Transcriptional regulation of Fas gene expression by GA-binding protein and AP-1 in T cell antigen receptor.CD3 complex-stimulated T cells

E2f2 Attenuates Apoptosis of Activated T Lymphocytes and Protects from Immune-Mediated Injury through Repression of Fas and FasL

Targeted disruption of E2f2 in mice causes T-cell hyperactivation and a disproportionate cell cycle entry upon stimulation. However, E2f2^−/− mice do not develop a lymphoproliferative condition. We report that E2f2 plays a Fas-dependent anti-apoptotic function in vitro and in vivo. TCR-stimulated murine E2f2^−/− T cells overexpress the proapoptotic genes Fas and FasL and exhibit enhanced apoptosis, which is prevented by treatment with neutralizing anti-FasL antibodies. p53 pathway is activated in TCR-stimulated E2f2^−/− lymphocytes, but targeted disruption of p53 in E2f2^−/− mice does not abrogate Fas/FasL expression or apoptosis, implying a p53-independent apoptotic mechanism. We show that E2f2 is recruited to Fas and FasL gene promoters to repress their expression. in vivo, E2f2^−/− mice are prone to develop immune-mediated liver injury owing to an aberrant lymphoid Fas/FasL activation. Taken together, our results suggest that E2f2-dependent inhibition of Fas/FasL pathway may play a direct role in limiting the development of immune-mediated pathologies.

Analysis of DNA methylation in chondrocytes in rats with knee osteoarthritis

BACKGROUND

Knee osteoarthritis (KOA) is a degenerative knee disease commonly found in the ageing population. DNA methylation works with histone acetylation to participate in aging. Alterations of DNA methylation may involve the joint chondrocyte degeneration in KOA. The aim of this study is to detect DNA methylation changes in chondrocytes of rats with KOA.

METHODS

The rat KOA model was established with the Hulth method (n = 10), while rats receiving sham operation served as the control (n = 10). At 16 weeks after modeling, the knee joint tissue was collected from half of the rats in each group for Micro-CT scanning, Haematoxylin& Eosin (HE) staining, ABH/OG staining, immunohistochemistry for Bax, Bcl-2 and Fas, and TUNNEL staining. Meanwhile, the articular cartilage was collected from the other half to detect promoter methylation in target genes with the MethylTarget approach.

RESULTS

Micro-CT scanning, HE staining, ABH/OG staining, immunohistochemistry, and TUNNEL staining all showed more severe cartilage injury in the KOA group than in the control group, indicating successful establishment of KOA model. The methylation rate in the KOA group was significantly decreased for C/ebpα-2 (within a CpG island -452 bp to the initiation codon on chromosome 1 91,363,511), Cdk2 (within a CpG island -55 bp to the initiation codon on chromosome 7 3,132,362), Bak1 (within a CpG island 6452 bp to the initiation codon on chromosome 20 5,622,277), and Fas (within a CpG island on the entire chromosome 1 gene), compared with the sham group (P = 0.005, 0.008, 0.022 and 0.027, respectively).

CONCLUSION

The chondrocyte apoptosis and significantly reduced methylation levels of C/ebpα-2, Cdk2, Bak1, and Fas may participate in the pathogenesis of KOA. However, the exact mechanisms remain to be determined.

Fas signal promotes the immunosuppressive function of regulatory dendritic cells via the ERK/β-catenin pathway

Dendritic cells (DCs) play important roles in the initiation of immune response and also in the maintenance of immune tolerance. Now, many kinds of regulatory DCs with different phenotypes have been identified to suppress immune response and contribute to the control of autoimmune diseases. However, the mechanisms by which regulatory DCs can be regulated to exert the immunosuppressive function in the immune microenvironment remain to be fully investigated. In addition, how T cells, once activated, can feedback affect the function of regulatory DCs during immune response needs to be further identified. We previously identified a unique subset of CD11b(hi)Ia(low) regulatory DCs, differentiated from mature DCs or hematopoietic stem cells under a stromal microenvironment in spleen and liver, which can negatively regulate immune response in a feedback way. Here, we show that CD11b(hi)Ia(low) regulatory DCs expressed high level of Fas, and endothelial stromal cell-derived TGF-β could induce high expression of Fas on regulatory DCs via ERK activation. Fas ligation could promote regulatory DCs to inhibit CD4(+) T cell proliferation more significantly. Furthermore, Fas ligation preferentially induced regulatory DCs to produce IL-10 and IP-10 via ERK-mediated inactivation of GSK-3 and subsequent up-regulation of β-catenin. Interestingly, activated T cells could promote regulatory DCs to secrete more IL-10 and IP-10 partially through FasL. Therefore, our results demonstrate that Fas signal, at least from the activated T cells, can promote the immunosuppressive function of Fas-expressing regulatory DCs, providing a new manner for the regulatory DCs to regulate adaptive immunity.

A unique role for ITK in survival of invariant NKT cells associated with the p53-dependent pathway in mice

Invariant NKT (iNKT) cells play important roles in the immune response. ITK and TXK/RLK are Tec family kinases that are expressed in iNKT cells; the expression level of ITK is ∼7-fold higher than that of TXK. Itk(-/-) mice have reduced iNKT cell frequency and numbers, with defects in development and cytokine secretion that are exacerbated in Itk/Txk double-knockout mice. In contrast, there is no iNKT cell defect in Txk(-/-) mice. To determine whether ITK and TXK play distinct roles in iNKT cell development and function, we examined mice that overexpress TXK in T cells at levels similar to Itk. Overexpression of TXK rescues the maturation and cytokine secretion of Itk(-/-) iNKT cells, as well as altered expression of transcription factors T-bet, eomesodermin, and PLZF. In contrast, the increased apoptosis observed in Itk(-/-) splenic iNKT cells is not affected by TXK overexpression, likely due to the lack of effect on the elevated expression of p53 regulated proapoptotic pathways Fas, Bax, and Bad in those cells. Supporting this idea, p53(-/-) and Bax(-/-) mice have increased splenic iNKT cells. Our results suggest that TXK plays an overlapping role with ITK in iNKT cell development and function but that ITK also has a unique function in the survival of iNKT cells, likely via a p53-dependent pathway.

[Biological functions of the duplicated GGAA-motifs in various human promoter regions]

Transcription is one of the most fundamental cellular functions and is an enzyme-complex mediated reaction that converts DNA sequences into mRNA. TATA-box is known to be an important motif for transcription. However, there are majority of promoters that have no TATA-box. They are called as TATA-less promoters and possess other elements that determine the transcription start site (TSS) of the genes. Multiple protein factors including ETS family proteins are known to recognize and bind to the GGAA containing sequences. In addition, it has been reported that the ETS binding motifs play important roles in regulation of various promoters. Here, we propose that the duplication and multiplication of the GGAA motifs are responsible for the initiation of transcription from TATA-less promoters.

Structural alterations of the FAS gene in cutaneous T-cell lymphoma (CTCL)

FAS (TNF receptor superfamily member 6, also known as CD95) plays a major role in T-cell apoptosis and is often dysregulated in CTCL. We searched for structural alterations of the FAS gene with the potential to affect its function. Although several heterozygous FAS promoter single nucleotide polymorphisms (SNPs) were detected, the only homozygous one was the -671 GG SNP present in 24/80 CTCL cases (30%). This SNP maps to an interferon response element activated by STAT-1. EMSA and supershift EMSA showed decreased CTCL nuclear protein/STAT-1 binding to oligonucleotides bearing this SNP. Luciferase reporters showed significantly less interferon-alfa responsive expression by FAS promoter constructs containing this SNP in multiple CTCL lines. Finally, FAS was upregulated by interferon-alfa in wildtype CTCL cells but not those bearing the -671 GG SNP. These findings indicate that many CTCL patients harbor the homozygous FAS promoter -671 GG SNP capable of blunting its response to interferon. This may have implications for CTCL pathogenesis, racial incidence and the response of patients to interferon-alfa therapy. In contrast, functionally significant mutations in FAS coding sequences were detected uncommonly. Among CTCL lines with the potential to serve as models of FAS regulation, FAS-high MyLa had both FAS alleles, FAS-low HH was FAS-hemizygous and FAS-negative SeAx was FAS-null.

The possible functions of duplicated ets (GGAA) motifs located near transcription start sites of various human genes

Transcription is one of the most fundamental nuclear functions and is an enzyme complex-mediated reaction that converts DNA sequences into mRNA. Analyzing DNA sequences of 5′-flanking regions of several human genes that respond to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in HL-60 cells, we have identified that the ets (GGAA) motifs are duplicated, overlapped, or clustered within a 500-bp distance from the most 5′-upstream region of the cDNA. Multiple protein factors including Ets family proteins are known to recognize and bind to the GGAA containing sequences. In addition, it has been reported that the ets motifs play important roles in regulation of various promoters. Here, we propose a molecular mechanism, defined by the presence of duplication and multiplication of the GGAA motifs, that is responsible for the initiation of transcription of several genes and for the recruitment of binding proteins to the transcription start site (TSS) of TATA-less promoters.

Induction of heparanase-1 expression by mutant B-Raf kinase: role of GA binding protein in heparanase-1 promoter activation

Heparanase-1 (HPR1), an endoglycosidase that specifically degrades heparan sulfate (HS) proteoglycans, is overexpressed in a variety of malignancies. Our present study sought to determine whether oncogene BRAF and RAS mutations lead to increased HPR1 expression. Reverse transcription-polymerase chain reaction analysis revealed that HPR1 gene expression was increased in HEK293 cells transiently transfected with a mutant BRAF or RAS gene. Flow cytometric analysis revealed that B-Raf activation led to loss of the cell surface HS, which could be blocked by two HPR1 inhibitors: heparin and PI-88. Cotransfection of a BRAF or RAS mutant gene with HPR1 promoter-driven luciferase reporters increased luciferase reporter gene expression in HEK293 cells. Knockdown of BRAF expression in a BRAF-mutated KAT-10 tumor cell line led to the suppression of HPR1 gene expression, subsequently leading to increased cell surface HS levels. Truncational and mutational analyses of the HPR1 promoter revealed that the Ets-relevant elements in the HPR1 promoter were critical for BRAF activation-induced HPR1 expression. Luciferase reporter gene expression driven by a four-copy GA binding protein (GABP) binding site was significantly lower in BRAF siRNA-transfected KAT-10 cells than in the control siRNA-transfected cells. We further showed that BRAF knockdown led to suppression of the expression of the GABPβ, an Ets family transcription factor involved in regulating HPR1 promoter activity. Taken together, our study suggests that B-Raf kinase activation plays an important role in regulating HPR1 expression. Increased HPR1 expression may contribute to the aggressive behavior of BRAF-mutated cancer.

Creation of the two isoforms of rodent NKG2D was driven by a B1 retrotransposon insertion

The mouse gene for the natural killer (NK) cell-activating receptor Nkg2d produces two protein isoforms, NKG2D-S and NKG2D-L, which differ by 13 amino acids at the N-terminus and have different signalling capabilities. These two isoforms are produced through differential splicing, but their regulation has not been investigated. In this study, we show that rat Nkg2d has the same splicing pattern as that of the mouse, and we mapped transcriptional start sites in both species. We found that the splice forms arise from alternative promoters and that the NKG2D-L promoter is derived from a rodent B1 retrotransposon that inserted before mouse–rat divergence. This B1 insertion is associated with loss of a nearby splice acceptor site that subsequently allowed creation of the short NKG2D isoform found in mouse but not human. Transient reporter assays indicate that the B1 element is a strong promoter with no inherent lymphoid tissue-specificity. We have also identified different binding sites for the ETS family member GABP within both the mouse and rat B1 elements that are necessary for high-promoter activity and for full Nkg2d-L expression. These findings demonstrate that a retroelement insertion has led to gene-regulatory change and functional diversification of rodent NKG2D.

Proteomics and pathway analysis identifies JNK signaling as critical for high linear energy transfer radiation-induced apoptosis in non-small lung cancer cells

During the past decade, we have witnessed an explosive increase in generation of large proteomics data sets, not least in cancer research. There is a growing need to extract and correctly interpret information from such data sets to generate biologically relevant hypotheses. A pathway search engine (PSE) has recently been developed as a novel tool intended to meet these requirements. Ionizing radiation (IR) is an anticancer treatment modality that triggers multiple signal transduction networks. In this work, we show that high linear energy transfer (LET) IR induces apoptosis in a non-small cell lung cancer cell line, U-1810, whereas low LET IR does not. PSE was applied to study changes in pathway status between high and low LET IR to find pathway candidates of importance for high LET-induced apoptosis. Such pathways are potential clinical targets, and they were further validated in vitro. We used an unsupervised shotgun proteomics approach where high resolution mass spectrometry coupled to nanoflow liquid chromatography determined the identity and relative abundance of expressed proteins. Based on the proteomics data, PSE suggested the JNK pathway (p = 6.10(-6)) as a key event in response to high LET IR. In addition, the Fas pathway was found to be activated (p = 3.10(-5)) and the p38 pathway was found to be deactivated (p = 0.001) compared with untreated cells. Antibody-based analyses confirmed that high LET IR caused an increase in phosphorylation of JNK. Moreover pharmacological inhibition of JNK blocked high LET-induced apoptotic signaling. In contrast, neither an activation of p38 nor a role for p38 in high LET IR-induced apoptotic signaling was found. We conclude that, in contrast to conventional low LET IR, high LET IR can trigger activation of the JNK pathway, which in turn is critical for induction of apoptosis in these cells. Thus PSE predictions were largely confirmed, and PSE was proven to be a useful hypothesis-generating tool.

Low FAS/CD95 expression by CTCL correlates with reduced sensitivity to apoptosis that can be restored by FAS upregulation

FAS expression was generally low in 30 of 31 cutaneous T-cell lymphoma (CTCL) cases (mycosis fungoides/Sezary syndrome, SS) as well as in 5 of 6 large plaque parapsoriasis cases (a CTCL precursor). To investigate this phenomenon, we explored FAS transcript levels, cell-surface FAS protein expression and susceptibility to FAS-mediated apoptosis in four CTCL lines (MyLa, HH, SZ4, and SeAx), freshly isolated leukemic cells from a patient with SS, an acute lymphoblastic leukemia T-cell line (Jurkat), and JFL (a FAS-low variant of Jurkat). Results confirmed low FAS expression by the leukemic SS cells, HH, SZ4, SeAx, and JFL relative to normal peripheral blood mononuclear leukocytes and the other cell lines. There was a direct correlation among FAS transcript level, FAS protein level, and FAS-mediated apoptotic sensitivity in the CTCL samples. When the FAS-deficient cell lines were transfected with a wild-type FAS construct, FAS expression and sensitivity to FAS-mediated apoptosis were restored. In aggregate, these findings provide evidence that like normal T cells, CTCL cells exhibit a mechanistic connection between transcriptional regulation of FAS and sensitivity to FAS-mediated apoptosis, point to the development of FAS deficiency as one molecular mechanism responsible for acquired resistance to apoptosis in CTCL, and indicate that upregulation of FAS expression can restore sensitivity to apoptosis.

GABPbeta2 is dispensible for normal lymphocyte development but moderately affects B cell responses

GA-binding protein (GABP) is the only Ets family transcription factor that functions as a heterodimer. The GABPalpha subunit binds to DNA, and the GABPbeta subunit possesses the ability to transactivate target genes. Inactivation of GABPalpha caused embryonic lethality and defective lymphocyte development and immune responses. There are 3 isoforms of the GABPbeta subunit, but whether they have distinct functions has not been addressed. In this study, we selectively ablated the expression of GABPbeta2 using a gene trap strategy. GABPbeta2-deficient mice were viable and had normal T and B cell development, suggesting that loss of GABPbeta2 is compensated for by other GABPbeta isoforms during these processes. GABPbeta2-deficient T cells can be activated and proliferate similarly to wild-type controls. In contrast, B cells lacking GABPbeta2 showed 2-3-fold increases in proliferation in response to B cell receptor stimulation. In addition, GABPbeta2-deficient mice exhibited moderately increased antibody production and germinal center responses when challenged with T-dependent antigens. These results indicate that albeit GABPbeta isoforms are redundant in lymphocyte development, GABPbeta2 has a distinct role in restraining B cell expansion and humoral responses.

Targeting the GA binding protein beta1L isoform does not perturb lymphocyte development and function

GA binding protein (GABP) is a ubiquitously expressed Ets family transcription factor that consists of two subunits, GABPalpha and GABPbeta. GABPalpha binds to DNA, and GABPbeta heterodimerizes with GABPalpha and possesses the ability to transactivate target genes. Our previous studies using GABPalpha-deficient mice revealed that GABPalpha is required for the development of both T and B cells. Two splice variants of GABPbeta are generated from the Gabpb1 locus and differ in their carboxy-terminal lengths and sequences. The longer isoform (GABPbeta1L) can homodimerize and thus form alpha(2)beta(2) tetramers depending on the gene context, whereas the shorter isoform (GABPbeta1S) cannot. In this study, we generated mice that are deficient in GABPbeta1L but that retain the expression of GABPbeta1S. Surprisingly, GABPbeta1L-/- mice had normal T- and B-cell development, and mature T and B cells showed normal responses to various stimuli. In contrast, targeting both GABPbeta1L and GABPbeta1S resulted in early embryonic lethality. Because of its incapability of forming homodimers, GABPbeta1S has been suspected to have a dominant negative role in regulating GABP target genes. Our findings argue against such a possibility and rather suggest that GABPbeta1S has a critical role in maintaining the transcriptional activity of the GABPalpha/beta complex.

Involvement of NF-κB subunit p65 and retinoic acid receptors, RARα and RXRα, in transcriptional regulation of the human GnRH II gene

Gonadotropin-releasing hormone (GnRH) I and II are hypothalamic decapeptides with pivotal roles in the development of reproductive competence and regulation of reproductive events. In this study, transcriptional regulation of the human GnRH II gene was investigated. By scanning mutation analysis coupled with transient promoter assays, the motif at -641/-636 (CATGCC, designated GII-Sil) was identified as a repressor element. Mutation of this motif led to full restoration of promoter activity in TE671 medulloblastoma and JEG-3 placenta choriocarcinoma cells. Supershift and chromatin immunoprecipitation assays showed in vitro and in vivo binding of NF-kappaB subunit p65 and the retinoic acid receptors, RARalpha and RXRalpha, to the promoter sequences. Over-expression of these protein factors indicated that p65 is a potent repressor, and the RARalpha/RXRalpha heterodimer is involved in the differential regulation of the GnRH II gene in neuronal and placental cells. This was confirmed by quantitative real-time PCR. Treatment of cells with the RARalpha/RXRalpha ligands, all-trans retinoic acid and 9-cis-retinoic acid, reduced and increased GnRH II gene expression in TE671 and JEG-3 cells, respectively. Taken together, these data demonstrate the differential roles of NF-kappaB p65 and RARalpha/RXRalpha, interacting with the same sequence in the promoter of the human GnRH II gene to influence gene expression in a cell-specific manner.

Crosstalk between extrinsic and intrinsic cell death pathways in pancreatic cancer: synergistic action of estrogen metabolite and ligands of death receptor family

2-Methoxyestradiol is a physiologic metabolite of 17beta-estradiol. This orally active compound can inhibit tumor growth or metastasis in tumor models without inducing any clinical sign of toxicity. Our previous studies indicated that 2-methoxyestradiol-mediated apoptosis involves the disappearance of intact 21-kDa Bid protein, cytochrome c release, and predominant procaspase-3 cleavage. Here, using MIA PaCa-2 cells as a model, we investigated whether this estrogen metabolite induces apoptosis by converging two major pathways: the death receptor-mediated extrinsic and the mitochondrial intrinsic pathway. Exogenous expression of dominant-negative caspase-8 or dominant-negative FADD reverts the effect of 2-methoxyestradiol-mediated cell death. In parallel with this observation, Z-IETD-FMK, a cell permeable irreversible inhibitor of caspase-8, can render significant protection against 2-methoxyestradiol-induced apoptosis. RNase protection assay and cell surface receptor analysis by flow cytometry show the up-regulation of members of death receptor family in 2-methoxyestradiol-exposed pancreatic cancer cells. Our mechanistic studies also implicate that oxidative stress precedes 2-methoxyestradiol-mediated c-Jun NH2-terminal kinase activation, leading to elevated Fas level. Because 2-methoxyestradiol is able to trigger death receptor signaling, we were interested in examining the effects of 2-methoxyestradiol and Fas ligand (FasL)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) together on pancreatic cancer cell death. Interestingly, the endogenous angiogenesis inhibitor 2-methoxyestradiol augments FasL/TRAIL-induced apoptosis in these cells. Moreover, the combination of 2-methoxyestradiol and TRAIL reduces the tumor burden in vivo in MIA PaCa-2 tumor xenograft model by caspase-3 activation.

Identification of a crucial site for synoviolin expression

Synoviolin is an E3 ubiquitin ligase localized in the endoplasmic reticulum (ER) and serving as ER-associated degradation system. Analysis of transgenic mice suggested that synoviolin gene dosage is implicated in the pathogenesis of arthropathy. Complete deficiency of synoviolin is fatal embryonically. Thus, alternation of Synoviolin could cause breakdown of ER homeostasis and consequently lead to disturbance of cellular homeostasis. Hence, the expression level of Synoviolin appears to be important for its biological role in cellular homeostasis under physiological and pathological conditions. To examine the control of protein level, we performed promoter analysis to determine transcriptional regulation. Here we characterize the role of synoviolin transcription in cellular homeostasis. The Ets binding site (EBS), termed EBS-1, from position -76 to -69 of the proximal promoter, is responsible for synoviolin expression in vivo and in vitro. Interestingly, transfer of EBS-1 decoy into NIH 3T3 cells conferred not only the repression of synoviolin gene expression but also a decrease in cell number. Fluorescence-activated cell sorter analysis using annexin V staining confirmed the induction of apoptosis by EBS-1 decoy and demonstrated recovery of apoptosis by overexpression of Synoviolin. Our results suggest that transcriptional regulation of synoviolin via EBS-1 plays an important role in cellular homeostasis. Our study provides novel insight into the transcriptional regulation for cellular homeostasis.

Microcompetition and the origin of cancer

Abnormal gene expression is a common observation in cancer cells. Although genetic alterations via somatic mutations or DNA modifications are considered to be the cause of cancer, they do not explain the observed abnormal gene expression of many wild-type genes in cancer. Now, a new theory, called "Microcompetition", identifies a non-genetic-alteration event as the cause of the observed abnormal gene expression, and therefore, the cause of cancer and other chronic diseases.

The ETS transcription factor GABPalpha is essential for early embryogenesis

The ETS transcription factor complex GABP consists of the GABPalpha protein, containing an ETS DNA binding domain, and an unrelated GABPbeta protein, containing a transactivation domain and nuclear localization signal. GABP has been shown in vitro to regulate the expression of nuclear genes involved in mitochondrial respiration and neuromuscular signaling. We investigated the in vivo function of GABP by generating a null mutation in the murine Gabpalpha gene. Embryos homozygous for the null Gabpalpha allele die prior to implantation, consistent with the broad expression of Gabpalpha throughout embryogenesis and in embryonic stem cells. Gabpalpha(+/-) mice demonstrated no detectable phenotype and unaltered protein levels in the panel of tissues examined. This indicates that Gabpalpha protein levels are tightly regulated to protect cells from the effects of loss of Gabp complex function. These results show that Gabpalpha function is essential and is not compensated for by other ETS transcription factors in the mouse, and they are consistent with a specific requirement for Gabp expression for the maintenance of target genes involved in essential mitochondrial cellular functions during early cleavage events of the embryo.

Signaling and protein associations of a cell permeable CD40 complex in B cells

Signaling through the CD40 receptor activates diverse molecular pathways in a variety of immune cell types. To study CD40 signaling complexes in B cells, we produced soluble CD40 cytoplasmic domain multimers that translocate across cell membranes and engage intracellular CD40 signaling pathways. As visualized by fluorescence microscopy, rapid transduction of recombinant Antennapedia-isoleucine zipper (Izip)-CD40 cytoplasmic domain fusion protein (Antp-CD40) occurred in both the DND39 B cell line and human tonsillar B cells. Upon cellular entry, Antp-CD40 activated NF-kappaB-dependent transcription, induced proteolytic processing of p100 to the p52/NF-kappaB2 subunit, and increased expression of CD80 and CD54 on the surface of B cells. Antp-CD40 transduction of B cells did not, however, activate detectable levels of p38 mitogen-activated protein kinase or c-Jun N-terminal kinase and did not up-regulate CD95 expression. Analysis of Antp-CD40 complexes recovered from transduced B cells revealed that Antp-CD40 associated with endogenous TRAF3 and Ku proteins. Multimerization of Antp-CD40, or extensive clustering of transmembrane CD40, diminished the disruptive effect of the T254A mutation in the TRAF2/3 binding site of the CD40 cytoplasmic domain. Taken together, these results indicate that Antp-CD40 mimics some of the natural CD40 signaling pathways in B cells by assembling partially functional signaling intermediates that do not require plasma membrane localization. We present a novel approach for delivering pre-activated, soluble receptor cytoplasmic domains into cells and recovering intact signaling complexes for molecular analysis.

Induction of apoptosis through the activation of SAPK/JNK followed by the expression of death receptor Fas in X-irradiated cells

A post-irradiation treatment of the human leukemia cell line MOLT-4 with the antioxidant Trolox attenuated caspase-3 dependent apoptosis. The increase in the p53 expression and SAPK/JNK activation after X irradiation was also inhibited by a Trolox treatment, but the expression of BCL-2 and BAX, which would occur downstream from p53, was not changed. Studies on the effects of the intracellular calcium chelator BAPTA-AM on the induction of apoptosis and the activation of SAPK/JNK and caspase-3 proved that the chelation of calcium merely delayed the onset of radiation-induced apoptosis and the activation of SAPK/JNK and caspase-3. When the effects of the protein synthesis inhibitor cycloheximde on the apoptotic signaling pathways, including the activation of caspase family proteins and SAPK/JNK, were investigated, the expression of death receptor Fas through SAPK/JNK activation was found to be required for radiation-induced apoptosis. Finally, the relationship between the amounts of DNA dsb and induction of apoptosis was examined by irradiating BrdU-incorporated cells. An increase in DNA dsb caused by BrdU was found, but the induction of apoptosis was not enhanced. From these data, we could get no positive evidence for DNA as a target of X-rays and p53 as an indispensable factor to induced apoptosis in X-irradiated MOLT-4 cells.

Bunyamwera virus nonstructural protein NSs counteracts interferon regulatory factor 3-mediated induction of early cell death

The genome of Bunyamwera virus (BUN; family Bunyaviridae, genus Orthobunyavirus) consists of three segments of negative-sense RNA. The smallest segment, S, encodes two proteins, the nonstructural protein NSs, which is nonessential for viral replication and transcription, and the nucleocapsid protein N. Although a precise role in the replication cycle has yet to be attributed to NSs, it has been shown that NSs inhibits the induction of alpha/beta interferon, suggesting that it plays a part in counteracting the host antiviral defense. A defense mechanism to limit viral spread is programmed cell death by apoptosis. Here we show that a recombinant BUN that does not express NSs (BUNdelNSs) induces apoptotic cell death more rapidly than wild-type virus. Screening for apoptosis pathways revealed that the proapoptotic transcription factor interferon regulatory factor 3 (IRF-3) was activated by both wild-type BUN and BUNdelNSs infection, but only wild-type BUN was able to suppress signaling downstream of IRF-3. Studies with a BUN minireplicon system showed that active replication induced an IRF-3-dependent promoter, which was suppressed by the NSs protein. In a cell line (P2.1) defective in double-stranded RNA signaling due to low levels of IRF-3, induction of apoptosis was similar for wild-type BUN and BUNdelNSs. These data suggest that the BUN NSs protein can delay cell death in the early stages of BUN infection by inhibiting IRF-3-mediated apoptosis.

Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention

The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.

Molecular sequelae of proteasome inhibition in human multiple myeloma cells

The proteasome inhibitor PS-341 inhibits IkappaB degradation, prevents NF-kappaB activation, and induces apoptosis in several types of cancer cells, including chemoresistant multiple myeloma (MM) cells. PS-341 has marked clinical activity even in the setting of relapsed refractory MM. However, PS-341-induced apoptotic cascade(s) are not yet fully defined. By using gene expression profiling, we characterized the molecular sequelae of PS-341 treatment in MM cells and further focused on molecular pathways responsible for the anticancer actions of this promising agent. The transcriptional profile of PS-341-treated cells involved down-regulation of growth/survival signaling pathways, and up-regulation of molecules implicated in proapoptotic cascades (which are both consistent with the proapoptotic effect of proteasome inhibition), as well as up-regulation of heat-shock proteins and ubiquitin/proteasome pathway members (which can correspond to stress responses against proteasome inhibition). Further studies on these pathways showed that PS-341 decreases the levels of several antiapoptotic proteins and triggers a dual apoptotic pathway of mitochondrial cytochrome c release and caspase-9 activation, as well as activation of Jun kinase and a Fas/caspase-8-dependent apoptotic pathway [which is inhibited by a dominant negative (decoy) Fas construct]. Stimulation with IGF-1, as well as overexpression of Bcl-2 or constitutively active Akt in MM cells also modestly attenuates PS-341-induced cell death, whereas inhibitors of the BH3 domain of Bcl-2 family members or the heat-shock protein 90 enhance tumor cell sensitivity to proteasome inhibition. These data provide both insight into the molecular mechanisms of antitumor activity of PS-341 and the rationale for future clinical trials of PS-341, in combination with conventional and novel therapies, to improve patient outcome in MM.

Cooperation of protein kinase A and Ras/ERK signaling pathways is required for AP-1-mediated activation of fibroblast growth factor-inducible response element (FiRE)

Recent studies suggest a crucial role for protein kinase A (PKA) in the regulation of growth factor signaling. However, the effect of PKA on the transcription of growth factor-responsive genes has drawn far less attention. Here we have investigated the signaling mechanisms involved in the activation of an activator protein-1 (AP-1)-driven, growth factor-specific enhancer element, fibroblast growth factor-inducible response element (FiRE). The activation was found to be mediated by three phorbol 12-O-tetradecanoate-13-acetate-response element-related DNA elements of FiRE, including motif 4 and two distinct elements of motif 5 (referred to as M5-1 and M5-2). All three elements were required for full FiRE activity. Stimulation of cells with fibroblast growth factor-2 (FGF-2) induced the binding of AP-1 to motif 4 and M5-2, whereas M5-1 did not show detectable binding. The FGF-2-induced FiRE activation appeared to require cooperational function of the Ras/ERK and PKA pathways. Inhibition of either of the pathways abolished the binding of AP-1 complexes to motif 4 and motif 5 and the subsequent FiRE activation. By contrast, costimulation of cells with FGF-2 and the PKA activator 8-bromo-cyclic AMP increased the binding of AP-1 to FiRE and potentiated the level of transcriptional activity. The cooperational function of these two pathways was confirmed by experiments with cell lines stably expressing 4-hydroxytamoxifen-inducible oncogenic Raf-1 (DeltaRaf-1:ER[DD]). Noticeably, the induction systems showed variations with respect to regulation of AP-1-driven activation of FiRE. These differences were likely to originate from the ability of these two systems to induce the differential activation pattern of the Ras/ERK pathway.

Cloning and characterization of the human heparanase-1 (HPR1) gene promoter: role of GA-binding protein and Sp1 in regulating HPR1 basal promoter activity

Heparanase-1 (HPR1) is an endoglycosidase that specifically degrades the heparan sulfate chains of proteoglycan, a component of blood vessel walls and the extracellular matrix. Recent studies demonstrated that HPR1 expression is increased in a variety of malignancies and may play a critical role in tumor metastases. The HPR1 gene and its genomic structure have been recently cloned and characterized. To understand the mechanisms of HPR1 gene expression and regulation, we first mapped the transcription start site of the HPR1 gene and found that HPR1 mRNA was transcribed from the nucleotide position 101 bp upstream of the ATG codon. A 3.5-kb promoter region of the HPR1 gene was cloned. Sequence analysis revealed that the TATA-less, GC-rich promoter of the HPR1 gene belongs to the family of housekeeping genes. This 3.5-kb promoter region exhibited strong promoter activity in two thyroid tumor cell lines. Truncation analysis of the HPR1 promoter identified a minimal 0.3-kb region that had strong basal promoter activity. Truncation and mutational analysis of the HPR1 promoter revealed three Sp1 sites and four Ets-relevant elements (ERE) significantly contributing to basal HPR1 promoter activity. Binding to the Sp1 sites by Sp1 and to the ERE sites by GA-binding protein (GABP) was confirmed by electrophoretic mobility shift assay and competition and supershift electrophoretic mobility shift assays. Cotransfection of Sp- and GABP-deficient Drosophila SL-2 cells with the HPR1 promoter-driven luciferase construct plus the expression vector encoding the Sp1, Sp3, or GABP gene induced luciferase gene expression. Mutation or truncation of the Sp1 or ERE sites reduced luciferase expression in both SL-2 cells and thyroid tumor cell lines. Coexpression of GABPalpha/beta and Sp1 or Sp3 further increased luciferase reporter gene expression. Our results collectively suggest that Sp1 cooperates with GABP to regulate HPR1 promoter activity.

Defective Fas ligand expression and activation-induced cell death in the absence of IL-2-inducible T cell kinase

The Tec family tyrosine kinase, IL-2-inducible T cell kinase (Itk), plays an important role in TCR signaling. Studies of T cells from Itk-deficient mice have demonstrated that Itk is critical for the activation of phospholipase-Cgamma1, leading to calcium mobilization in response to TCR stimulation. This biochemical defect results in reduced IL-2 production by Itk-deficient T cells. To further characterize the downstream effects of the Itk deficiency, we crossed Itk-/- mice to a TCR-transgenic line and examined T cell responses to stimulation by peptide plus APC. These studies show that Itk is required for maximal activation of early growth responses 2 and 3 and Fas ligand transcription after TCR stimulation. These transcriptional defects lead to reduced activation-induced cell death of stimulated Itk-/- T cells, both in vitro and in vivo. Together these studies define an important role for Itk in TCR signaling, leading to cytokine gene expression and activation-induced cell death.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Transcription of the catalytic 180-kDa subunit gene of mouse DNA polymerase alpha is controlled by E2F, an Ets-related transcription factor, and Sp1

We have isolated a genomic DNA fragment spanning the 5'-end of the gene encoding the catalytic subunit of mouse DNA polymerase alpha. The nucleotide sequence of the upstream region was G/C-rich and lacked a TATA box. Transient expression assays in cycling NIH 3T3 cells demonstrated that the GC box of 20 bp (at nucleotides -112/-93 with respect to the transcription initiation site) and the palindromic sequence of 14 bp (at nucleotides -71/-58) were essential for basal promoter activity. Electrophoretic mobility shift assays showed that Sp1 binds to the GC box. We also purified a protein capable of binding to the palindrome and identified it as GA-binding protein (GABP), an Ets- and Notch-related transcription factor. Transient expression assays in synchronized NIH 3T3 cells revealed that three variant E2F sites near the transcription initiation site (at nucleotides -23/-16, -1/+7 and +17/+29) had no basal promoter activity by themselves, but were essential for growth-dependent stimulation of the gene expression. These data indicate that E2F, GABP and Sp1 regulate the gene expression of this principal replication enzyme.

Regulation of the human fas promoter by YB-1, Puralpha and AP-1 transcription factors

Fas (CD95/Apo-1) gene expression is dysregulated in a number of diseased states. Towards understanding the regulation of fas gene expression, we previously identified activator and repressor elements within the human fas promoter. Using a combination of expression screening and reporter gene assays, we have identified transcription factors which bind to these elements and thereby regulate transcription of the fas promoter. These are three single-stranded DNA binding proteins, YB-1, Puralpha and Purbeta and two components of the AP-1 complex, c-Fos and c-Jun. c-Jun is a potent transcriptional activator of fas and stimulated expression levels up to 184-fold in reporter gene assays. Co-expression with c-Fos abrogated c-Jun-mediated activation. YB-1 and Puralpha are transcriptional repressors of fas and decreased basal transcription by 60-fold in reporter gene assays. Purbeta was predominantly an antagonist of YB-1/Puralpha-mediated repression. Overexpression of YB-1 and Puralpha in Jurkat cells was shown to reduce the level of cell surface Fas staining, providing further evidence that these proteins regulate the fas promoter. It has been suggested that YB-1 plays a role in cell proliferation as an activator of growth-associated gene expression. We have shown that YB-1 is a repressor of a cell death-associated gene fas. These results suggest that YB-1 may play an important role in controlling cell survival by co-ordinately regulating the expression of cell growth-associated and death-associated genes.