Sp1-dependent regulation of Myeloid Elf-1 like factor in human epithelial cells

Transcription factor ELF4 in physiology and diseases: Molecular roles and clinical implications

Transcription factor E74 like ETS transcription factor 4 (ELF4), a member of the ETS family, is highly expressed in normal human hematopoietic tissue, ovary, placenta, colon, and certain pathological cell lines. During normal physiological processes, ELF4 regulates differentiation in osteogenic, adipocyte, and neuronal types. It also exerts a critical impact on the development of the immune system. However, its function is dysregulated through posttranslational modifications, gene fusions, and complex signaling crosstalk under pathological conditions. Furthermore, serving as a double-edged sword in cancer, ELF4 exhibits both tumor-suppressing and tumor-promoting effects. Specifically, ELF4 plays a critical role in cancer metastasis, proliferation, and modulation of the tumor microenvironment. This review provides an in-depth overview of the molecular structure and post-translational modifications of ELF4. It also summarizes the hallmarks of ELF4 in physiology and diseases, with a particular focus on its significance in oncology. Notably, this review underscores the potential of ELF4 as a prognostic biomarker, highlighting its clinical relevance. Finally, it discusses unresolved questions and future research directions of ELF4. An in-depth understanding of ELF4 biology could facilitate its clinical translation and offer promising targeted therapeutic strategies.

Elf4 regulates lysosomal biogenesis and the mTOR pathway to promote clearance of Staphylococcus aureus in macrophages

Staphylococcus aureus is a major cause of infectious disease. Macrophages can directly destroy most of the invading bacteria through the phagolysosomal pathway. E74-like factor 4 (Elf4) is one of the important transcription factors that controls diverse pathogens, but the role of Elf4 in macrophage-mediated S. aureus eradication is unknown. Our data show that Elf4 is induced by S. aureus in macrophages. Elevated expression of Elf4 results in decreased bacterial load and inflammatory responses during S. aureus infection in vivo and in vitro. Elf4-overexpressed macrophages have decreased mTOR activity and increased lysosomal mass. Collectively, these results suggest that S. aureus induces Elf4 expression, which enhances lysosomal function and increases the capacity of macrophages to eliminate intracellular pathogens.

Roles and regulations of the ETS transcription factor ELF4/MEF

Most E26 transformation-specific (ETS) transcription factors are involved in the pathogenesis and progression of cancer. This is in part due to the roles of ETS transcription factors in basic biological processes such as growth, proliferation, and differentiation, and also because of their regulatory functions that have physiological relevance in tumorigenesis, immunity, and basal cellular homoeostasis. A member of the E74-like factor (ELF) subfamily of the ETS transcription factor family—myeloid elf-1-like factor (MEF), designated as ELF4—has been shown to be critically involved in immune response and signalling, osteogenesis, adipogenesis, cancer, and stem cell quiescence. ELF4 carries out these functions as a transcriptional activator or through interactions with its partner proteins. Mutations in ELF4 cause aberrant interactions and induce downstream processes that may lead to diseased cells. Knowing how ELF4 impinges on certain cellular processes and how it is regulated in the cells can lead to a better understanding of the physiological and pathological consequences of modulated ELF4 activity.

The ETS Factor Myeloid Elf-1-Like Factor (MEF)/Elf4 Is Transcriptionally and Functionally Activated by Hypoxia

Hypoxia-inducible factor (HIF)-1α is a transcription factor belonging to the HIF family that is activated in mammalian cells during conditions of low oxygen tension or hypoxia to induce an adaptive response and promote cell survival. Some of the genes targeted by HIF-1α are important for angiogenesis and proliferation. Here, we found that the E26 transformation-specific (ETS) transcription factor myeloid elf-1-like factor (MEF)/Elf4 is activated by HIF-1α. MEF induces genes such as human beta-defensin 2 (HβD2) and perforin (PRF1), and is known to affect the cell cycle. Treatment with hypoxia mimetic CoCl2 or low O2 incubation up-regulated MEF mRNA and protein levels in various cell lines. HIF-1α overexpression in HEK293 cells also increased MEF mRNA and protein levels. In contrast, HIF-1α knockdown by small interfering RNA (siRNA) suppressed the induction of MEF in response to hypoxia. HIF-1α binds to the hypoxia response element in the MEF promoter region (-200 bp) and activates MEF promoter under hypoxia condition. The induction of MEF by hypoxia/HIF-1α correlated with the increase of MEF target genes HβD2 and PRF1. Intriguingly, the hypoxia-induced expression of HIF-1α target gene vascular endothelial growth factor (VEGF) was enhanced by the exogenous addition of MEF. Overall, these data indicate that hypoxia or HIF-1α positively regulates MEF expression and function.

Endoplasmic Reticulum (ER) Stress Induces Sirtuin 1 (SIRT1) Expression via the PI3K-Akt-GSK3β Signaling Pathway and Promotes Hepatocellular Injury

Sirtuin 1 (SIRT1), an NAD(+)-dependent histone deacetylase, plays crucial roles in various biological processes including longevity, stress response, and cell survival. Endoplasmic reticulum (ER) stress is caused by dysfunction of ER homeostasis and exacerbates various diseases including diabetes, fatty liver, and chronic obstructive pulmonary disease. Although several reports have shown that SIRT1 negatively regulates ER stress and ER stress-induced responses in vitro and in vivo, the effect of ER stress on SIRT1 is less explored. In this study, we showed that ER stress induced SIRT1 expression in vitro and in vivo. We further determined the molecular mechanisms of how ER stress induces SIRT1 expression. Surprisingly, the conventional ER stress-activated transcription factors XBP1, ATF4, and ATF6 seem to be dispensable for SIRT1 induction. Based on inhibitor screening experiments with SIRT1 promoter, we found that the PI3K-Akt-GSK3β signaling pathway is required for SIRT1 induction by ER stress. Moreover, we showed that pharmacological inhibition of SIRT1 by EX527 inhibited the ER stress-induced cellular death in vitro and severe hepatocellular injury in vivo, indicating a detrimental role of SIRT1 in ER stress-induced damage responses. Collectively, these data suggest that SIRT1 expression is up-regulated by ER stress and contributes to ER stress-induced cellular damage.

The transcription factor MEF/Elf4 is dually modulated by p53-MDM2 axis and MEF-MDM2 autoregulatory mechanism

Myeloid Elf-1-like factor (MEF) or Elf4 is an ETS transcription factor that activates innate immunity-associated genes such as lysozyme (LYZ), human β-defensin 2 (HβD2), and interleukin-8 (IL-8) in epithelial cells and is also known to influence cell cycle progression. MEF is transcriptionally activated by E2F1, but the E2F1-mediated transcriptional activation is inhibited by p53 through E2F1-p53 protein interaction. Although the transcriptional activation of MEF has been investigated in depth, its post-translational regulation is not well explored. By overexpressing MEF cDNA in human cell lines, here we show that MEF protein expression is suppressed by p53. By screening a number of E3 ligases regulated by p53, we found that MDM2 is involved in the effect of p53 on MEF. MDM2 is transcriptionally activated by p53 and interacts with MEF protein to enhance MEF degradation. MDM2 reduces MEF protein expression, as well as stability and function of MEF as transcriptional activator. Furthermore, MDM2 was able to down-regulate MEF in the absence of p53, indicating a p53-independent effect on MEF. Notably, MEF transcriptionally activates MDM2, which was previously demonstrated to be the mechanism by which MEF suppresses the p53 protein. These results reveal that in addition to the potential of MEF to down-regulate p53 by transcriptionally activating E3 ligase MDM2, MEF participates with MDM2 in a novel autoregulatory feedback loop to regulate itself. Taken together with the findings on the effect of p53 on MEF, these data provide evidence that the p53-MDM2-MEF axis is a feedback mechanism that exquisitely controls the balance of these transcriptional regulators.

Cell-Type Specific Determinants of NRAMP1 Expression in Professional Phagocytes

The Natural resistance-associated macrophage protein 1 (Nramp1 or Solute carrier 11 member 1, Slc11a1) transports divalent metals across the membrane of late endosomes and lysosomes in professional phagocytes. Nramp1 represents an ancient eukaryotic cell-autonomous defense whereas the gene duplication that yielded Nramp1 and Nramp2 predated the origin of Sarcopterygians (lobe-finned fishes and tetrapods). SLC11A1 genetic polymorphisms associated with human resistance to tuberculosis consist of potential regulatory variants. Herein, current knowledge of the regulation of SLC11A1 gene expression is reviewed and comprehensive analysis of ENCODE data available for hematopoietic cell-types suggests a hypothesis for the regulation of SLC11A1 expression during myeloid development and phagocyte functional polarization. SLC11A1 is part of a 34.6 kb CTCF-insulated locus scattered with predicted regulatory elements: a 3' enhancer, a large 5' enhancer domain and four elements spread around the transcription start site (TSS), including several C/EBP and PU.1 sites. SLC11A1 locus ends appear mobilized by ETS-related factors early during myelopoiesis; activation of both 5' and 3' enhancers in myelo-monocytic cells correlate with transcription factor binding at the TSS. Characterizing the corresponding cis/trans determinants functionally will establish the mechanisms involved and possibly reveal genetic variation that impacts susceptibility to infectious or immune diseases.

Integration of Elf-4 into stem/progenitor and erythroid regulatory networks through locus-wide chromatin studies coupled with in vivo functional validation

The ETS transcription factor Elf-4 is an important regulator of hematopoietic stem cell (HSC) and T cell homeostasis. To gain insights into the transcriptional circuitry within which Elf-4 operates, we used comparative sequence analysis coupled with chromatin immunoprecipitation (ChIP) with microarray technology (ChIP-chip) assays for specific chromatin marks to identify three promoters and two enhancers active in hematopoietic and endothelial cell lines. Comprehensive functional validation of each of these regulatory regions in transgenic mouse embryos identified a tissue-specific enhancer (-10E) that displayed activity in fetal liver, dorsal aorta, vitelline vessels, yolk sac, and heart. Integration of a ChIP-sequencing (ChIP-Seq) data set for 10 key stem cell transcription factors showed Pu.1, Fli-1, and Erg were bound to the -10E element, and mutation of three highly conserved ETS sites within the enhancer abolished its activity. Finally, the transcriptional repressor Gfi1b was found to bind to and repress one of the Elf-4 promoters (-30P), and we show that this repression of Elf-4 is important for the maturation of primary fetal liver erythroid cells. Taken together, our results provide a comprehensive overview of the transcriptional control of Elf-4 within the hematopoietic system and, thus, integrate Elf-4 into the wider transcriptional regulatory networks that govern hematopoietic development.

Sp1 upregulates survivin expression in adenocarcinoma of lung cell line A549

Survivin has been implicated in tumor genesis, progression, and resistance to anticancer agents. However, the precise regulatory mechanism for survivin expression is not thoroughly defined. In this study, we showed that Sp1 was co-overexpressed with survivin in adenocarcinoma of lung cells A549, but not in differentiated human bronchial epithelial cells 4F0439 or small airway epithelial cells 3F1584. Subsequently, transfection experiments demonstrated that the inhibition of Sp1 signaling suppressed survivin expression in A549 cells, whereas Sp1 overexpression increased the level of survivin protein as well as its mRNA. We also found that Sp1 could decrease capase-9 activity, which is shown to be suppressed by survivin during apoptosis inhibition. Finally, Luciferase activity and ChIP assays revealed that Sp1 activated survivin promoter by direct interaction with it. Taken together, our data suggest Sp1 plays a potent role in the upregulation of survivin expression in lung cancer cells at the transcriptional level.

MEF/ELF4 transactivation by E2F1 is inhibited by p53

Myeloid elf-1-like factor (MEF) or Elf4 is an E-twenty-six (ETS)-related transcription factor with strong transcriptional activity that influences cellular senescence by affecting tumor suppressor p53. MEF downregulates p53 expression and inhibits p53-mediated cellular senescence by transcriptionally activating MDM2. However, whether p53 reciprocally opposes MEF remains unexplored. Here, we show that MEF is modulated by p53 in human cells and mice tissues. MEF expression and promoter activity were suppressed by p53. While we found that MEF promoter does not contain p53 response elements, intriguingly, it contains E2F consensus sites. Subsequently, we determined that E2F1 specifically binds to MEF promoter and transactivates MEF. Nevertheless, E2F1 DNA binding and transactivation of MEF promoter was inhibited by p53 through the association between p53 and E2F1. Furthermore, we showed that activation of p53 in doxorubicin-induced senescent cells increased E2F1 and p53 interaction, diminished E2F1 recruitment to MEF promoter and reduced MEF expression. These observations suggest that p53 downregulates MEF by associating with and inhibiting the binding activity of E2F1, a novel transcriptional activator of MEF. Together with previous findings, our present results indicate that a negative regulatory mechanism exists between p53 and MEF.

Transcription factor Sp1 regulates expression of cancer-associated molecule CD147 in human lung cancer

CD147 is a novel cancer-associated biomarker that plays an important role in the invasion and metastasis of human lung cancer. In spite of its many known functions, little is known about CD147 transcriptional regulation. In this study, we explored the regulation of CD147 in human lung cancer tissues. Over 60% of the human lung cancer tissues expressed differential high levels of CD147. We then cloned the 5'-flanking region of the human CD147 gene and identified a critical promoter region at -108 to -42 which contained one binding site for Sp1, which was essential in up-regulating CD147 promoter activity. These results were proven by blocking Sp1 using RNAi or mithramycin A treatment and up-regulating Sp1 using transfection with eukaryotic expression vector. Consistent with the CD147 transcription activation, a high level of Sp1 expression was detected in lung cancer cell lines overexpressing CD147. Chromatin immunoprecipitation assay showed that much more Sp1 could bind to the CD147 promoter in 95-D with CD147 high expression than in SK-MES-1 with CD147 low expression. There was a significant positive correlation between CD147 expression and Sp1 expression level detected by immunohistochemistry (r = 0.831). Collectively, our results suggest that Sp1 is essential for regulating the CD147 gene expression in human lung cancer.

The mechanism involved in the repression of the μ opioid receptor gene expression in CEM ×174 cells infected by simian immunodeficiency virus

Morphine can promote the pathogenesis of human acquired immunodeficiency syndrome through binding to the μ opioid receptor (MOR) in immune cells. Previous investigation has suggested that expression of the MOR gene in lymphocytes is triggered by cooperative interaction between transcription factors, specificity protein 1 (Sp1) and Ying Yang 1 (YY1), in the promoter region. However, the specific molecular mechanism by which immunodeficiency virus infection impacts regulation of the MOR gene expression in lymphocytes is still unclear. In this study, it was demonstrated that SIV (SIVmac239) infection may result in gradual reduction of the MOR gene expression and Sp1 during a period of 48 h postinfection by analysis of quantitative real-time RT-PCR and Western blotting. The results of methylation-specific PCR showed that two of 14 CpG islands adjacent to the Sp1 and YY1 elements in the promoter region were methylated, which together with reduced Sp1, contributed to the failure of interaction of Sp1 with YY1 and their binding to the elements, as determined by coimmunoprecipitation, chromatin immunoprecipitation-real-time PCR, and EMSAs. The repression of the MOR gene secondary to SIVmac239 infection could be abolished by the demethylating agent 5-aza-2′-deoxycytidine. Transfection with Sp1-expressing vector (PN3-Sp1) was also able to enhance the activity of the promoter in SIVmac239-infected cells. We therefore concluded that aberrant methylation of the promoter and reduction of Sp1 resulting from SIVmac239 infection led to the silencing of the MOR gene. This finding will be helpful in understanding the synergistic mechanism of HIV infection and morphine addiction in the pathogenesis of AIDS.

DNA demethylation-dependent enhancement of toll-like receptor-2 gene expression in cystic fibrosis epithelial cells involves SP1-activated transcription

Background

The clinical course of cystic fibrosis (CF) is characterized by recurrent pulmonary infections and chronic inflammation. We have recently shown that decreased methylation of the toll-like receptor-2 (TLR2) promoter leads to an apparent CF-related up-regulation of TLR2. This up-regulation could be responsible, in part, for the CF-associated enhanced proinflammatory responses to various bacterial products in epithelial cells. However, the molecular mechanisms underlying DNA hypomethylation-dependent enhancement of TLR2 expression in CF cells remain unknown.

Results

The present study indicates that there is a specific CpG region (CpG#18-20), adjacent to the SP1 binding site that is significantly hypomethylated in several CF epithelial cell lines. These CpGs encompass a minimal promoter region required for basal TLR2 expression, and suggests that CpG#18-20 methylation regulates TLR2 expression in epithelial cells. Furthermore, reporter gene analysis indicated that the SP1 binding site is involved in the methylation-dependent regulation of the TLR2 promoter. Inhibition of SP1 with mithramycin A decreased TLR2 expression in both CF and 5-azacytidine-treated non-CF epithelial cells. Moreover, even though SP1 binding was not affected by CpG methylation, SP1-dependent transcription was abolished by CpG methylation.

Conclusion

This report implicates SP1 as a critical component of DNA demethylation-dependent up-regulation of TLR2 expression in CF epithelial cells.

Tumor suppressor cylindromatosis acts as a negative regulator for Streptococcus pneumoniae-induced NFAT signaling

Gram-positive bacterium Streptococcus pneumoniae is an important human pathogen that colonizes the upper respiratory tract and is also the major cause of morbidity and mortality worldwide. S. pneumoniae causes invasive diseases such as pneumonia, meningitis, and otitis media. Despite the importance of pneumococcal diseases, little is known about the molecular mechanisms by which S. pneumoniae-induced inflammation is regulated, especially the negative regulatory mechanisms. Here we show that S. pneumoniae activates nuclear factor of activated T cells (NFAT) signaling pathway and the subsequent up-regulation of inflammatory mediators via a key pneumococcal virulence factor, pneumolysin. We also demonstrate that S. pneumoniae activates NFAT transcription factor independently of Toll-like receptors 2 and 4. Moreover, S. pneumoniae induces NFAT activation via both Ca(2+)-calcineurin and transforming growth factor-beta-activated kinase 1 (TAK1)-mitogen-activated protein kinase kinase (MKK) 3/6-p38alpha/beta-dependent signaling pathways. Interestingly, we found for the first time that tumor suppressor cylindromatosis (CYLD) acts as a negative regulator for S. pneumoniae-induced NFAT signaling pathway via a deubiquitination-dependent mechanism. Finally, we showed that CYLD interacts with and deubiquitinates TAK1 to negatively regulate the activation of the downstream MKK3/6-p38alpha/beta pathway. Our studies thus bring new insights into the molecular pathogenesis of S. pneumoniae infections through the NFAT-dependent mechanism and further identify CYLD as a negative regulator for NFAT signaling, thereby opening up new therapeutic targets for these diseases.

Transcriptional regulation of the human CD97 promoter by Sp1/Sp3 in smooth muscle cells

The EGF-TM7 receptor CD97 shows different features of expression and function in muscle cells compared to hematopoetic and tumor cells. Since the molecular function and regulation of CD97 are poorly understood, this study aimed at defining its basal transcriptional regulation in smooth muscle cells (SMCs). The computational analysis of the CD97 5'-flanking region revealed that the TATA box-lacking promoter possesses several GC-rich regions as putative Sp1/Sp3 binding sites. Transfection studies with serially deleted promoter constructs demonstrated that the minimal promoter fragment resided in the -218/+45 region containing one out of five identified GC-boxes in the leiomyosarcoma cell line SK-LMS-1 and human bronchial smooth muscle cells (HbSMCs). Mutation of the most proximal GC-site in CD97 reporter gene constructs caused a significant decrease in promoter activity. Gel shift assays and chromatin immunoprecipitation revealed that Sp1 and Sp3 bound specifically to the most proximal GC-site. Furthermore, we showed that Sp1 and Sp3 over-expression activates CD97 promoter activity in HEK293 cells. Our data characterize for the first time the activity of the human CD97 promoter which is controlled by Sp1/Sp3 transcription factors in SMCs.

APC promoter methylation and protein expression in hepatocellular carcinoma

PURPOSE

We investigated the impact of promoter methylation on APC protein expression in patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

50 patients [HCC (n=19), liver metastasis (n=19), cholangiocellular cancer (n=7), and benign liver tumors (n=5)] were studied for methylation using Methylight analysis. APC mutation was investigated by protein truncation test and direct sequencing of genomic DNA. The protein expression was evaluated by immunohistochemistry and Western blot analysis.

RESULTS

The APC promoter was hypermethylated in 81.8% of non-cancerous liver tissue samples. All HCC samples and ten patients with liver metastasis (52.6%) exhibited APC promoter methylation. The degree of methylation was significantly higher in samples from HCC compared to the non-cancerous liver tissue samples (63.1% vs. 24.98%; p=0.001). The level of APC protein expression was significantly reduced in HCC samples compared to that of the corresponding non-tumor liver tissue (p<0.05).

CONCLUSIONS

Promoter methylation of the APC gene seems to be of significance in hepatocarcinogenesis and results in reduced protein expression in HCC. Interestingly, APC promoter methylation is also present in the vast majority of non-cancerous liver tissue whose (patho)physiological function remains unresolved.

Transcriptional control of human T-BET expression: the role of Sp1

Murine T-bet (T-box expressed in T cells) is a master regulator of IFN-gamma gene expression in NK and T cells. T-bet also plays a critical role in autoimmunity, asthma and other diseases. However, cis elements or trans factors responsible for regulating T-bet expression remain largely unknown. Here, we report on our discovery of six Sp1-binding sites within the proximal human T-BET promoter that are highly conserved among mammalian species. Electrophoretic mobility shift assays demonstrate a physical association between Sp1 and the proximal T-BET promoter with a direct dose response between Sp1 expression and T-BET promoter activity. Ectopic overexpression of Sp1 also enhanced T-BET expression and cytokine-induced IFN-gamma secretion in NK cells and T cells. Mithramycin A, which blocks the binding of Sp1 to the T-BET promoter, diminished both T-BET expression and IFN-gamma protein production in monokine-stimulated primary human NK cells. Collectively, our results suggest that Sp1 is a positive transcriptional regulator of T-BET. As T-BET and IFN-gamma are critically important in inflammation, infection, and cancer, targeting Sp1, possibly with mithramycin A, may be useful for preventing and/or treating diseases associated with aberrant T-BET or IFN-gamma expression.

Properties of the various Botmar1 transcripts in imagoes of the bumble bee, Bombus terrestris (Hymenoptera: Apidae)

Botmar1 elements are mariner-like elements (MLEs), class II transposable elements that occur in the genome of the bumble bee, Bombus terrestris. Each haploid B. terrestris genome contains about 230 Botmar1, consisting entirely of 1.3-kb and 0.85-kb elements. During their evolution in the B. terrestris genome, two Botmar1 lineages have been differentiated in terms of their nucleic acid sequences and the differences found in their 5' untranslated regions suggest that they could be transcribed differently in B. terrestris. Here, we show that small amounts of Botmar1 mRNA occur in RNA extracts purified from B. terrestris imagoes. This indicates that the Botmar1 transcription is either weak in imagoes, or is restricted to very few cells. The cloning of several mRNAs reveals that only lineage-2 Botmar1 elements are transcribed. This transcription is specific, and uses cardinal initiators and terminators of eukaryotic elements in the Botmar1 elements. The intrastrand stem-loop folds in the mRNA theoretically synthesized by elements of the first lineage suggest that mRNA maintenance in cells might be self-regulated by RNA interference.

Sp1 and Sp3 regulate basal transcription of the survivin gene

Survivin, a unique member of the inhibitor of apoptosis protein family, is overexpressed in many cancers and considered to play an important role in oncogenesis. In this study, we cloned and identified the proximal 269 bp promoter of survivin gene, which exhibited strong promoter activity in HeLa cells. The TATA-less, GC-rich promoter contains 7 putative binding sites for Sp1, two of which (one at position -148 to -153, the other at position -127 to -140) are essential in regulating basal survivin promoter activity. Not only Sp1 but also Sp3 can activate the survivin promoter, which were proven by EMSA, blocking Sp1 or Sp3 using RNAi or mithramycin treatment of HeLa cells, and overexpression of Sp1 or Sp3. Our results collectively suggest that Sp1 cooperates with Sp3 to regulate survivin promoter activity.

Mithramycin A sensitizes cancer cells to TRAIL-mediated apoptosis by down-regulation of XIAP gene promoter through Sp1 sites

Mithramycin A is a DNA-binding antitumor agent, which has been clinically used in the therapies of several types of cancer and Paget's disease. In this study, we investigated the combined effect of mithramycin A and tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) on apoptosis of cancer cells. In Caki renal cancer cells, which are resistant to TRAIL, cotreatment with subtoxic doses of mithramycin A and TRAIL resulted in a marked increase in apoptosis. This combined treatment was also cytotoxic to Caki cells overexpressing Bcl-2 but not to normal mesengial cells. Moreover, apoptosis by the combined treatment with mithramycin A and TRAIL was dramatically induced in various cancer cell types, thus offering an attractive strategy for safely treating malignant tumors. Mithramycin A-stimulated TRAIL-induced apoptosis was blocked by pretreatment with the broad caspase inhibitor zVAD-fmk or Crm-A overexpression, showing its dependence on caspases. We found that mithramycin A selectively down-regulated XIAP protein levels in various cancer cells. Luciferase reporter assay and the chromatin immunoprecipitation assay using the XIAP promoter constructs show that mithramycin A down-regulates the transcription of XIAP gene through inhibition of Sp1 binding to its promoter. Although XIAP overexpression significantly attenuated apoptosis induced by mithramycin A plus TRAIL, suppression of XIAP expression by transfection with its small interfering RNA prominently enhanced TRAIL-induced apoptosis. We present here for the first time that mithramycin A-induced suppression of XIAP transcription plays a critical role in the recovery of TRAIL sensitivity in various cancer cells.

Computational promoter analysis of mouse, rat and human antimicrobial peptide-coding genes

BACKGROUND

Mammalian antimicrobial peptides (AMPs) are effectors of the innate immune response. A multitude of signals coming from pathways of mammalian pathogen/pattern recognition receptors and other proteins affect the expression of AMP-coding genes (AMPcgs). For many AMPcgs the promoter elements and transcription factors that control their tissue cell-specific expression have yet to be fully identified and characterized.

RESULTS

Based upon the RIKEN full-length cDNA and public sequence data derived from human, mouse and rat, we identified 178 candidate AMP transcripts derived from 61 genes belonging to 29 AMP families. However, only for 31 mouse genes belonging to 22 AMP families we were able to determine true orthologous relationships with 30 human and 15 rat sequences. We screened the promoter regions of AMPcgs in the three species for motifs by an ab initio motif finding method and analyzed the derived promoter characteristics. Promoter models were developed for alpha-defensins, penk and zap AMP families. The results suggest a core set of transcription factors (TFs) that regulate the transcription of AMPcg families in mouse, rat and human. The three most frequent core TFs groups include liver-, nervous system-specific and nuclear hormone receptors (NHRs). Out of 440 motifs analyzed, we found that three represent potentially novel TF-binding motifs enriched in promoters of AMPcgs, while the other four motifs appear to be species-specific.

CONCLUSION

Our large-scale computational analysis of promoters of 22 families of AMPcgs across three mammalian species suggests that their key transcriptional regulators are likely to be TFs of the liver-, nervous system-specific and NHR groups. The computationally inferred promoter elements and potential TF binding motifs provide a rich resource for targeted experimental validation of TF binding and signaling studies that aim at the regulation of mouse, rat or human AMPcgs.

Constitutive expression of murine decay-accelerating factor 1 is controlled by the transcription factor Sp1

The complement regulatory protein decay-accelerating factor (DAF or CD55) protects host tissue from complement-mediated injury by inhibiting the classical and alternative complement pathways. Besides its role in complement regulation, DAF has also been shown to be a key player in T cell immunity. Modulation of DAF expression could therefore represent a critical regulatory mechanism in both innate and adaptive immune responses. To identify and characterize key transcriptional regulatory elements controlling mouse Daf1 expression, a 2.5-kb fragment corresponding to the 5' flanking region of the mouse Daf1 gene was cloned. Sequence analysis showed that the mouse Daf1 promoter lacks conventional TATA and CCAAT boxes and displays a high guanine and cytosine content. RACE was used to identify one major and two minor transcription start sites 47, 20, and 17 bp upstream of the translational codon. Positive and negative regulatory regions were identified by transiently transfecting sequential 5'deletion constructs of the 5'flanking region into NIH/3T3, M12.4, and RAW264.7 cells. Mutational analyses of the promoter region combined with Sp1-specific ELISA showed that the transcription factor Sp1 is required for basal transcription and LPS-induced expression of the Daf1 gene. These findings provide new information on the regulation of the mouse Daf1 promoter and will facilitate further studies on the expression of Daf1 during immune responses.

SUMO down-regulates the activity of Elf4/myeloid Elf-1-like factor

Myeloid elf-1-like factor (MEF) or Elf4 is an ETS protein known to regulate the basal expression of the anti-microbial peptides, lysozyme and human beta-defensin-2, in epithelial cells and activate the transcription of perforin in natural killer cells. The numerous target genes of MEF and its biological functions signify the importance of this Ets transcription factor. Here we show that MEF is modified by conjugation with SUMO-1/-2 (small ubiquitin-related modifier) both in mammalian cells and in Escherichia coli overexpressing human SUMO-1/-2. We identified by point mutation that lysine 657 of MEF is the site for sumoylation. This modification down-regulated MEF activity on lysozyme and perforin promoters, and decreased the lysozyme mRNA expression. Chromatin immuno-precipitation analysis revealed that SUMO-conjugation diminished the recruitment of MEF to the lysozyme promoter, which partly explains the down-regulation of MEF activity by SUMO. These findings contribute to our understanding of the regulation of the ETS factor MEF.