Bim mRNA Levels Research Articles

Co-inhibition of BET and proteasome enhances ER stress and Bim-dependent apoptosis with augmented cancer therapeutic efficacy

Agents that inhibit bromodomain and extra-terminal domain (BET) protein have been actively tested in the clinic as potential anticancer drugs. Proteasome inhibitors such as carfilzomib (CFZ) are FDA-approved for the treatment of patients with advanced multiple myeloma and have been tested against other cancers. The current study focuses on the combination of a BET inhibitor (e.g., JQ1) and a proteasome inhibitor (e.g., CFZ) as a novel cancer therapeutic strategy and the underlying mechanisms. The tested combination (JQ1 with CFZ) synergistically decreased cell survival and enhanced apoptosis in vitro and inhibited tumor growth in vivo. The dramatic induction of apoptosis was accompanied by enhanced elevation of Bim and ER stress. Bim knockout significantly attenuated apoptosis induced by the combination, suggesting a critical role of Bim induction in mediating the enhanced induction of apoptosis by BET and proteasome co-inhibition. The combination significantly increased Bim mRNA levels with limited effect on Bim protein stability, suggesting a primary transcriptional regulation of enhanced Bim expression. Our findings warrant further investigation of this combinatorial strategy as an effective regimen against cancer in the clinic.

Abstract 883: Alvocidib-mediated inhibition of CDK9 upregulates BIM via suppression of miR17-92

Abstract The positive-transcription elongation factor (P-TEFb) complex is critical in stimulating the transcription of non-abortive transcripts by RNA polymerase II. The CDK9/cyclin-T heterodimer comprises the P-TEFb complex and promotes transcription elongation through phosphorylation of serine 2 of the heptapeptide repeats of the c-terminal domain of RNA Polymerase II (RNAPII-CTD). Alvocidib, a potent CDK9 inhibitor, has been shown to suppress expression of MCL-1 and Myc mRNAs, and clinical pharmacodynamic data suggest that alvocidib's activity is primarily mediated through the suppression of MCL-1 mRNA and protein expression. In addition to MCL-1 suppression, we hypothesized that CDK9 inhibition affects other RNA Polymerase II target RNAs, such as microRNAs. Recently, it was reported that inhibition of bromodomain and extraterminal domain (BET) protein by JQ1 suppresses miR17-92 expression. miR17-92 negatively regulates expression of the pro-apoptotic BH3-only protein, BIM, leading to suppression of BIM expression, thereby decreasing the cells' ability to induce apoptosis. It was hypothesized that CDK9 kinase activity is key to miR17-92 expression and suppression of BIM expression and that targeting CDK9 would lead to a decrease in miR17-92, and increases in BIM. MV4-11, OCI-AML3, MOLM13, and THP1 AML cell lines were used to determine the effects of alvocidib treatment on microRNAs. RT-qPCR was utilized to determine microRNA expression levels of miR17-92 and mRNA levels of BIM and other markers. Protein changes were determined using standard gel electrophoresis and immunoblotting technique. CellTiter-Glo and Caspase-Glo were used for all cell viability and apoptosis assays interrogating alvocidib. With CDK9 inhibition mediated via alvocidib, a dose- and time-dependent decrease in miR17-92 expression in MV4-11, OCI-AML3, MOLM13, and THP1 cells was observed. A decrease was observed even 3 hours post-treatment, persisting for up to 24 hours. MicroRNA suppression following treatment ranged in magnitude, with a maximal effect of between 3.3 to 4.2-fold suppression, depending on the cell line and timepoint. This suppression coincided with an increase in BIM mRNA and protein expression in the MV4-11, OCI-AML3, and MOLM13 cells. However, BIM protein increase was not observed in THP1 cells. Maximal increase in BIM mRNA levels reached 5.4-fold in the MV4-11 cell line. Our data suggest that CDK9 inhibition suppresses RNA Polymerase II-mediated expression of miR17-92, which in turn leads to increased expression of BIM. Combined with MCL-1 reduction, increased BIM protein expression mediated by alvocidib leads to enhanced apoptosis. Taken together, the data provide additional understanding of CDK9 as a potential therapeutic target, and are consistent with the hypothesis that CDK9 activity is necessary for miR17-92 expression. Citation Format: Hillary Haws, Hubert F. Arokium, James L. Bogenberger, Adam Siddiqui-Jain, David J. Bearss, Raoul Tibes, Steven L. Warner, Clifford J. Whatcott. Alvocidib-mediated inhibition of CDK9 upregulates BIM via suppression of miR17-92 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 883.

Expression pattern of BIM, BCL-6, and c-MYC in adult B-cell acute lymphoblastic leukemia ⁎

Abstract Objective We aimed to evaluate the expression pattern of the genes BIM, BCL-6, and c-MYC in adult patients at initial diagnosis of B-cell acute lymphoblastic leukemia (B-ALL). Methods Relative mRNA levels of BIM, BCL-6, and c-MYC in peripheral blood mononuclear cells (PBMCs) from B-ALL patients were determined by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) using SYBR Green dye. PBMCs from healthy volunteers served as a control. GAPDH was used as a reference gene. Results Relative expression of BIM, BCL-6, and c-MYC mRNA in B-ALL patients was significantly lower than in healthy controls (P < 0.05). Furthermore, this result was observed for both newly diagnosed B-ALL patients and those incomplete remission (CR) (P < 0.05). There were no statistically significant differences in the expression levels of BIM, BCL-6, and c-MYC between these B-ALL patient groups (P > 0.05). Spearman’s rank correlation analyses revealed the expression level of BIM to be positively correlated with that of BCL-6 in B-ALL patients. Conclusion Expression of the genes BIM, BCL-6, and c-MYC is decreased in adult B-ALL patients. Moreover, the expression pattern of these genes may be similar in such patients at initial diagnosis and following CR. The expression characteristics of BIM, BCL-6, and c-MYC may constitute useful markers for the diagnosis of adult B-ALL.

Foxo3a-dependent Bim transcription protects mice from a high fat diet via inhibition of activation of the NLRP3 inflammasome by facilitating autophagy flux in Kupffer cells.

BackgroundThe role of Foxo3a in the regulation of autophagy flux and activation of the NLRP3 inflammasome in KCs suffering from HFD conditions is unknown.ResultsUp-regulation of Foxo3a restored autophagy flux and dampened the activation of the NLRP3 inflammasome in KCs stimulated with PA and LPS. In contrast, down-regulation of Foxo3a increased blockage of autophagy flux and promoted NLRP3 inflammasome activation. Additionally, mRNA levels of Bim were significantly changed with the alteration of Foxo3a in KCs under PA and LPS stimulation among foxo3a targeted genes. Overexpression of Bim restored autophagy influx and attenuated NLRP3 inflammasome pathway activation. In addition, autophagy formation was restored, and activation of NLRP3 inflammasome was inhibited in KCs isolated from mice treated with Iturin A and fed with a HFD.Materials and methodsAutophagy flux in KCs and activation levels of NLRP3 inflammasome were evaluated after altering the expression of Foxo3a in KCs before stimulation with PA and LPS. Additionally, various target genes of Foxo3a were measured in KCs pretreated with an agonist (Iturin A) or inhibitor (SC97) of Foxo3a after KCs stimulation with PA and LPS in order to hunt for targets of Foxo3a. Activation levels of NLRP3 inflammasome in isolated KCs, as well as autophagy flux, were measured after mice were treated with Iturin A and fed with a HFD for 16 weeks.ConclusionsFoxo3a restores autophagy flux and attenuates the activation of the NLRP3 inflammasome by promoting the transcription of Bim, suggesting a potential therapeutic target in NAFLD and other obesity-related diseases.

High BIM mRNA levels are associated with longer survival in advanced gastric cancer

Chemotherapy drugs, including 5-fluorouracil (5-FU), oxaliplatin and docetaxel, are commonly used in the treatment of gastric cancer (GC). Apoptosis-relevant genes may be associated with drug resistance. In the present study, the messenger RNA (mRNA) expression levels of B-cell lymphoma 2 interacting mediator of cell death (BIM), astrocyte elevated gene-1 (AEG-1) and AXL receptor tyrosine kinase (AXL) were investigated in 131 advanced GC samples, and the expression levels of these genes were correlated with patients' overall survival (OS). All 131 patients received first-line FOLFOX combination chemotherapy with folinic acid and 5-FU, in which 56 patients were further treated with second-line docetaxel-based chemotherapy. A correlation between the mRNA expression levels of BIM and AEG-1 was observed (rs=0.30; P=0.002). There was no association between the mRNA expression levels of any of the individual genes analyzed and OS in patients only receiving first-line FOLFOX chemotherapy. In a subgroup of patients receiving docetaxel-based second-line chemotherapy, those with high or intermediate levels of BIM exhibited a median OS of 18.2 months [95% confidence interval (CI), 12.8-23.6], compared with 9.6 months (95% CI, 8.9-10.3) in patients with low BIM levels (P=0.008). However, there was no correlation between the mRNA expression levels of AEG-1 or AXL and OS. The risk of mortality was higher in patients with low BIM mRNA levels than in those with high or intermediate BIM mRNA levels (hazard ratio, 2.61; 95% CI, 1.21-5.62; P=0.010). Therefore, BIM may be considered as a biomarker to identify whether patients could benefit from docetaxel-based second-line chemotherapy in GC.

BIM and mTOR expression levels predict outcome to erlotinib in EGFR-mutant non-small-cell lung cancer.

BIM is a proapoptotic protein that initiates apoptosis triggered by EGFR tyrosine kinase inhibitors (TKI). mTOR negatively regulates apoptosis and may influence response to EGFR TKI. We examined mRNA expression of BIM and MTOR in 57 patients with EGFR-mutant NSCLC from the EURTAC trial. Risk of mortality and disease progression was lower in patients with high BIM compared with low/intermediate BIM mRNA levels. Analysis of MTOR further divided patients with high BIM expression into two groups, with those having both high BIM and MTOR experiencing shorter overall and progression-free survival to erlotinib. Validation of our results was performed in an independent cohort of 19 patients with EGFR-mutant NSCLC treated with EGFR TKIs. In EGFR-mutant lung adenocarcinoma cell lines with high BIM expression, concomitant high mTOR expression increased IC50 of gefitinib for cell proliferation. We next sought to analyse the signalling pattern in cell lines with strong activation of mTOR and its substrate P-S6. We showed that mTOR and phosphodiesterase 4D (PDE4D) strongly correlate in resistant EGFR-mutant cancer cell lines. These data suggest that the combination of EGFR TKI with mTOR or PDE4 inhibitors could be adequate therapy for EGFR-mutant NSCLC patients with high pretreatment levels of BIM and mTOR.

A novel prohibitin-binding compound induces the mitochondrial apoptotic pathway through NOXA and BIM upregulation.

We previously described diaryl trifluorothiazoline compound 1a (hereafter referred to as fluorizoline) as a first-in-class small molecule that induces p53-independent apoptosis in a wide range of tumor cell lines. Fluorizoline directly binds to prohibitin 1 and 2 (PHBs), two proteins involved in the regulation of several cellular processes, including apoptosis. Here we demonstrate that fluorizoline-induced apoptosis is mediated by PHBs, as cells depleted of these proteins are highly resistant to fluorizoline treatment. In addition, BAX and BAK are necessary for fluorizoline-induced cytotoxic effects, thereby proving that apoptosis occurs through the intrinsic pathway. Expression analysis revealed that fluorizoline induced the upregulation of Noxa and Bim mRNA levels, which was not observed in PHB-depleted MEFs. Finally, Noxa(-/-)/Bim(-/-) MEFs and NOXA-downregulated HeLa cells were resistant to fluorizoline-induced apoptosis. All together, these findings show that fluorizoline requires PHBs to execute the mitochondrial apoptotic pathway.

P-055 High BIM mRNA levels associated with longer survival in advanced gastric cancer

P-055 High BIM mRNA levels associated with longer survival in advanced gastric cancer

Association of high BIM mRNA levels with longer survival in advanced gastric cancer.

e15075 Background: 5-fluorouracil,oxaliplatin, and docetaxel chemotherapy are commonly used in the treatment for gastric cancer (GC). Apoptosis relevant genes might be associated with drug resistan...

Pro-apoptotic BIM is an essential initiator of physiological endothelial cell death independent of regulation by FOXO3.

The growth of new blood vessels by angiogenesis is essential for normal development, but can also cause or contribute to the pathology of numerous diseases. Recent studies have shown that BIM, a pro-apoptotic BCL2-family protein, is required for endothelial cell apoptosis in vivo, and can contribute to the anti-angiogenic effect of VEGF-A inhibitors in certain tumor models. Despite its importance, the extent to which BIM is autonomously required for physiological endothelial apoptosis remains unknown and its regulation under such conditions is poorly defined. While the transcription factor FOXO3 has been proposed to induce Bim in response to growth factor withdrawal, evidence for this function is circumstantial. We report that apoptosis was reduced in Bim(-/-) primary endothelial cells, demonstrating a cell-autonomous role for BIM in endothelial death following serum and growth factor withdrawal. In conflict with in vitro studies, BIM-dependent endothelial death in vivo did not require FOXO3. Moreover, endothelial apoptosis proceeded normally in mice lacking FOXO-binding sites in the Bim promoter. Bim mRNA was upregulated in endothelial cells starved of serum and growth factors and this was accompanied by the downregulation of miRNAs of the miR-17∼92 cluster. Bim mRNA levels were also elevated in miR-17∼92(+/-) endothelial cells cultured under steady-state conditions, suggesting that miR-17∼92 cluster miRNAs may contribute to regulating overall Bim mRNA levels in endothelial cells.

MiR-17-5p Inhibitor Enhances Chemosensitivity to Gemcitabine Via Upregulating Bim Expression in Pancreatic Cancer Cells

miR-17-5p is reported to be overexpressed in pancreatic cancer, and it plays an important role in carcinogenesis and cancer progression. Gemcitabine is the standard first-line chemotherapeutic agent for pancreatic cancer, however the chemoresistance limits the curative effect. In the present study, we investigated whether inhibition of miR-17-5p could enhance chemosensitivity to gemcitabine in pancreatic cancer cells. miR-17-5p inhibitor was transfected to pancreatic cancer cell lines Panc-1 and BxPC3, and then cell proliferation, cell apoptosis, caspase-3 activation, and chemosensitivity to gemcitabine were measured in vitro. Our data showed that Panc-1 and BxPC3 cells transfected with miR-17-5p inhibitor showed growth inhibition, spontaneous apoptosis, higher caspase-3 activation, and increased chemosensitivity to gemcitabine. In addition, miR-17-5p inhibitor upregulated Bim protein expression in a dose-dependent manner without changing the Bim mRNA level, and it increased the activity of a luciferase reporter construct containing the Bim-3' untranslated region. These results prove that miR-17-5p negatively regulates Bim at the posttranscriptional level. We suggest that miR-17-5p inhibitor gene therapy would be a novel approach to chemosensitization for human pancreatic cancer.

The MEK-ERK pathway negatively regulates bim expression through the 3' UTR in sympathetic neurons

BackgroundApoptosis plays a critical role during neuronal development and disease. Developing sympathetic neurons depend on nerve growth factor (NGF) for survival during the late embryonic and early postnatal period and die by apoptosis in its absence. The proapoptotic BH3-only protein Bim increases in level after NGF withdrawal and is required for NGF withdrawal-induced death. The regulation of Bim expression in neurons is complex and this study describes a new mechanism by which an NGF-activated signalling pathway regulates bim gene expression in sympathetic neurons.ResultsWe report that U0126, an inhibitor of the prosurvival MEK-ERK pathway, increases bim mRNA levels in sympathetic neurons in the presence of NGF. We find that this effect is independent of PI3-K-Akt and JNK-c-Jun signalling and is not mediated by the promoter, first exon or first intron of the bim gene. By performing 3' RACE and microinjection experiments with a new bim-LUC+3'UTR reporter construct, we show that U0126 increases bim expression via the bim 3' UTR. We demonstrate that this effect does not involve a change in bim mRNA stability and by using PD184352, a specific MEK1/2-ERK1/2 inhibitor, we show that this mechanism involves the MEK1/2-ERK1/2 pathway. Finally, we demonstrate that inhibition of MEK/ERK signalling independently reduces cell survival in NGF-treated sympathetic neurons.ConclusionsThese results suggest that in sympathetic neurons, MEK-ERK signalling negatively regulates bim expression via the 3' UTR and that this regulation is likely to be at the level of transcription. This data provides further insight into the different mechanisms by which survival signalling pathways regulate bim expression in neurons.

Dasatinib Promotes BIM Dependent Apoptosis Via MEK/ERK without Need for Permanent BCR-ABL Inhibition

AbstractAbstract 4472Chronic myeloid leukaemia (CML) is a clonal disorder of haematopoietic stem cells, characterized by constitutively active BCR-ABL kinase. It was previously shown, that transient inhibition of BCR-ABL by tyrosin kinase inhibitor (TKI) dasatinib induces apoptosis in CML cells (Shah 2008). Dasatinib mediated apoptosis is accompanied by increasing expression level of proapoptotic protein BIM and inhibition of its degradation in proteasome.Our aim is to find alterations in BCR-ABL downstream pathways and changes in BIM expression after pulse (wash-out after 20min) or continuous treatment with TKI dasatinib alone or in combination with proteasome inhibitor bortezomib in K562 cells.Higher mRNA levels of BIM were confirmed in both transiently and continuously treated (100nM dasatinib) K562 cells compared to low dose continuous (1nM dasatinib) treatment. Western blot analysis of BCR-ABL induced signalling pathways activity revealed, among others, sustained inhibition of MEK/ERK pathway even in the case of re-activation of BCR-ABL after drug wash-out. MEK/ERK inhibition leads to activation of proapoptotic BIM expression and inhibition of its degradation. We used bortezomib, a reversible inhibitor of proteasome, in order to test the block of BIM degradation in dasatinib treated cells. However, we have not found any difference in cell viability caused by adding of 30nM bortezomib to dasatinib treated cells neither in continuous or transient exposure. These findings suggest that equal increase of BIM in the case of pulse and continuous dasatinib treatment is caused by MEK/ERK inhibition in cells with restored BCR-ABL activity.This project is supported by grants from the Ministry of Education of Czech Republic NPVII (2B06052) and MSM-0021622430. The substance (dasatinib) for this project was supplied by BMS company. Disclosures:Mayer:BMS: Consultancy, Research Funding.

Chronic Lymphocytic Leukemia Apoptotic Cell Death Induced by Glucocorticoids Is Mediated by BIM and GILZ and Can Be Predicted by FKBP5 Basal Expression Levels.

Abstract 1236Poster Board I-258Glucocorticoids (GC) apoptotic effect in chronic lymphocytic leukemia (CLL) cells is known for many years. However, in CLL their use is often confined to their immunosuppressive activity in order to control autoimmune phenomena or as palliation. The fact that GC, particularly dexamethasone (DEX), can overcome p53 mediated resistance to therapy has renewed the interest in the use of GC as therapeutic agents in CLL. GC apoptotic induced cell death mechanism seems to depend on cell type and few studies were performed in CLL. GC increasing importance as apoptotic agent in CLL prompted us to analyze DEX apoptotic activity in CLL cells in order to clarify GC apoptotic mechanisms. For this, peripheral blood samples from 45 patients with CLL were selected for in vitro studies. Patients were analyzed for IGHV mutational status and ZAP-70 expression. Tumour cells were cultured over 24 hours with DEX at 13.25uM and viability was then determined by surface annexin V binding and propidium iodide (PI) staining flow cytometry analysis. To determine early apoptotic signal onset, BIM mRNA GC induced expression was quantified at different time points by quantitative RT-PCR. Genome-wide expression profile of CLL cells was done to discriminate genes involved in DEX apoptotic action.After 24 hours of exposure to therapeutic concentrations of DEX, cell viability was higher in mutated cases (M-CLL) than in unmutated IGHV cases (UM-CLL) (85.6% vs 69.5% in mean, respectively; p=0.000). mRNA BIM expression after 24 hours of treatment with DEX correlated with induced apoptotic cell death (R=0.496; p=0.000). As a consequence, UM-CLL had higher levels of induced mRNA levels of BIM than M-CLL cases (p=0.036). Time course experiments have shown that at 6h after DEX treatment BIM mRNA levels were induced 3 times without influence on cell viability. Genome-wide expression analysis of 12 CLL cases (7 UM-CLL, 5 M-CLL) was done after 6 hours of DEX treatment and was compared to the baseline gene expression. In both groups many genes were up and down regulated by DEX (UM-CLL 3359 genes and M-CLL 1008 genes, p adjusted < 0.01). Analysis of genes involved in the GC pathway revealed that basal mRNA levels of FKBP5, a protein essential to maintain the GC receptor (GR) complex suitable for GC binding, was more expressed in UM-CLL than in M-CLL cases (1.85 times, p= 0.027). Analysis by quantitative RT-PCR performed in 45 CLL patients to validate micro-array data confirmed that at baseline, FKPB5 expression was higher in UM-CLL than M-CLL (0.97 vs. 0.74 arbitrary units, respectively; p=0.042). The same was observed at protein level, WB analysis of FKBP5 basal levels showed that UM-CLL cases expressed more this protein than M-CLL (Fig. 1). In addition to that, genome-wide analysis revealed that GILZ, a glucocorticoid-induced leucine zipper, was differently induced by DEX in the studied groups. GILZ mRNA was less induced in M-CLL cases than in UM-CLL cases (difference fold change=0.52, p=0.0005). These results were also confirmed in 45 CLL cases by quantitative RT-PCR: in M-CLL, GILZ was induced 3.67 times whilst it was induced 5.62 times in UM-CLL cases (p=0.0001). In conclusion, treatment with GC induces more apoptotic cell death in UM-CLL than in M-CLL. As a downstream effect, BIM expression after GC exposure correlates with GC-induced apoptosis. Moreover, GC apoptotic effect in CLL is the result of several cell pathways imbalance as revealed by gene expression analysis. GILZ induction was proved to be necessary for DEX induced apoptosis in other cell types like multiple myeloma cell lines. In CLL, GILZ differential induction was observed at different degrees in GC-responders and non-responders. Finally, FKBP5 expression, upstream effecter of the GC pathway, correlated with cellular effect of GC and can be used to predict GC apoptotic activity in CLL cases. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Bim is the key mediator of glucocorticoid-induced apoptosis and of its potentiation by rapamycin in human myeloma cells

Glucocorticoids are widely used in anti-myeloma therapy and their action is potentiated by rapamycin, a mTOR inhibitor. However, the molecular mechanisms underlying these effects remain poorly characterized. We show here that dexamethasone (Dex)-induced apoptosis in MM.1S and OPM-2 cells is characterized by Bax and Bak conformational changes, ΔΨ m loss, cytochrome c release and caspase-3 activation. Rapamycin, which had minimal cytotoxic effect by itself, strongly potentiated Dex-induced apoptosis. Apoptotic gene expression profiling showed an increase in mRNA levels of Bim in MM.1S cells after Dex treatment and further increases in both cell lines when co-treated with rapamycin. Western blot analysis revealed a moderate increase in Bim protein levels in both MM.1S and OPM-2 cells. Immunoprecipitation experiments revealed that most Bim was complexed to Mcl-1 in untreated cells. Upon treatment with Dex, and specially Dex plus rapamycin, Bim–Mcl-1 complex was disrupted and Bim was found associated to a CHAPS-insoluble fraction. Overexpression of Mcl-1 stabilized Bim–Mcl-1 complexes upon treatment with Dex or Dex + rapamycin and fully prevented apoptosis. Gene silencing of Bim inhibited for the most part Dex-induced apoptosis and, to a large extent, apoptosis induced by Dex plus rapamycin. These results, taken together, indicate that Bim protein is the key mediator of apoptosis induced by Dex and also responsible for the potentiating effect of rapamycin, providing molecular criteria for the use of glucocorticoids combined with mTOR inhibitors in myeloma therapy.

Effect of CD37 small modular immuno-pharmaceutical (SMIP) on direct apoptosis in chronic lymphocytic leukemia cells via transcriptional up-regulation of the BH3 family member BIM

3035 Background: CD37 is a tetraspan transmembrane family protein selectively expressed on normal and transformed B-cells. A novel CD37SMIP was previously demonstrated to mediate superior direct apoptosis and NK-cell mediated killing of chronic lymphocytic leukemia (CLL) and other B-cell malignancies. Methods: Given the superior in vitro apoptosis observed with CD37SMIP treatment and early clinical activity observed in highly refractory CLL patients, we hypothesized that a unique mechanism of cell killing was utilized by CD37SMIP. This was pursued in preclinical studies outlined below. Results: Unlike many other agents utilized to treat CLL, death mediated by CD37SMIP does not depend upon caspase activation. Nonetheless, CD37SMIP treatment of CLL cells promotes time-dependent induction of mitochondrial membrane depolarization, mitochondrial translocation of Bax, and up-regulation of Bim protein. CD37SMIP Bim protein induction occurred concomitantly with an increase in BIM mRNA levels. Electrophoretic mobility shift assay using oligonucleotides of the BIM promoter demonstrated increased protein binding activity in nuclear extracts derived from CD37SMIP treated cells and the physical interaction of FoxO3a transcription factor with the FoxO3a responsive element in the BIM promoter was demonstrated using a “protein pull down” assay and confirmed by chromatin immunoprecipitation assays. Furthermore, CD37SMIP treatment significantly increased BIM promoter regulated luciferase reporter expression in B-CLL cells. Consistent with a primary role of Bim up-regulation in mitochondrial membrane destabilization and apoptosis, transfection of CLL cells with BIM siRNA resulted in inhibition of CD37SMIP-induced mitochondrial membrane depolarization and apoptosis. Conclusions: These studies demonstrate CD37SMIP mediated apoptosis in CLL cells occurs via FoxO3a-dependent transcriptional up-regulation of BIM protein. This distinct mechanism of apoptosis utilized by CD37SMIP contrasts it with other agents used for CLL treatment. Additionally, it provides a mechanism for the promising clinical activity of TRU-016 (humanized CD37SMIP) observed to date in refractory CLL patients. [Table: see text]

Transcription Factors PU.1 and EGR2 Inhibits the Oncogenic Microrna Cluster Mir-17-92 during Macrophage Differentiation

PU.1 (Sfpi1) is an ets family transcription factor required for the proper generation of both myeloid and lymphoid lineages. Distinct nuclear levels of PU.1 are required for macrophage differentiation (DeKoter 2000). MicroRNAs are a novel class of 22nt long non-coding post-transcriptional regulators, associated with differentiation, development and carcinogenesis. To identify miRNAs involved in PU.1 dependent hematopoietic differentiation we used PU.1-null hematopoietic progenitor cells stably expressing PU.1 fused to the estrogen receptor ligand-binding domain inducible by tamoxifen (PUER) (Walsh 2002). PU.1 affected expression approximately 100 mature miRNA. Among them, we have observed that PU.1 downregulates members of miR-17~92 cluster and its paralog miR-106b~25 previously associated with macrophage differentiation, apoptosis and hematologic and other malignancies (Ota 2004, Hayashita 2005, Fontana 2008). During macrophage differentiation miR-17~92 becomes downregulated and its sustained expression is associated with the differentiation block (Fontana 2007). In tamoxifen-stimulated PUER cells, PU.1 efficiently downregulates mature miRNAs of the miR-17~92 (-17.5p, -20a, -92) cluster and its paralog miR-106b~25 (but not miR-106a~363) within 96 hours and in dose dependent manner. PU.1 in the same cells activates expression of Egr2, myeloid transcription factor promoting macrophage transcriptional program a putative 8-mer-seed sequence-containing target of miR-17~92 cluster (predicted by TargetScan). We tested whether PU.1 represses expression of miR-17~92 cluster by inducing Egr2. We demonstrate that ectopic expression of Egr2 in unstimulated PUER cells inhibited expression of miR-17~92 cluster, both at the levels of mature miRs and pri-miRNAs, and induced expression of macrophage differentiation markers (Cd14, Csf1r) coupled with cell cycle arrest. Trichostatin-dependent derepression of miR-17~92 indicated that its expression is regulated at the chromatin level. Chromatin immunoprecipitation revealed specific Egr2 occupancy within the regulatory region upstream of the miR-17~92 cluster. Our data indicate that in differentiating cells, a mechanism exists involving direct repression of the miR-17~92 cluster that in turn has the potential to inhibit Egr2 expression. We have tested this mechanisms in peripheral blood mononuclear cells isolated from acute myeloid leukemia (AML) patients (N=9) where levels of PU.1 and Egr2 are significantly lower that in normal controls. 5 out of 9 AML patients significantly overexpressed miR- 17.5p, miR-20a, miR-92 coinciding with downregulation of its established targets p21 and BIM. Rescue of Egr2 in AML cells (N=2) led to downregulation of miR-17~92 cluster and upregulation of BIM mRNA levels coincident with induction of apoptosis. We conclude that PU.1 regulates transcription of the miR-17~92 cluster by inducing Egr2 and demonstrate this mechanism in differentiating macrophages and its disruption in AML cells.

Effective Induction of Apoptosis in Chronic Myeloid Leukemia CD34+ Cells by the Histone Deacetylase Inhibitor LAQ824 in Combination with Imatinib.

Imatinib mesylate (IM) is highly effective in the treatment of chronic myeloid leukemia (CML). However IM does not eliminate quiescent, primitive CML hematopoietic cells, which persist through treatment and remain a potential source of relapse. Therefore additional interventions are required to more effectively target primitive CML cells. The hydroxamic acid analogue histone deacetylase (HDAC) inhibitors, LAQ824, and LBH589, are reported to induce apoptosis and inhibit cell cycle in CML cell lines and blast crisis (BC) CML cells. Although most pro-apoptotic agents preferentially target dividing cells, HDAC inhibitors are a rare class of drugs reported to induce apoptosis in non-dividing cells. We were therefore interested in investigating whether the HDAC inhibitor LAQ824 (LAQ) could induce apoptosis in CD34+ cells from chronic-phase (CP) CML patients. CML and normal CD34+ cells were cultured with LAQ (10–100nM) alone and in combination with IM (1μM) for 96 hours in growth factor-supplemented medium. Treatment with LAQ (25–100 nM) effectively enhanced Histone H3 acetylation in CML and normal CD34+ cells as detected by Western blotting with an anti-Histone H3 (Lys9/Lys14) antibody. Although LAQ treatment by itself induced significantly less apoptosis in CML compared to normal CD34+ cells, LAQ in combination with IM was highly effective in inducing apoptosis in CML CD34+ cells (11+/−3%, apoptosis with IM alone, 18+/−3% with IM+10 nM LAQ, 22+/−2% with IM+25 nM LAQ, and 32+/−3% with IM+50 nM LAQ824, n=5). Significantly higher levels of apoptosis were seen in CML compared with normal CD34+ cells at lower doses of LAQ (p=0.03 at 10 nM). LAQ combined with IM also resulted in enhanced apoptosis of non-dividing CML CD34+ cells, identified using CFSE labeling, with 43% apoptosis observed in cells treated with 50 nM LAQ [n=5]. Combined LAQ and IM treatment also resulted in significant inhibition of CML progenitor proliferation measured in CFSE assays [n=4] and in the number of CML progenitors measured in methylcellulose progenitor assays [n=5]. In contrast to what has been described for BCR-ABL expressing cell lines and BC CML cells, LAQ treatment did not result in significant change in BCR-ABL levels in CML CD34+ cells on Western blotting. Significant down-regulation of MCL-1, a critical apoptosis regulator in early hematopoietic cells, was observed on Western blotting of CML cells treated with the LAQ and IM combination [n=5]. Levels of other anti-apoptotic proteins BCL-xL and BCL-2 were not affected. MCL-1 inhibition was not observed in normal CD34+ cells [n=4]. In contrast, normal cells treated with LAQ or LAQ and IM demonstrated enhanced levels of the pro-apoptotic protein Bim, but Bim levels were not increased in CML CD34+ cells. Q-PCR analysis revealed changes in MCL-1 and BIM mRNA levels in CML and normal CD34+ cells with LAQ and IM treatment that were consistent with the results of Western blotting. We conclude that treatment with the HDAC inhibitor LAQ in combination with imatinib results in significantly enhanced apoptosis of CML CD34+ cells, including non-dividing cells, compared with IM alone. Different mechanisms appear to be responsible for HDAC induced apoptosis in CML and normal CD34+ cells. Our results provide a strong rationale for future clinical application of HDAC inhibitors to enhance elimination of CML progenitors in combination with BCR-ABL tyrosine kinase inhibitors.

TNF-α Induces Apoptosis Through JNK/Bax-Dependent Pathway in Differentiated, but not Naïve PC12 Cells

Differentiated PC12 cells have been used widely as a model for the analysis of neuronal degeneration. Some evidences showed that differentiated PC12 cells were more sensitive than naïve PC12 against apoptosis stimuli. However, the apoptosis mechanism of both types of PC12 cells was not fully known. In this study, the signaling pathways involved in tumor necrosis factor-α (TNF-α)-induced apoptosis in living differentiated and naïve PC12 cells were investigated using confocal microscope for the first time. Our results showed that during TNF-α-induced apoptosis, Bax translocation to mitochondria and cytochrome C (Cyt c) release from mitochondria were observed in differentiated PC12 cells, but not in naïve PC12 cells. Furthermore, the mRNA levels of bim, c-Jun N-terminal protein kinase 1 and 2 (JNK1 and JNK2) increased noticeably in differentiated PC12 cells. The apoptosis induced by TNF-α was inhibited by Z-IETD-fmk (specific inhibitor of caspase-8) but not SP600125 (specific inhibitor of JNK) in naïve PC12 cells. While in differentiated PC12 cells, the process of apoptosis could only be inhibited effectively by Z-IETD-fmk and SP600125 co-treatment, and SP600125 inhibited the Bax translocation to mitochondria implying that JNK mediated activation of Bax. The experimental data strongly demonstrated that TNF-α induced apoptosis through JNK/Bax-dependent pathway in differentiated, but not naïve PC12 cells.

ER Stress Triggers Apoptosis by Activating BH3-Only Protein Bim

Endoplasmic reticulum (ER) stress caused by misfolded proteins or cytotoxic drugs can kill cells and although activation of this pathway has been implicated in the etiology of certain degenerative disorders its mechanism remains unresolved. Bim, a proapoptotic BH3-only member of the Bcl-2 family is required for initiation of apoptosis induced by cytokine deprivation or certain stress stimuli. Its proapoptotic activity can be regulated by several transcriptional or posttranslational mechanisms, such as ERK-mediated phosphorylation, promoting its ubiquitination and proteasomal degradation. We found that Bim is essential for ER stress-induced apoptosis in a diverse range of cell types both in culture and within the whole animal. ER stress activates Bim through two novel pathways, involving protein phosphatase 2A-mediated dephosphorylation, which prevents its ubiquitination and proteasomal degradation and CHOP-C/EBPalpha-mediated direct transcriptional induction. These results define the molecular mechanisms of ER stress-induced apoptosis and identify targets for therapeutic intervention in ER stress-related diseases.