Cellular commitment to oncogene-induced transformation or apoptosis is dependent on the transcription factor IRF-1

Role of IFN regulatory factor 5 transcription factor in antiviral immunity and tumor suppression

Host defense consists of two main aspects, namely, immune response to invading pathogens and suppression of tumor development. A family of transcription factors, IFN regulatory factors (IRFs), has recently gained much attention in terms of its critical role in linking these two aspects of host defense, wherein IRF5 was previously shown to play a critical role in the induction of proinflammatory cytokines by activation of Toll-like receptors. In the present study, using IRF5 gene-targeted mice (Irf5(-/-) mice), we demonstrate another facet of the IRF5 function in the regulation of immune response and tumor suppression. We show that IRF5 is critical for antiviral immunity by showing that Irf5(-/-) mice are highly vulnerable to viral infections, accompanied by a decrease in type I IFN induction in the sera. Furthermore, we show that Irf5(-/-) fibroblasts are resistant to apoptosis upon viral infection, resulting in an enhanced viral propagation. Finally, we provide evidence that IRF5 is critical for the induction of apoptosis, but not in cell cycle arrest, in response to DNA damage and that IRF5 functions as a tumor suppressor by acting on a pathway that may be distinct from that for p53. These results, together with the dual regulation of IRF5 gene expression by IFN signaling and p53, may provide a new link in the transcriptional network underlying antiviral immunity and tumor suppression.

Overexpression of phosphorylated STAT-1alpha in the labial salivary glands of patients with Sjögren's syndrome

OBJECTIVE

To clarify the molecular mechanisms of Sjögren's syndrome (SS), we analyzed the functional role of the STAT-1 gene, one of the interferon-gamma (IFNgamma)-inducible genes, in labial salivary glands (LSGs) from SS patients.

METHODS

The expression of STAT-1 messenger RNA (mRNA) was examined by real-time polymerase chain reaction (PCR) analysis, and the phosphorylation of STAT-1 protein (Tyr(701) and Ser(727) pSTAT-1) was investigated by Western blot and immunohistochemical analyses. The expression of IFNgamma-inducible 10-kd protein (IP-10), IFN regulatory factor 1 (IRF-1), and Fas was also examined by real-time PCR and immunohistochemical analyses.

RESULTS

STAT-1alpha and STAT-1beta mRNA were highly expressed in LSGs from SS patients. The level of STAT-1alpha protein in SS LSGs was higher than that in 3 control LSGs, whereas STAT-1beta protein was not clearly detected by Western blot analysis. Moreover, Tyr(701) and Ser(727) pSTAT-1alpha proteins were specifically detected in SS LSGs. Immunohistochemical analysis showed localization of Tyr(701) pSTAT-1 in infiltrating lymphocytes and the adjacent ductal epithelium from SS patients. Ser(727) pSTAT-1 was localized only in the ductal epithelium of SS LSGs. The STAT-1-inducible genes IP-10 and IRF-1 and the Fas genes were highly expressed in SS LSGs and were colocalized with Ser(727) pSTAT-1-positive, but not Tyr(701) pSTAT-1-positive, cells.

CONCLUSION

We found evidence of the up-regulation of STAT-1alpha mRNA and protein in LSGs from SS patients, as well as the presence of pSTAT-1alpha in ductal epithelium from SS patients. Our findings suggest that STAT-1alpha, especially Ser(727) pSTAT-1, may function as a key molecule in the pathogenesis of SS.

p21 delays tumor onset by preservation of chromosomal stability

The p53 protein suppresses tumorigenesis by initiating cellular functions such as cell cycle arrest and apoptosis in response to DNA damage. A p53 mutant, p53R172P, which is deficient for apoptosis but retains a partial cell cycle arrest function, delays tumor onset in mice. Remarkably, lymphomas arising in Trp53(515C/515C) mice (encoding p53R172P) retain stable genomes. Given the dominant role of p21 in p53 cell cycle control, we crossed Trp53(515C/515C) mice onto a p21-null background to determine whether p21 was required for maintaining chromosomal stability and delaying tumor onset. Loss of p21 completely abolished the cell cycle arrest function of p53R172P and accelerated tumor onset in Trp53(515C/515C) mice. Cytogenetic examination of Trp53(515C/515C) p21(-/-) sarcomas and lymphomas revealed aneuploidy and chromosomal aberrations that were absent in Trp53(515C/515C) malignancies. Thus, p21 coupled p53-dependent checkpoint control and preservation of chromosomal stability, and cooperated with apoptosis in suppressing tumor onset in mice.

Peptide YY Reverses TNF-α Induced Transcription Factor Binding of Interferon Regulatory Factor-1 and p53 in Pancreatic Acinar Cells

BACKGROUND

Cytokine activation in the pancreatitis induces local and systemic cellular damage. Transcription factors interferon regulatory factor-1 (IRF-1) and the tumor suppressor gene p53 collaborate to enhance p21 related cell cycle regulation during pathological disease progression. However, little is known about their role in the pancreas after cytokine challenge. Our laboratory has previously shown that TNF-alpha induces the binding of many transcription factors, including NF-kappa B, and treatment with the gut hormone, Peptide YY (PYY), ameliorates the effects. We hypothesized that TNF-alpha would induce IRF-1 and p53 protein binding in pancreatic acinar cells and that PYY would attenuate the effect.

MATERIALS AND METHODS

Rat pancreatic acinar AR42J cells were treated with rat recombinant TNF-alpha (200 ng/ml). To verify that our model was inducing pancreatitis, alpha-amylase activity was measured in the cell culture supernatant by fluorescence spectroscopy. PYY [3-36] was added at 500 pM 30 min post-TNF treatment; cells were harvested at 2 h for extraction of nuclear protein. Transcription factor binding of IRF-1 and p53 were determined by protein/DNA array analysis using chemiluminescence detection, and relative spot densities were measured by densitometry. A two-fold increase or decrease in density was considered significant.

RESULTS

Amylase enzyme activity was significantly (P < 0.05) elevated in the TNF-alpha-treated cells by 2 h. Protein/DNA array analysis revealed significant up-regulation of both IRF-1 and p53 protein in nuclear extracts. Induction by TNF-alpha increased IRF-1 protein binding 3.5-fold, while binding levels of p53 protein increased six-fold. The addition of PYY to TNF-treated cells reduced IRF-1 and p53 binding to control levels.

CONCLUSIONS

We have shown for the first time that short-term exposure to TNF-alpha induces the binding activity of transcription factors IRF-1 and p53 in rat pancreatic acinar cells, and that addition of PYY reduces it. Regulation of transcription factor activity by PYY may have therapeutic potential in altering the progression of pancreatitis.

Ras-dependent recruitment of c-Myc for transcriptional activation of nucleophosmin/B23 in highly malignant U1 bladder cancer cells

U1 bladder cancer cells of high malignancy exhibited higher proliferation capacity than U4 premalignant cells. Higher expression of Ras, c-Myc, and nucleophosmin/B23 and greater c-Myc transactivation and nucleophosmin/B23 promoter activities were detected in U1 cells compared with U4 cells. Moreover, c-Myc and nucleophosmin/B23 were increased in U1 but not in U4 cells upon serum stimulation from quiescence. Likewise, only in U1 cells could serum stimulate transcriptional activity of nucleophosmin/B23 promoter and c-Myc response element. The increase of nucleophosmin/B23 promoter activity could be abrogated by mitogen-activated protein kinase/extracellular signal-regulated kinase activating kinase inhibitor and was associated with recruitment of c-Myc to the promoter. U1 cells constitutively expressing dominant-negative Ras reduced the levels of Ras, nucleophosmin/B23, and p-ERK, and consequently abolished the serum-induced up-regulation of nucleophosmin/B23 promoter activity and c-Myc promoter recruitment. Our results indicate that Ras and c-Myc play important roles in the up-regulation of nucleophosmin/B23 during proliferation of cells associated with a high degree of malignancy, thus outlining a signaling cascade involving these factors in the cancer cells.

Identification of proteins immunologically related to interferon regulatory factor-1 that bind with interferon regulatory factor element

Interferon regulatory factor (IRF)-1 expression was surveyed in nontransformed and oncogene-transformed mouse fibroblasts, using Western immunoblot with an IRF-1-specific antiserum, to examine possible differences resulting from cellular transformation. Ten additional proteins that reacted with the IRF-1 antibody and that underwent specific competition by peptide antigen were observed in extracts of both nontransformed and oncogene-transformed cell lines. Cross-reacting proteins were also observed in mouse macrophage extracts. Protein was captured from fibroblast nuclear extracts, using oligonucleotides representing IRF-binding sequences linked to magnetic beads. Captured proteins were eluted and analyzed by immunoblot with anti-IRF-1. Along with 43-kDa IRF-1, 4 of the 7 nuclearly located cross-reacting proteins (97, 90, 66, and 33 kDa) were found to complex with the IRF binding element. These proteins, with an epitope in common with the IRF-1 C-terminal region and IRF element DNA sequence-binding capability, may represent new members of the IRF family.

Interferon regulatory factor-5-regulated pathways as a target for colorectal cancer therapeutics

Colorectal cancer is the second most common cause of cancer-related death. A significant obstacle to successful management of patients with colorectal cancer is intrinsic drug resistance or, in patients who initially responded to chemotherapy, acquired drug resistance. Failure in normal apoptotic pathways often contributes to resistance to anticancer drugs or radiotherapy. As a result, the identification of genes that control cell death and apoptosis has come to the forefront of cancer research, leading to new targets and novel therapeutic strategies in the treatment of colorectal cancer. To this effect, the authors have recently identified a new apoptotic signaling pathway that occurs through the transcription factor interferon regulatory factor-5. Here, the different strategies for targeting the interferon regulatory factor-5 signaling pathway in colorectal cancer are discussed. These strategies can be applied to a new generation of cytotoxic agents, as well as to novel biological compounds that are directed at inducing and/or activating interferon regulatory factor-5 or key components of this pathway.

Retinoic acid exerts dual regulatory actions on the expression and nuclear localization of interferon regulatory factor-1

Interferon regulatory factor-1 (IRF-1), a transcription factor and tumor suppressor involved in cell growth regulation and immune responses, has been shown to be induced by all-trans retinoic acid (ATRA). However, the factors controlling the cellular location and activity of IRF-1 are not well understood. In this study, we examined the expression of IRF-1 and its nuclear localization, DNA-binding activity, and target gene expression in human mammary epithelial MCF10A cells, a model of breast epithelial cell differentiation and carcinogenesis. Following initial treatment with ATRA, IRF-1 mRNA and protein were induced within 2 hrs, reached a peak (>30-fold induction) at 8 hrs, and declined afterwards. IRF-1 protein was predominantly cytoplasmic during this treatment. Although a second dose of ATRA or Am580 (a related retinoid selective for retinoic acid receptor-alpha [RARalpha]), given 16 hrs after the first dose, restimulated IRF-1 mRNA and protein levels to a similar level to that obtained by the first dose, IRF-1 was predominantly concentrated in the nucleus after restimulation. ATRA and Am580 also increased nuclear RARalpha, whereas retinoid X receptor-alpha (RXRalpha)--a dimerization partner for RARalpha, was localized to the nucleus upon second exposure to ATRA. However, ATRA and Am580 did not regulate the expression or activation of signal transducer and activator of transcription-1 (STAT-1), a transcription factor capable of inducing the expression of IRF-1, indicating an STAT-1-independent mechanism of regulation by ATRA and Am580. The increase in nuclear IRF-1 after retinoid restimulation was accompanied by enhanced binding to an IRF-E DNA response element, and elevated expression of an IRF-1 target gene, 2',5'-oligoadenylate synthetase-2. The dual effect of retinoids in increasing IRF-1 mRNA and protein and in augmenting the nuclear localization of IRF-1 protein may be essential for maximizing the tumor suppressor activity and the immunosurveillance functions of IRF-1 in breast epithelial cells.

Regional vulnerability of mesencephalic dopaminergic neurons prone to degenerate in Parkinson's disease: a post-mortem study in human control subjects

Parkinson's disease (PD) is characterized by loss of dopaminergic (DA) neurons in the human midbrain, which varies greatly among mesencephalic subregions. The genetic expression profiles of mesencephalic DA neurons particularly prone to degenerate during PD (nigrosome 1 within the substantia nigra pars compacta-SNpc) and those particularly resistant in the disease course (central grey substance-CGS) were compared in five control subjects by immuno-laser capture microdissection followed by RNA arbitrarily primed PCR. 8 ESTs of interest were selected for analysis by real time quantitative reverse transcription PCR. DA neurons in the CGS preferentially expressed implicated in cell survival (7 out of 8 genes selected), whereas SNpc DA neurons preferentially expressed one gene making them potentially susceptible to undergo cell death in PD. We propose that factors making CGS DA neurons more resistant may be helpful in protecting SNpc DA neurons against a pathological insult.

Colocalization of interferon regulatory factor 7 (IRF7) with latent membrane protein 1 (LMP1) of Epstein-Barr virus

Interferon regulatory factor 7 (IRF7) is one of the transcriptional factors for the activation of type I Interferon (IFN) genes. It is known that IRF7 and the latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) are highly expressed in EBV type III latency cells, and LMP1 induces mRNA expression of IRF7. In this study, the expression pattern of endogenous IRF7 was observed in several B cell lines with or without EBV infection by immunofluorescence staining. IRF7 was localized in the cytoplasm of EBV-negative B cells and EBV type I latency B cell lines. However, IRF7 was located both in the cytoplasm and nucleus of EBV type III latency cell lines. In the Jijoye cell (type III latency cell), IRF7 was colocalized with LMP1 in the cytoplasm in a capping configuration, and their interaction was confirmed by co-immunoprecipitation of LMP1 and IRF7. This colocalization was confirmed by co-transfection of IRF7 and LMP1 plasmids in EBV-negative B cells. These results suggest that the IRF7 and LMP1 interact with each other, and this may relate to the mechanism whereby LMP1 exerts functional effects in B-lymphocytes.

A novel repressor domain is required for maximal growth inhibition by the IRF-1 tumor suppressor

Interferon regulatory factor-1 (IRF-1) is a transcription factor and tumor suppressor that can regulate gene expression in a manner requiring either its sequence specific DNA binding activity or its ability to bind the p300 coactivator. We show that IRF-1-mediated growth inhibition is dependent on the integrity of a C-terminal transcriptional enhancer domain. An enhancer subdomain (amino acids 301-325) that differentially regulates IRF-1 activity has been identified and this region mediates the repression of Cdk2. The repressor domain encompasses an LXXLL coregulator signature motif and mutations or deletions within this region completely uncouple transcriptional activation from repression. The loss of growth suppressor activity when the Cdk2-repressor domain of IRF-1 is mutated implicates repression as a determinant of its maximal growth inhibitory potential. The data link IRF-1 regulatory domains to its growth inhibitory activity and provide information about how differential gene regulation may contribute to IRF-1 tumor suppressor activity.

Nucleophosmin/B23 regulates transcriptional activation of E2F1 via modulating the promoter binding of NF-kappaB, E2F1 and pRB

Expression of nucleophosmin/B23 and E2F1 and E2F1-dependent transcription increased in U1 bladder cancer cells upon serum stimulation from quiescence. Nucleophosmin/B23-siRNA treatment abrogated such increase of E2F1-dependent transcriptional activity. In identifying physiologically important factors that may occupy E2F1 promoter and regulate its activity in vivo, we found that the pattern of NF-kappaB, E2F1 and pRB recruitment to E2F1 promoter changed in a strikingly dynamic fashion as cells progressed from quiescence into serum-stimulated growth. E2F1 promoter activity in quiescent cells was associated with recruitment of NF-kappaB. NF-kappaB was replaced largely by E2F1 in concert with gene activation during the early stage (12 h) of serum stimulation. At late stage (24 h) of serum stimulation, pRB was then recruited to the E2F1-promoter complex to counterbalance its activity. Upon siRNA-mediated reduction of intracellular nucleophosmin/B23, E2F1 and pRB were recruited to the promoter with the dissociation of NF-kappaB concomitant with gene inactivation. Based on immunoprecipitation experiments, nucleophosmin/B23 was found to be associated with NF-kappaB in cells grown in serum-supplemented but not in serum-deprived medium. Furthermore, nucleophosmin/B23 could also be co-immunoprecipitated with ppRB at the early stage (12 h) but not at the late stage (24 h) of serum stimulation. The results demonstrate a novel mechanism for transcriptional regulation of E2F1 and identify the functional role of nucleophosmin/B23 in modulating the binding of NF-kappaB, E2F1 and pRB to activate E2F1 promoter.

Identification of an NF-kappaB-dependent gene network in cells infected by mammalian reovirus

Reovirus infection activates NF-kappaB, which leads to programmed cell death in cultured cells and in the murine central nervous system. However, little is known about how NF-kappaB elicits this cellular response. To identify host genes activated by NF-kappaB following reovirus infection, we used HeLa cells engineered to express a degradation-resistant mutant of IkappaBalpha (mIkappaBalpha) under the control of an inducible promoter. Induction of mIkappaBalpha inhibited the activation of NF-kappaB and blocked the expression of NF-kappaB-responsive genes. RNA extracted from infected and uninfected cells was used in high-density oligonucleotide microarrays to examine the expression of constitutively activated genes and reovirus-stimulated genes in the presence and absence of an intact NF-kappaB signaling axis. Comparison of the microarray profiles revealed that the expression of 176 genes was significantly altered in the presence of mIkappaBalpha. Of these genes, 64 were constitutive and not regulated by reovirus, and 112 were induced in response to reovirus infection. NF-kappaB-regulated genes could be grouped into four distinct gene clusters that were temporally regulated. Gene ontology analysis identified biological processes that were significantly overrepresented in the reovirus-induced genes under NF-kappaB control. These processes include the antiviral innate immune response, cell proliferation, response to DNA damage, and taxis. Comparison with previously identified NF-kappaB-dependent gene networks induced by other stimuli, including respiratory syncytial virus, Epstein-Barr virus, tumor necrosis factor alpha, and heart disease, revealed a number of common components, including CCL5/RANTES, CXCL1/GRO-alpha, TNFAIP3/A20, and interleukin-6. Together, these results suggest a genetic program for reovirus-induced apoptosis involving NF-kappaB-directed expression of cellular genes that activate death signaling pathways in infected cells.

DNA damage signaling and p53-dependent senescence after prolonged beta-interferon stimulation

Interferons are cytokines with potent antiviral and antiproliferative activities. We report that although a transient exposure to beta-interferon induces a reversible cell cycle arrest, a sustained treatment triggers a p53-dependent senescence program. Beta-interferon switched on p53 in two steps. First, it induced the acetylation of p53 at lysine 320 and its dephosphorylation at serine 392 but not p53 activity. Later on, it triggered a DNA signaling pathway, the phosphorylation of p53 at serine 15 and its transcriptional activity. In agreement, beta-interferon-treated cells accumulated gamma-H2AX foci and phosphorylated forms of ATM and CHK2. The DNA damage signaling pathway was activated by an increase in reactive oxygen species (ROS) induced by interferon and was inhibited by the antioxidant N-acetyl cysteine. More important, RNA interference against ATM inhibited p53 phosphorylation at serine 15, p53 activity and senescence in response to beta-interferon. Beta-interferon-induced senescence was more efficient in cells expressing either, p53, or constitutive allele of ERK2 or RasV12. Hence, beta-interferon-induced senescence targets preferentially cells with premalignant changes.

Biological functions of maspin

Maspin (Mammary Serine Protease Inhibitor) was first reported in 1994 as a serpin with tumor suppressive properties. Maspin was initially isolated through subtractive hybridization and differential display analysis as a 42-kDa protein that is expressed in normal mammary epithelial cells but reduced or absent in breast carcinomas (Zou et al., 1994). Further research led to maspin's characterization as a class II tumor suppressor based on its ability to inhibit cell invasion, promote apoptosis, and inhibit angiogenesis (Sheng et al., 1996; Zhang et al., 2000b; Jiang et al., 2002). Since then, efforts have been made to characterize maspin's tumor suppressive mechanisms. In particular, researchers have studied maspin localization, the regulation of maspin expression, and more recently, maspin protein interactions. By elucidating these mechanisms, researchers are beginning to understand the complex, pleiotropic nature of maspin and the pathways through which maspin exerts its tumor suppressive properties. These new findings not only further enhance our understanding of cancer biology but also provide an avenue to develop maspin's potential as a diagnostic marker for cancer progression, and as a potentially powerful therapeutic agent in the fight against breast cancer.

Expression and DNA binding activity of the recombinant interferon regulatory factor-1 (IRF-1) of mouse

Interferon regulatory factor-1 (IRF-1) is a positive transcription factor for genes involved in immune response, cell growth regulation and apoptosis in mammalian cells. Many agents like virus, interferon (IFN), double-stranded RNA (dsRNA), proinflammatory cytokines, prolactin etc. induce IRF-1 at transcriptional level. IRF-1 transcriptionally activates many IRF-1-regulated genes during normal physiological and pathological conditions. We have expressed recombinant mouse IRF-1 (329 amino acids) as a GST(glutathione-S-transferase)-IRF-1 fusion protein from a 1029 bp IRF-1 cDNA in pGEX-2TK expression vector in Escherichia coli XL-1 blue cells. Recombinant GST-IRF-1 was highly expressed as a approximately 66 kDa soluble protein by IPTG-induction, and was biologically active in terms of its DNA binding activity with a 24 bp specific oligonucleotide, i.e. 32P(GAAAGT)4 but not with a similar but nonspecific oligonucleotide i.e. 32P(GAAA)6. GST-alone expressed from the vector did not bind 32P(GAAAGT)4. We observed multiple (1-4) GST-IRF-1-(GAAAGT)4 protein-DNA complexes which were competed out by 25x- to 100x-fold molar excess of (GAAAGT)4 showing that the complexes 1-4 were specific for IRF-1. Such GAAANN (N = any nucleotide) hexanucleotides occur in the promoters of many virus- and interferon-inducible mammalian genes. Multimeric GAAAGT/C sequences are inducible by virus, IFN, dsRNA and IRF-1. Specificity of DNA binding by IRF-1 lies in the 5th and 6th nucleotides in the GAAAGT sequence. Multiple IRF-1-DNA complexes should stimulate transcription by IRF-1.

Physiological and receptor-selective retinoids modulate interferon gamma signaling by increasing the expression, nuclear localization, and functional activity of interferon regulatory factor-1

Synergistic actions between all-trans-retinoic acid (atRA) and interferon gamma (IFNgamma) on modulation of cellular functions have been reported both in vitro and in vivo. However, the mechanism of atRA-mediated regulation of IFNgamma signaling is poorly understood. In this study, we have used the human lung epithelial cell line A549 to examine the effect of atRA on IFNgamma-induced expression of IFN regulatory factor-1 (IRF-1), an important transcription factor involved in cell growth and apoptosis, differentiation, and antiviral and antibacterial immune responses. At least 4 h of pretreatment with atRA followed by suboptimal concentrations of IFNgamma induced a faster, higher, and more stable expression of IRF-1 than IFNgamma alone. Actinomycin D completely blocked the induction of IRF-1 by the combination, suggesting regulation at the transcriptional level. Further, we found that activation of signal transducer and activator of transcription-1 was induced more dramatically by atRA and IFNgamma than by IFNgamma alone. Expression of IFNgamma receptor-1 on the cell surface was also increased upon atRA pretreatment. Experiments using receptor-selective retinoids revealed that ligands for retinoic acid receptor-alpha (RARalpha), including atRA, 9-cis-retinoic acid, and Am580, sequentially increased the levels of IFNgamma receptor-1, activated signal transducer and activator of transcription-1, and IRF-1 and that an RARalpha antagonist was able to inhibit the effects of atRA and Am580. In addition, atRA pretreatment affected the transcriptional functions of IFNgamma-induced IRF-1, increasing its nuclear localization and DNA binding activity as well as the transcript levels of IRF-1 target genes. These results suggest that atRA, an RARalpha ligand, regulates IFNgamma-induced IRF-1 by affecting multiple components of the IFNgamma signaling pathway, from the plasma membrane to the nuclear transcription factors.

Signaling through IFN regulatory factor-5 sensitizes p53-deficient tumors to DNA damage-induced apoptosis and cell death

Human IFN regulatory factor-5 (IRF-5) is a candidate tumor suppressor gene that mediates cell arrest, apoptosis, and immune activation. Here we show that ectopic IRF-5 sensitizes p53-proficient and p53-deficient colon cancer cells to DNA damage-induced apoptosis. The combination IFN-beta and irinotecan (CPT-11) cooperatively inhibits cell growth and IRF-5 synergizes with it to further promote apoptosis. The synergism is due to IRF-5 signaling since a striking defect in apoptosis and cell death was observed in IRF-5-deficient cells, which correlated well with a reduction in DNA damage-induced cellular events. Components of this IRF-5 signaling pathway are investigated including a mechanism for DNA damage-induced IRF-5 activation. Thus, IRF-5-regulated pathways may serve as a target for cancer therapeutics.

Epstein-Barr virus-encoded poly(A)- RNA confers resistance to apoptosis mediated through Fas by blocking the PKR pathway in human epithelial intestine 407 cells

Our recent findings demonstrated that the Epstein-Barr virus-encoding small nonpolyadenylated RNA (EBER) confers resistance to various apoptotic stimuli and contributes to the maintenance of malignant phenotypes in Burkitt's lymphoma. In this study we investigated the role of EBER in the human epithelial Intestine 407 cell line, which is known to be susceptible to Fas (Apo1/CD95)-mediated apoptosis. Fas, a member of the tumor necrosis factor receptor family, transduces extracellular signals to the apoptotic cellular machinery, leading to cell death. Transfection of the EBER gene into Intestine 407 cells significantly protected the cells from Fas-mediated apoptosis, whereas EBER-negative cell lines underwent apoptosis after Fas treatment. EBER bound double-stranded RNA-dependent protein kinase R (PKR), an interferon-inducible serine/threonine kinase, and abrogated its kinase activity. Moreover, expression of the catalytically inactive dominant-negative PKR provided resistance to Fas-induced apoptosis. Expression of EBER or dominant-negative PKR also inhibited the cleavage of poly(ADP-ribose) polymerase, a mediator of the cellular response to DNA damage, downstream of the Fas-mediated apoptotic pathway. These results in combination indicate that EBER confers resistance to Fas-mediated apoptosis by blocking PKR activity in Intestine 407 cells, consistent with the idea that EBER contributes to the maintenance of epithelioid malignancies.

Mammary serine protease inhibitor (Maspin) binds directly to interferon regulatory factor 6: identification of a novel serpin partnership

Since its reported discovery in 1994, maspin (mammary serine protease inhibitor) has been characterized as a class II tumor suppressor by its ability to promote apoptosis and inhibit cell invasion. Maspin is highly expressed in normal mammary epithelial cells but reduced or absent in aggressive breast carcinomas. However, despite efforts to characterize the mechanism(s) by which maspin functions as a tumor suppressor, its molecular characterization has remained somewhat elusive. Therefore, in an attempt to identify maspin-interacting proteins and thereby gain insight into the functional pathways of maspin, we employed a maspin-baited yeast two-hybrid system and subsequently identified Interferon Regulatory Factor 6 (IRF6) as a maspin-binding protein. IRF6 belongs to the IRF family of transcription factors, which is best known for its regulation of interferon and interferon-inducible genes following a pathogenic stimulus. Although many of the IRF family members have been well characterized, IRF6 remains poorly understood. We report that IRF6 is expressed in normal mammary epithelial cells and that it directly associates with maspin in a yeast two-hybrid system and in vitro. The interaction occurs via the conserved IRF protein association domain and is regulated by phosphorylation of IRF6. We have shown that, similar to maspin, IRF6 expression is inversely correlated with breast cancer invasiveness. We further demonstrated that the transient re-expression of IRF6 in breast cancer cells results in an increase of N-cadherin and a redistribution of vimentin commensurate with changes in cell morphology, suggestive of an epithelial-to-mesenchymal transition event. Concomitantly, we showed that maspin acts as a negative regulator of this process. These findings help to elucidate the molecular mechanisms of maspin and suggest an interactive role between maspin and IRF6 in regulating cellular phenotype, the loss of which can lead to neoplastic transformation.

Retinoic-acid-induced apoptosis in leukemia cells

Retinoic acid (RA) cures more than 75% of patients with acute promyelocytic leukemia (APL). Here, we review the various anti-cancer activities of retinoids and rexinoids, alone and in combination with other drugs, with emphasis on the RA-dependent induction of a cancer-cell-selective apoptosis signaling pathway to which multiple anti-cancer signals converge. These findings identify the TRAIL (tumor-necrosis-factor-related apoptosis-inducing ligand) pathway as a central cell-autonomous anti-cancer weapon that can act independently of the immune system.

Interferon regulatory factor-1 (IRF-1) exhibits tumor suppressor activities in breast cancer associated with caspase activation and induction of apoptosis

We have directly assessed the ability of interferon regulatory factor-1 (IRF-1) to act as a tumor suppressor gene in human breast cancer cells and explored whether this suppressor function is mechanistically conferred by affecting cell cycle transition, apoptosis and/or caspase activation. We have used a dual approach, measuring whether overexpression of wild-type IRF-1 or a dominant negative IRF-1 (dnIRF-1) produce opposing effects on breast cancer cell proliferation in vitro or tumorigenicity in athymic nude mice. Mechanistic studies determined the effects of blocking endogenous IRF-1 expression on cell cycle transition by flow cytometry, on apoptosis by Annexin V staining, and on caspase activation by fluorescent substrate cleavage. IRF-1 mRNA (P < or = 0.001) and protein (P < or = 0.001) are highly expressed in non-tumorigenic, normal, mammary epithelial cells, with intermediate expression in tumorigenic, but non-metastatic, cells and very low expression in metastatic cell lines. In MCF-7 cells transfected with a wild-type IRF-1 (MCF-7/IRF-1), IRF-1 mRNA expression inversely correlates with the rate of cell proliferation (r = -0.91; P = 0.002). Conversely, expression of dnIRF-1 in both MCF-7 (MCF-7/dnIRF-1; p53 wild-type) and T47D cells (T47D/dnIRF-1; p53 mutant) increases cell proliferation (P < or = 0.001). In athymic nude mice, the incidence of MCF-7/IRF-1 xenografts is reduced (P = 0.045), whereas MCF-7/dnIRF-1 xenografts exhibit a significantly higher tumor incidence (P < or = 0.001). Effects of IRF-1/dnIRF-1 are mediated through changes in the rates of apoptosis and not through cell cycle regulation. MCF-7/dnIRF-1 cells exhibit a 50% decrease in basal apoptosis (P = 0.007) and a significant reduction in caspase 8 activity (P = 0.03); similar effects occur in T47D/dnIRF-1 cells, where the effects on apoptosis appear to be mediated through inhibition of caspases 3/7 (P < 0.001) and caspase 8 (P = 0.03). These data establish a functional role for IRF-1 in the growth suppression of breast cancer cells and strongly implicate IRF-1 as a tumor suppressor gene in breast cancer that acts, independent of p53, to control apoptosis.

Iron regulates T-lymphocyte sensitivity to the IFN-gamma/STAT1 signaling pathway in vitro and in vivo

The refractoriness of T cells to the interferon-gamma (IFN-gamma)/signal transducer and activator of transcription 1 (STAT1) pathway, which shields them from the antiproliferative effect of IFN-gamma, is attributed mainly to down-regulation of the IFN-gammaR2 signaling chain. However, the mechanisms responsible for this down-regulation are unclear. Here we show that iron uptake mediated by the transferrin receptor (TfR) delivers a signal that leads to IFN-gammaR2 internalization and thus plays an essential role in attenuating activation of the IFN-gamma/STAT1 pathway in human T lymphocytes. The effect of iron on IFN-gammaR2 internalization was specific as it did not affect expression of the IFN-gammaR1 binding chain. Deferoxamine (DFO), an iron-chelating agent, up-regulated IFN-gammaR2 surface expression and reinstated IFN-gamma/STAT1 activation in proliferating T lymphocytes. Resistance of malignant T cells to the antiproliferative effect of IFN-gamma in vitro was abrogated by addition of DFO. Conversely, iron inhibited IFN-gamma-induced apoptosis in malignant T cells in serum-free conditions. In combination but not individually, DFO and IFN-gamma strongly inhibited growth of human malignant T cells in an in vivo severe combined immunodeficient (SCID) mouse model. These data provide valuable insights for novel therapeutic approaches aimed at reinstating the IFN-gamma/STAT1 apoptotic signaling pathway in autoreactive or neoplastic T cells by means of iron chelation.

A role for synGAP in regulating neuronal apoptosis

The brain-specific Ras/Rap GTPase-activating protein synGAP is a major component of the postsynaptic density at glutamatergic synapses. It is a target for phosphorylation by Ca(2+)/calmodulin-dependent protein kinase II, which up-regulates its GTPase-activating activity. Thus, SynGAP may play an important role in coupling N-methyl-D-aspartate-type glutamate receptor activation to signaling pathways downstream of Ras or Rap. Homozygous deletion of synGAP is lethal within the first few days after birth. Therefore, to study the functions of synGAP, we used the cre/loxP recombination system to produce conditional mice mutants in which gradual loss of synGAP begins at approximately 1 week, and usually becomes maximal by 3 weeks, after birth. The resulting phenotypes fall into two groups. In a small group, the level of synGAP protein is reduced to 20-25% of wild type, and they die at 2-3 weeks of age. In a larger group, the levels remain higher than approximately 40% of wild type, and they survive and remain healthy. In all mutants, however, an abnormally high number of neurons in the hippocampus and cortex undergo apoptosis, as detected by caspase-3 activation. The effect is cell autonomous, occurring only in neuronal types in which the synGAP gene is eliminated. The level of caspase-3 activation in neurons correlates inversely with the level of synGAP protein measured at 2 and 8 weeks after birth, indicating that neuronal apoptosis is enhanced by reduction of synGAP. These data show that synGAP plays a role in regulation of the onset of apoptotic neuronal death.

N-Ras–Induced Growth Suppression of Myeloid Cells Is Mediated by IRF-1

Activating mutations in ras oncogenes occur at high frequency in human malignancies and expression of activated ras in immortalized cells lines is generally transforming. However, somewhat paradoxically, ectopic expression of ras in some myeloid cell lines has been shown to induce growth suppression associated with up-regulation of the cyclin-dependent kinase inhibitor p21CIP1/WAF1 in a p16INK4a, p15INK4b, and p53 independent fashion. We have used cDNA array technology to compare the expression profile induced by activated N-ras (N-rasG13R) in growth-suppressed myeloid cells with that induced in myeloid cells, which are transformed by N-rasG13R. The expression profile induced in growth suppressed cells was consistent with differentiation and included the up-regulation of the transcription factor IFN regulatory factor-1 (IRF-1), a known transcriptional activator of p21CIP/WAF1 expression and a target of oncogenic mutations associated with myeloid leukemia. Antisense suppression of IRF-1 prevented N-rasG13R–associated growth arrest and up-regulation of p21CIP1/WAF1. These results define a novel tumor suppressive response to oncogenic signaling and provide a mechanistic link between growth suppression and differentiation in myeloid cells.

c-Myc-mediated expression of nucleophosmin/B23 decreases during retinoic acid-induced differentiation of human leukemia HL-60 cells

The retinoic acid-induced differentiation of human leukemia HL-60 cells towards mature granulocytic cells was accompanied by the decline in the protein levels of c-myc, nucleophosmin/B23 and its promoter activity. These RA-induced effects were further enhanced by the concurrent treatment of HL-60 cells with p38 map kinase inhibitor SB203580 (SB). It seems that there is a strong correlation of nucleophosmin/B23 and c-Myc expressions in cells under RA treatment. Furthermore, nucleophosmin/B23 promoter activity decreased upon c-Myc antisense-mediated reduction of intracellular amount of c-Myc. CHIP assays showed that binding of c-Myc to the nucleophosmin/B23 promoter decreased in RA-treated cells. Thus, nucleophosmin/B23 expression is targeted by c-Myc during RA-induced differentiation. These results provide evidence for a novel mechanism of transcriptional downregulation of nucleophosmin/B23 and the functional role of c-Myc in RA-induced differentiation.

Glycolytic Enzymes Can Modulate Cellular Life Span

An unbiased screen for genes that can immortalize mouse embryonic fibroblasts identified the glycolytic enzyme phosphoglycerate mutase (PGM). A 2-fold increase in PGM activity enhances glycolytic flux, allows indefinite proliferation, and renders cells resistant to ras-induced arrest. Glucosephosphate isomerase, another glycolytic enzyme, displays similar activity and, conversely, depletion of PGM or glucosephosphate isomerase with short interfering RNA triggers premature senescence. Immortalized mouse embryonic fibroblasts and mouse embryonic stem cells display higher glycolytic flux and more resistance to oxidative damage than senescent cells. Because wild-type p53 down-regulates PGM, mutation of p53 can facilitate immortalization via effects on PGM levels and glycolysis.

IFN-gamma enhances TRAIL-induced apoptosis through IRF-1

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family and a potent inducer of apoptosis. TRAIL has been shown to effectively limit tumor growth in vivo without detectable cytotoxic side-effects. Interferon (IFN)-gamma often modulates the anticancer activities of TNF family members including TRAIL. However, little is known about the mechanism. To explore the mechanism, A549, HeLa, LNCaP, Hep3B and HepG2 cells were pretreated with IFN-gamma, and then exposed to TRAIL. IFN-gamma pretreatment augmented TRAIL-induced apoptosis in all these cell lines. A549 cells were selected and further characterized for IFN-gamma action in TRAIL-induced apoptosis. Western blotting analyses revealed that IFN-gamma dramatically increased the protein levels of interferon regulatory factor (IRF)-1, but not TRAIL receptors (DR4 and DR5) and pro-apoptotic (FADD and Bax) and anti-apoptotic factors (Bcl-2, Bcl-XL, cIAP-1, cIAP-2 and XIAP). To elucidate the functional role of IRF-1 in IFN-gamma-enhanced TRAIL-induced apoptosis, IRF-1 was first overexpressed by using an adenoviral vector AdIRF-1. IRF-1 overexpression minimally increased apoptotic cell death, but significantly enhanced apoptotic cell death induced by TRAIL when infected cells were treated with TRAIL. In further experiments using an antisense oligonucleotide, a specific repression of IRF-1 expression abolished enhancer activity of IFN-gamma for TRAIL-induced apoptosis. Therefore, our data indicate that IFN-gamma enhances TRAIL-induced apoptosis through IRF-1.

The GRIMs: a new interface between cell death regulation and interferon/retinoid induced growth suppression

Cytokines and vitamins play a central role in controlling neoplastic cell growth. The interferon (IFN) family of cytokines regulates antiviral, anti-tumor, antimicrobial, differentiation, and immune responses in mammals. Significant advances have been made with respect to IFN-induced signal transduction pathways and antiviral responses. However, the IFN-induced anti-tumor actions are poorly defined. Although IFNs themselves inhibit tumor growth, combination of IFNs with retinoids (a class of Vitamin A related compounds) strongly potentiates the IFN-regulated anti-tumor action in a number of cell types. To define the molecular mechanisms involved in IFN/retinoid (RA)-induced apoptosis we have employed a genetic approach and identified several critical genes. In this review, I provide the current picture of IFN- RA- and IFN/RA-regulated growth suppressive pathways. In particular, I focus on a novel set of genes, the genes-associated with retinoid-interferon induced mortality (GRIM). GRIMs may be novel types of tumor suppressors, useful as biological response markers and potentially novel targets for drug development.

Interferon regulatory factor 1 binding to p300 stimulates DNA-dependent acetylation of p53

Interferon regulatory factor 1 (IRF-1) and p53 control distinct sets of downstream genes; however, these two antioncogenic transcription factors converge to regulate p21 gene expression and to inhibit tumor formation. Here we investigate the mechanism by which IRF-1 and p53 synergize at the p21 promoter and show that stimulation of p21 transcription by IRF-1 does not require its DNA-binding activity but relies on the ability of IRF-1 to bind the coactivator p300 and to stimulate p53-dependent transcription by an allosteric mechanism. Deletion of the p300-binding sites in IRF-1 eliminates the ability of IRF-1 to stimulate p53 acetylation and associated p53 activity. Complementing this, small peptides derived from the IRF-1-p300 interface can bind to p300, stabilize the binding of p300 to DNA-bound p53, stimulate p53 acetylation in trans, and up-regulate p53-dependent activity from the p21 promoter. The nonacetylatable p53 mutant (p53-6KR) cannot be stimulated by IRF-1, further suggesting that p53 acetylation is the mechanism whereby IRF-1 modifies p53 activity. These data expand the core p300-p53 protein LXXLL and PXXP interface by including an IRF-1-p300 interface as an allosteric modifier of DNA-dependent acetylation of p53 at the p21 promoter.

Myelodysplasia-associated autoimmunity: clinical and pathophysiologic concepts

Myelodysplastic syndrome (MDS), an acquired clonal disorder of haemopoietic progenitor cells, is characterized by haemopoietic insufficiency associated with cytopenias, leading to serious morbidity plus the additional risk of leukaemic transformation. In MDS an acquired insult to the haemopoietic stem cell leads to impaired differentiation and myelodysplasia. However, there is increasing evidence that the marrow failure of MDS is immune-mediated. A model of MDS pathophysiology suggests that transformation of normal stem cells induces an autoimmune T-cell response with the bone marrow as the target organ. This autoimmune attack results in chronic overproduction of pro-apoptotic cytokines, especially tumour necrosis factor alpha (TNFalpha). In addition, several reports have revealed that approximately 10% of MDS patients have clinical autoimmune disorders. This review illustrates the cellular/molecular mechanisms and the implication of the tumour suppressor gene interferon regulatory factor-1 (IRF-1) in the pathophysiology of MDS-associated autoimmune deregulation.

Association of nucleophosmin/B23 mRNA expression with clinical outcome in patients with bladder carcinoma

OBJECTIVES

To determine whether nucleophosmin/B23 mRNA expression in bladder carcinoma predicts recurrence, progression, and survival.

METHODS

Real-time reverse transcriptase-polymerase chain reaction was performed on 50 fresh cancer specimens. The change in the cycle of threshold (Ct)was the difference in the Ct values derived from the nucleophosmin/B23 gene assayed and the 18S ribosomal RNA control [Ct (18S)-Ct (nucleophosmin/B23)].

RESULTS

Fifty patients diagnosed with bladder cancer were followed up postoperatively for a median of 24 months. Overexpression of nucleophosmin/B23 mRNA was observed in 37.1% of patients with Stage pT1 and 73.3% of those with pT2-T4 disease. Nucleophosmin/B23 overexpression was not associated with tumor grade (P = 0.163) but was associated with bladder cancer recurrence (68.2%) and progression (88.9%) when adjusted for the effects of clinical stage. Multivariate analysis revealed that the overall tumor stage and nucleophosmin/B23 mRNA overexpression were important prognostic indicators for bladder carcinoma (P <0.05). Patients with nucleophosmin/B23 mRNA overexpression were at a significantly greater risk of disease recurrence and progression than those with low expression of nucleophosmin/B23 mRNA.

CONCLUSIONS

Overexpression of nucleophosmin/B23 mRNA was independently associated with bladder cancer recurrence and progression. In patients with muscular invasion disease, overexpression of nucleophosmin/B23 mRNA was associated with the greatest risk of recurrence and progression, suggesting a potential rationale for early definitive therapy in these patients.

Involvement of interferon regulatory factor 1 and S100C/A11 in growth inhibition by transforming growth factor beta 1 in human hepatocellular carcinoma cells

Growth inhibition by transforming growth factor (TGF)-beta 1 has been attributed to the induction of cyclin-dependent kinase inhibitors, among which p21/Waf1 plays a major role in many biological contexts. In the present study, two new intracellular mediators for the induction of p21/Waf1 by TGF-beta 1 were identified in a human hepatocellular carcinoma cell line (JHH-5) expressing mutant-type p53. After addition of TGF-beta 1 to JHH-5 cells, a marked increase of the p21/Waf1 expression preceded the inhibition of DNA synthesis. Expression of IFN regulatory factor (IRF)-1, a known transacting factor for p21/Waf1 promoter, was elevated just before or in parallel with the increase of p21/Waf1. Transduction of antisense IRF-1 inhibited the increase in p21/Waf1 in JHH-5 cells treated with TGF-beta 1 and partially released the cells from the growth arrest by TGF-beta 1. Expression of S100C/A11, a member of the Ca(2+)-binding S100 protein family, also markedly increased after addition of TGF-beta 1. S100C/A11 protein was translocated to and accumulated in nuclei of TGF-beta 1-treated JHH-5 cells, where p21/Waf1 was concomitantly accumulated. When a recombinant S100C/A11 protein was introduced into nuclei of JHH-5 cells, DNA synthesis was markedly inhibited in a dose-dependent manner in the absence of TGF-beta 1. Prior transfection of p21/Waf1-targeted small interfering RNA efficiently blocked decrease of DNA synthesis in JHH-5 cells caused by TAT-S100C/A11 or TGF-beta 1 and markedly inhibited expression of p21/Waf1 protein in the cells. These results indicate that IRF-1 and S100C/A11 mediate growth inhibition by TGF-beta 1 via induction of p21/Waf1.

Tumor suppressor IRF-1 mediates retinoid and interferon anticancer signaling to death ligand TRAIL

Retinoids and interferons are signaling molecules with pronounced anticancer activity. We show that in both acute promyelocytic leukemia and breast cancer cells the retinoic acid (RA) and interferon signaling pathways converge on the promoter of the tumoricidal death ligand TRAIL. Promoter mapping, chromatin immunoprecipitation and RNA interference reveal that retinoid-induced interferon regulatory factor-1 (IRF-1), a tumor suppressor, is critically required for TRAIL induction by both RA and IFNgamma. Exposure of breast cancer cells to both antitumor agents results in enhanced TRAIL promoter occupancy by IRF-1 and coactivator recruitment, leading to strong histone acetylation and synergistic induction of TRAIL expression. In coculture experiments, pre-exposure of breast cancer cells to RA and IFNgamma induced a dramatic TRAIL-dependent apoptosis in heterologous cancer cells in a paracrine mode of action, while normal cells were not affected. Our results identify a novel TRAIL-mediated tumor suppressor activity of IRF-1 and suggest a mechanistic basis for the synergistic antitumor activities of certain retinoids and interferons. These data argue for combination therapies that activate the TRAIL pathway to eradicate tumor cells.

Sensitization to the Lysosomal Cell Death Pathway upon Immortalization and Transformation

Tumorigenesis is associated with several changes that alter the cellular susceptibility to programmed cell death. Here, we show that immortalization and transformation sensitize cells in particular to the cysteine cathepsin-mediated lysosomal death pathway. Spontaneous immortalization increased the susceptibility of wild-type murine embryonic fibroblasts (MEFs) to tumor necrosis factor (TNF)-mediated cytotoxicity >1000-fold, whereas immortalized MEFs deficient for lysosomal cysteine protease cathepsin B (CathB) retained the resistant phenotype of primary cells. This effect was specific for cysteine cathepsins, because also lack of cathepsin L (a lysosomal cysteine protease), but not that of cathepsin D (a lysosomal aspartyl protease) or caspase-3 (the major executioner protease in classic apoptosis) inhibited the immortalization-associated sensitization of MEFs to TNF. Oncogene-driven transformation of immortalized MEFs was associated with a dramatic increase in cathepsin expression and additional sensitization to the cysteine cathepsin-mediated death pathway. Importantly, exogenous expression of CathB partially reversed the resistant phenotype of immortalized CathB-deficient MEFs, and the inhibition of CathB activity by pharmacological inhibitors or RNA interference attenuated TNF-induced cytotoxicity in immortalized and transformed wild-type cells. Thus, tumorigenesis-associated changes in lysosomes may counteract cancer progression and enhance therapeutic responses by sensitizing cells to programmed cell death.

interferon regulatory factor-1 mediates the proapoptotic but not cell cycle arrest effects of the steroidal antiestrogen ICI 182,780 (faslodex, fulvestrant)

Antiestrogens induce both cytostasis (cell cycle arrest) and apoptosis, but the relationship between these end points and the signaling that regulates their induction are unclear. We have previously implicated the transcription factor and putative tumor suppressor IFN regulatory factor-1 (IRF-1) in acquired antiestrogen resistance (Gu et al., Cancer Res, 62: 3428-3437, 2002). We now show the functional significance of IRF-1 in affecting antiestrogen responsiveness in estrogen receptor-positive antiestrogen-sensitive models (MCF-7, T47D, and ZR-75-1), a model of acquired antiestrogen resistance (MCF7/LCC9; estrogen receptor positive), and a model of de novo antiestrogen resistance (MDA-MB-231; estrogen receptor negative). Basal IRF-1 mRNA expression is lower in MCF7/LCC9 cells when compared with MCF-7, T47D, and ZR-75-1 cells. IRF-1 transcriptional activity in MCF-7/LCC9 cells is 18-fold lower than that seen in the parental cells (MCF-7/LCC1) and is comparable with that in MDA-MB-231 cells. Although IRF-1 mRNA expression is induced by ICI 182,780 in sensitive cells, this regulation is lost in MCF-7/LCC9 and is absent in MDA-MB-231 cells. Loss of IRF-1 regulation appears specific to antiestrogen resistance-resistant cells induce IRF-1 mRNA in response to the cytotoxic drug doxorubicin. A dominant-negative IRF-1 eliminates the ICI 182,780-induced apoptotic response (reduced >4-fold) and reduces MCF-7 and T47D cell sensitivity to the antiproliferative effects of ICI 182,780. This effect is not mediated by changes in cell cycle distribution; rather, dominant-negative IRF-1 reduces ICI 182,780-induced apoptosis. These data identify a novel mechanism of antiestrogen resistance and implicate IRF-1 as a key component in signaling some ER-mediated effects on apoptosis/cell survival.

Deregulated expression of interferon regulatory factor-1 in oncogene-transformed mouse fibroblasts

Interferon (IFN) regulatory factor-1 (IRF-1) is a transcription factor that has been historically associated with type I IFN activation and antioncogenic properties. We studied IRF-1 expression and DNA-binding capacity in nontransformed and transformed mouse fibroblasts. A 43-kDa nuclear IRF-1 protein was expressed biphasically during the cell cycle in primary mouse embryo fibroblasts, nontransformed NIH 3T3 cells, and ras revertants. IRF-1 expression became constitutive in ras-transformed NIH 3T3 cells and in cells transformed by oncogenes ets, fes, fos, her-2/neu, met, mos, raf, or trk, suggesting that deregulated IRF-1 expression may be associated with loss of growth control. Lysyl oxidase (LO), a ras suppressor that is downregulated in ras transformants, is an IRF-1 target gene, but it is not stimulated by abundant IRF-1 present in transformants, while another IRF-1 target gene (iNOS) is transcribed. IRF-1 from either normal or ras-transformed cells bound to IRF elements in the IFN-beta and LO promoters. IRF-1 in transformants can, therefore, bind to but not transactivate the LO promoter, and the presence of IRF-1 is not sufficient to suppress ras transformation. LO expression may effect the regulated expression of IRF-1: a ras revertant, which was generated by stable transfection of LO cDNA, regained the normal biphasic IRF-1 pattern. A mainly cytoplasmic, constitutively expressed 46-kDa protein with immunologic identity to the 43-kDa nuclear IRF-1 was also present in normal and transformed cells, but as it did not bind to the IRF elements, its function is unclear.

Autoimmune manifestations in human myelodysplasia: a positive correlation with interferon regulatory factor-1 (IRF-1) expression

BACKGROUND

Patients with myelodysplasia may have autoimmune manifestations (AIM). Interferon regulatory factor-1 (IRF-1) is a transcription factor involved in interferon signalling, leukaemogenesis, and the development of the immune system.

OBJECTIVES

To determine whether IRF-1 is implicated in the pathophysiology of AIM in myelodysplasia.

METHODS

14 patients with myelodysplasia were studied, seven with AIM and seven without. Five patients with vasculitis and seven normal subjects served as controls. The expression of IRF-1 was studied in bone marrow mononuclear cells taken from patients and controls, using a relative quantitative reverse transcriptase polymerase chain reaction.

RESULTS

A 10-fold reduction in full length IRF-1 mRNA was detected in the myelodysplasia patients without AIM compared with the normal controls. In contrast, the group with AIM had increased IRF-1 transcripts, to a level almost equal to that observed in patients with vasculitis and normal controls.

CONCLUSIONS

Myelodysplasia patients without IRF-1 expression had a decreased incidence of AIM. Thus the absence of IRF-1 transcription factor appears to protect against the development of autoimmunity in myelodysplasia.

Study of the effects of interferon a on several human hepatoma cell lines: analysis of the signalling pathway of the cytokine and of its effects on apoptosis and cell proliferation

BACKGROUND

Interferon alpha (IFNalpha), currently used for the treatment of chronic viral hepatitis, is also known to prevent the development of hepatocellular carcinoma (HCC), the mechanism of this action being still debatable.

AIMS

To study thoroughly in human hepatoma cell lines (HHL)--Hep3B, HepG2, HuH7, SKHep1, and Chang-Liver--submitted to rhIFNalpha, the signalling pathway of IFNalpha, the binding activity of the cytokine on specific gamma-activated sequence (GAS) and interferon-stimulated regulatory element (ISRE) nuclear sequences, and its effects on apoptosis and cell proliferation.

METHODS

The behaviour of signal transducer and activator of transcription (STAT)1, STAT2, p48(IRF9) and the binding of nuclear proteins were investigated by immunoblot and electro-mobility shift assay. Expression of some IFNalpha-dependent proteins--p21/(WAF1), inducible nitric oxide synthase, IRF1 and 2--were studied by immunoblot. Apoptosis and the cell cycle were studied by morphological and biochemical methods.

RESULTS

Transduction of INFalpha was unaltered, although there were some variations in the different HHL. Nuclear protein binding to GAS or ISRE showed that ISRE was mainly involved. Apoptosis did not occur. The cell cycle was slightly modified in HuH7. Three GAS- and/or ISRE-dependent proteins increased, suggesting that IFNalpha may have some biological effects on HHL.

CONCLUSIONS

The IFNalpha signalling pathway is functional in several HHL, but the cytokine has no apoptotic effect and a moderate anti-proliferative effect. This suggests that the preventive role of IFNalpha on HCC cannot be explained by an apoptotic and/or an anti-proliferative effect, but possibly by its action on several specific nuclear sequences that protect liver cells from transformation.

Endogenous oncogenic K-ras(G12D) stimulates proliferation and widespread neoplastic and developmental defects

Activating mutations in the ras oncogene are not considered sufficient to induce abnormal cellular proliferation in the absence of cooperating oncogenes. We demonstrate that the conditional expression of an endogenous K-ras(G12D) allele in murine embryonic fibroblasts causes enhanced proliferation and partial transformation in the absence of further genetic abnormalities. Interestingly, K-ras(G12D)-expressing fibroblasts demonstrate attenuation and altered regulation of canonical Ras effector signaling pathways. Widespread expression of endogenous K-ras(G12D) is not tolerated during embryonic development, and directed expression in the lung and GI tract induces preneoplastic epithelial hyperplasias. Our results suggest that endogenous oncogenic ras is sufficient to initiate transformation by stimulating proliferation, while further genetic lesions may be necessary for progression to frank malignancy.

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.

IRF-1 expression induces apoptosis and inhibits tumor growth in mouse mammary cancer cells in vitro and in vivo

Interferon regulatory factor-1 (IRF-1) is a nuclear transcription factor that mediates interferon and other cytokine effects and appears to have antitumor activity in vitro and in vivo in cancer cells. We have constructed a recombinant adenoviral vector (Ad-IRF-1) that infects mammary cells with high efficiency and results in high levels of functional IRF-1 protein in transfected cells. Overexpression of IRF-1 in two mouse breast cancer cell lines, C3-L5 and TS/A, resulted in apoptosis in these cell lines as assessed by Annexin V staining. The involvement of caspases was confirmed by significant inhibition of apoptosis by a caspase inhibitor, and by demonstration of caspase-3 activity, cleavage of caspase-3, and PARP cleavage. Interestingly, the growth of nonmalignant breast cell lines C127I and NMuMG did not appear to be inhibited by IRF-1 overexpression. Suppression of growth for breast cancer cell lines in vivo was demonstrated by both preinfection of breast cancer cells ex vivo and by intratumoral injection of Ad-IRF-1 into established tumors in their natural hosts. The mechanism of apoptosis may involve the transcriptional upregulation of bak, caspase-8, and caspase-7 expression. These data support the antitumor potential of IRF-1 and the use of agents that increase IRF-1 in breast cancer.

Role of antiproliferative B cell translocation gene-1 as an apoptotic sensitizer in activation-induced cell death of brain microglia

Mouse brain microglial cells undergo apoptosis on exposure to inflammatory stimuli, which is considered as an autoregulatory mechanism to control their own activation. Here, we present evidence that an antiproliferative B cell translocation gene 1 (BTG1) constitutes a novel apoptotic pathway of LPS/IFN-gamma-activated microglia. The expression of BTG1 was synergistically enhanced by LPS and IFN-gamma in BV-2 mouse microglial cells as well as in primary microglia cultures. Levels of BTG1 expression inversely correlated with a proliferative capacity of the microglial cells. Tetracycline-based conditional expression of BTG1 not only suppressed microglial proliferation but also increased the sensitivity of microglial cells to NO-induced apoptosis, suggesting a novel mechanism of cooperation between LPS and IFN-gamma in the induction of microglial apoptosis. An increase in BTG1 expression, however, did not affect microglial production of NO, TNF-alpha, or IL-1beta, indicating that the antiproliferative BTG1 is important in the activation-induced apoptosis of microglia, but not in the activation itself. The synergistic action of LPS and IFN-gamma in the microglial BTG1 induction and apoptosis was dependent on the Janus kinase/STAT1 pathway, but not IFN-regulatory factor-1, as demonstrated by a pharmacological inhibitor of Janus kinase (AG490), STAT1 dominant negative mutant, and IFN-regulatory factor-1-deficient mice. Taken together, antiproliferative BTG1 may participate in the activation-induced cell death of microglia by lowering the threshold for apoptosis; BTG1 increases the sensitivity of microglia to apoptogenic action of autocrine cytotoxic mediator, NO. Our results point out an important link between the proliferative state of microglia and their sensitivity to apoptogenic agents.

Mechanism of LIGHT/interferon-?-induced cell death in HT-29 cells

LIGHT is a member of tumor necrosis factor (TNF) superfamily, and previous studies have indicated that in the presence of interferon-gamma (IFN-gamma), LIGHT through LTbetaR signaling can induce cell death with features unlike classic apoptosis. In present study, we investigated the mechanism of LIGHT/IFN-gamma-induced cell death in HT-29 cells, where the cell death was profoundly induced when sub-toxic concentrations of LIGHT and IFN-gamma were co-treated. LIGHT/IFN-gamma-induced cell death was accompanied by DNA fragmentation and slight LDH release. This effect was not affected by caspase, JNK nor cathepsin B inhibitors, but was partially prevented by p38 mitogen-activated protein kinase (MAPK) and poly (ADP-ribose) polymerase (PARP) inhibitors, and abolished by aurintricarboxylic acid (ATA), which is an inhibitor of endonuclease and STATs signaling of IFN-gamma. Immunobloting reveals that LIGHT/IFN-gamma could induce p38 MAPK activity, Bak and Fas expression, but down-regulate Mcl-1. Besides, LIGHT/IFN-gamma could not activate caspase-3 and -9, but decreased mitochondrial membrane potential. Although LIGHT could not affect IFN-gamma-induced STAT1 phosphorylation and transactivation activity, which was required for the sensitization of cell death, survival NF-kappaB signaling of LIGHT was inhibited by IFN-gamma. These data suggest that co-presence of LIGHT and IFN-gamma can induce an integrated interaction in signaling pathways, which lead to mitochondrial dysfunction and mix-type cell death, not involving caspase activation.

Interferon regulatory factor-1 mediates PPARgamma-induced apoptosis in vascular smooth muscle cells

OBJECTIVE

Peroxisome proliferator-activated receptor gamma (PPARgamma) possesses general beneficial effects on the cardiovascular system, such as inhibition of vascular lesion formation and atherosclerosis. However, molecular mechanisms for these effects are yet to be fully defined. The aim of this study is to elucidate whether interferon regulatory factor-1 (IRF-1), a transcriptional factor with anti-proliferative and pro-apoptotic properties, mediates PPARgamma-induced apoptosis in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Using Northern and Western blot analyses, we documented that PPARgamma ligands, including ciglitazone, troglitazone, and GW7845, significantly increased IRF-1 expression in VSMCs; however, the PPARalpha ligand (Wy14643) and PPARdelta ligand (GW0742) did not affect its expression. PPARgamma-induced IRF-1 expression was abrogated by pretreatment with the PPARgamma antagonist GW9662. In contrast, adenoviral expression of PPARgamma in VSMCs dramatically increased IRF-1 level. Furthermore, PPARgamma activation increased IRF-1 promoter activity but did not affect IRF-1 mRNA stability. Finally, reducing IRF-1 expression by antisense technology attenuated PPARgamma-induced VSMC apoptosis through decreasing cyclin-dependent kinase inhibitor p21(cip1) and caspase-3 activity.

CONCLUSIONS

Our data demonstrate that IRF-1 is a novel PPARgamma target gene and mediates PPARgamma-induced VSMC apoptosis.

Involvement of nucleophosmin/B23 in TPA-induced megakaryocytic differentiation of K562 cells

Human myelogenous leukaemia K562 cells were induced to undergo megakaryocytic differentiation by treatment with phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (20 nM, 24–72 h). The steady-state level of nucleophosmin/B23 mRNA decreased during the TPA-induced differentiation. There was also decrease in the level of cellular nucleophosmin/B23 protein and appearance of its degraded product (25 kDa) during the TPA-induced differentiation. Furthermore, K562/B23 (wild type), K562/D1 (Δ280–294) and K562/D2 (Δ263–294) cells were less, while K562/D3 (Δ244–294) cells were more responsive to TPA-induced differentiation as compared to K562/vector or parental K562 cells. Activation of the ERK/MAPK was observed in parental K562 cells upon TPA treatment (5 nM, 5–30 min). As compared to K562/vector cells, less activation of ERK/MAPK was observed in K562/D2 cells, while ERK/MAPK was highly activated in K562/D3 cells upon TPA treatment. Our results indicate that nucleophosmin/B23 plays an important role in TPA-induced differentiation of K562 cells and the amino acids 244–294 at C-terminal of nucleophosmin/B23 could be an important site for regulation of cellular response to differentiation.

Oncogenic Ki-ras inhibits the expression of interferon-responsive genes through inhibition of STAT1 and STAT2 expression

Endogenous interferon gamma (IFNgamma) promotes the host response to primary tumors, and IFNgamma-insensitive tumors display increased tumorigenicity and can evade tumor surveillance mechanisms. Here we demonstrate that activating mutations of Ki-ras are sufficient to inhibit the expression of STAT1 and STAT2, transcription factors required for signaling by IFNs, providing a potential mechanism for the insensitivity of tumors to IFNs. We demonstrated that colon cancer cell lines with Ki-ras mutations display reduced expression of IFN-responsive genes compared with the cell lines that have retained wild type Ras and that inactivation of the mutant Ki-ras allele in the HCT116 colon cancer cell line is sufficient to restore the expression of STAT1, STAT2, and IRF-9. Accordingly, the expression of 27 interferon-inducible genes was reduced in HCT116 cells compared with the isogenic clones with targeted deletion of the mutant Ki-ras allele, Hkh2 and Hke-3. The expression of IFNgamma receptors did not differ among the isogenic cell lines. IFNgamma stimulated transcription of a STAT1-dependent reporter gene was impaired by RasV12, demonstrating a transmodulation of IFN/STAT signaling by activated Ras. Finally, we demonstrated that the expression of RasV12 in 293T cells is sufficient to inhibit the endogenous expression of STAT1 and STAT2, confirming the negative regulation of IFN signaling by oncogenic Ras. Our data demonstrate that the signaling initiated by activated Ki-ras interferes with the IFN/STAT signaling pathway and modulates the responsiveness of cancer cells to interferons. Furthermore, the data suggest that tumors harboring activating Ki-ras mutations may escape tumor surveillance mechanisms due to reduced responsiveness to IFNgamma.

Development of CD30+ lymphoproliferative disease in mice lacking interferon regulatory factor-1

Human lymphomas continue to represent a major challenge in oncology, and in particular occur at very high frequencies in AIDS patients. We report here the development of a CD30+ lymphoproliferative disease in mice lacking the proapoptotic transcription factor, interferon regulatory factor-1. These mice most closely represent a model of human anaplastic large-cell lymphoma (ALCL). This mouse model of lymphoma will likely be useful in understanding the development of ALCL and in understanding the development of other closely related CD30+ forms of lymphoma, such as CD30+ Hodgkin's disease and CD30+ cutaneous T-cell lymphoma. This mouse model will also be useful in testing therapies for different forms of CD30+ lymphoma, in particular anti-CD30-based therapies.

Interferon-gamma: an overview of signals, mechanisms and functions

Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.