Biomedical subjects

Dhananjaya V Kalvakolanu

Publications and source records attributed to Dhananjaya V Kalvakolanu.

At least 19 recordsLinked to original sources

PubMed2006

A JNK-independent signaling pathway regulates TNF alpha-stimulated, c-Jun-driven FRA-1 protooncogene transcription in pulmonary epithelial cells.

Among the several effectors that mediate TNF-alpha action is AP-1, which consists of transcription factors belonging to the JUN and FOS families. Although the effects of TNF-alpha in immune cells, such as the induction of NF-kappaBeta, are well known, the mechanisms by which it induces transcriptional activation of AP-1 in pulmonary epithelial cells are not well defined. In this study, we report that TNF-alpha stimulates the expression of the FRA-1 protooncogene in human pulmonary epithelial cells using c-Jun, acting via a 12-O-tetradecanoylphorbol-13 acetate response element located at -318. Although TNF-alpha stimulates phosphorylation of c-Jun, the inhibition of JNK activity had no significant effect on FRA-1 induction. Consistent with this result, ectopic expression of a c-Jun mutant lacking JNK phosphorylation sites had no effect on the TNF-alpha-induced expression of the promoter. In contrast, inhibition of the ERK pathway or ectopic expression of an ERK1 mutant strikingly reduced FRA-1 transcription. ERK inhibition not only blocked phosphorylation of Elk1, CREB, and ATF1, which constitutively bind to the FRA-1 promoter, but also suppressed the recruitment of c-Jun to the promoter. We found that short interfering RNA-mediated silencing of FRA-1 enhances TNF-alpha-induced IL-8 expression, whereas overexpression causes an opposite effect. Our findings collectively indicate that ERK signaling plays key roles in both Elk1, CREB, and ATF-1 activation and the subsequent recruitment of c-Jun to the FRA-1 promoter in response to TNF-alpha in pulmonary epithelial cells.

Animals↗

PubMed2006

A Phosphatidylinositol 3-kinase-regulated Akt-independent signaling promotes cigarette smoke-induced FRA-1 expression.

The FRA-1 proto-oncogene is overexpressed in a variety of human tumors and is known to up-regulate the expression of genes involved in tumor progression and invasion. The phosphatidylinositol 3-kinase (PI3K)-Akt pathway is also known to regulate these cellular processes. More importantly, respiratory toxicants and carcinogens activate both the PI3K-Akt pathway and FRA-1 expression in human bronchial epithelial (HBE) cells. In this study we investigated a potential link between the PI3K-Akt pathway and the cigarette smoke (CS)-stimulated epidermal growth factor receptor-mediated FRA-1 induction in non-oncogenic HBE cells. Treatment of cells with LY294002, an inhibitor of the PI3K-Akt pathway, completely blocked CS-induced FRA-1 expression. Surprisingly pharmacological inhibition of Akt had no significant effect on CS-induced FRA-1 expression. Likewise the inhibition of protein kinase C zeta, which is a known downstream effector of PI3K, did not alter FRA-1 expression. We found that the PI3K through p21-activated kinase 1 regulates FRA-1 proto-oncogene induction by CS and the subsequent activation of the Elk1 and cAMP-response element-binding protein transcription factors that are bound to the promoter in HBE cells.

Carcinogens↗

PubMed2006

A role for Stat1 in the regulation of lipopolysaccharide-induced interleukin-1beta expression.

Because the induction of interleukin-1beta (IL-1beta) is critical to antibacterial host defenses and its excessive generation is a prominent component of sepsis, regulation of this proinflammatory cytokine is a critical factor in the immune response to lipopolysaccharide (LPS). We previously showed that LPS-induced IL-1beta expression was regulated by a Stat1-dependent, nitric oxide (NO)-mediated mechanism. Subsequent in vivo studies showed that whereas Stat1 had a role in the downregulation of IL-1beta expression, it had a more significant effect on its initial induction. Although both interferon-beta (IFN-beta) and IFN-gamma activate Stat1, the early appearance of IFN-beta in the circulation after LPS administration suggested its pivotal role in Stat1-mediated IL-1beta expression in vivo. Further in vitro analysis of peritoneal macrophages from IFN-beta (/), Stat1(/), and caspase-1(/) mice and their wild-type controls following LPS stimulation demonstrated that IL-1beta mRNA was expressed in these mice but not in macrophages from MyD88(/) mice. Despite the presence of IL-1beta mRNA, IL-1beta protein was markedly reduced in the absence of Stat1 activation in macrophages derived from IFN-beta (/) and Stat1(/) mice or in the absence of caspase-1 activity, which itself was dependent on Stat1 activation. These studies support the hypothesis that the expression of IL-1beta requires both the MyD88-dependent induction of IL-1beta mRNA and pro-IL-1beta as well as the MyD88-independent, Stat1-mediated processing of that gene product into active cytokine.

Animals↗

PubMed2005

Down-regulation of signal transducer and activator of transcription 3 expression using vector-based small interfering RNAs suppresses growth of human prostate tumor in vivo.

PURPOSE: Signal transducer and activator of transcription 3 (Stat3) is constitutively activated in a variety of cancers and it is a common feature of prostate cancer. Thus, Stat3 represents a promising molecular target for tumor therapy. We applied a DNA vector-based Stat3-specific RNA interference approach to block Stat3 signaling and to evaluate the biological consequences of Stat3 down-modulation on tumor growth using a mouse model. EXPERIMENTAL DESIGN: To investigate the therapeutic potential of blocking Stat3 in cancer cells, three small interfering RNAs (siRNA; Stat3-1, Stat3-2, and Stat3-3) specific for different target sites on Stat3 mRNA were designed and used with a DNA vector-based RNA interference approach expressing short hairpin RNAs to knockdown Stat3 expression in human prostate cancer cells in vitro as well as in vivo. RESULTS: Of the three equivalently expressed siRNAs, only Stat3-3 and Stat3-2, which target the region coding for the SH2 domain and the coiled-coil domain, respectively, strongly suppressed the expression of Stat3 in PC3 and LNCaP cells. The Stat3-1 siRNA, which targeted the DNA-binding domain, exerted no effect on Stat3 expression, indicating that the gene silencing efficiency of siRNA may be dependent on the local structure of Stat3 mRNA. The Stat3 siRNAs down-regulated the expression of Bcl-2 (an anti-apoptotic protein), and cyclin D1 and c-Myc (cell growth activators) in prostate cancer cells. Inhibition of Stat3 and its related genes was accompanied by growth suppression and induction of apoptosis in cancer cells in vitro and in tumors implanted in nude mice. CONCLUSIONS: These data indicate that Stat3 signaling is a promising molecular target for prostate cancer therapy and that vector-based Stat3 siRNA may be useful as a therapeutic agent for treatment of prostate cancer.

Animals↗

PubMed2005

IFN-gamma-stimulated transcriptional activation by IFN-gamma-activated transcriptional element-binding factor 1 occurs via an inducible interaction with CAAAT/enhancer-binding protein-beta.

IFN-gamma-activated transcriptional element (GATE)-binding factor 1 (GBF1) was identified as a transactivator that induces gene expression through GATE, a novel IFN-inducible element. Although it can induce gene expression, it is an extremely weak DNA-binding protein on its own. GATE also binds another transcription factor, C/EBP-beta. Therefore, we explored whether GBF1 physically interacts with C/EBP-beta to induce IFN-gamma-regulated transcription. In response to IFN-gamma, C/EBP-beta undergoes phosphorylation at a critical ERK1/2 phosphorylation motif. Mutational inactivation of this motif and/or interference with the ERK1/2 activation prevented the IFN-gamma-induced interactions between GBF1 and C/EBP-beta. A 37-aa long peptide derived from the GBF1 protein can associate with C/EBP-beta in an IFN-inducible manner. These results identify a converging point for two transactivators that exert their effects through a single response element. Together, our studies identify a novel regulatory mechanism that controls IFN-induced transcription.

Amino Acid Motifs↗

PubMed2005

A role for mixed lineage kinases in regulating transcription factor CCAAT/enhancer-binding protein-{beta}-dependent gene expression in response to interferon-{gamma}.

Transcription factor CCAAT/enhancer-binding protein-beta (C/EBP-beta) regulates a variety of cellular functions in response to exogenous stimuli. We have reported earlier that C/EBP-beta induces gene transcription through a novel interferon (IFN)-response element called gamma-IFN-activated transcriptional element. We show here that IFN-gamma-induced, C/EBP-beta/gamma-IFN-activated transcriptional element-dependent gene expression is regulated by mixed lineage kinases (MLKs), members of the mitogen-activated protein kinase kinase kinase family. MLK3 appears to activate C/EBP-beta in response to IFN-gamma by a mechanism involving decreased phosphorylation of a specific phosphoacceptor residue, Ser(64), within the transactivation domain. Decreased phosphorylation of Ser(64) was independent of IFN-gamma-stimulated ERK1/2 activation and did not require the ERK phosphorylation site Thr(189) located in regulatory domain 2 of C/EBP-beta. Together these studies provide the first evidence that MLK3 is involved in IFN-gamma signaling and identify a novel mechanism of transcriptional activation by IFN-gamma.

Animals↗

PubMed2005

Development of monoclonal antibodies against GBF1 and their use in studying its functions.

Interferon-gamma (IFN-gamma) regulates a number of cellular genes using a variety of cellular signaling pathways. Previously, we identified a novel IFN-regulated element, IFN-gamma-activated transcriptional element (GATE), in the promoter of the murine IFN regulatory factor-9 (IRF-9) gene. This element binds to novel factors. We have recently characterized a novel regulatory factor, GATE binding factor 1 (GBF1), which promoted IFN-gamma-induced transcription. Although GBF1 was a potent inducer of transcription, it did not bind to DNA well in vitro. To understand its role in IFN-gamma-induced actions, we raised monoclonal antibodies (mAb) against GBF1. These antibodies are highly useful in Western, immunoprecipitation, and immunocytochemical analyses. Employing these antibodies, we show that GBF1 is recruited to the endogenous IRF-9 promoter. We also show GBF1 interacts with CAAAT/enhancer binding protein-beta (C/EBP-beta), the other GATE binding factor. Furthermore, other cytokines, such as interleukin-1 (IL-1) and IL-6, induced the expression of GBF1. These antibodies may be useful tools for investigating the role of GBF1 in cytokine-induced responses.

Animals↗

PubMed2005

CCAAT/enhancer binding proteins and interferon signaling pathways.

Interferons (IFNs) regulate a number of host responses, including innate and adaptive immunity against viruses, microbes, and neoplastic cells. These responses are dependent on the expression of IFN-stimulated genes (ISGs). Given the diversities in these responses and their kinetics, it is conceivable that a number of different factors are required for controlling them. Here, we describe one such pathway wherein transcription factor CAAAT/enhancer binding protein-beta (C/EBP-beta) is controlled via IFN-gamma-induced MAPK signaling pathways. At least two IFN-gamma-induced MAPK signals converge on to C/EBP-beta for inducing transcription. One of these, driven by extracellular signal-regulated kinases (ERKs), phosphorylates the C/EBP-beta protein in its regulatory domain. The second, driven by the mixed-lineage kinases (MLKs), induces a dephosphorylation leading to the recruitment of transcriptional coactivators.

Amino Acid Sequence↗

PubMed2004

NADPH oxidase and ERK signaling regulates hyperoxia-induced Nrf2-ARE transcriptional response in pulmonary epithelial cells.

Oxidative stress plays a major role in hyperoxia-induced acute lung injury. We have shown previously that mice lacking the Nrf2 are more susceptible to hyperoxia than are wild-type mice. Nrf2 activates antioxidant response element (ARE)-mediated gene expression involved in cellular protection against toxic insults. The present study was designed to investigate the mechanisms that control the activation of Nrf2 by hyperoxia using a non-malignant murine alveolar epithelial cell line, C10. No significant alteration in the levels of Nrf2 mRNA and protein was found following exposure to hyperoxia. In contrast, hyperoxia caused the translocation of Nrf2 from the cytoplasm to the nucleus within 30-60 min of exposure. Consistent with these observations, gel shift and reporter analyses demonstrated a correlation between the hyperoxia-enhanced ARE DNA-binding activity of Nrf2 and an up-regulation of ARE-driven transcription. Inhibition of NADPH oxidase with diphenyleneiodonium (DPI) blocked both Nrf2 translocation and ARE-mediated transcription. Inhibition of the MEK/ERK pathway caused a similar effect. Consistent with this finding, hyperoxia stimulated ERK-1 and ERK-2 phosphorylation, whereas DPI or N-acetyl-l-cysteine blocked such activation. Hyperoxia stimulated the phosphorylation of endogenous Nrf2, but not in the presence of U0126, suggesting a critical role for ERK signaling in the activation of Nrf2. Consistent with this notion, hyperoxia did not stimulate the phosphorylation of Nrf2 in fibroblasts lacking the ERK-1. Collectively, our findings suggest that hyperoxia-induced, ARE-driven, Nrf2-dependent transcription is controlled by NADPH oxidase and ERK-1 signaling.

Active Transport, Cell Nucleus↗

PubMed2003

Simultaneous activation of apoptosis and inflammation in pathogenesis of septic shock: a hypothesis.

Sepsis, a widely prevalent disease with increasing morbidity and mortality, is thought to result from uncontrolled inflammatory responses to microbial infection and/or components. However, failure of several experimental anti-inflammatory therapies has necessitated re-evaluation of the paradigm underlying the pathogenesis of this complex disorder. Apoptotic cell death forms a second dominant feature of septic shock in patients and animal models. Anti-apoptotic strategies may protect animals from septic death. However, simultaneous occurrence of apoptosis and inflammation is necessary for septic death. At the cellular level, apoptosis plays a central role in the development of the lymphoid system and regulation of immune responses. Immune activation renders cells refractory to apoptosis while apoptosis of activated lymphocytes is an important immunoregulatory mechanism. Factors such as complement factor 5a, caspase-1 and mitogen-activated protein kinase, which participate in apoptosis as well as pro-inflammatory pathways, may be responsible for simultaneous activation of apoptosis and inflammation in sepsis. Further identification of other similar biochemical events capable of co-activating inflammation and apoptosis may provide new targets for therapy of this hitherto untreatable disease.

Animals↗

PubMed2003

Multiple cis-elements mediate the transcriptional activation of human fra-1 by 12-O-tetradecanoylphorbol-13-acetate in bronchial epithelial cells.

Recent studies indicate a potential role for Fra-1, a heterodimeric partner of activator protein 1 (AP1), in toxicant-induced epithelial injury, repair, and cellular transformation. Here, we have investigated the transcriptional regulation of fra-1 by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human bronchial epithelial (HBE) cells, which are the direct targets of inhaled toxins/carcinogens. In contrast to a transient induction by H2O2, TPA persistently activated fra-1 transcription, principally at the transcriptional level. A deletion analysis of the fra-1 promoter revealed that several cis-elements located between -105/+32 and -283/-105 bp mediate minimal and basal promoter activities, respectively. A region between -379 and -283 bp, which harbors a putative TPA response element, a GC box, and an Ets-like binding site, was required for high level TPA-inducible expression. Mutations in any of these cis-elements markedly reduced both basal and TPA-inducible expression. Thus, cooperative interactions between factors binding to multiple cis-elements of the -379/-283 promoter region appear to regulate TPA-induced fra-1 transcription in HBE cells. Consistent with this finding, electrophoretic mobility shift assays indicated the formation of multiple complexes consisting of the AP1-, Sp-, and ETS-specific family of transcription factors with the -379/-283 fragment. Members of the AP1 family distinctly regulated the fra-1 promoter. In particular, coexpression of c-Jun, Jun-D, and Fra-2 up-regulated fra-1 transcription. Chromatin immunoprecipitation assays revealed an enhanced recruitment of c-Jun, Jun-D, and Fra-2 to the endogenous fra-1 promoter upon TPA stimulation. These results underscore the regulatory role of c-Jun, Jun-D, and Fra-2 in TPA-inducible fra-1 expression in HBE cells in vivo.

Base Sequence↗

PubMed2003

The cell death regulator GRIM-19 is an inhibitor of signal transducer and activator of transcription 3.

GRIM-19 (gene associated with retinoid-IFN-induced mortality 19), isolated as a cell death activator in a genetic screen used to define mechanisms involved in IFN-beta- and retinoic acid-induced cell death, codes for a approximately 16-kDa protein that induces apoptosis in a number of cell lines. Antisense ablation of GRIM-19 caused resistance to cell death induced by IFN plus retinoic acid and conferred a growth advantage to cells. To understand the molecular bases for its cell death regulatory activity, we used a yeast two-hybrid screen and identified that the transcription factor STAT3 (signal transducer and activator of transcription 3) binds to GRIM-19. GRIM-19 inhibits transcription driven by activation of STAT3, but not STAT1. It neither inhibits the ligand-induced activation of STAT3 nor blocks its ability to bind to DNA. Mutational analysis indicates that the transactivation domain of STAT3, especially residue S727, is required for GRIM-19 binding. Because GRIM-19 does not bind significantly to other STATs, our studies identify a specific inhibitor of STAT3. Because constitutively active STAT3 up-regulates antiapoptotic genes to promote tumor survival, its inhibition by GRIM-19 also demonstrates an antioncogenic effect exerted by biological therapeutics.

Animals↗

PubMed2003

Activation of protein kinase C delta by all-trans-retinoic acid.

All-trans-retinoic acid (RA) is a potent inhibitor of leukemia cell proliferation and induces differentiation of acute promyelocytic leukemia cells in vitro and in vivo. For RA to induce its biological effects in target cells, binding to specific retinoic acid nuclear receptors is required. The resulting complexes bind to RA-responsive elements (RAREs) in the promoters of RA-inducible genes to initiate gene transcription and to generate protein products that mediate the biological effects of RA. In this report, we provide evidence that a member of the protein kinase C (PKC) family of proteins, PKC delta, is activated during RA treatment of the NB-4 and HL-60 acute myeloid leukemia cell lines as well as the MCF-7 breast cancer cell line. Such RA-dependent phosphorylation was also observed in primary acute promyelocytic leukemia cells and resulted in activation of the kinase domain of PKC delta. In studies aimed at understanding the functional relevance of PKC delta in the induction of RA responses, we found that pharmacological inhibition of PKC delta (but not of other PKC isoforms) diminished RA-dependent gene transcription via RAREs. On the other hand, overexpression of a constitutively active form of the kinase strongly enhanced RA-dependent gene transcription via RAREs. Gel shift assays and chromatin immunoprecipitation studies demonstrated that PKC delta associated with retinoic acid receptor-alpha and was present in an RA-inducible protein complex that bound to RAREs. Pharmacological inhibition of PKC delta activity abrogated the induction of cell differentiation and growth inhibition of NB-4 blast cells, demonstrating that its function is required for such effects. Altogether, our data provide strong evidence that PKC delta is activated in an RA-dependent manner and plays a critical role in the generation of the biological effects of RA in malignant cells.

Cell Differentiation↗

PubMed2003

Alternate interferon signaling pathways.

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Animals↗

PubMed2002

Activation of Rac1 and the p38 mitogen-activated protein kinase pathway in response to arsenic trioxide.

Arsenic trioxide induces differentiation and apoptosis of malignant cells in vitro and in vivo, but the mechanisms by which such effects occur have not been elucidated. In the present study we provide evidence that arsenic trioxide induces activation of the small G-protein Rac1 and the alpha and beta isoforms of the p38 mitogen-activated protein (MAP) kinase in several leukemia cell lines. Such activation of Rac1 and p38-isoforms results in downstream engagement of the MAP kinase-activated protein kinase-2 and is enhanced by pre-treatment of cells with ascorbic acid. Interestingly, pharmacological inhibition of p38 potentiates arsenic-dependent apoptosis and suppression of growth of leukemia cell lines, suggesting that this signaling cascade negatively regulates induction of antileukemic responses by arsenic trioxide. Consistent with this, overexpression of a dominant-negative p38 mutant (p38betaAGF) enhances the antiproliferative effects of arsenic trioxide on target cells. To further define the relevance of activation of the Rac1/p38 MAP kinase pathway in the induction of arsenic-dependent antileukemic effects, studies were performed using bone marrows from patients with chronic myelogenous leukemia. Arsenic trioxide suppressed the growth of leukemic myeloid (CFU-GM) progenitors from such patients, whereas concomitant pharmacological inhibition of the p38 pathway enhanced its growth-suppressive effects. Altogether, these data provide evidence for a novel function of the p38 MAP kinase pathway, acting as a negative regulator of arsenic trioxide-induced apoptosis and inhibition of malignant cell growth.

Antioxidants↗

PubMed2002

Thioredoxin reductase regulates AP-1 activity as well as thioredoxin nuclear localization via active cysteines in response to ionizing radiation.

A recently identified class of signaling factors uses critical cysteine motif(s) that act as redox-sensitive 'sulfhydryl switches' to reversibly modulate specific signal transduction cascades regulating downstream proteins with similar redox-sensitive sites. For example, signaling factors such as redox factor-1 (Ref-1) and transcription factors such as the AP-1 complex both contain redox-sensitive cysteine motifs that regulate activity in response to oxidative stress. The mammalian thioredoxin reductase-1 (TR) is an oxidoreductase selenocysteine-containing flavoprotein that also appears to regulate multiple downstream intracellular redox-sensitive proteins. Since ionizing radiation (IR) induces oxidative stress as well as increases AP-1 DNA-binding activity via the activation of Ref-1, the potential roles of TR and thioredoxin (TRX) in the regulation of AP-1 activity in response to IR were investigated. Permanently transfected cell lines that overexpress wild type TR demonstrated constitutive increases in AP-1 DNA-binding activity as well as AP-1-dependent reporter gene expression, relative to vector control cells. In contrast, permanently transfected cell lines expressing a TR gene with the active site cysteine motif deleted were unable to induce AP-1 activity or reporter gene expression in response to IR. Transient genetic overexpression of either the TR wild type or dominant-negative genes demonstrated similar results using a transient assay system. One mechanism through which TR regulates AP-1 activity appears to involve TRX sub-cellular localization, with no change in the total TRX content of the cell. These results identify a novel function of the TR enzyme as a signaling factor in the regulation of AP-1 activity via a cysteine motif located in the protein.

Cysteine↗

PubMed2002

IL-18 levels and the outcome of innate immune response to lipopolysaccharide: importance of a positive feedback loop with caspase-1 in IL-18 expression.

LPS enhanced antibacterial host defenses (ABHD) when given at low (75 micro g) doses (16 of 19 mice survived 3x LD(50) Escherichia coli vs 3 of 19 LPS-naive mice; p = 0.0001), but induced lethal inflammation at high (500 micro g) doses (5 of 5 died). Differences in the cytokine profiles induced by these LPS doses may provide insight into the mechanism(s) of transition from beneficial to lethal LPS responses. The 75 micro g LPS induced 5.9 +/- 0.9 ng/ml serum IL-18 at 8 h, which decreased to 2.3 +/- 0.4 ng/ml by 24 h, whereas 500 micro g LPS induced 11.1 +/- 1.6 ng/ml serum IL-18 levels at 8 h, which increased until death. Compared with 75 micro g, higher but sublethal (150 micro g) doses of LPS induced greater serum IL-18 levels and less effectively induced ABHD (3 of 8 survived). Reduction of serum IL-18 with neutralizing Ab improved the ABHD induced by 150 micro g, but reduced that produced by 75 micro g LPS, suggesting an optimal range of serum IL-18 level was essential for efficient ABHD. Increased expression of caspase-1 mRNA in response to the higher IL-18 levels induced at the 150 and 500 micro g, but not at the 75 micro g doses of LPS may represent a positive feedback regulatory loop leading to sustained serum IL-18 levels. We conclude that the regulation of serum IL-18 expression is critical to the outcome of innate immune responses to LPS.

Adjuvants, Immunologic↗

PubMed2002

A novel transactivating factor that regulates interferon-gamma-dependent gene expression.

We have previously identified a novel interferon (IFN)-stimulated cis-acting enhancer element, gamma-IFN-activated transcriptional element (GATE). GATE differs from the known IFN-stimulated elements in its primary sequence. Preliminary analysis has indicated that the GATE-dependent transcriptional response requires the binding of novel transacting factors. A cDNA expression library derived from an IFN-gamma-stimulated murine macrophage cell line was screened with a (32)P-labeled GATE probe to identify the potential GATE-binding factors. A cDNA coding for a novel transcription-activating factor was identified. Based on its discovery, we named it as GATE-binding factor-1 (GBF-1). GBF-1 homologs are present in mouse, human, monkey, and Drosophila. It activates transcription from reporter genes carrying GATE. It possesses a strong transactivating activity but has a weak DNA binding property. GBF-1 is expressed in most tissues with relatively higher steady-state levels in heart, liver, kidney, and brain. Its expression is induced by IFN-gamma treatment. GBF-1 is present in both cytosolic and nuclear compartments. These studies thus identify a novel transactivating factor in IFN signaling pathways.

Amino Acid Sequence↗