Interleukin-3 stimulation of mcl-1 gene transcription involves activation of the PU.1 transcription factor through a p38 mitogen-activated protein kinase-dependent pathway

Deregulation of apoptotic proteins by induction of Dendropthae falcata (L.f.) Ettingsh plant extract in breast cancer cells: A proteome-wide analysis

Objectives

The present study evaluated the protein-based analysis to unravel the role and mechanism behind the Dendropthae falcata plant extract treatment in breast cancer cells.

Materials and Methods

The protein sample was extracted from the cancer cells after treatment with the plant extract and subjected to two-dimensional electrophoresis for protein separation. Further, the proteins that were differentially regulated among the samples which were treated and non-treated were selected and processed further for protein identification using a tandem mass spectrometry approach.

Results

Using these strategies, we identified 16 potential candidates which were showing remarkable changes in treated samples. All the candidates were analyzed further for gene ontology analysis, and it was observed that all proteins were involved in multiple pathways pertaining to the carcinogenesis process. Specifically, apoptotic pathway proteins including BAD, BIK, BID, CASP8, MCL1, BCL2, and BAK1 were highly impacted by treatment with D. falcata plant extract. All these protein hits were further taken for validation experiments using RT PCR analysis.

Conclusion

Initiation of these apoptotic proteins by D. falcata plant extract treatment in breast cancer cells shows a positive direction toward nature-based alternative medicine.

The role of post-translational modifications in the regulation of MCL1

Apoptosis is an evolutionarily conserved form of programed cell death (PCD) that has a vital effect on early embryonic development, tissue homeostasis and clearance of damaged cells. Dysregulation of apoptosis can lead to many diseases, such as Alzheimer's disease, cancer, AIDS and heart disease. The anti-apoptotic protein MCL1, a member of the BCL2 family, plays important roles in these physiological and pathological processes. Its high expression is closely related to drug resistances in the treatment of tumor. This review summarizes the structure and function of MCL1, the types of post-translational modifications of MCL1 and their effects on the functions of MCL1, as well as the treatment strategies targeting MCL1 in cancer therapy. The research on the fine regulation of MCL1 will be favorable to the provision of a promising future for the design and screening of MCL1 inhibitors.

Toward Targeting Antiapoptotic MCL-1 for Cancer Therapy

Apoptosis is critical for embryonic development, tissue homeostasis, and the removal of infected or otherwise dangerous cells. It is controlled by three subgroups of the BCL-2 protein family—the BH3-only proteins that initiate cell death; the effectors of cell killing, BAX and BAK; and the antiapoptotic guardians, including MCL-1 and BCL-2. Defects in apoptosis can promote tumorigenesis and render malignant cells refractory to anticancer therapeutics. Activation of cell death by inhibiting antiapoptotic BCL-2 family members has emerged as an attractive strategy for cancer therapy, with the BCL-2 inhibitor venetoclax leading the way. Large-scale cancer genome analyses have revealed frequent amplification of the locus encoding antiapoptotic MCL-1 in human cancers, and functional studies have shown that MCL-1 is essential for the sustained survival and expansion of many types of tumor cells. Structural analysis and medicinal chemistry have led to the development of three distinct small-molecule inhibitors of MCL-1 that are currently undergoing clinical testing.

Ferulic Acid Induces Apoptosis of HeLa and Caski Cervical Carcinoma Cells by Down-Regulating the Phosphatidylinositol 3-Kinase (PI3K)/Akt Signaling Pathway

Background

Ferulic acid is an antioxidant phenolic compound derived from plants, which has effects on cancer cells. This study aimed to investigate the effects of ferulic acid on HeLa and Caski human cervical carcinoma cells and the molecular mechanisms involved.

Material/Methods

HeLa and Caski human cervical carcinoma cells were grown in culture and treated with increasing doses of ferulic acid. The MTT assay was used to evaluate cell viability. Flow cytometry was performed with 4′,6-diamidino-2-phenylindole (DAPI) and Annexin V staining for cell apoptosis. The expression of myeloid leukemia cell differentiation-1 (Mcl-1) protein and MCL-1 mRNA were determined by Western blot and reverse transcription-polymerase chain reaction (RT-PCR).

Results

Ferulic acid significantly reduced HeLa and Caski cell viability in the concentration range of 4–20 μM (P<0.05). Ferulic acid treatment promoted DNA condensation and significantly increased apoptosis in Caski cells (P<0.05). Ferulic acid treatment resulted in the activation of pro-caspase-3, pro-caspase-8, pro-caspase-9, and PARP. The MTT assay showed that ferulic acid did not reduce the viability of Caski cells treated with the caspase inhibitor, z-VAD-fmk. Ferulic acid reduced the levels of Bcl-2 and Mcl-1, and increased the levels of Bax and reactive oxygen species (ROS). In Caski cells, Akt and PI3K phosphorylation were reduced by ferulic acid in a concentration-dependent manner.

Conclusions

The effects of ferulic acid were dose-dependent and resulted in cell cytotoxicity and apoptosis of HeLa and Caski cells, and the PI3K/Akt signaling pathway was down-regulated in Caski cells.

3-Chloroplumbagin Induces Cell Death in Breast Cancer Cells Through MAPK-Mediated Mcl-1 Inhibition

Resistance acquired toward anti-cancer agents is a significant drawback in breast cancer therapy. A key factor contributing to drug resistance is apoptosis suppression associated with the upregulation of anti-apoptotic Bcl-2 family proteins. Specifically, the anti-apoptotic Mcl-1 protein has been shown to play a significant role in drug resistance, making it an important therapeutic target. The present study aimed at determining the antiproliferative activity of 3-chloroplumbagin (ChPL), a naphthoquinone derived from a Dionaea sp., toward breast cancer cells and examining the involvement of Mcl-1 inhibition in ChPL-induced cell death. The results showed that ChPL inhibited breast cancer cell proliferation and induced apoptosis through the intrinsic pathway through down-regulation of anti-apoptotic Bcl-2 family proteins. The induction of apoptosis by ChPL was found to be mediated through MAP kinase signaling inhibition. ChPL inhibited the phosphorylation of MEK and ERK proteins in breast cancer cells, and increased apoptosis induction in cells with reduced ERK expression. Furthermore, ERK silencing decreased the expression of Mcl-1 in ChPL-treated cells. The results of this research indicate that ChPL induces apoptosis in breast cancer cells through MAPK-mediated Mcl-1 inhibition, suggesting further research into its potential in breast cancer treatment.

Immunomodulatory germline variation associated with the development of multiple primary melanoma (MPM)

Multiple primary melanoma (MPM) has been associated with a higher 10-year mortality risk compared to patients with single primary melanoma (SPM). Given that 3–8% of patients with SPM develop additional primary melanomas, new markers predictive of MPM risk are needed. Based on the evidence that the immune system may regulate melanoma progression, we explored whether germline genetic variants controlling the expression of 41 immunomodulatory genes modulate the risk of MPM compared to patients with SPM or healthy controls. By genotyping these 41 variants in 977 melanoma patients, we found that rs2071304, linked to the expression of SPI1, was strongly associated with MPM risk reduction (OR = 0.60; 95% CI = 0.45–0.81; p = 0.0007) when compared to patients with SPM. Furthermore, we showed that rs6695772, a variant affecting expression of BATF3, is also associated with MPM-specific survival (HR = 3.42; 95% CI = 1.57–7.42; p = 0.0019). These findings provide evidence that the genetic variation in immunomodulatory pathways may contribute to the development of secondary primary melanomas and also associates with MPM survival. The study suggests that inherited host immunity may play an important role in MPM development.

Myeloid cell leukemia 1 (MCL-1), an unexpected modulator of protein kinase signaling during invasion

Myeloid cell leukemia-1 (MCL-1), closely related to B-cell lymphoma 2 (BCL-2), has a well-established role in cell survival and has emerged as an important target for cancer therapeutics. We have demonstrated that inhibiting MCL-1 is efficacious in suppressing tumour progression in pre-clinical models of breast cancer and revealed that in addition to its role in cell survival, MCL-1 modulated cellular invasion. Utilizing a MCL-1-specific genetic antagonist, we found two possible mechanisms; firstly MCL-1 directly binds to and alters the phosphorylation of the cytoskeletal remodeling protein, Cofilin, a protein important for cytoskeletal remodeling during invasion, and secondly MCL-1 modulates the levels SRC family kinases (SFKs) and their targets. These data provide evidence that MCL-1 activities are not limited to endpoints of extracellular and intracellular signaling culminating in cell survival as previously thought, but can directly modulate the output of SRC family kinases signaling during cellular invasion. Here we review the pleotropic roles of MCL-1 and discuss the implications of this newly discovered effect on protein kinase signaling for the development of cancer therapeutics.

Identification of Interleukin-1 by Functional Screening as a Key Mediator of Cellular Expansion and Disease Progression in Acute Myeloid Leukemia

Secreted proteins in the bone marrow microenvironment play critical roles in acute myeloid leukemia (AML). Through an ex vivo functional screen of 94 cytokines, we identified that the pro-inflammatory cytokine interleukin-1 (IL-1) elicited profound expansion of myeloid progenitors in ∼67% of AML patients while suppressing the growth of normal progenitors. Levels of IL-1β and IL-1 receptors were increased in AML patients, and silencing of the IL-1 receptor led to significant suppression of clonogenicity and in vivo disease progression. IL-1 promoted AML cell growth by enhancing p38MAPK phosphorylation and promoting secretion of various other growth factors and inflammatory cytokines. Treatment with p38MAPK inhibitors reversed these effects and recovered normal CD34+ cells from IL-1-mediated growth suppression. These results highlight the importance of ex vivo functional screening to identify common and actionable extrinsic pathways in genetically heterogeneous malignancies and provide impetus for clinical development of IL-1/IL1R1/p38MAPK pathway-targeted therapies in AML.

PTBP1 modulation of MCL1 expression regulates cellular apoptosis induced by antitubulin chemotherapeutics

Myeloid cell leukemia sequence 1 (MCL1), an anti-apoptotic BCL2 family protein, is a key regulator of intrinsic apoptosis. Normal cells require strict control over MCL1 expression with aberrant MCL1 expression linked to the emergence of various diseases and chemoresistance. Previous studies have detailed how MCL1 expression is regulated by multiple mechanisms both transcriptionally and translationally. However, characterization of the post-transcriptional regulators of MCL1 mRNA is limited. Polypyrimidine tract binding protein 1 (PTBP1) is a known regulator of post-transcriptional gene expression that can control mRNA splicing, translation, stability and localization. Here we demonstrate that PTBP1 binds to MCL1 mRNA and that knockdown of PTBP1 upregulates MCL1 expression in cancer cells by stabilizing MCL1 mRNA and increasing MCL1 mRNA accumulation in cytoplasm. Further, we show that depletion of PTBP1 protects cancer cells from antitubulin agent-induced apoptosis in a MCL1-dependent manner. Taken together, our findings suggest that PTBP1 is a novel regulator of MCL1 mRNA by which it controls apoptotic response to antitubulin chemotherapeutics.

MicroRNA-29b inhibits migration and proliferation of vascular smooth muscle cells in neointimal formation

The proliferation and migration of smooth muscle cells (SMCs) are considered to be key steps in the progression of atherosclerosis and restenosis. Certain stimuli, such as, interleukin-3 (IL-3) are known to stimulate proliferation and migration in vascular diseases. Meanwhile, microRNAs (miRs) have been revealed as critical modulators of various diseases in which miR-29b is known to regulate cell growth by targeting Mcl-1 and MMP2. However, roles of miR-29b in vascular smooth muscle cells remain almost unknown. We hypothesized that miR-29b may control the proliferation and migration processes induced by IL-3 stimulation by inhibiting its own specific targets in SMCs. MiR-29b significantly suppressed the proliferation and migration of SMCs through the inhibition of the signaling pathway related to Mcl-1 and MMP2. We also found that miR-29b expression levels significantly declined in balloon-injured rat carotid arteries and that the overexpression of miR-29b by local oligonucleotide delivery can inhibit neointimal formation. Consistent with the critical role of miR-29b in vitro, we observed down-regulated expression levels of Mcl-1 and MMP2 from the neointimal region. These results indicate that miR-29b suppressed the proliferation and migration of SMCs, possibly through the inhibition of Mcl-1 and MMP2, and suggest that miR-29b may serve as a useful therapeutic tool to treat cardiovascular diseases such as, atherosclerosis and restenosis.

Epigenetic control of hematopoiesis: the PU.1 chromatin connection

Purine-rich box1 (PU.1) is a transcription factor that not only has a key role in the development of most hematopoietic cell lineages but also in the suppression of leukemia. To exert these functions, PU.1 can cross-talk with multiple different proteins by forming complexes in order to activate or repress transcription. Among its protein partners are chromatin remodelers, DNA methyltransferases, and a number of other transcription factors with important roles in hematopoiesis. While a great deal of knowledge has been acquired about PU.1 function over the years, it was the development of novel genome-wide technologies, which boosted our understanding of how PU.1 acts on the chromatin to drive its repertoire of target genes. This review summarizes current knowledge and ideas of molecular mechanisms by which PU.1 controls hematopoiesis and suppresses leukemia.

Gö6976, a FLT3 kinase inhibitor, exerts potent cytotoxic activity against acute leukemia via inhibition of survivin and MCL-1

Mutations of the FMS-like tyrosine kinase 3 (FLT3) have been reported in about a third of patients with acute myeloid leukemia (AML). The presence of FLT3 mutations confers a poor prognosis. Thus, pharmacological inhibitors of FLT3 are of therapeutic interest for AML. Gö6976 is an indolocarbazole with a similar structural backbone to staurosporine. In the present study, we demonstrated that Gö6976 displays a potent inhibitory activity against recombinant FLT3 using an in vitro kinase assay, with an IC50 value of 0.7nM. Gö6976 markedly inhibited the proliferation of human leukemia cells having FLT3-ITD such as MV4-11 and MOLM13. We also observed that Gö6976 showed minimal toxicity for human normal CD34(+) cells. Gö6976 suppressed the phosphorylation of FLT3 and downstream signaling molecules such as STAT3/5, Erk1/2, and Akt in MV4-11 and MOLM13 cells. Interestingly, induction of apoptosis by Gö6976 was associated with rapid and pronounced down-regulation of the anti-apoptotic protein survivin and MCL-1. Suppression of survivin protein expression by Gö6976 was due to the inhibition of transcription via the suppression of STAT3/5. On the other hand, Gö6976 induced proteasome-mediated degradation of MCL-1. Previously described FLT3 inhibitors such as PKC412 are bound by the human plasma protein, α1-acid glycoprotein, resulting in diminished inhibitory activity against FLT3. In contrast, we found that Gö6976 potently inhibited phosphorylation of FLT3 and exerted cytotoxicity in the presence of human serum. In conclusion, Gö6976 is a potent FLT3 inhibitor that displays a significant antiproliferative activity against leukemia cells with FLT3-ITD through the profound down-regulation of survivin and MCL-1.

Regulation of Mcl-1 by constitutive activation of NF-κB contributes to cell viability in human esophageal squamous cell carcinoma cells

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the most lethal malignancies with a 5-year survival rate less than 15%. Understanding of the molecular mechanisms involved in the pathogenesis of ESCC becomes critical to develop more effective treatments.

METHODS

Mcl-1 expression was measured by reverse transcription (RT)-PCR and Western blotting. Human Mcl-1 promoter activity was evaluated by reporter gene assay. The interactions between DNA and transcription factors were confirmed by electrophoretic mobility shift assay (EMSA) in vitro and by chromatin immunoprecipitation (ChIP) assay in cells.

RESULTS

Four human ESCC cell lines, TE-1, Eca109, KYSE150 and KYSE510, are revealed increased levels of Mcl-1 mRNA and protein compare with HaCaT, an immortal non-tumorigenic cell line. Results of reporter gene assays demonstrate that human Mcl-1 promoter activity is decreased by mutation of kappaB binding site, specific NF-kappaB inhibitor Bay11-7082 or dominant inhibitory molecule DNMIkappaBalpha in TE-1 and KYSE150 cell lines. Mcl-1 protein level is also attenuated by Bay11-7082 treatment or co-transfection of DNMIkappaBalpha in TE-1 and KYSE150 cells. EMSA results indicate that NF-kappaB subunits p50 and p65 bind to human Mcl-1-kappaB probe in vitro. ChIP assay further confirm p50 and p65 directly bind to human Mcl-1 promoter in intact cells, by which regulates Mcl-1 expression and contributes to the viability of TE-1 cells.

CONCLUSIONS

Our data provided evidence that one of the mechanisms of Mcl-1 expression in human ESCC is regulated by the activation of NF-kappaB signaling. The newly identified mechanism might provide a scientific basis for developing effective approaches to treatment human ESCC.

Ionizing radiation-inducible microRNA miR-193a-3p induces apoptosis by directly targeting Mcl-1

The functions of microRNAs (miRNAs) as either oncogenes or tumor suppressors in regulating cancer-related events have been established. We analyzed the alterations in the miRNA expression profile of the glioma cell line U-251 caused by ionizing radiation (IR) by using an miRNA array and identified several miRNAs whose expression was significantly affected by IR. Among the IR-responsive miRNAs, we further examined the function of miR-193a-3p, which exhibited the most significant growth-inhibiting effect. miR-193a-3p was observed to induce apoptosis in both U-251 and HeLa cells. We also demonstrated that miR-193a-3p induces the accumulation of intracellular reactive oxygen species (ROS) and DNA damage as determined by the level of γH2AX and by performing the comet assay. The induction of both apoptosis and DNA damage by miR-193a-3p was blocked by antioxidant treatment, indicating the crucial role of ROS in the action of miR-193a-3p. Among the putative target proteins, the expression of Mcl-1, an anti-apoptotic Bcl-2 family member, decreased because of miR-193a-3p transfection. A reporter assay using a luciferase construct containing the 3'-untranslated region of Mcl-1 confirmed that Mcl-1 is a direct target of miR-193a-3p. Down-regulation of Mcl-1 by siRNA transfection closely mimicked the outcome of miR-193a-3p transfection showing increased ROS, DNA damage, cytochrome c release, and apoptosis. Ectopic expression of Mcl-1 suppressed the pro-apoptotic action of miR-193a-3p, suggesting that Mcl-1 depletion is critical for miR-193a-3p induced apoptosis. Collectively, our results suggest a novel function for miR-193a-3p and its potential application in cancer therapy.

Notch signaling regulates expression of Mcl-1 and apoptosis in PPD-treated macrophages

Macrophages are cellular targets for infection by bacteria and viruses. The fate of infected macrophages plays a key role in determining the outcome of the host immune response. Apoptotic cell death of macrophages is considered to be a protective host defense that eliminates pathogens and infected cells. In this study, we investigated the involvement of Notch signaling in regulating apoptosis in macrophages treated with tuberculin purified protein derivative (PPD). Murine bone marrow-derived macrophages (BMMs) treated with PPD or infected with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) induced upregulation of Notch1. This upregulation correlated well with the upregulation of the anti-apoptotic gene mcl-1 both at the transcriptional and translational levels. Decreased levels of Notch1 and Mcl-1 were observed in BMM treated with PPD when a gamma secretase inhibitor (GSI), which inhibits the processing of Notch receptors, was used. Moreover, silencing Notch1 in the macrophage-like cell line RAW264.7 decreased Mcl-1 protein expression, suggesting that Notch1 is critical for Mcl-1 expression in macrophages. A significant increase in apoptotic cells was observed upon treatment of BMM with PPD in the presence of GSI compared to the vehicle-control treated cells. Finally, analysis of the mcl-1 promoter in humans and mice revealed a conserved potential CSL/RBP-Jκ binding site. The association of Notch1 with the mcl-1 promoter was confirmed by chromatin immunoprecipitation. Taken together, these results indicate that Notch1 inhibits apoptosis of macrophages stimulated with PPD by directly controlling the mcl-1 promoter.

Sorafenib and its derivative SC-49 sensitize hepatocellular carcinoma cells to CS-1008, a humanized anti-TNFRSF10B (DR5) antibody

BACKGROUND AND PURPOSE

Previously, we have shown that sorafenib sensitizes hepatocellular carcinoma (HCC) to apoptosis induced by TNF-related apoptosis-inducing ligand (TNFSF10; TRAIL). Here, we report that sorafenib and SC-49 sensitize HCC cells to CS-1008, a novel anti-human death receptor 5 (TNFRSF10B) antibody.

EXPERIMENTAL APPROACH

HCC cell lines (PLC5, Huh-7, and Hep3B) were treated with CS-1008 and/or sorafenib and analysed in terms of apoptosis and signal transductions.

KEY RESULTS

SC-49 is a sorafenib derivative, which is devoid of kinase inhibitory activity. Both sorafenib and SC-49 down-regulated the phosphorylation of STAT3 at Tyr(705) and subsequently reduced the levels of STAT3-regulated proteins, Mcl-1, survivin and cylcin D1, in CS-1008-treated HCC cells. Knockdown of STAT3 by RNA interference overcame apoptotic resistance to CS-1008 in HCC cells, and ectopic expression of STAT3 in HCC cells abolished the sensitizing effects of sorafenib and SC-49 on CS-1008-induced apoptosis, indicating that inhibition of STAT3 mediates the enhancing effects of these compounds when combined with CS-1008. Importantly, inhibition of SHP-1 by adding a specific SHP-1 inhibitor reduced the effects of SC-49 and CS-1008 on p-STAT3 and apoptosis, whereas co-treatment of CS-1008 with SC-49 increased the activity of SHP-1. These data indicate that the combined effects of CS-1008 and SC-49 on HCC are mediated by SHP-1. Moreover, the combination of CS-1008 and SC-49 inhibited HCC xenograft tumour growth in vivo.

CONCLUSIONS AND IMPLICATIONS

Sorafenib and its derivative SC-49 sensitize HCC cells to the antitumour effects of CS-1008 through SHP-1-dependent inactivation of STAT3.

Contrasting historical and recent gene flow among African buffalo herds in the Caprivi Strip of Namibia

Population genetic structure is often used to infer population connectivity, but genetic structure may largely reflect historical rather than recent processes. We contrasted genetic structure with recent gene-flow estimates among 6 herds of African buffalo (Syncerus caffer) in the Caprivi Strip, Namibia, using 134 individuals genotyped at 10 microsatellite loci. We tested whether historical and recent gene flows were influenced by distance, potential barriers (rivers), or landscape resistance (distance from water). We also tested at what scales individuals were more related than expected by chance. Genetic structure across the Caprivi Strip was weak, indicating that historically, gene flow was strong and was not affected by distance, barriers, or landscape resistance. Our analysis of simulated data suggested that genetic structure would be unlikely to reflect human disturbances in the last 10-20 generations (75-150 years) because of slow predicted rates of genetic drift, but recent gene-flow estimates would be affected. Recent gene-flow estimates were not consistently affected by rivers or distance to water but showed that isolation by distance appears to be developing. Average relatedness estimates among individuals exceeded random expectations only within herds. We conclude that historically, African buffalo moved freely throughout the Caprivi Strip, whereas recent gene flow has been more restricted. Our findings support efforts to maintain the connectivity of buffalo herds across this region and demonstrate the utility of contrasting genetic inferences from different time scales.

T cell lineage commitment: identity and renunciation

Precursors undertaking T cell development shed their access to other pathways in a sequential process that begins before entry into the thymus and continues through many cell cycles afterward. This process involves three levels of regulatory change, in which the cells' intrinsic transcriptional regulatory factors, expression of signaling receptors (e.g., Notch1), and expression of distinct homing receptors separately contribute to confirmation of T cell identity. Each alternative potential has a different underlying molecular basis that is neutralized and then permanently silenced through different mechanisms in early T cell precursors. This regulatory mosaic has notable implications for the hierarchy of relationships linking T lymphocytes to other hematopoietic fates.

The molecular mechanisms of glucocorticoids-mediated neutrophil survival

Neutrophil-dominated inflammation plays an important role in many airway diseases including asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis and cystic fibrosis. In cases of asthma where neutrophil-dominated inflammation is a major contributing factor to the disease, treatment with corticosteroids can be problematic as corticosteroids have been shown to promote neutrophil survival which, in turn, accentuates neutrophilic inflammation. In light of such cases, novel targeted medications must be developed that could control neutrophilic inflammation while still maintaining their antibacterial/anti-fungal properties, thus allowing individuals to maintain effective innate immune responses to invading pathogens. The aim of this review is to describe the molecular mechanisms of neutrophil apoptosis and how these pathways are modulated by glucocorticoids. These new findings are of potential clinical value and provide further insight into treatment of neutrophilic inflammation in lung disease.

Ets-1 mediates upregulation of Mcl-1 downstream of XBP-1 in human melanoma cells upon ER stress

Past studies have shown that upregulation of the anti-apoptotic Bcl-2 family protein Mcl-1 is a major adaptive mechanism of melanoma cells to endoplasmic reticulum (ER) stress, and has an important role in resistance of the cells to apoptosis. In this study, we show that the increase in transcription of Mcl-1 in melanoma cells triggered by pharmacological ER stress inducers is mediated by the transcription factor Ets-1. By incremental deletion analysis of the Mcl-1 promoter, we identified a DNA fragment containing an Ets-1 binding site that is transcriptionally responsive to ER stress. Mutations in the Ets-1 binding site or knockdown of Ets-1 inhibited the increase in Mcl-1, indicating that Ets-1 has a critical role in transcriptional upregulation of Mcl-1. Similar to Mcl-1, Ets-1 was transcriptionally upregulated by ER stress. This was mediated by the IRE1α/XBP-1 branch of the unfolded protein response, as upregulation of Ets-1 was inhibited in melanoma cell lines deficient in IRE1α or XBP-1 established by short hairpin RNA knockdown. Activation of the PI3k/Akt pathway downstream of XBP-1 was also involved, in that inhibition of the pathway blocked upregulation of Ets-1. Inhibition of Ets-1 enhanced ER stress-induced apoptosis in melanoma cell lines and in fresh melanoma isolates, recapitulating the effect of inhibition of Mcl-1. These results reveal a key mechanism by which Mcl-1 is transcriptionally upregulated in melanoma cells by ER stress, and identify Ets-1 as a potential target for inhibition to sensitize melanoma cells to apoptosis.

Molecular and cellular pathobiology of Ehrlichia infection: targets for new therapeutics and immunomodulation strategies

Ehrlichia are small obligately intracellular bacteria in the order Rickettsiales that are transmitted by ticks and associated with emerging life-threatening human zoonoses. Vaccines are not available for human ehrlichiosis, and therapeutic options are limited to a single antibiotic class. New technologies for exploring host-pathogen interactions have yielded recent advances in understanding the molecular interactions between Ehrlichia and the eukaryotic host cell and identified new targets for therapeutic and vaccine development, including those that target pathogen virulence mechanisms or disrupt the processes associated with ehrlichial effector proteins. Animal models have also provided insight into immunopathological mechanisms that contribute significantly to understanding severe disease manifestations, which should lead to the development of immunomodulatory approaches for treating patients nearing or experiencing severe disease states. In this review, we discuss the recent advances in our understanding of molecular and cellular pathobiology and the immunobiology of Ehrlichia infection. We identify new molecular host-pathogen interactions that can be targets of new therapeutics, and discuss prospects for treating the immunological dysregulation during acute infection that leads to life-threatening complications.

CEBPD reverses RB/E2F1-mediated gene repression and participates in HMDB-induced apoptosis of cancer cells

PURPOSE

Recent evidence indicates that a tumor suppressor gene CEBPD (CCAAT/enhancer-binding protein delta) is downregulated in many cancers including cervical cancer, which provides a therapeutic potential associated with its reactivation. However, little is known for CEBPD activators and the effect of reactivation of CEBPD transcription upon anticancer drug treatment. In this study, we identified a novel CEBPD activator, 1-(2-hydroxy-5-methylphenyl)-3-phenyl-1,3-propanedione (HMDB). The purpose of this study is to characterize the mechanism of HMDB-induced CEBPD activation and its potential effect in cancer therapy.

EXPERIMENTAL DESIGN

Methylation-specific PCR assay, reporter assay, and chromatin immunoprecipitation (ChIP) assay were performed to dissect the signaling pathway of HMDB-induced CEBPD transcription. Furthermore, a consequence of HMDB-induced CEBPD expression was linked with E2F1 and retinoblastoma (RB), which discloses the scenario of CEBPD, E2F1, and RB bindings and transcriptional regulation on the promoters of proapoptotic genes, PPARG2 and GADD153. Finally, the anticancer effect of HMDB was examined in xenograft mice.

RESULTS

We demonstrate that CEBPD plays an essential role in HMDB-mediated apoptosis of cancer cells. HMDB up-regulates CEBPD transcription through the p38/CREB pathway, thus leading to transcriptional activation of PPARG2 and GADD153. Furthermore, increased level of CEBPD attenuates E2F1-induced cancer cell proliferation and partially rescues RB/E2F1-mediated repression of PPARG2 and GADD153 transcription. Moreover, HMDB treatment attenuates the growth of A431 xenografts in severe combined immunodeficient mice mice.

CONCLUSIONS

These results clearly demonstrate that HMDB kills cancer cells through activation of CEBPD pathways and suggest that HMDB can serve as a superior chemotherapeutic agent with limited potential for adverse side effects.

The fast-mobility isoform of mouse Mcl-1 is a mitochondrial matrix-localized protein with attenuated anti-apoptotic activity

The full-length pro-survival protein Mcl-1 predominantly resides on the outer membrane of mitochondria. Here, we identified a mitochondrial matrix-localized isoform of Mcl-1 that lacks 33 amino acid residues at the N-terminus which serve both as a mitochondrial targeting and processing signal. Ectopically-expressed Mcl-1 without the N-terminal 33 residues failed to enter the mitochondrial matrix but retained wt-like activities both for interaction with BH3-only proteins and anti-apoptosis. In contrast, the mitochondrial matrix-localized isoform failed to interact with BH3-only proteins and manifested an attenuated anti-apoptotic activity. This study reveals that import of Mcl-1 into the mitochondrial matrix results in the attenuation of Mcl-1's anti-apoptotic function.

Mcl-1; the molecular regulation of protein function

Apoptosis, an essential and basic biological phenomenon, is regulated in a complex manner by a multitude of factors. Myeloid cell leukemia 1 (Mcl-1), an anti-apoptotic member of the B-cell lymphoma 2 (Bcl-2) family of apoptosis-regulating proteins, exemplifies a number of the mechanisms by which a protein's contribution to cell fate may be modified. The N-terminus of Mcl-1 is unique amongst the Bcl-2 family, in that it is rich in experimentally confirmed and putative regulatory residues and motifs. These include sites for ubiquitination, cleavage and phosphorylation, which influence the protein's stability, localisation, dimerization and function. Here we review what is known about the regulation of Mcl-1 expression and function, with particular focus on post-translational modifications and how phosphorylation interconnects the complex molecular control of Mcl-1 with cellular state.

TRAIL-activated stress kinases suppress apoptosis through transcriptional upregulation of MCL-1

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potentially useful anticancer agent with exquisite selectivity for cancer cells. Unfortunately, many cancers show or acquire resistance to TRAIL. In this study we report that TRAIL activates a TGF-beta-activated kinase 1 --> mitogen-activated protein kinase (MAPK) kinase 3 (MKK3)/MKK6 --> p38 pathway in prostate cancer cells that transcriptionally upregulates expression of the antiapoptotic BCL-2 family member MCL-1. TRAIL alone triggered robust formation of the 'death-inducing signaling complex' (DISC), activation of the initiator caspase-8, and truncation of the BH3-only protein BID (tBID). Nevertheless, simultaneous disruption of the p38 MAPK pathway was required to suppress MCL-1 expression, thereby allowing tBID to activate the proapoptotic BCL-2 family member BAK and stimulate mitochondrial outer membrane permeabilization (MOMP). Release of the inhibitor-of-apoptosis (IAP) antagonist, Smac/DIABLO, from the intermembrane space was sufficient to promote TRAIL-induced apoptosis, whereas release of cytochrome c and activation of the apoptosome was dispensable. Even after MOMP, however, mitochondrial-generated reactive oxygen species (ROS) activated a secondary signaling pathway, involving c-Jun N-terminal kinases (JNKs), that similarly upregulated MCL-1 expression and partially rescued some cells from death. Thus, stress kinases activated at distinct steps, before and after mitochondrial injury, mediate TRAIL resistance through maintenance of MCL-1 expression.

A review of post-translational modifications and subcellular localization of Ets transcription factors: possible connection with cancer and involvement in the hypoxic response

Post-translational modifications and subcellular localizations modulate transcription factors, generating a code that is deciphered into an activity. We describe our current understanding of these processes for Ets factors, which have recently been recognized for their importance in various biological processes. We present the global picture for the family, and then focus on particular aspects related to cancer and hypoxia. The analysis of Post-translational modification and cellular localization is only beginning to enter the age of "omic," high content, systems biology. Our snap-shots of particularly active fields point to the directions in which new techniques will be needed, in our search for a more complete description of regulatory pathways.

Deubiquitinase USP9X stabilizes MCL1 and promotes tumour cell survival

MCL1 is essential for the survival of stem and progenitor cells of multiple lineages, and is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases. B- and mantle-cell lymphomas, chronic myeloid leukaemia, and multiple myeloma, however, express abnormally high levels of MCL1, contributing to chemoresistance and disease relapse. The mechanism of MCL1 overexpression in cancer is not well understood. Here we show that the deubiquitinase USP9X stabilizes MCL1 and thereby promotes cell survival. USP9X binds MCL1 and removes the Lys 48-linked polyubiquitin chains that normally mark MCL1 for proteasomal degradation. Increased USP9X expression correlates with increased MCL1 protein in human follicular lymphomas and diffuse large B-cell lymphomas. Moreover, patients with multiple myeloma overexpressing USP9X have a poor prognosis. Knockdown of USP9X increases MCL1 polyubiquitination, which enhances MCL1 turnover and cell killing by the BH3 mimetic ABT-737. These results identify USP9X as a prognostic and therapeutic target, and they show that deubiquitinases may stabilize labile oncoproteins in human malignancies.

Improvement of rituximab efficiency in chronic lymphocytic leukemia by CpG-mediated upregulation of CD20 expression independently of PU.1

Lipopolysaccharide (LPS), CpG-containing phosphothioate oligonucleotides (CpG) and various cytokines impact chronic lymphocytic leukemia (CLL) B cells. For example, they influence cell cycle entry, expression of co-receptors, and CD20. Rituximab (RTX), for which CD20 molecule is the target, proved to be less efficient in CLL than in lymphoma. This is accounted for by a lower CD20 level in the former than in the latter B lymphocytes. CD20 transcription is mediated by four transcription factors, of which only purine-rich box-1 (PU.1) is reduced in CLL. We thus examined the effects of LPS, CpG, tumor necrosis factor-alpha, interferon-alpha, interleukin (IL)-3, IL-4, IL-21, granulocyte macrophage-colony stimulating factor (CSF), and granulocyte-CSF on the transcription of PU.1, and the subsequent expression of CD20. It appeared that CpG was unique in that it raised the membrane expression of CD20 on malignant B cells, owing to a PU.1 independent increase in its gene transcription. Moreover, RTX-induced complement-mediated lysis was also ameliorated. Thus, CpG accelerates the transcription of CD20 independently of PU.1, and thereby improves the efficacy of RTX in CLL.

5-Lipoxygenase inhibitors potentiate 1alpha,25-dihydroxyvitamin D3-induced monocytic differentiation by activating p38 MAPK pathway

The treatment of human promyelocytic leukemia cell lines HL-60, and to some extent NB-4, with 1alpha,25-dihydroxyvitamin D(3) (VD3) induces differentiation toward the monocytic/macrophage lineage, demonstrated by the increased expression of CD11b and CD14, and the production of opsonized zymosan particles (OZP)-stimulated reactive oxygen species (ROS). Moreover, in more sensitive HL-60 cells, increased expression of 5-lipoxygenase (5-LPO), Mcl-1, IkappaB, and c-Jun, accompanied by the activation of p38 MAPK, was detected. These VD3 effects on HL-60 cell differentiation were significantly potentiated by 5-LPO inhibitors MK-886 and AA-861 and were inverted by SB202190 (SB), a p38 MAPK inhibitor. The inhibition of differentiation by SB was demonstrated by a reduction of CD14 expression and by a decrease in OZP-activated ROS production. These results indicated that p38 MAPK pathway is involved in 5-LPO inhibitors-dependent potentiation of VD3-induced monocytic differentiation.

Promoter knock-in mutations reveal a role of Mcl-1 in thymocyte-positive selection and tissue or cell lineage-specific regulation of Mcl-1 expression

We previously demonstrated that IL-3 stimulates transcription of the antiapoptotic gene mcl-1 via two promoter elements designated as the SIE and CRE-2 sites. To further study the functional role of these two DNA elements, mutant mice with targeted mutations of both SIE and CRE-2 sites (SC mutants) were generated. Homozygous SC mutants manifested a markedly reduced level of Mcl-1 in thymus but not in other major organs such as spleen, liver, lung, or heart. Reduced expression of Mcl-1 in SC mutant thymus resulted in attenuated positive selection of double-positive thymocytes into both CD4 and CD8 lineages, a result likely due to reduced survival of SC mutant double-positive thymocytes that were supposed to be positively selected. In contrast, in the peripheral lymphoid organs, only CD8(+) but not CD4(+) T cells were significantly reduced in homozygous SC mutant mice, a result consistent with a more dramatic decrease both of Mcl-1 expression and cell viability in mutant CD8(+) compared with mutant CD4(+) T cells. Impaired T cell development and peripheral CD8(+) lymphopenia in homozygous SC mutant mice were both cell autonomous and could be rescued by enforced expression of human Mcl-1. Together, the promoter-knock-in mouse model generated in this study not only revealed a role of Mcl-1 in thymocyte-positive selection, but also uncovered that Mcl-1 expression is regulated in a tissue or cell lineage-specific manner.

Lipopolysaccharide-dependent interaction between PU.1 and c-Jun determines production of lipocalin-type prostaglandin D synthase and prostaglandin D2 in macrophages

Previously, we reported that expression of lipocalin-prostaglandin D synthase (L-PGDS) is inducible in macrophages and protects from Pseudomonas pneumonia. Here, we investigated the mechanism by which L-PGDS gene expression is induced in macrophages. A promoter analysis of the murine L-PGDS promoter located a binding site of PU.1, a transcription factor essential for macrophage development and inflammatory gene expression. A chromatin immunoprecipitation assay showed that PU.1 bound to the cognate site in the endogenous L-PGDS promoter in response to LPS. Overexpression of PU.1, but not of PU.1(S148A), a mutant inert to casein kinase II (CKII) or NF-kappaB-inducing kinase (NIK), induced L-PGDS in RAW 264.7 cells. Conversely, siRNA silencing of PU.1 expression blunted productions of L-PGDS and prostaglandin D2 (PGD(2)). LPS treatment induced formation of the complex of PU.1 and cJun on the PU.1 site, but inactivation of cJun by treatment with JNK or p38 kinase inhibitor abolished the complex, and suppressed PU.1 transcriptional activity for L-PGDS gene expression. Together, these results show that PU.1, activated by CKII or NIK, cooperates with MAPK-activated cJun to maximally induce L-PGDS expression in macrophages following LPS treatment, and suggest that PU.1 participates in innate immunity through the production of L-PGDS and PGD(2).

p38 MAPK contributes to CD54 expression and the enhancement of phagocytic activity during macrophage development

p38 is a subfamily of the mitogen-activated protein kinase (MAPK) superfamily with four isoforms. It has been well established that p38 plays a central role in the production of inflammatory molecules and is therefore required for the activation of macrophages in response to inflammatory stimuli. However, little is known about the roles of p38 in macrophage development. The difficulty to get mice deficient in multiple p38 isoforms complicates the study of p38 in macrophage development. With the model of bone marrow-derived murine macrophages and highly selective p38alpha/beta inhibitors SB203580 and SB239063, here we report that macrophage colony-stimulating factor (M-CSF) induces p38 activation during macrophage development. Inhibition of p38 activity showed minor effects on macrophage proliferation or survival, and did not block CD14, F4/80 expression. However, p38 inhibitors resulted in a significant reduction in CD54 expression and impaired phagocytic activity. Taken together, our data suggest that p38 contributes to macrophage development.

Translation inhibition during cell cycle arrest and apoptosis: Mcl-1 is a novel target for RNA binding protein CUGBP2

CUGBP2, a translation inhibitor, induces colon cancer cells to undergo apoptosis. Mcl-1, an antiapoptotic Bcl-2 family protein, interferes with mitochondrial activation to inhibit apoptosis. Here, we have determined the effect of CUGBP2 on Mcl-1 expression. We developed a HCUG2 cell line by stably expressing CUGBP2 in the HCT-116 colon cancer cells. HCUG2 cells demonstrate decreased levels of proliferation and increased apoptosis, compared with HCT-116 cells. Flow cytometry analysis demonstrated higher levels of cells in the G(2)-M phase. Western blot analyses demonstrated that there was decreased Bcl-2 and Mcl-1 protein but increased expression of Bax, cyclin B1, and Cdc2. Immunocytochemistry also demonstrated increased levels of cyclin B1 and Cdc2 in the nucleus of HCUG2 cells. However, there was colocalization of phosphorylated histone H3 with transferase-mediated dUTP nick-end labeling (TUNEL). Furthermore, immunostaining for alpha-tubulin demonstrated that there was disorganization of microtubules. These data suggest that CUGBP2 expression in HCUG2 cells induces the cells to undergo apoptosis during the G(2)-M phase of the cell cycle. We next determined the mechanism of CUGBP2-mediated reduction in Mcl-1 expression. Mcl-1 protein, but not Mcl-1 mRNA, was lower in HCUG2 cells, suggesting translation inhibition. CUGBP2 binds to Mcl-1 3'-untranslated region (3'-UTR) both in vitro and in HCUG2 cells. Furthermore, CUGBP2 increased the stability of both endogenous Mcl-1 and luciferase mRNA containing the Mcl-1 3'-UTR. However, luciferase protein expression from the luciferase-Mcl-1 3'-UTR mRNA was suppressed. Taken together, these data demonstrate that CUGBP2 inhibits Mcl-1 expression by inhibiting Mcl-1 mRNA translation, resulting in driving the cells to apoptosis during the G(2) phase of the cell cycle.

NF-kappaB-inducing kinase regulates cyclooxygenase 2 gene expression in macrophages by phosphorylation of PU.1

Selective expression of cyclooxygenase 2 (COX-2) by macrophages could have an important role in the pathobiology of inflammation. We reported a functional synergism between PU.1 and other transcription factors that contributes to COX-2 gene expression in macrophages. PU.1 resides in the nuclear compartment and is activated by phosphorylation to bind to cognate DNA elements containing a 5'-GGAA/T-3' motif, but the involved kinase has not been discovered. We tested the hypothesis that NF-kappaB-inducing kinase (NIK) regulates COX-2 gene expression in macrophages through inducible phosphorylation of PU.1. Our initial experiments showed an in vitro protein-protein binding interaction between myc-NIK and GST-PU.1. Purified myc-NIK had a strong in vitro kinase activity for purified GST-PU.1, and this activity and production of COX-2 protein is blocked by treatment with a nonspecific kinase inhibitor, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. We used short interfering RNA to develop a stable NIK knockdown macrophage cell line that had an approximately 50% decrease in COX-2 protein production and decreased generation of PGD(2), and this was correlated with decreased binding of activated PU.1 to the COX-2 promoter in response to treatment with endotoxin. These findings suggest a novel role for NIK in mediating COX-2 gene expression in endotoxin-treated macrophages by a mechanism that involves phosphorylation of PU.1.

Identification of adiponectin as a novel hemopoietic stem cell growth factor

The hemopoietic microenvironment consists of a diverse repertoire of cells capable of providing signals that influence hemopoietic stem cell function. Although the role of osteoblasts and vascular endothelial cells has recently been characterized, the function of the most abundant cell type in the bone marrow, the adipocyte, is less defined. Given the emergence of a growing number of adipokines, it is possible that these factors may also play a role in regulating hematopoiesis. Here, we investigated the role of adiponectin, a secreted molecule derived from adipocytes, in hemopoietic stem cell (HSC) function. We show that adiponectin is expressed by components of the HSC niche and its receptors AdipoR1 and AdipoR2 are expressed by HSCs. At a functional level, adiponectin influences HSCs by increasing their proliferation, while retaining the cells in a functionally immature state as determined by in vitro and in vivo assays. We also demonstrate that adiponectin signaling is required for optimal HSC proliferation both in vitro and in long term hemopoietic reconstitution in vivo. Finally we show that adiponectin stimulation activates p38 MAPK, and that inhibition of this pathway abrogates adiponectin's proliferative effect on HSCs. These studies collectively identify adiponectin as a novel regulator of HSC function and suggest that it acts through a p38 dependent pathway.

Serine 64 phosphorylation enhances the antiapoptotic function of Mcl-1

Mcl-1 is an antiapoptotic Bcl-2 family member that is highly regulated and when dysregulated contributes to cancer. The Mcl-1 protein is phosphorylated at multiple sites in response to different signaling events. Phosphorylations at Thr163 (by ERK) and Ser159 (by glycogen-synthase kinase 3beta) have recently been shown to slow and enhance, respectively, Mcl-1 protein turnover. Phosphorylation is also known to be stimulated at other, as-yet uncharacterized sites in the G2/M phase of the cell cycle. Using an S peptide-tagged Mcl-1 T163A mutant, Ser64 was identified as a novel Mcl-1 phosphorylation site by mass spectrometry. Immunoblotting demonstrated that phosphorylation at this site was maximal in cells in G2/M phase, was enhanced by tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) treatment, was blocked by inhibitors of CDK (but not ERK or glycogen-synthase kinase 3beta), and was stimulated in vitro by CDK 1, CDK2, and JNK1. The half-life of a nonphosphorylatable S64A Mcl-1 mutant was indistinguishable from that of the wild type polypeptide. In contrast, this mutant failed to protect cells from TRAIL-mediated apoptosis, whereas reconstitution with the phosphomimetic S64E Mcl-1 mutant rendered cells TRAIL-resistant. This anti-apoptotic phenotype of the S64E Mcl-1 mutant was also associated with enhanced binding to the proapoptotic proteins Bim, Noxa, and Bak. A pharmacological CDK inhibitor that reduced Ser64 phosphorylation also sensitized cells to TRAIL cytotoxicity. Collectively, these observations not only identify G2/M-associated phosphorylation at Ser64 as a critical determinant of the antiapoptotic activity of Mcl-1 but also elucidate a novel mechanism by which CDK1/2 inhibitors can enhance the effectiveness of the cytotoxic cytokine TRAIL.

Ebola virus-like particle-induced activation of NF-kappaB and Erk signaling in human dendritic cells requires the glycoprotein mucin domain

Dendritic cells (DCs), important early targets of Ebola virus (EBOV) infection in vivo, are activated by Ebola virus-like particles (VLPs). To better understand this phenomenon, we have systematically assessed the response of DCs to VLPs of different compositions. VLPs containing the viral matrix protein (VP40) and the viral glycoprotein (GP), were found to induce a proinflammatory response highly similar to a prototypical DC activator, LPS. This response included the production of several proinflammatory cytokines, activation of numerous transcription factors including NF-kappaB, the functional importance of which was demonstrated by employing inhibitors of NF-kappaB activation, and activation of ERK1/2 MAP kinase. In contrast, VLPs constituted with a mutant GP lacking the heavily glycosylated mucin domain showed impaired NF-kappaB and Erk activation and induced less DC cytokine production. We conclude that the GP mucin domain is required for VLPs to stimulate human dendritic cells through NF-kappaB and MAPK signaling pathways.

How the Bcl-2 family of proteins interact to regulate apoptosis

Commitment of cells to apoptosis is governed largely by protein-protein interactions between members of the Bcl-2 protein family. Its three sub-families have distinct roles: the BH3-only proteins trigger apoptosis by binding via their BH3 domain to pro-survival relatives, while the pro-apoptotic Bax and Bak have an essential downstream role involving disruption of organellar membranes and induction of caspase activation. The BH3-only proteins act as damage sensors, held inert until their activation by stress signals. Once activated, they were thought to bind promiscuously to pro-survival protein targets but unexpected selectivity has recently emerged from analysis of their interactions. Some BH3-only proteins also bind to Bax and Bak. Whether Bax and Bak are activated directly by these BH3-only proteins, or indirectly as a consequence of BH3-only proteins neutralizing their pro-survival targets is the subject of intense debate. Regardless of this, a detailed understanding of the interactions between family members, which are often selective, has notable implications for designing anti-cancer drugs to target the Bcl-2 family.

Inducer-and cell type-specific regulation of antiapoptotic MCL1 in myeloid leukemia and multiple myeloma cells exposed to differentiation-inducing or microtubule-disrupting agents

The antiapoptotic BCL2 family member MCL1 is rapidly upregulated upon exposure of ML-1 myeloid leukemia cells to either differentiation-inducing phorbol 12'-myristate 13'-acetate (PMA) or chemotherapeutic microtubule disrupting agents (MTDAs). This report examined how signaling for MCL1 upregulation is coupled to these two different phenotypic changes, and tested for upregulation in other hematopoietic cancers. With PMA, ERK stimulated MCL1 mRNA expression and ML-1 cell differentiation, and ERK additionally stabilized expression of the MCL1 protein. However, with MTDAs, transient ERK and ensuing JNK activation contributed to initial MCL1 upregulation and viability-retention, but sustained JNK activation eventually resulted in cell death. MCL1 was upregulated by PMA in THP-1 and U937 myeloid leukemia cells, but by MTDAs only in THP-1 cells. MCL1 expression was constitutively elevated in multiple myeloma cell lines, and was not affected by PMA/ERK or MTDAs. Thus, MCL1 expression level and sensitivity to regulation are important considerations in selecting approaches for targeting this antiapoptotic gene product to kill cancer cells.

PU.1 phosphorylation correlates with hydroquinone-induced alterations in myeloid differentiation and cytokine-dependent clonogenic response in human CD34+ hematopoietic progenitor cells

The transcriptional regulatory factor PU.1 is important for the regulation of a diverse group of hematopoietic and myeloid genes. Posttranslational phosphorylation of PU.1 has been demonstrated in the regulation of a variety of promoters in normal cells. In leukemia cells, differing patterns of PU.1 phosphorylation have been described among acute myelogenous leukemia (AML) subtypes. Therefore, we hypothesized that modulation of PU.1-dependent gene expression might be a molecular mediator of alterations in myeloid cell growth and differentiation that have been demonstrated to be early events in benzene-induced leukemogenesis. We found that freshly isolated human CD34(+) hematopoietic progenitor cells (HPC) exhibit multiple PU.1-DNA binding species that represent PU.1 proteins in varying degrees of phosphorylation states as determined by phosphatase treatment in combination with electrophoretic mobility shift assay (EMSA). Maturation of granulocyte and monocyte lineages is also accompanied by distinct changes in PU.1-DNA binding patterns. Experiments reveal that increasing doses of the benzene metabolite, hydroquinone (HQ) induce a time-and dose-dependent alteration in the pattern of PU.1-DNA binding in cultured human CD34(+) cells, corresponding to hyperphosphorylation of the PU.1 protein. HQ-induced alterations in PU.1-DNA binding are concomitant with a sustained immature CD34(+) phenotype and cytokine-dependent enhanced clonogenic activity in cultured human HPC. These results suggest that HQ induces a dysregulation in the external signals modulating PU.1 protein phosphorylation and this dysregulation may be an early event in the generation of benzene-induced AML.

The JNK are important for development and survival of macrophages

We report in this study that activation of the JNK by the growth factor, CSF-1 is critical for macrophage development, proliferation, and survival. Inhibition of JNK with two distinct classes of inhibitors, the pharmacological agent SP600125, or the peptide D-JNKI1 resulted in cell cycle inhibition with an arrest at the G(2)/M transition and subsequent apoptosis. JNK inhibition resulted in decreased expression of CSF-1R (c-fms) and Bcl-x(L) mRNA in mature macrophages and repressed CSF-1-dependent differentiation of bone marrow cells to macrophages. Macrophage sensitivity to JNK inhibitors may be linked to phosphorylation of the PU.1 transcription factor. Inhibition of JNK disrupted PU.1 binding to an element in the c-fms gene promoter and decreased promoter activity. Promoter activity could be restored by overexpression of PU.1. A comparison of expression profiles of macrophages with 22 other tissue types showed that genes that signal JNK activation downstream of tyrosine kinase receptors, such as focal adhesion kinase, Nck-interacting kinase, and Rac1 and scaffold proteins are highly expressed in macrophages relative to other tissues. This pattern of expression may underlie the novel role of JNK in macrophages.

Immune cell-specific amplification of interferon signaling by the IRF-4/8-PU.1 complex

Both type I interferon (IFN-alpha/beta) and type II IFN (IFN-gamma) exert many functions that are restricted to immune cells. Thus, they play critical roles in innate and adaptive immunity. IFN regulatory factor-4 (IRF-4) and IRF-8 (formerly PU.1 interaction partner [Pip] and IFN consensus sequence binding domain [ICSBP], respectively) are immune cell-specific members of the IRF family that regulate the development of myeloid, lymphoid, and dendritic cells. They form a heterodimeric complex with another immune cell-specific transcription factor PU.1-Spi-1 and regulate transcription of genes in the immune system. This review describes the role of the IRF-8-PU.1 complex in modulating IFN signaling in an immune cell-specific manner. Our studies revealed that some but not all IFN-gamma-inducible genes carry an IFN-gamma activation site (GAS) element that contains a binding site for the IRF- 8-PU.1 complex. The IRF-8-PU.1 complex can take part in GAS-mediated transcription and amplify expression of IFN-gamma-responsive genes initiated by Stat1 in macrophages. Similarly, some but not all IFN-alpha/beta-responsive genes are shown to carry an IFN-stimulated response element (ISRE) that contains an IRF-8-PU.1 binding site. The participation of IRF-8-PU.1 in ISRE-mediated transcription results in the augmentation of IFN-stimulated gene factor 3 (ISGF3)-induced transcription in macrophages. Thus, GAS and ISRE elements, classically defined as universal IFN-alpha/beta and IFN-gamma response sequences, are not the same, and some harbor an embedded motif for IRF- 8-PU.1 binding that functions only in immune cells. Accordingly, the IRF-8-PU.1complex provides secondary IFN signaling pathways unique to the immune system. Collectively, the contribution of IRF-8 and PU.1 to IFN-regulated gene expression may in part account for immune cell-specific functions of IFNs.

Mcl-1: a highly regulated cell death and survival controller

Mcl-1 is one member of the Bcl-2 family that has a very short protein half-life. Since its identification in 1993, a great number of studies have implicated that Mcl-1 plays an important role in various cell survival pathways. However, not until recently did the molecular mechanism by which Mcl-1 antagonizes apoptosis have begun to be elucidated. Mcl-1 is rapidly degraded in response to cell death signals and is immediately re-induced by survival stimuli. These results indicate that Mcl-1 plays an apical role in many cell death and survival regulatory programs.

The interleukin-1beta gene is transcribed from a poised promoter architecture in monocytes

Cytokine transcription is usually regulated by transcription factor binding and chromatin remodeling following an inducing signal. By contrast, these data showed the interleukin (IL)-1beta promoter assembles into a "poised" structure, as evidenced by nuclease accessibility and loss of core histones immediately surrounding the transcription start site. Strikingly, these properties do not change upon transcriptional activation by lipopolysaccharide. Furthermore, association of two key transcriptional activators, PU.1 and C/EBPbeta, is robust pre- and post-stimulation indicating the IL-1beta promoter is packaged into a nontranscribed but poised promoter architecture in cells capable of rapidly inducing IL-1beta. Monocyte stimulation causes recruitment of a third factor, IRF-4, to the IL-1beta enhancer. PU.1 phosphorylation at a CK2 kinase consensus element is required for this recruitment. We showed that CK2 phosphorylates PU.1, CK2 inhibitors abrogate IL-1beta induction, and CK2 inducibly associates with the IL-1beta enhancer. Taken together, these data indicate a novel two-step mechanism for IL-1beta transcription: 1) formation of a poised chromatin architecture, and 2) phosphorylation of an enhancer-bound factor that recruits other activators. We propose that this poised structure may generally characterize rapidly activated genes.

Transcription Factors Mediating Interleukin‐3 Survival Signals

Interleukin-3 (IL-3) is one of the major hematopoietic cytokines that regulate the survival of hematopoietic cells of various lineages. Although the mechanism underlying the survival effect of IL-3 has been investigated intensively for more than a decade, our knowledge of the survival-signaling network remains incomplete. Binding of IL-3 to its cognate receptors initiates rapid tyrosine phosphorylation of Janus kinases (JAKs) and of signal transducer and activator of transcription (STAT) proteins, as well as activation of the phosphatidylinositol-3 kinase (PI-3K)/Akt and Ras/Raf/MAPK kinase (MEK)/mitogen-activated protein kinase (MAPK) pathways. These signals culminate in induction of a constellation of antiapoptotic genes and prevent cell death from occurring. Thus IL-3 signaling has substantial effects on kinase activation and gene transcription. Previous articles have summarized the roles of these kinase pathways in cell proliferation and survival. In this chapter, we will focus on the role of several newly characterized transcriptional factors, which are targets of these initial kinase cascades and bridge the gap between kinases and survival effector genes, in transducing the IL-3 survival signal. The biological significance of the existence of these multiple survival-specific transcription pathways will also be discussed.

Cytokine-induced myeloid differentiation is dependent on activation of the MEK/ERK pathway

The intracellular signaling pathways that mediate cytokine-induced granulocytic and monocytic differentiation are incompletely understood. In this study, we examined the importance of the MEK/ERK signal transduction pathway in granulocyte-colony stimulating factor (G-CSF)-induced granulocytic differentiation of murine 32 Dc l3 cells, and in interleukin-6 (IL-6)-induced monocytic differentiation of murine M1 cells. Induction of granulocytic differentiation with G-CSF, or monocytic differentiation with IL-6, led to rapid and sustained activation of the MEK-1/-2 and ERK-1/-2 enzymes. Inhibition of the MEK/ERK pathway by pretreatment with the MEK inhibitor U 0126 dramatically attenuated G-CSF-induced granulocytic differentiation and IL-6-induced monocytic differentiation. Inhibition of MEK/ERK signaling also significantly reduced cytokine-induced DNA binding activities of STAT 3 and PU.1, transcription factors that have been implicated in myeloid differentiation. Additionally, interleukin-3, which inhibits G-CSF-induced differentiation of 32 Dc l3 cells, also inhibited the ability of G-CSF to stimulate prolonged MEK/ERK activation. Thus, the opposing actions of different hematopoietic cytokines on myeloid progenitors may be mediated at the level of MEK/ERK activation. Taken together, these studies demonstrate an important requirement for MEK/ERK activation during cytokine-induced granulocytic and monocytic differentiation.

Differential involvement of PU.1 and Id2 downstream of TGF-beta1 during Langerhans-cell commitment

Langerhans cells (LCs) are highly abundant dendritic cells (DCs) in epidermal and mucosal tissues. The transcription factors PU.1 and Id2 have been implicated as positive regulators of LC development from hematopoietic progenitor cells. LC differentiation from progenitors is absolutely dependent on transforming growth factor beta 1 (TGF-beta1) in vitro as well as in vivo; however, downstream mechanisms are poorly defined. We found that both PU.1 and Id2 are induced by TGF-beta1 in human CD34+ monocyte/LC (M/LC) progenitor cells, and that neither ectopic PU.1 or Id2 alone, nor both together, could replace TGF-beta1 in its instructive function on LC commitment. However, both factors critically contributed to LC differentiation by acting at 2 distinct intersection points. Ectopic PU.1 strongly enhanced TGF-beta1-dependent LC development. Additionally, Notch-induced generation of interstitial-type DCs was associated with PU.1 up-regulation. Thus, PU.1 is generally increased during myeloid DC development. Ectopic Id2 inhibits the acquisition of early monocytic characteristics by cells generated in the absence of TGF-beta1 and also inhibits monocyte induction by alternative stimuli. Since TGF-beta1 represses a default monocyte pathway of common progenitor cells, PU.1 and Id2 seem to modulate lineage options of M/LC precursors, downstream of TGF-beta1.

Impaired repressor activity and biological functions of PU.1 in MEL cells induced by mutations in the acetylation motifs within the ETS domain

PU.1, a hematopoietic Ets transcription factor, is required for development of the lymphoid and myeloid lineages. We have previously shown that PU.1 functions as both a transcriptional activator and repressor through complex formation with CBP/p300 and HDAC1/mSin3A/MeCP2, respectively. To determine whether modification of PU.1 is responsible for switching its association between co-activators and co-repressors, we examined whether acetylation regulates the physical and functional activities of PU.1. PU.1 was acetylated in vivo and its repressor activity was reduced when the putative acetylation motifs in the Ets domain were mutated. The mutant cooperated with CBP similar to wild type PU.1, but insufficiently with GATA-1 and mSin3A. Whereas overexpression of wild type PU.1 induced differentiation block, growth inhibition, and apoptotic cell death in MEL erythroleukemia cells as we reported previously, overexpression of the mutant-acetylation motif PU.1 did not. Taken together, our data suggest that acetylation might regulate the biological functions of PU.1 in erythroid cells.