetrazolium salt (MTT) by mitochondrial enzymes and chemiluminiscent assay based on intracellular adenosine triphosphate (ATP) determination were compared with the impedance-based system. Cell morphology was compared by microscopic evaluation. Normal human epidermal keratinocytes (NHEK) and normal human dermal fibroblasts (NHDF), together with 3T3 mouse fibroblast and HaCaT keratinocyte cell lines were employed.

RESULTS

The progress of cell growth curves obtained by different methods during 72 hours reflected cell type and cell seeding densities. The impedance-based method was found to be applicable for the determination of the cell proliferation of 3T3 fibroblasts, HaCaT and NHDF, since the comparison of this method with ATP and MTT determinations showed a comparable results. In contrast, the proliferation of NHEK measured by the impedance-based method did not correlate with other methodological approaches. This could be accounted to the specific morphological appearance of these cells.

CONCLUSION

The study shows the impedance-based detection of viable adherent cells is a valuable approach for cytokinetics and pharmacological studies. However, the specific morphological characteristics of cell lines have to be considered employing this method for determination of cell proliferation without using other reference methods.

Heavy metals induce phosphorylation of the Bcl-2 protein by Jun N-terminal kinase

The Bcl-2 protein is one of the key components of biochemical pathways controlling programmed cell death. The function of this protein can be regulated by posttranslational modifications. Phosphorylation of Bcl-2 has been considered to be significantly associated with cell cycle arrest in the G2/M phase of the cell cycle, and with cell death caused by defects of microtubule dynamics. This study shows that phosphorylation of Bcl-2 can be induced by heavy metals due to activation of the Jun N-terminal kinase pathway that is not linked to the G2/M cell cycle arrest. Furthermore, we demonstrate that hyperphosphorylated Bcl-2 protein is a more potent inhibitor of zinc-induced cell death than its hypophosphorylated mutant form. These data suggest that regulation of Bcl-2 protein function by phosphorylation is an important part of cell responses to stress.

Alternative pathways of programmed cell death are activated in cells with defective caspase-dependent apoptosis

Loss of programmed cell death pathways is one of the features of malignancy that complicate the response of cancer cells to a therapy. Activation of alternative cell death pathways offers a promising approach to enhance efficiency of cancer chemotherapy. We analysed programmed cell death pathways of v-myb-transformed BM2 monoblasts induced by arsenic trioxide, cycloheximide and camptothecin with U937 promonocytes as a reference cell line. We show that induced death of BM2 cells is not executed by caspases but rather by alternative cell death pathways. Camptothecin induces the lysosome-dependent cell death, arsenic trioxide induces autophagy, and most of cycloheximide-treated BM2 cells die by necrosis. The fact that alternative cell death pathways can be switched in cells with defects in activation and/or function of caspases suggests that understanding and targeting of these pathways could improve therapy of cancer cells suffering from defective apoptosis.

Rottlerin inhibits the nuclear factor kappaB/cyclin-D1 cascade in MCF-7 breast cancer cells

In the course of a project aimed to clarify the molecular mechanisms by which phorbol 12-myristate 13-acetate (PMA)-activated forms of protein kinase C (PKC) promote growth arrest in an MCF-7 cell line, we found that the PKCdelta inhibitor Rottlerin was able by itself to block cell proliferation. In the current study, we investigated further the antiproliferative response to Rottlerin. Western blotting analysis of cytoplasmic/nuclear extracts showed that the drug did not prevent either extracellular signal-regulated kinase (ERK) activation by PMA or Akt phosphorylation, but did interfere with the NFkappaB activation process (both basal and PMA-stimulated), by lowering the levels of phospho-IkappaBalpha and preventing p65 nuclear migration. The growth arrest evoked by Rottlerin was not mediated by cell-cycle inhibitors p21 and p27 but was accompanied by a dramatic fall in the cyclin-D1 protein, the levels of which were not altered by the pan-PKC inhibitor GF 109203X, thus excluding a PKC-mediated mechanism in the Rottlerin effect. The parallel drop in cyclin-D1 mRNA suggested a down-regulation of the gene caused by the inhibition of nuclear factor-kappa B (NFkappaB), which occurs via a PKC-, Akt-, ERK- and mitochondrial uncoupling-independent mechanism. We provide preliminary evidence that the interference on the NFkappaB activation process likely occurs at the level of calcium/calmodulin-dependent protein kinase II (CaMKII), a known Rottlerin target. Indeed the drug prevented calcium-induced CaMKII autophosphorylation which, in turn, led to decreased NFkappaB activation.

Different cell cycle modulation following treatment of human ovarian carcinoma cells with a new platinum(IV) complex vs cisplatin

Platinum (IV) derivative with adamantylamine-LA-12-represents a new generation of highly efficient anti-cancer drug derived from cisplatin and is currently in the final stage of phase I clinical trials. Understanding the specific mechanisms of its effects on cell cycle is necessary for defining the mode of action of LA-12. In this study, we characterized the ability of LA-12 to induce cell cycle perturbations in ovarian cancer cell line A2780 as compared to equitoxic cisplatin treatment. LA-12 induced a permanent accumulation of A2780 cells in S phase while cisplatin caused G2/M arrest at 24-h time point, where we also detected an increased expression of Gadd45alpha protein. Although both derivatives induced a rapid increase of p53 expression, this was not associated with a down-regulation of Mdm2 protein. Increased expression of p21(Cip1/WAF1) protein and its association with cyclins A and B1 suggested that this cyclin-dependent kinase inhibitor might contribute significantly to the observed perturbations of cell cycle. The results of this study provide insight into the mechanism of action of platinum-based derivative with adamantylamine on cell cycle in ovarian cancer cells. The differences between effects of LA-12 and cisplatin suggest that more attention should be paid to elucidation of modes of action of novel platinum(IV) complexes at cellular level.

Posttranslational nitrotyrosination of α-tubulin induces cell cycle arrest and inhibits proliferation of vascular smooth muscle cells

Hyperproliferation of vascular smooth muscle cells is a hallmark of atherosclerosis and related vascular complications. Microtubules are important for many aspects of mammalian cell responses including growth, migration and signaling. alpha-Tubulin, a component of the microtubule cytoskeleton, is unique amongst cellular proteins in that it undergoes a reversible posttranslational modification whereby the C-terminal tyrosine residue is removed (Glu-tubulin) and re-added (Tyr-tubulin). Whereas the reversible detyrosination/tyrosination cycle of alpha-tubulin has been implicated in regulating various aspects of cell biology, the precise function of this posttranslational modification has remained poorly characterized. Herein, we provide evidence suggesting that alpha-tubulin detyrosination is a required event in the proliferation of vascular smooth muscle cells. Proliferation of rat aortic smooth muscle cells in response to serum was temporally associated with the detyrosination of alpha-tubulin, but not acetylation of alpha-tubulin; Glu-tubulin reached maximal levels between 12 and 18h following cell cycle initiation. Inclusion of 3-nitro-l-tyrosine (NO(2)Tyr) in the culture medium resulted in the selective nitrotyrosination of alpha-tubulin, that was paralleled by decreased elaboration of Glu-tubulin, decreased expression of cyclins A and E, decreased association of the microtubule plus-end binding protein EB1, and inhibited cell proliferation. Nitrotyrosination of alpha-tubulin did not induce necrotic or apoptotic death of rat aortic smooth muscle cells, but instead led to cell cycle arrest at the G(1)/S boundary coincident with decreased DNA synthesis. Collectively, these results suggest that the C-terminus of alpha-tubulin and its detyrosination are functionally important as a molecular switch that regulates cell cycle progression in vascular smooth muscle cells.

Different modulation of TRAIL-induced apoptosis by inhibition of pro-survival pathways in TRAIL-sensitive and TRAIL-resistant colon cancer cells

Epithelial cells can be manipulated to undergo apoptosis depending on the balance between pro-survival and apoptotic signals. We showed that TRAIL-induced apoptosis may be differentially regulated by inhibitors of MEK ERK (U0126) or PI3K/Akt (LY294002) pathway in TRAIL-sensitive (HT-29) and TRAIL-resistant (SW620) human epithelial colon cancer cells. U0126 or LY294002 significantly enhanced TRAIL-induced apoptosis in HT-29 cells, but not in SW620 cells. We report a different regulation of the level of an anti-apoptotic Mcl-1 protein under MEK/ERK or PI3K/Akt pathway inhibition and suggest the mechanisms involved. A special attention was paid to the role of the ERK1/2, Akt, and glycogen synthase kinase 3beta.

Normal and prostate cancer cells display distinct molecular profiles of alpha-tubulin posttranslational modifications

BACKGROUND

Multiple diverse posttranslational modifications of alpha-tubulin such as detyrosination, further cleavage of the penultimate glutamate residue (Delta2-tubulin), acetylation, and polyglutamylation increase the structural and functional diversity of microtubules.

METHODS

Herein, we characterized the molecular profile of alpha-tubulin posttranslational modifications in normal human prostate epithelial cells (PrEC), immortalized normal prostate epithelial cells (PZ-HPV-7), androgen-dependent prostate cancer cells (LNCaP), transitional androgen-independent prostate cancer cells (LNCaP-cds and CWR22Rv1), and androgen-independent prostate cancer cells (PC3).

RESULTS

Compared to PrEC and PZ-HPV-7 cells, all cancer cells exhibited elevated levels of detyrosinated and polyglutamylated alpha-tubulin, that was paralleled by decreased protein levels of tubulin tyrosine ligase (TTL). In contrast, PrEC and PZ-HPV-7 cells expressed markedly higher levels of Delta2-tubulin. Whereas alpha-tubulin acetylation levels were generally equivalent in all the cell lines, PC3 cells did not display detectable levels of Ac-tubulin.

CONCLUSION

These data may reveal novel biomarkers of prostate cancer and new therapeutic targets.

Transforming growth factor-β1 inhibits all-trans retinoic acid-induced apoptosis

The interaction between retinoids and transforming growth factor-beta1 (TGF-beta1) leading to regulation of proliferation, differentiation and apoptosis is not still fully understood. In this study, we demonstrated that a combination treatment with all-trans retinoic acid (ATRA) and TGF-beta1 led to the enhancement of ATRA-induced suppression of cell proliferation, which is accompanied by inhibition of ATRA-induced apoptosis in human leukemia HL-60 cells. This effect was preceded by the arrest of cells in G0/G1 cell cycle phase linked with pRb protein dephosphorylation, continuous accumulation of p21 and transiently increased level of p27, inhibitors of cyclin-dependent kinases. Inhibition of ATRA-induced apoptosis by TGF-beta1 was associated with an increased level of Mcl-1 protein, an anti-apoptotic member of Bcl-2 family, but not with inhibition of mitochondrial membrane depolarization. Levels of other Bcl-2 family proteins (Bcl-2, Bcl-X(L), Bad, Bak, Bax) were unaffected by simultaneous ATRA and TGF-beta1 treatment, when compared to ATRA alone. Upregulation of c-FLIP(L) protein, an inhibitor of apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), correspond with inhibition of ATRA-induced (autocrine TRAIL-mediated) caspase-8 activation and apoptosis. These results suggest that apoptosis inhibition associated with proliferation block could depend on modulation of the TRAIL apoptotic pathway and regulation of the Mcl-1 protein level. In summary, we demonstrate that the balance of processes leading to regulation of proliferation and differentiation of myeloid cells can modulate cell sensitivity to apoptosis-inducing stimuli.

Dimethyl sulfoxide potentiates death receptor-mediated apoptosis in the human myeloid leukemia U937 cell line through enhancement of mitochondrial membrane depolarization

Dimethyl sulfoxide (DMSO) is a widely used prototypical chemical inducer of cell differentiation. In the present study, the effects of DMSO on susceptibility of human myeloid leukemia U937 cells towards ligation of distinct death receptors (DRs) were investigated. DMSO sensitized cells towards induction of apoptosis by anti-Fas antibody, tumour necrosis factor-alpha or Apo2 ligand/TNF-related apoptosis-inducing ligand (TRAIL). Apart from increasing Fas levels, DMSO did not affect expression of proteins in death signal transduction, such as Bcl-2 family proteins, FADD, caspase-3 and -8, the inhibitor of apoptosis proteins (IAPs) or cFLIP(L). However, DMSO significantly potentiated mitochondrial membrane depolarization, suggesting that this mechanism might be involved in sensitisation of myeloid cells to DR-mediated apoptosis.

Platinum(IV) complex with adamantylamine overcomes intrinsic resistance to cisplatin in ovarian cancer cells

OBJECTIVES

The resistance of tumor cells to cisplatin remains a major cause of treatment failure in cancer patients. In this study, the ability of Pt(IV) complex with adamantylamine-LA-12 and its reduced counterpart with lower oxidation state Pt(II)-LA-9 to overcome intrinsic cisplatin resistance was investigated.

METHODS

The ovarian adenocarcinoma SK-OV-3 cells were exposed to cisplatin, LA-9, or LA-12 for 72 h and the effects of drug concentrations that caused 10% or 50% inhibition of cell proliferation were determined. After 24-72 h of sustained exposure viability, apoptosis and inhibition of proliferation were analyzed. DNA synthesis and cell cycle analysis were performed simultaneously in order to determine the modulation of cell cycle after platinum complexes treatment.

RESULTS

Lung Resistance-related Protein (LRP/MVP) was detected in SK-OV-3 cells but not in the other two ovarian cancer lines with different sensitivity to cisplatin. LRP/MVP overexpression may be an important factor contributing to intrinsic cisplatin resistance. Interestingly, Pt(IV) complex-LA-12 had approximately 2.7-fold lower IC(50) concentration than LA-9 or cisplatin in SK-OV-3 cells. Moreover, LA-12 caused persistent accumulation of cells in S-phase of the cell cycle while LA-9 and cisplatin treatment-induced S-phase arrest was transient and shifted to G(2)/M-phase at later intervals. Apoptosis seemed to be not the dominant type of cell death caused by such the derivatives, but it was the most intensive after LA-12 treatment.

CONCLUSIONS

We found strong differences between effects of Pt(IV) complex-LA-12 and Pt(II) derivatives-LA-9 and cisplatin on cytokinetic parameters. Overall, LA-12 but not its reduced Pt(II) counterpart LA-9 is the compound effective in p53 null human ovarian cancer cells and it is able to overcome intrinsic cisplatin resistance in these cells.

A reappraisal of the genomic organization of human Nox1 and its splice variants

The recent discovery of non-phagocytic NAD(P)H oxidases belonging to the Nox family of enzymes sharing extensive homology to the leukocyte NAD(P)H oxidase has revolutionized our understanding of oxidative signaling related to fundamental biological processes and disease states. One form of this enzyme, Nox1, is a growth factor-responsive enzyme that catalyzes formation of the reactive oxygen species superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)). Its expression is linked to a number of biological responses including cellular proliferation, angiogenesis, and activation of cellular signaling pathways. Whereas early published studies have described three distinct isoforms of Nox1, the current body of literature fails to adequately recognize this notion. Also, functional differences between isoforms remain relatively unexplored. Herein, we report that expression of human Nox1 is restricted to two distinct isoforms derived from a single gene; that is, the full-length gene product and a shorter spliced variant which lacks one of the NAD(P)H binding domains. We have developed PCR primer sets that distinguish between the two forms of Nox1 in several human cell lines. We could not find evidence for expression of the shortest reported form of Nox1 (NOH-1S), previously identified as a proton channel, and the absence of paired splice sites in the gene suggests that it represents a reverse transcriptase artifact. A survey of the scientific literature reveals that the majority of studies related to Nox1 do not utilize molecular strategies that would adequately discern between the two Nox1 variants. The current literature suggest the two identified isoforms of human Nox1 (which we have named Nox1-L and Nox1-S) may be functionally distinct. Future studies related to Nox1 will benefit from establishing the identity of the Nox1 isoform expressed and the functions attributed to each variant.

Ethanol acts as a potent agent sensitizing colon cancer cells to the TRAIL-induced apoptosis

Identification of mechanisms of modulation of the TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis is important for its potential use in anticancer therapy. Ethanol can induce cell death in vitro and in vivo by different signalling pathways. Its effect in combination with death ligands is unknown. We investigated how ethanol modulates the effects of TRAIL in colon cancer cells. After combined TRAIL and ethanol treatment, a potentiation of caspase-8, -9, -3 activation, a proapoptotic Bid protein cleavage, a decrease of mitochondrial membrane potential, a complete poly(ADP)ribose polymerase cleavage, and disappearance of antiapoptotic Mcl-1 protein were demonstrated. Ethanol acts as a potent agent sensitizing colon cancer cells to TRAIL-induced apoptosis.

High effectiveness of platinum(IV) complex with adamantylamine in overcoming resistance to cisplatin and suppressing proliferation of ovarian cancer cells in vitro

[(OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum(IV)], coded as LA-12, is an octahedral platinum(IV) complex containing a bulky hydrophobic ligand - adamantylamine. The use of bulky hydrophobic amines as non-leaving ligands, may increase uptake of the compound by the cancer cells. Therefore, the effects of LA-12 on sensitive (A2780) and cisplatin resistant (A2780cis) ovarian cancer cell lines were investigated and compared to those of cisplatin. IC(50) and IC(90) concentrations of LA-12 were 6- (A2780) or 18-fold (A2780cis) lower than those for cisplatin (MTT assay). Equitoxic concentrations (IC(50) or IC(90)) of both compounds caused a significant and similar time- and dose-dependent inhibition of cell proliferation and an increase in the number of floating cells which corresponded to the decrease of total cell viability. A different type and dynamics of cell cycle perturbation after cisplatin and LA-12 treatment were detected. Exposure to LA-12 resulted in transient accumulation of A2780 and A2780cis cells in S phase, while cisplatin caused G(2)/M arrest in sensitive and S phase arrest in resistant cells. A relatively low rate of apoptosis after exposure to IC(50) or IC(90) of both complexes was observed, markedly higher in resistant A2780cis cells. Western blot analysis indicated a concentration-dependent p53 level increase in both lines (higher after cisplatin treatment). PARP cleavage was observed only in A2780cis cells. In conclusion, LA-12 was found to be significantly more efficient than cisplatin, and it was able to overcome the acquired cisplatin resistance (showing resistance factor 2.84-fold lower than those for cisplatin). In spite of the low rate of apoptosis, LA-12 caused increase of p53 level and cell cycle perturbations in the ovarian cancer cell lines studied.

In vitro proliferation of fibrosarcoma cells depends on intact functions of lipoxygenases and cytochrome P-450-monooxygenase

Proliferation of mouse fibrosarcoma cells G:5:113 was studied in vitro after affecting particular pathways of arachidonic acid metabolism by selected inhibitors. After 48 hours of cultivation with nonspecific lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA) and esculetin; a specific 12-lipoxygenase inhibitor, baicalein; and inhibitor of five-lipoxygenase activating protein, MK-886, markedly suppressed the number of cells and induced significant changes in cell cycle distribution in a dose-dependent manner. While proadifen, an inhibitor of cytochrome P-450-monooxygenase, applied in low concentrations, increased the cell number, at higher concentrations, it inhibited cell proliferation and significantly changed the cell cycle. Cyclooxygenase inhibitors, ibuprofen, flurbiprofen, and diclofenac suppressed cell numbers only moderately without any changes in the cell cycle. The occurrence of apoptosis was not significant for any of the selected drugs in comparison with untreated control cells. Moreover, not even one of the drugs caused the specific cleavage of poly (ADP-ribose) polymerase to the 89-kDa fragment, however, a decrease in total amount of this protein was observed after treatment with NDGA and esculetin. We conclude that the proliferation ability of fibrosarcoma cells G:5:113 in vitro depends on intact functions of 5-lipoxygenase, 12-lipoxygenase, and cytochrome P-450-monooxygenases, and that the effects of inhibitors do not include regulation of apoptosis.

Increased apoptosis in differentiating p27-deficient mouse embryonic stem cells

In mouse embryonic stem (mES) cells, the expression of p27 is elevated when differentiation is induced. Using mES cells lacking p27 we tested the importance of p27 for the regulation of three critical cellular processes: proliferation, differentiation, and apoptosis. Although cell cycle distribution, DNA synthesis, and the activity of key G1/S-regulating cyclin-dependent kinases remained unaltered in p27-deficient ES cells during retinoic acid-induced differentiation, the amounts of cyclin D2 and D3 in such cells were much lower compared with normal mES cells. The onset of differentiation induces apoptosis in p27-deficient cells, the extent of which can be reduced by artificially increasing the level of cyclin D3. We suggest that the role of p27 in at least some differentiation pathways of mES cells is to prevent apoptosis, and that it is not involved in slowing cell cycle progression. We also propose that the pro-survival function of p27 is realized via regulation of metabolism of D-type cyclin(s).

The effects of TNF-α and inhibitors of arachidonic acid metabolism on human colon HT-29 cells depend on differentiation status

The level of differentiation could influence sensitivity of colonic epithelial cells to various stimuli. In our study, the effects of TNF-alpha, inhibitors of arachidonic acid (AA) metabolism (baicalein, BA; indomethacin, INDO; niflumic acid, NA; nordihydroguaiaretic acid, NDGA), and/or their combinations on undifferentiated or sodium butyrate (NaBt)-differentiated human colon adenocarcinoma HT-29 cells were compared. NaBt-treated cells became growth arrested (blocked in G0/G1 phase of the cell cycle), and showed down-regulated Bcl-xL and up-regulated Bak proteins and increased expression of cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX). These cells were more perceptive to anti-proliferative and apoptotic effects of TNF-alpha. Both inhibitors of LOX (BA and NDGA) and COX (INDO and NA) in higher concentrations modulated cell cycle changes accompanying NaBt-induced differentiation and induced various level of cell death in undifferentiated and differentiated cells. Most important is our finding that TNF-alpha action on proliferation and cell death can be potentiated by co-treatment of cells with AA metabolism inhibitors, and that these effects were more significant in undifferentiated cells. TNF-alpha and INDO co-treatment was associated with accumulation of cells in G0/G1 cell cycle phase, increased reactive oxygen species production, and elevated caspase-3 activity. These results indicate the role of differentiation status in the sensitivity of HT-29 cells to the anti-proliferative and proapoptotic effects of TNF-alpha, AA metabolism inhibitors, and their combinations, and imply promising possibility for novel anti-cancer strategies.

c-Fos but not v-Fos protein induces programmed cell death of v-myb-transformed monoblasts

c-Fos and v-Fos belong to a group of proteins forming the transcription factor AP-1 that is important for regulation of proliferation, differentiation and programmed cell death in multiple cell types. In this study, we examined the role of c-Fos and v-Fos proteins in v-myb-transformed BM2 monoblasts. We show that while the v-Fos protein prolongs the G0G1 phase of the BM2 cell cycle, c-Fos leaves the cell cycle unaffected and, rather, induces programmed cell death. The apoptosis-promoting activity of the c-Fos protein is markedly enhanced in cells cultivated under serum-free conditions. c-Fos-induced apoptosis of BM2 cells occurred in the presence of Bcl-2 and was not dependent on the transcription activation function of the c-Fos protein. No differentiation-promoting activity of the Fos proteins was observed. The effects of Fos proteins on BM2 cells differ from those induced by Jun proteins, suggesting differential roles of individual components of the AP-1 transcription factor in regulation of essential cellular processes.

Lipoxygenase inhibitors enhance tumor suppressive effects of Jun proteins on v-myb-transformed monoblasts BM2

Inhibitors of arachidonic acid (AA) conversion were described as suppressors of proliferation and inducers of differentiation of various leukemic cells. Certain AA metabolites have been shown to cooperate with Jun proteins that are important factors controlling cell proliferation, differentiation and apoptosis. Using lipoxygenase (LOX) inhibitors of various specifity we studied possible participation of lipoxygenase pathway in regulation of proliferation and apoptosis of v-myb-transformed chicken monoblasts BM2 and its functional interaction with Jun proteins. We found that nordihydroguaiaretic acid (NDGA) and esculetin (Esc) negatively regulate proliferation of BM2 cells causing accumulation in either G0/G1-phase (nordihydroguaiaretic acid) or S-phase (esculetin) of the cell cycle. BM2 cells can be also induced to undergo growth arrest and partial differentiation by ectopic expression of Jun proteins. We demonstrated that lipoxygenase inhibitors further enforce tumor suppressive capabilities of Jun proteins by inducing either more efficient cell cycle block and/or apoptosis in BM2 cells. This suggests that there is a cross-talk between the lipoxygenase- and Jun-directed pathways in regulation of differentiation and proliferation of monoblastic cells. Thus pharmacologic agents that specifically block lipoxygenase-catalyzed activity and enforce the effects of differentiation-inducers may be important components in anti-tumor therapies.

Chromosomal territory segmentation in apoptotic cells

The nuclear architecture of selected chromosomes in apoptotic nuclei of human leukemic cells K-562 and HL-60 was investigated. Etoposide and prolonged confluence were used for the induction of apoptosis. DAPI as well as TUNEL labeling of apoptotic nuclear bodies was combined with visualization of chromosomal territories by the FISH technique. Simultaneous vital staining by annexin V, propidium iodide, and Hoechst 33342 was applied to distinguish apoptotic, necrotic, and intact cell fraction of tested populations. Our FISH analyses revealed that the three-dimensional (3D) structure of apoptotic nuclei as well as the 3D structure of apoptotic bodies is preserved in formaldehyde-fixed cells. High-molecular-weight DNA fragmentation was determined in apoptotic K-562 cells in contrast to oligonucleosomal cleavage observed in apoptotic HL-60 cells. In K-562 populations, chromosomal territories were located separately either in one apoptotic body or underwent disassembly into chromosomal segments dispersed into single and/or several apoptotic bodies. The apoptotic disorganization of chromosomal territories was irregular, leading mainly to chromosomal segments of different sizes and, consequently, chromosomal disassembly was not observed at specific sites. In comparison with the control, an increased number of centromeric FISH signals were observed in prolonged confluence-treated K-562 cells induced to apoptosis. This finding can be explained either as a consequence of apoptosis or by polyploidization. Sequential staining of the same apoptotic nuclei by the FISH and TUNEL techniques revealed that chromosomal territory segmentation precedes the formation of nuclear apoptotic bodies.

Trichostatin A suppresses transformation by the v-myb oncogene in BM2 cells

BM2 cells are chicken monoblasts transformed by the v-myb oncogene of avian myeloblastosis virus. The constitutively high v-myb expression interferes with the terminal differentiation of BM2 cells, but these cells can be induced to differentiate into macrophage-like cells by phorbol esters. Histone acetylation plays an important role in regulation of transcription and is particularly relevant to the regulation and pathology of hematopoiesis. In the present study, we examined the contribution of elevated histone acetylation to the differentiation of BM2 cells. Inhibition of the activity of endogenous histone deacetylases by trichostatin A (TSA) resulted in histone hyperacetylation causing cell cycle arrest and differentiation of BM2 cells into macrophage polykaryons. TSA did not affect the level of v-Myb protein in BM2 cells, but it downregulated its transcription activation capability. This suggests that chromatin remodeling can be significantly engaged in regulation of proliferation and differentiation of leukemic cells.

Tumor-host interactions accompanying the growth of the G:5:113 fibrosarcoma in the mouse: possibilities for a new therapeutic approach?

The experiments were aimed at describing in detail some interactions between a solid tumor growing from subcutaneously transplanted G:5:113 fibrosarcoma cells in vivo and its mouse host. The tumor was found to elevate significantly the number of granulocytes in the peripheral blood of the host after having achieved the volume of about 1 cm3 (day 40 after transplantation). Blood plasma from fibrosarcoma-bearing mice stimulated proliferation of progenitor cells for granulocytes and macrophages (GM-CFC) in vitro and suppressed growth of G:5:113 cell population in culture. Interestingly, both effects were observable as early as week 1 when the tumor was still macroscopically invisible and unpalpable. Conditioned medium from cultures of G:5:113 fibrosarcoma cells stimulated proliferation of GM-CFC in vitro. These findings might represent a starting point for studies aimed at designing new therapeutic approaches for the treatment of fibrosarcoma.

Lipoxygenase inhibitors induce arrest of tumor cells in S-phase of the cell cycle

Inhibitors of the lipoxygenase pathway of arachidonic acid metabolism represent a potential anti-tumor drugs. These compounds have been found to inhibit the growth and induce the apoptosis of various tumor cells both in vitro and in vivo. In this study, the effects of the lipoxygenase inhibitors esculetin and nordihydroguaiaretic acid (NDGA) on the progression of the cell cycle were investigated in eight mammalian cell lines of different origin. Flow cytometric analyses of cell cycle distribution after staining of DNA with propidium iodide or 7-aminoactinomycin D and DNA synthesis using incorporation of 5-bromo-2'-deoxy-uridine showed that both esculetin and NDGA suppress cell growth by interrupting the progression of cells through S-phase that results in their accumulation in this phase of the cell cycle. The possible mechanisms of these effects and the significance of the findings for the improvement of anticancer therapy targeted on cell cycle is discussed.

Differential effects of v-Jun and c-Jun proteins on v-myb-transformed monoblasts

The v-myb oncogene of avian myeloblastosis virus transforms myelomonocytic cells in vitro. The line of v-myb-transformed chicken monoblasts BM2 can be induced to terminal differentiation using phorbol esters. The fact that Jun proteins are up-regulated in the phorbol ester-treated BM2 cells prompted us to investigate the role of the Jun proteins in regulation of myeloid differentiation. We ectopically expressed v-jun and c-jun in BM2 cells and evaluated their effects on differentiation and proliferation. c-Jun up-regulated the transactivation activity of v-Myb and induced a proliferation block and differentiation of BM2 cells. In contrast, v-Jun down-regulated v-Myb transactivation causing no dramatic effects on BM2 cells. This confirms that there is no strong correlation between transcriptional activation and strength of oncogenic transformation by v-Myb. Both c-Jun and v-Jun proteins affected sensitivity of BM2 cells to retinoic acid and phorbol ester. Sensitivity of BM2 cells to retinoic acid was enhanced by both Jun proteins, while sensitivity to phorbol 12-myristate 13-acetate was reduced by v-Jun. These data suggest thate Jun plays a major role in macrophage differentiation.

The effect of nonsteroidal antiinflammatory drugs ibuprofen, flurbiprofen, and diclofenac on in vitro and in vivo growth of mouse fibrosarcoma

For suppression of primary G:5:113 fibrosarcoma growth, three structurally different cyclooxygenase (COX) inhibitors (ibuprofen, flurbiprofen, and diclofenac) were administered intraperitoneally (i.p.) in two regimens starting on day 5 after tumor-cell inoculation. Repeated application of 0.15 mg/mouse/day during 14 consecutive days significantly suppressed the tumor growth and increased the percentage of surviving mice. Similar tendency, however without significant differences, was observed when animals were given 0.5 mg/day for five consecutive days. These results suggest that a time schedule of drug application is important for the therapeutic effect. Suppressive effect of diclofenac and flurbiprofen on tumor growth was also observed under in vitro conditions. We conclude that suppressive effect of these drugs on tumor growth in vivo comprises both direct effects of COX inhibitors on fibrosarcoma cells and indirect effects that are presumably mediated by extratumoral sources. Our findings encourage the use of COX inhibitors in the therapy of fibrosarcoma.

Tumor necrosis factor-alpha induces apoptosis associated with poly(ADP-ribose) polymerase cleavage in HT-29 colon cancer cells

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is known for its selective cytotoxic activity on tumour cells. We analysed the response of HT-29 human colon carcinoma cells to this cytokine.

MATERIALS AND METHODS

After TNF-alpha treatment, cell proliferation, cell cycle, reactive oxygen species (ROS) production (flow cytometry), the amount of apoptotic cells (flow cytometry, fluorescence microscopy), cleavage of poly (ADP-ribose) polymerase (PARP) and caspase-3 activity (Western blotting) were detected.

RESULTS

TNF-alpha induced a decrease of cell growth and viability, an accumulation of cells in the S-phase of the cell cycle, an increase of subdiploid cell population and nuclear chromatin condensation and fragmentation, but not sooner than 96-120 hours. However, earlier events characteristic of apoptosis occurred, such as caspase-3 activation, PARP cleavage to 89 kDa fragment and changes in ROS production.

CONCLUSION

We demonstrated that, in addition to being an early marker of apoptosis, activation of caspase-3 and degradation of PARP may play a causative role in HT-29 cell death induced by TNF-alpha.

Multiple biological effects of inhibitors of arachidonic acid metabolism on human keratinocytes

BACKGROUND

Various compounds that inhibit processing of arachidonic acid (AA) are being intensively tested for their antitumour activity. However, the mechanisms responsible for such activity remain rather elusive. To approach this issue, we examined the effects of several structurally different inhibitors of AA metabolism in the human keratinocyte HaCaT cell line.

METHODS

Several parameters were determined in HaCaT cells exposed to increasing concentrations of the inhibitors for 24 and/or 48 h. These included (1) oxidoreductase activity, total protein mass and cell cycle distribution to assess cell proliferation, (2) degradation of PARP protein to assess apoptosis, and (3) cell morphology, distribution of F-actin and expression of cytokeratins and E-cadherin to evaluate changes in differentiation status.

RESULTS

While eicosatetraynoic acid (ETYA), nordihydroguaiaretic acid (NDGA), esculetin and MK-886 reduced proliferation of HaCaT cells, the cyclooxygenase inhibitors indomethacin and piroxicam had no such effects. Esculetin and NDGA arrested cells in S phase, and ETYA and MK-886 delayed cell progression through G(1) phase. Higher concentrations of NDGA, MK886 and/or ETYA caused cleavage of PARP. No changes in the expression of cytokeratins and E-cadherin were observed upon treatment with any of the inhibitors. However, esculetin induced redistribution of F-actin accompanied by increased cell adhesion and size.

CONCLUSION

Our findings indicate that, in addition to their ability to inhibit cell proliferation and to induce apoptosis, lipoxygenase inhibitors and/or ETYA may also elicit other important physiological responses in HaCaT keratinocytes.

Inhibitors of arachidonic acid metabolism potentiate tumour necrosis factor-alpha-induced apoptosis in HL-60 cells

We investigated whether and how could various modulators of arachidonic acid metabolism affect apoptosis induced by tumour necrosis factor-alpha (TNF-alpha) in human myeloid leukaemia HL-60 cells. These included arachinonyltrifluoromethyl ketone (AACOCF3; cytosolic phospholipase A2 inhibitor), indomethacin (cyclooxygenase inhibitor), MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2-dimethyl propanoic acid; 5-lipoxygenase-activating protein inhibitor), nordihydroguaiaretic acid (general lipoxygenase inhibitor), and arachidonic acid itself. Incubation of HL-60 cells with nordihydroguaiaretic acid resulted in apoptosis and it was characterised by mitochondria membrane depolarisation, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. Indomethacin and nordihydroguaiaretic acid synergistically potentiated TNF-alpha-induced apoptosis, while arachidonic acid, AACOCF3 and MK-886 did not modulate its effects. Furthermore, indomethacin potentiated apoptosis in cells treated with a differentiating agent, all-trans retinoic acid, which induces resistance to TNF-alpha. However, the observed effects were probably not associated either with the cyclooxygenase- or lipoxygenase-dependent activities of indomethacin and nordihydroguaiaretic acid, respectively. Since indomethacin may reportedly activate peroxisome proliferator-activated receptors (PPARs), the effects of specific ligands of PPARs on apoptosis were studied as well. It was found that selective PPARs ligands had no effects on TNF-alpha-induced apoptosis. The findings suggest that arachidonic acid metabolism does not play a key role in regulation of apoptosis induced by TNF-alpha in the present model. Nevertheless, our data raise the possibility that indomethacin could potentially be used to improve the treatment of human myeloid leukaemia.

Transforming growth factor-beta1 induces junB mRNA accumulation, G1-phase arrest, and pRb dephosphorylation in human leukemia HL-60 cells

Although TGF-beta1 unambiguously functions as a regulator of hematopoietic differentiation, its significance for the development of myeloid lineage is still questionable. In this study three components of early response to TGF-beta1 treatment were investigated in human promyelocytic leukemia HL-60 cells. Changes in junB mRNA accumulation and pRb dephosphorylation were accompained by accumulation of cells in G1 phase of the cell cycle. Time dependence of these changes may implicate mutual cooperation of the pRb and junB in the cell cycle control. It can be concluded that, although myeloid HL-60 cells are known to require rather complex cytokine stimulation to fully differentiate, they clearly possess the ability to respond to TGF-beta1.

Inhibition of the cytochrome P-450 modulates all-trans-retinoic acid-induced differentiation and apoptosis of HL-60 cells

We studied the effects of inhibition of cytochrome P-450 by proadifen (SKF525A) on the processes induced in myeloid leukemia HL-60 cells by all-trans-retinoic acid (ATRA). The parameters reflecting cell proliferation, differentiation, and apoptosis were detected by flow cytometry as the principal method at selected time intervals (24-96 hours). Changes in the expression of Bcl-2 protein were detected by Western blotting. The majority of experiments were designed as a factorial combination of the treatment and assessed for significance of the interactions. Proadifen was demonstrated synergistically (1) to potentiate the antiproliferative and differentiation effects of ATRA, and (2) to increase cell viability and prevent ATRA-induced apoptosis. Moreover, proadifen weakened ATRA-induced downregulation of the Bcl-2 protein. Our results may be of practical importance because cytochrome P-450 inhibitors are used clinically in treating cancer patients. Assuming that effects on the leukemic cells in vivo would be similar, this type of combined therapy could help to achieve better results even with lower doses of ATRA.

The effects of RARalpha and RXRalpha proteins on growth, viability, and differentiation of v-myb-transformed monoblasts

Retinoids are important agents which regulate differentiation and proliferation processes in various cell types, including cancer cells. Growth arrest and induction of terminal differentiation demonstrate the tumor-suppressive effects of retinoids on leukemic cells. We studied differentiation, proliferation, and death processes in the cell line of v-myb-transformed monoblasts BM2 and their retinoic acid receptor (RAR) alpha- and retinoid X receptor (RXR) alpha-expressing derivatives after exposure to four different retinoids: all-trans retinoic acid, 9-cis retinoic acid, TTNPB, and LG1000153. The effects of retinoids on the phenotype of BM2, BM2RAR, and BM2RXR cells were correlated with the transcription activation function of the v-Myb oncoprotein of avian myeloblastosis virus. We found that the efficiency of terminal differentiation of BM2RAR and BM2RXR cells induced by retinoids is indirectly proportional to the v-Myb transcription activation activity. In contrast, the effects of liganded retinoid receptors on growth of BM2 cells are more complex. Activated RAR protein induces growth inhibition of BM2 cells by suppression of v-Myb function. However, liganded RXR protein is less efficient in cell cycle arrest and rather decreases cellular viability. This process can occur in the presence of active v-Myb protein. These results suggest that ligand-activated RARalpha protein is primarily engaged in control of proliferation and differentiation of v-myb-transformed monoblasts, while activated RXRalpha protein controls their differentiation and death.