Identification of a phorbol ester-responsive element in the interferon-gamma receptor 1 chain gene

NF90-NF45 is essential for β cell compensation under obesity-inducing metabolic stress through suppression of p53 signaling pathway

The Nuclear Factor 90 (NF90)-NF45 complex has been known to regulate the progression of transcription, mRNA stability, translational inhibition, RNA export and microRNA biogenesis. However, the physiological functions of the NF90-NF45 complex remain unclear. We newly discovered that the NF90-NF45 complex was expressed in primary β cells and established cell lines. Therefore, in this study, we focused on the function of the endogenous NF90-NF45 complex in the β cells. To investigate this issue, we generated β-cell-specific NF90-NF45 deficient mice. These mice exhibited hyperglycaemia and lower plasma insulin levels under a high fat diet together with decreased islet mass. To uncover this mechanism, we performed a whole-genome expression microarray of the total RNA prepared from β cell lines treated with siRNAs targeting both NF90 and NF45. In this result, we found an activation of p53 signaling in the NF90-NF45-knockdown cells. This activation was supported by elevation of luciferase activity derived from a reporter plasmid harboring p53 binding sites in the NF90-NF45-knockdown cells. Furthermore, the knockdown of NF90-NF45 resulted in a significant retardation of the β cell line growth rates. Importantly, a dominant negative form of p53 rescues the growth retardation in BTC6 cells depleted of NF90-NF45, suggesting that NF90-NF45 would be positively involved in β cell proliferation through suppression of p53 signal pathway. Taken together, NF90-NF45 is essential for β cell compensation under obesity-inducing metabolic stress via repression of p53 signaling.

Analysis of interferon-γ receptor IFNGR1 and IFNGR2 expression and regulation at the maternal-conceptus interface and the role of interferon-γ on endometrial expression of interferon signaling molecules during early pregnancy in pigs

It has long been known that pig conceptuses produce interferon-γ (IFNG) at the time of implantation, but the role of IFNG and its mechanism of action at the maternal-conceptus interface are not fully understood. Accordingly, we analyzed the expression and regulation of IFNG receptors IFNGR1 and IFNGR2 in the endometrium during the estrous cycle and pregnancy in pigs. Levels of IFNGR1 and IFNGR2 messenger RNA (mRNA) expression changed in the endometrium, with the highest levels during mid pregnancy for IFNGR1 and on Day 12 of pregnancy for IFNGR2. The expression of IFNGR1 and IFNGR2 mRNAs was also detected in conceptuses during early pregnancy and chorioallantoic tissues during mid to late pregnancy. IFNGR1 and IFNGR2 mRNAs were localized to endometrial epithelial and stromal cells and to the chorionic membrane during pregnancy. IFNGR2 protein was also localized to endometrial epithelial and stromal cells, and increased epithelial expression of IFNGR2 mRNA and protein was detectable during early pregnancy than the estrous cycle. Explant culture studies showed that estrogen increased levels of IFNGR2, but not IFNGR1, mRNAs, while interleukin-1β did not affect levels of IFNGR1 and IFNGR2 mRNAs. Furthermore, IFNG increased levels of IRF1, IRF2, STAT1, and STAT2 mRNAs in the endometrial explants. These results in pigs indicate that IFNGR1 and IFNGR2 are expressed in a stage of pregnancy- and cell-type specific manner in the endometrium and that sequential cooperative action of conceptus signals estrogen and IFNG may be critical for endometrial responsiveness to IFNs for the establishment of pregnancy in pigs.

Suppression of MicroRNA-7 (miR-7) Biogenesis by Nuclear Factor 90-Nuclear Factor 45 Complex (NF90-NF45) Controls Cell Proliferation in Hepatocellular Carcinoma

MicroRNA-7 (miR-7)has been characterized as an anti-oncogenic microRNA (miRNA) in several cancers, including hepatocellular carcinoma (HCC). However, the mechanism for the regulation of miR-7 production in tumors remains unclear. Here, we identified nuclear factor 90 (NF90) and NF45 complex (NF90-NF45) as negative regulators of miR-7 processing in HCC. Expression of NF90 and NF45 was significantly elevated in primary HCC tissues compared with adjacent non-tumor tissues. To examine which miRNAs are controlled by NF90-NF45, we performed an miRNA microarray and quantitative RT-PCR analyses of HCC cell lines. Depletion of NF90 resulted in elevated levels of mature miR-7, whereas the expression of primary miR-7-1 (pri-miR-7-1) was decreased in cells following knockdown of NF90. Conversely, the levels of mature miR-7 were reduced in cells overexpressing NF90 and NF45, although pri-miR-7-1 was accumulated in the same cells. Furthermore, NF90-NF45 was found to bind pri-miR-7-1 in vitro These results suggest that NF90-NF45 inhibits the pri-miR-7-1 processing step through the binding of NF90-NF45 to pri-miR-7-1. We also found that levels of the EGF receptor, an oncogenic factor that is a direct target of miR-7, and phosphorylation of AKT were significantly decreased in HCC cell lines depleted of NF90 or NF45. Of note, knockdown of NF90 or NF45 caused a reduction in the proliferation rate of HCC cells. Taken together, NF90-NF45 stimulates an elevation of EGF receptor levels via the suppression of miR-7 biogenesis, resulting in the promotion of cell proliferation in HCC.

Overexpression of NF90-NF45 Represses Myogenic MicroRNA Biogenesis, Resulting in Development of Skeletal Muscle Atrophy and Centronuclear Muscle Fibers

MicroRNAs (miRNAs) are involved in the progression and suppression of various diseases through translational inhibition of target mRNAs. Therefore, the alteration of miRNA biogenesis induces several diseases. The nuclear factor 90 (NF90)-NF45 complex is known as a negative regulator in miRNA biogenesis. Here, we showed that NF90-NF45 double-transgenic (dbTg) mice develop skeletal muscle atrophy and centronuclear muscle fibers in adulthood. Subsequently, we found that the levels of myogenic miRNAs, including miRNA 133a (miR-133a), which promote muscle maturation, were significantly decreased in the skeletal muscle of NF90-NF45 dbTg mice compared with those in wild-type mice. However, levels of primary transcripts of the miRNAs (pri-miRNAs) were clearly elevated in NF90-NF45 dbTg mice. This result indicated that the NF90-NF45 complex suppressed miRNA production through inhibition of pri-miRNA processing. This finding was supported by the fact that processing of pri-miRNA 133a-1 (pri-miR-133a-1) was inhibited via binding of NF90-NF45 to the pri-miRNA. Finally, the level of dynamin 2, a causative gene of centronuclear myopathy and concomitantly a target of miR-133a, was elevated in the skeletal muscle of NF90-NF45 dbTg mice. Taken together, we conclude that the NF90-NF45 complex induces centronuclear myopathy through increased dynamin 2 expression by an NF90-NF45-induced reduction of miR-133a expression in vivo.

The stress-related hormone norepinephrine induced upregulation of Nix, contributing to ECM protein expression

Organ fibrosis has been viewed as a major medical problem that leads to progressive dysfunction of the organ and eventually the death of patients. Stress-related hormone norepinephrine (NE) has been reported to exert fibrogenic actions in the injured organ. Nix plays a critical role in pressure overload-induced cardiac remodeling and heart failure through mediating cardiomyocyte apoptosis. However, cardiac remodeling also includes fibrosis. Whether Nix is involved in stress-induced fibrosis remains unclear. The present study was designed to determine the role of Nix in NE-induced NIH/3T3 fibroblasts. The results showed that Nix was upregulated and closely associated with cell proliferation, collagen and fibronectin expression in NIH/3T3 fibroblasts following NE treatment. Overexpression of Nix promoted collagen and fibronectin expression, whereas the suppression of Nix resulted in a strong reduction in collagen and fibronectin expression. Moreover, the increases in collagen and fibronectin expression induced by NE were successively increased when Nix was overexpressed and reduced when Nix was inhibited. Furthermore, we demonstrated that the PKC activation is responsible for the upregulation of Nix induced by NE. Inhibition of Nix expression with α-adrenoceptor antagonist, β-adrenoceptor antagonist or PKC inhibitor attenuated NE-induced collagen and fibronectin expression. Our data revealed that Nix is a novel mediator of NE-induced fibrosis. Thus, it would provide a new insight into the development of effective preventative measures and therapies of tissue fibrosis.

Type I IFNs downregulate myeloid cell IFN-γ receptor by inducing recruitment of an early growth response 3/NGFI-A binding protein 1 complex that silences ifngr1 transcription

The ability of type I IFNs to increase susceptibility to certain bacterial infections correlates with downregulation of myeloid cell surface IFNGR, the receptor for the type II IFN (IFN-γ), and reduced myeloid cell responsiveness to IFN-γ. In this study, we show that the rapid reductions in mouse and human myeloid cell surface IFNGR1 expression that occur in response to type I IFN treatment reflect a rapid silencing of new ifngr1 transcription by repressive transcriptional regulators. Treatment of macrophages with IFN-β reduced cellular abundance of ifngr1 transcripts as rapidly and effectively as actinomycin D treatment. IFN-β treatment also significantly reduced the amounts of activated RNA polymerase II (pol II) and acetylated histones H3 and H4 at the ifngr1 promoter and the activity of an IFNGR1-luc reporter construct in macrophages. The suppression of IFNGR1-luc activity required an intact early growth response factor (Egr) binding site in the proximal ifngr1 promoter. Three Egr proteins and two Egr/NGFI-A binding (Nab) proteins were found to be expressed in bone macrophages, but only Egr3 and Nab1 were recruited to the ifngr1 promoter upon IFN-β stimulation. Knockdown of Nab1 in a macrophage cell line prevented downregulation of IFNGR1 and prevented the loss of acetylated histones from the ifngr1 promoter. These data suggest that type I IFN stimulation induces a rapid recruitment of a repressive Egr3/Nab1 complex that silences transcription from the ifngr1 promoter. This mechanism of gene silencing may contribute to the anti-inflammatory effects of type I IFNs.

High expression of nuclear factor 90 (NF90) leads to mitochondrial degradation in skeletal and cardiac muscles

While NF90 has been known to participate in transcription, translation and microRNA biogenesis, physiological functions of this protein still remain unclear. To uncover this, we generated transgenic (Tg) mice using NF90 cDNA under the control of β-actin promoter. The NF90 Tg mice exhibited a reduction in body weight compared with wild-type mice, and a robust expression of NF90 was detected in skeletal muscle, heart and eye of the Tg mice. To evaluate the NF90 overexpression-induced physiological changes in the tissues, we performed a number of analyses including CT-analysis and hemodynamic test, revealing that the NF90 Tg mice developed skeletal muscular atrophy and heart failure. To explore causes of the abnormalities in the NF90 Tg mice, we performed histological and biochemical analyses for the skeletal and cardiac muscles of the Tg mice. Surprisingly, these analyses demonstrated that mitochondria in those muscular tissues of the Tg mice were degenerated by autophagy. To gain further insight into the cause for the mitochondrial degeneration, we identified NF90-associated factors by peptide mass fingerprinting. Of note, approximately half of the NF90-associated complexes were ribosome-related proteins. Interestingly, protein synthesis rate was significantly suppressed by high-expression of NF90. These observations suggest that NF90 would negatively regulate the function of ribosome via its interaction with the factors involved in the ribosome function. Furthermore, we found that the translations or protein stabilities of PGC-1 and NRF-1, which are critical transcription factors for expression of mitochondrial genes, were significantly depressed in the skeletal muscles of the NF90 Tg mice. Taken together, these findings suggest that the mitochondrial degeneration engaged in the skeletal muscle atrophy and the heart failure in the NF90 Tg mice may be caused by NF90-induced posttranscriptional repression of transcription factors such as PGC-1 and NRF-1 for regulating nuclear-encoded genes relevant to mitochondrial function.

Modulation of IFN-γ receptor 1 expression by AP-2α influences IFN-γ sensitivity of cancer cells

Interferon (IFN)-γ plays crucial roles in regulating both innate and adaptive immunity. The existence of IFN-γ receptor 1 (IFNGR1) molecules on the cell surface is a prerequisite to the initiation of IFN-γ signaling; low expression of IFNGR1 leads to a functional blockade of IFN-γ signaling. However, the molecular mechanisms by which IFNGR1 expression is controlled are unclear. In the present study, we demonstrated that IFNGR1 expression was reduced or lost in breast cancer. Heterogeneous IFNGR1 immunoreactivity appeared to be associated with the morphological heterogeneity of breast cancer, and loss of IFNGR1 expression was predominantly observed in poorly differentiated areas. We identified the functional activating protein (AP)-2 and specificity protein (SP)-1 sites within the IFNGR1 promoter. Ectopic expression of AP-2α drastically repressed the expression of IFNGR1 and hindered IFN-γ signaling, whereas AP-2α gene silencing elevated IFNGR1 levels. Overexpression of SP-1 effectively antagonized the repressive effects of AP-2α. Simultaneous recruitment of both transcription factors to the AP-2 and SP-1 motifs, respectively, in the IFNGR1 promoter was demonstrated, implying that AP-2α and SP-1 may synergistically modulate IFNGR1 transcription. Moreover, AP-2α overexpression in AP-2-deficient SW480 cells remarkably inhibited Stat1 phosphorylation and the anti-proliferative effects of IFN-γ, whereas knockdown of the AP-2α expression dramatically enhanced the sensitivities of HeLa cells highly expressing AP-2 to IFN-γ, indicating that dysregulation of AP-2α expression is associated with impaired IFN-γ actions in cancer cells.

The NF90-NF45 complex functions as a negative regulator in the microRNA processing pathway

The positive regulatory machinery in the microRNA (miRNA) processing pathway is relatively well characterized, but negative regulation of the pathway is largely unknown. Here we show that a complex of nuclear factor 90 (NF90) and NF45 proteins functions as a negative regulator in miRNA biogenesis. Primary miRNA (pri-miRNA) processing into precursor miRNA (pre-miRNA) was inhibited by overexpression of the NF90 and NF45 proteins, and considerable amounts of pri-miRNAs accumulated in cells coexpressing NF90 and NF45. Treatment of cells overexpressing NF90 and NF45 with an RNA polymerase II inhibitor, alpha-amanitin, did not reduce the amounts of pri-miRNAs, suggesting that the accumulation of pri-miRNAs is not due to transcriptional activation. In addition, the NF90 and NF45 complex was not found to interact with the Microprocessor complex, which is a processing factor of pri-miRNAs, but was found to bind endogenous pri-miRNAs. NF90-NF45 exhibited higher binding activity for pri-let-7a than pri-miR-21. Of note, depletion of NF90 caused a reduction of pri-let-7a and an increase of mature let-7a miRNA, which has a potent antiproliferative activity, and caused growth suppression of transformed cells. These findings suggest that the association of the NF90-NF45 complex with pri-miRNAs impairs access of the Microprocessor complex to the pri-miRNAs, resulting in a reduction of mature miRNA production.

Negative feedback regulation of IFN-gamma pathway by IFN regulatory factor 2 in esophageal cancers

IFN-gamma is an antitumor cytokine that inhibits cell proliferation and induces apoptosis after engagement with the IFN-gamma receptors (IFNGR) expressed on target cells, whereas IFN regulatory factor 2 (IRF-2) is able to block the effects of IFN-gamma by repressing transcription of IFN-gamma-induced genes. Thus far, few studies have explored the influences of IFN-gamma on human esophageal cancer cells. In the present study, therefore, we investigated in detail the functions of IFN-gamma in esophageal cancer cells. The results in clinical samples of human esophageal cancers showed that the level of IFN-gamma was increased in tumor tissues and positively correlated with tumor progression and IRF-2 expression, whereas the level of IFNGR1 was decreased and negatively correlated with tumor progression and IRF-2 expression. Consistently, in vitro experiments showed that low concentration of IFN-gamma induced the expression of IRF-2 with potential promotion of cell growth, and moreover, IRF-2 was able to suppress IFNGR1 transcription in human esophageal cancer cells by binding a specific motif in IFNGR1 promoter, which lowered the sensitivity of esophageal cancer cells to IFN-gamma. Taken together, our results disclosed a new IRF-2-mediated inhibitory mechanism for IFN-gamma-induced pathway in esophageal cancer cells: IFN-gamma induced IRF-2 up-regulation, then up-regulated IRF-2 decreased endogenous IFNGR1 level, and finally, the loss of IFNGR1 turned to enhance the resistance of esophageal cancer cells to IFN-gamma. Accordingly, the results implied that IRF-2 might act as a mediator for the functions of IFN-gamma and IFNGR1 in human esophageal cancers.

Modulation of gamma interferon receptor 1 by Mycobacterium tuberculosis: a potential immune response evasive mechanism

Mycobacterium tuberculosis inhibits gamma interferon (IFN-gamma)-mediated antimycobacterial action by adopting diverse mechanisms. IFN-gamma binds to its receptor, IFN-gammaR, in order to initiate proper signaling. We have observed reduced surface expression levels of IFN-gamma receptor 1 (IFN-gammaR1) in untreated pulmonary tuberculosis patients compared to those in healthy individuals (P < 0.01). Following antitubercular therapy, the expression of IFN-gammaR1 was restored in these patients. To delineate the mechanism by which M. tuberculosis modulates IFN-gammaR1, in vitro experiments were designed, wherein the down modulation of IFN-gammaR1 surface expression was observed for CD14+ cells in peripheral blood mononuclear cells (PBMCs) cocultured with live M. tuberculosis compared to that for uninfected cells (P < 0.01). No modulation of IFN-gammaR1 expression was observed for CD14+ cells in PBMCs infected with Mycobacterium smegmatis. A time-dependent decrease in IFN-gammaR1 mRNA expression was observed for PBMCs infected with M. tuberculosis. Similar down modulation of IFN-gammaR1 protein and mRNA expression in phorbol myristate acetate-differentiated THP-1 cells (pdTHP-1) by M. tuberculosis was observed (P < 0.01). Using reporter gene analysis of 5' deletion constructs of the IFN-gammaR1 gene (IFNGR1) promoter, the decrease in IFN-gammaR1 mRNA in M. tuberculosis-infected pdTHP-1 cells was shown to be due to the decreased transcription of IFNGR1. By immunoblotting and electrophoretic mobility shift assays, the down regulation of stimulating protein 1 (Sp1) expression and its recruitment on the phorbol ester-responsive element of the IFNGR1 promoter in M. tuberculosis-infected pdTHP-1 cells was observed. This down regulation of Sp1 in pdTHP-1 cells cocultured with M. tuberculosis may be responsible for the down regulation of IFN-gammaR1 expression, thereby potentially altering its receptivity to IFN-gamma.

Distinct pathways regulate proapoptotic Nix and BNip3 in cardiac stress

Up-regulation of myocardial Nix and BNip3 is associated with apoptosis in cardiac hypertrophy and ischemia, respectively. To identify mechanisms of gene regulation for these critical cardiac apoptosis effectors, the determinants of Nix and BNip3 promoter activation were elucidated by luciferase reporter gene expression in neonatal rat cardiac myocytes. BNip3 transcription was increased by hypoxia but not by phenylephrine (10 microM), angiotensin II (100 nM), or isoproterenol (10 microM). In contrast, Nix transcription was increased by phenylephrine but not by isoproterenol, angiotensin II, or hypoxia. Since phenylephrine stimulates cardiomyocyte hypertrophy via protein kinase C (PKC), the effects of phorbol myristate acetate (PMA, 10 nM for 24 h) and adenoviral PKC expression were assessed. PMA and PKC alpha, but not PKC epsilon or dominant negative PKC alpha, increased Nix transcription. Multiple Nix promoter GC boxes bound transcription factor Sp-1, and basal and PMA- or PKC alpha-stimulated Nix promoter activity was suppressed by mithramycin inhibition of Sp1-DNA interactions. In vivo determinants of Nix expression were evaluated in Nix promoter-luciferase (NixP) transgenic mice that underwent ischemia-reperfusion (1 h/24 h), transverse aortic coarctation (TAC), or cross-breeding with the G(q) overexpression model of hypertrophy. Luciferase activity increased in G alpha(q)-NixP hearts 3.2 +/- 0.4-fold and in TAC hearts 2.8 +/- 0.4-fold but did not increase with infarction-reperfusion. NixP activity was proportional to the extent of TAC hypertrophy and was inhibited by mithramycin. These studies revealed distinct mechanisms of transcriptional regulation for cardiac Nix and BNip3. BNip3 is hypoxia-inducible, whereas Nix expression was induced by G alpha(q)-mediated hypertrophic stimuli. PKC alpha, a G(q) effector, transduced Nix transcriptional induction via Sp1.

Repression of 5-aminolevulinate synthase gene by the potent tumor promoter, TPA, involves multiple signal transduction pathways

The potent tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) induces activator protein-1 (AP-1) transcription factors, early response genes involved in a diverse set of transcriptional regulatory processes, and protein kinase C (PKC) activity. This work was designed to explore the signal transduction pathways involved in TPA regulation of 5-aminolevulinate synthase (ALAS) gene expression, the mitochondrial matrix enzyme that catalyzes the first and rate-limiting step of heme biosynthesis. We have previously reported that TPA causes repression of ALAS gene, but the signaling pathways mediating this effect remain elusive. The present study investigates the role of different cascades often implicated in the propagation of phorbol ester signaling. To explore this, we combined the transient overexpression of regulatory proteins involved in these pathways and the use of small cell permeant inhibitors in human hepatoma HepG2 cells. In these experimental conditions, we analyzed TPA action upon endogenous ALAS mRNA levels, as well as the promoter activity of a fusion reporter construct, harboring the TPA-responsive region of ALAS gene driving chloramphenicol acetyl transferase gene expression. We demonstrated that the participation of alpha isoform of PKC, phosphatidylinositol 3-kinase (PI3K), extracellular-signal regulated kinase (ERK1/2), and c-Jun N-terminal kinase (JNK) is crucial for the end point response. Remarkably, in this case, ERK activation is achieved in a Ras/Raf/MEK-independent manner. We also propose that p90RSK would be a convergent point between PI3K and ERK pathways. Furthermore, we elucidated the crosstalk among the components of the cascades taking part in TPA-mediated ALAS repression. Finally, by overexpression of a constitutively active p90RSK and the coactivator, cAMP-response element protein (CREB)-binding protein (CBP), we reinforced our previous model, that implies competition between AP-1 and CREB for CBP.

Toll-like receptor 2 stimulation decreases IFN-gamma receptor expression in mouse RAW264.7 macrophages

Interferon-gamma (IFN-gamma) is a key cytokine in the immune defense against mycobacteria. IFN-gamma activates macrophages to resist the growth of mycobacteria and induces expression of MHC class II molecules required for antigen presentation. Macrophages infected with mycobacteria or stimulated by the interaction of mycobacterial products with toll-like receptor 2 (TLR2) have reduced responses to IFN-gamma. Previous research has shown that infection of mouse macrophages with Mycobacterium avium causes decreased expression of the IFN-gamma receptor (IFNGR). In the present study, we show that TLR2 stimulation of RAW264.7 macrophages with a synthetic lipoprotein, Pam3CSK4, also causes rapid decrease in expression of IFNGR-1 protein, with little change in IFNGR-2 protein levels. The decrease in IFNGR-2 expression in TLR2-stimulated cells required receptor internalization and proteasomal degradation. The level of IFNGR-1 mRNA also decreased in TLR2-stimulated RAW264.7 cells and M. avium-infected cells. The decrease in IFNGR-1 mRNA was shown to be due to decreased transcription. In spite of the decrease in IFNGR-2 receptor expression, activation of Stat1 activation by an optimal dose of IFN-gamma was identical between control and TLR2-stimulated RAW264.7 cells. However, at low suboptimal doses of IFN-gamma, Stat1 activation was decreased in TLR2-stimulated cells.

Sp1 and Sp3 are involved in up-regulation of human deoxyribonuclease II transcription during differentiation of HL-60 cells

Expression of DNase II in macrophages is potentially crucially important in the removal of unwanted DNA. We have previously shown that DNase II expression is up-regulated at the transcriptional level during the phorbol 12-myristate-13-acetate (PMA)-induced differentiation of HL-60 and THP-1 cells. In this study, we investigated the cis-regulatory elements and transcription factors involved in this process in HL-60 cells. cis-Regulatory elements in the DNase II promoter were located by 5' deletion and site-directed mutagenesis of promoter-luciferase constructs and transient transfection of HL-60 cells. Furthermore, the binding proteins were identified by electrophoretic mobility shift assay (EMSA) in the presence of specific antibodies. In the DNase II promoter, 249 base pairs upstream of the transcription start site were essential for maximal promoter activity in both untreated and PMA-treated HL-60 cells and, within this region, three Sp1 and Sp3 binding sites were identified as essential for transcriptional regulation and PMA induction. Western blot analysis showed that PMA treatment resulted in increased levels of Sp1 and Sp3 proteins. Furthermore, cotransfection analysis in Drosophila SL2 cells showed that Sp1 was more potent than Sp3 in activating the DNase II promoter. We therefore conclude that Sp1 and/or Sp3 are involved in the up-regulation of DNase II expression during the differentiation of HL-60 cells.

Inhibitory effect of AP-1 complex on 5-aminolevulinate synthase gene expression through sequestration of cAMP-response element protein (CRE)-binding protein (CBP) coactivator

Activation protein-1 (AP-1) transcription factors are early response genes involved in a diverse set of transcriptional regulatory processes. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) is often used to induce AP-1 activity. The purpose of this work was to explore the molecular mechanisms involved in the TPA regulation of ubiquitous 5-aminolevulinate synthase (ALAS) gene expression, the first and rate-controlling step of the heme biosynthesis. Previous analysis of the 5'-flanking sequence of ALAS revealed the existence of two cAMP-response elements (CRE) required for basal and cAMP-stimulated expression. The fragment -833 to +42 in the 5'-flanking region of rat ALAS gene was subcloned into a chloramphenicol acetyltransferase (CAT) reporter vector. The expression vector pALAS/CAT produced a significant CAT activity in transiently transfected HepG2 human hepatoma cells, which was repressed by TPA. Sequence and deletion analysis detected a TPA response element (TRE), located between -261 and -255 (TRE-ALAS), that was critical for TPA regulation. We demonstrated that c-Fos, c-Jun, and JunD are involved in TPA inhibitory effect due to their ability to bind TRE-ALAS, evidenced by supershift analysis and their capacity to repress promoter activity in transfection assays. Repression of ALAS promoter activity by TPA treatment or Fos/Jun overexpression was largely relieved when CRE protein-binding protein or p300 was ectopically expressed. When the TRE site was placed in a different context with respect to CRE sites, it appeared to act as a transcriptional enhancer. We propose that the decrease in ALAS basal activity observed in the presence of TPA may reflect a lower ability of this promoter to assemble the productive pre-initiation complex due to CRE protein-binding protein sequestration. We also suggest that the transcriptional properties of this AP-1 site would depend on a spatial-disposition-dependent manner with respect to the CRE sites and to the transcription initiation site.

Up-regulation of human deoxyribonuclease II gene expression during myelomonocytic differentiation of HL-60 and THP-1 cells

Several recent studies have suggested that intracellular deoxyribonuclease II (DNase II) is responsible for the degradation of DNA from apoptotic cells that are engulfed by macrophages. In this study, we studied DNase II expression during the phorbol 12-myristate-13-acetate (PMA)-induced differentiation of HL-60 and THP-1 cells. Basal levels of DNase II mRNA and protein were low, with expression being up-regulated approximately 15- and 7-fold, respectively, in HL-60 and THP-1 cells 72 h after PMA treatment. Nuclear run-on and luciferase reporter assays showed that transcription of DNase II gene was increased in PMA-treated cells. Together, these results demonstrate that DNase II gene transcription is increased during myelomonocytic differentiation, resulting in increased levels of mRNA and protein. This increase in DNase II levels in differentiated HL-60 and THP-1 cells suggests that it may play an important role in macrophages.