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

Interferon modulates the messenger RNA of G1-controlling genes to suppress the G1-to-S transition in Daudi cells

Interferon (IFN) is one of the potent antiproliferative cytokines and is used to treat some selected cancers. IFN arrests the growth of Burkitt Lymphoma derived cell line Daudi cells in the G1 phase. G1-to-S progression is controlled by positive and negative regulatory genes. Therefore, we investigated the effects of IFN on G1-controlling genes. Expression of cyclin-dependent kinases (Cdks 2, 3, 4, 5, 6), MO15/Cdk7, and cyclins E and H was studied to assess positive regulators, while p15Ink4B, p16Ink4, p18, p21Cip1, and p27Kip1 were assessed as negative regulators. Cdks 2, 4, 6 and cyclin E were markedly down-regulated. MO15/Cdk7 expression showed little change, but its regulatory subunit (cyclin H) was down-regulated like cyclin E. Expression of p15Ink4B and p16Ink4 was not observed. p18 was induced until 48 h and its expression returned to the initial level at 72 h. In contrast, p21Cip1 mRNA expression remained at the baseline level throughout IFN treatment, while the expression of p27Kip1 increased at 48 and 72 h. Taken together, these data indicate that IFN changes the messenger RNA of G1-controlling genes towards the suppression of G1-to-S transition.

Radiotherapy for genes that cause cancer

Many approaches to cancer gene radiotherapy are possible. Even existing strategies, devised with other goals in mind, can cause radiosensitization by altering the intrinsic radiosensitivity of tumour cells or by modifying the tumour microenvironment. Small increases in the levels of radiosensitization could, over a fractionated radiation course, have major effects on the probability of tumour cure. The clinical application of gene radiotherapy will require use of in vivo gene delivery systems that still need validation but, because radiation is effective at decreasing tumour burden, genes will not have to be expressed in all cells in order to achieve a cure.

Spatial, temporal and hormonal regulation of programmed muscle cell death during metamorphosis of the frog Xenopus laevis

No examination to date has been made of apoptosis during vertebrate muscle development. The authors recently reported programmed muscle cell death to be important in tail degeneration as well as in the larval-to-adult conversion of the dorsal body muscles of Xenopus laevis during metamorphosis [30]. In the present study, we examined programmed cell death (PCD) of the dorsal body and tail muscle morphologically and biochemically, with special attention to whether apoptotic processes, such as chromatin fragmentation and apoptotic body-formation actually occur, and whether triiodothyronine (T3) induces such processes. Light microscopic observation indicated muscle fibers break down into short fragments (sarcolytes or muscle apoptotic bodies) during the metamorphic climax, not only in tail but also in larval-type fibers of dorsal body muscles. Apoptotic bodies first appeared near the base of the tail in early climax (stage 59) when the T3 level is quite high, and thereafter expanded in an anterior direction in the dorsal body and posteriorly in the tail. The ratio of apoptotic area to total muscle area became maximum (10%-30% in dorsal body muscles and 50% in the tail) at the climax (stages 63-64). During these stages, genomic DNA fragmented into oligonucleosome-sized units (200 bp, 400 bp, 600 bp ...) in both body and tail muscles. To confirm whether this chromatin fragmentation is associated with apoptotic bodies, in situ DNA nick end labeling (TUNEL) was applied to sections of the dorsal body and tail muscles. Labeled muscle nuclei could be found only in muscle apoptotic bodies but not in intact muscle fibers, indicating DNA fragmentation was associated with cell fragmentation during metamorphosis. It thus follows that morphological (apoptotic body formation) and biochemical (fragmentation of chromatin) processes occurring during PCD of dorsal body and tail muscles are identical. To determine whether T3 regulates programmed muscle cell death, the effects of T3 on DNA ladder formation were examined in tails cultured in vitro. The oligonucleosomal DNA ladder was found to form only in tails incubated with T3, thus showing T3 to induce programmed muscle cell death without interaction with other endocrine organs during metamorphosis.

Vascular system defects and neuronal apoptosis in mice lacking ras GTPase-activating protein

The gene encoding p120-rasGAP, a negative regulator of Ras, has been disrupted in mice. This Gap mutation affects the ability of endothelial cells to organize into a highly vascularized network and results in extensive neuronal cell death. Mutati ons in the Gap and Nf1 genes have a synergistic effect, such that embryos homozygous for mutations in both genes show an exacerbated Gap phenotype. Thus rasGAP and neurofibromin act together to regulate Ras activity during embryonic development.

The killer and the executioner: how apoptosis controls malignancy

An escalating research effort focused on apoptotic cell death continues to chip away at the central mechanisms of this intriguing process. One of the areas in which this research has already yielded fundamental insights is in the analysis of oncogenesis, where defects in cell death can have profound effects. Recent progress has been made in understanding the processes of apoptosis induction, transduction, and effect (or 'execution'), especially with respect to our understanding of malignancy, hyperplasia and related phenomena.

Activation of a cell-cycle-regulated histone gene by the oncogenic transcription factor IRF-2

The human histone H4 gene FO108 is regulated during the cell cycle with a peak in transcription during early S phase. The cell-cycle element (CCE) required for H4 histone activation is a sequence of 11 base pairs that binds a protein factor in electrophoretic mobility shift assays that has been designated histone nuclear factor M (HiNF-M). Here we report the purification of HiNF-M, and show it to be a protein of relative molecular mass (M(r)) 48K that is identical to interferon (IFN) regulatory factor 2 (IRF-2), a negative transcriptional regulator of the IFN response. Recombinant IRF-2 (as well as the related protein IRF-1 (ref. 5)) binds the CCE specifically and activates transcription of this H4 histone gene. IRF-2 has been shown to have oncogenic potential, and our results demonstrate a link between IRF-2 and a gene that is functionally coupled to DNA replication and cell-cycle progression at the G1/S phase transition.

Regulation of the interferon system and cell growth by the IRF transcription factors

Induction of gene transcription in response to extracellular stimuli constitutes an essential aspect of host defense mechanisms. Interferons (IFN) are families of cytokines that have been discovered and extensively characterized in the context of host defense against viral infections. In elucidating the mechanism of transcriptional induction of the IFN genes by viruses, we have discovered two structurally related transcription factors, Interferon regulatory factor 1 (IRF-1) and IRF-2. These two factors, however, function not only as regulators of the IFN system, but are also key transcription factors in the regulation of cell growth and apoptosis. Thus, these studies uncover a complex gene transcription network in which the fate of cellular responses is determined by how the IRF transcription factors function in conjunction with other factors on the promoters of distinct genes under different conditions of the cells.

The growth-dependent expression of angiotensin II type 2 receptor is regulated by transcription factors interferon regulatory factor-1 and -2

Angiotensin II type 2 (AT2) receptor is abundantly and widely expressed in fetal tissues but present only in restricted tissues in the adult such as brain and atretic ovary. This receptor is speculated to be involved in tissue growth and/or differentiation. To elucidate the molecular mechanism of growth-regulated AT2 receptor expression, we cloned the mouse AT2 receptor genomic DNA and studied its promoter function in mouse fibroblast-derived R3T3 cells, which express AT2 receptor in the confluent, quiescent state but very low levels of the receptor in actively growing state. Promoter/luciferase reporter deletion analysis of AT2 receptor in R3T3 cells showed that the putative negative regulatory region is located between the positions -453 and -225, which plays an important role in the transcriptional control of AT2 receptor gene expression along with the cell growth. We identified the interferon regulatory factor (IRF) binding motif in this region using DNase foot-printing analysis and demonstrated that IRF binding oligonucleotide treatment increased the AT2 receptor expression in growing R3T3 cells but not in confluent cells. Furthermore, by antisense treatment, we demonstrated that IRF-2 attenuated the AT2 receptor expression in both growing and confluent R3T3 cells, whereas IRF-1 enhanced AT2 receptor expression in the confluent cells only. Consistent with this result, gel mobility shift assay demonstrated that growing R3T3 cells exhibited only IRF-2 binding, whereas confluent cells exhibited both IRF-1 and IRF-2 binding. Furthermore, we observed using reverse transcription-polymerase chain reaction that the IRF-1 mRNA expression was more abundant in confluent cells than growing cells, whereas IRF-2 expression did not change with R3T3 cell growth. We conclude that, in confluent cells, the enhanced expression of IRF-1 antagonizes the IRF-2 effect and increases the AT2 receptor expression. We speculate that these transcriptional factors influence cell growth in part by regulating AT2 receptor expression.

An IRF-1-dependent pathway of DNA damage-induced apoptosis in mitogen-activated T lymphocytes

Lymphocytes are particularly susceptible to DNA damage-induced apoptosis, a response which may serve as a form of 'altruistic suicide' to counter their intrinsic high potential for mutation and clonal expansion. The tumour suppressor p53 has been shown to regulate this type of apoptosis in thymocytes, but an as yet unknown, p53-independent pathway(s) appears to mediate the same event in mitogen-activated mature T lymphocytes. Here we show DNA damage-induced apoptosis in these T lymphocytes is dependent on the antioncogenic transcription factor interferon regulatory factor (IRF)-1. Thus two different anti-onco-genic transcription factors, p53 and IRF-1, are required for distinct apoptotic pathways in T lymphocytes. We also show that mitogen induction of the interleukin-1 beta converting enzyme (ICE) gene, a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, is IRF-1-dependent. Ectopic overexpression of IRF-1 results in the activation of the endogenous gene for ICE and enhances the sensitivity of cells to radiation-induced apoptosis.

Interleukin-3, erythropoietin, and prolactin activate a STAT5-like factor in lymphoid cells

Interleukin-3 (IL-3)-, erythropoietin (EPO)-, and prolactin (PRL)-induced signal transduction via the JAK/STAT pathway was studied in the IL-3-dependent BAF-3 lymphoid cell line. Transfected cells expressing either the long form of the PRL receptor or the EPO receptor were used. We demonstrated that IL-3, EPO, and PRL activated a transcription factor related to the mammary transcription factor STAT5 but not to STAT1, -2, -3, or -4 as opposed to interferon gamma (IFN gamma) which activated STAT1 in the same cells. Similarly, PRL and EPO activated a STAT5-like factor (STAT5-L) in the rat Nb2 and the human UT7 cells expressing endogenous PRL and EPO receptors, respectively. The hematopoietic STAT5-L activated by IL-3, EPO, or PRL was identified as a 97-kDa tyrosine-phosphorylated protein. These results confer to STAT5 a much broader role than previously suggested.

Reduced contact-inhibition and substratum adhesion in epithelial cells expressing GlcNAc-transferase V

Malignant transformation of fibroblast and epithelial cells is accompanied by increased beta 1-6 N-acetylglucosaminyltransferase V (GlcNAc-TV) activity, a Golgi N-linked oligosaccharide processing enzyme. Herein, we report that expression of GlcNAc-TV in Mv1Lu cells, an immortalized lung epithelial cell line results in loss of contact-inhibition of cell growth, an effect that was blocked by swainsonine, an inhibitor of Golgi processing enzyme alpha-mannosidase II. In serum-deprived and high density monolayer cultures, the GlcNAc-TV transfectants formed foci, maintained microfilaments characteristic of proliferating cells, and also experienced accelerated cell death by apoptosis. Injection of the GlcNAc-TV transfectants into nude mice produced a 50% incidence of benign tumors, and progressively growing tumors in 2:12 mice with a latency of 6 mo, while no growth was observed in mice injected with control cells. In short term adhesion assays, the GlcNAc-TV expressing cells were less adhesive on surfaces coated with fibronectin and collagen type IV, but no changes were observed in levels of cell surface alpha 5 beta 1 or alpha v beta 3 integrins. The larger apparent molecular weights of the LAMP-2 glycoprotein and integrin glycoproteins alpha 5, alpha v and beta 1 in the transfected cells indicates that their oligosaccharide chains are substrates for GlcNAc-TV. The results suggest that beta 1-6GlcNAc branching of N-linked oligosaccharides contributes directly to relaxed growth controls and reduce substratum adhesion in premalignant epithelial cells.

cIRF-3, a new member of the interferon regulatory factor (IRF) family that is rapidly and transiently induced by dsRNA

In mammals, some of the effects of interferon (IFN) on gene transcription are known to be mediated by a family of IFN-inducible DNA-binding proteins, the IFN regulatory factor (IRF) family, which includes both activators and repressors of transcription. Although IFN activities have been described in many vertebrates, little is known about regulation of IFN- or IFN-stimulated genes in species other than human and mouse. Here, we report the cloning of a chicken cDNA, cIRF-3, encoding a protein with a DNA-binding domain similar to that found in the mammalian IRF family of proteins. Similarity between cIRF-3 and the mammalian IRFs is comparable with that between known members of the family. It is most similar to the IRF proteins ICSBP and ISGF3 gamma but is equally divergent from both. Gel mobility shift assays indicate that cIRF-3 is capable of binding a known IFN-stimulated response element that is conserved between the mammalian and chicken Mx genes. Expression of the cIRF-3 gene can be induced to high levels by poly(I).poly(C). Induction is rapid and transient with no requirement for protein synthesis. Co-treatment of cells with cycloheximide results in superinduction of cIRF-3 mRNA. The structural and regulatory characteristics of cIRF-3 indicate that it is the first example of a non-mammalian IRF protein.

Functional domain analysis of interferon consensus sequence binding protein (ICSBP) and its association with interferon regulatory factors

Interferon consensus sequence binding protein (ICSBP) is a member of the interferon regulatory factor (IRF) family of proteins that include IRF-1, IRF-2, and ISGF3gamma which share sequence similarity at the putative DNA binding domain (DBD). ICSBP is expressed exclusively in cells of the immune system and acts as a repressor of interferon consensus sequence (ICS) containing promoters that can be alleviated by interferons. In this communication, we have searched for functional domains of ICSBP by dissecting the DBD from the repression activity. The putative DBD of ICSBP (amino acids 1-121) when fused in frame to the transcriptional activation domain of the herpes simplex VP16 (ICSBP-VP16) is a very strong activator of ICS-containing promoters. In addition, ICSBP-VP16 fusion construct transfected into adenovirus (Ad) 12 transformed cells enabled cell surface expression of major histocompatibility complex class I antigens as did treatment with interferon. On the other hand, the DBD of the yeast transcriptional activator GAL4 was fused in frame to a truncated ICSBP in which the DBD was impaired resulting in a chimeric construct GAL4-ICSBP. This construct is capable of repressing promoters containing GAL4 binding sites. Thus, ICSBP contains at least two independent domains: a DBD and a transcriptional repressor domain. Furthermore, we have tested possible interactions between ICSBP and IRFs. The chimeric construct GAL4-ICSBP inhibited the stimulated effect of IRF-1 on a reporter gene, implying for a possible interaction between IRF-1 and ICSBP. Electromobility shift assays, demonstrated that ICSBP can associate with IRF-2 or IRF-1 in vitro as well as in vivo. Thus, ICSBP contains a third functional domain that enables the association with IRFs. These associations are probably important for the fine balance between positive and negative regulators involved in the interferon-mediated signal transduction pathways in cells of the immune system.

R-Ras promotes apoptosis caused by growth factor deprivation via a Bcl-2 suppressible mechanism

The Bcl-2 protein is an important regulator of programmed cell death, but the biochemical mechanism by which this protein prevents apoptosis remains enigmatic. Recently, Bcl-2 has been reported to physically interact with a member of the Ras superfamily of small GTPases, p23-R-Ras. To examine the functional significance of R-Ras for regulation of cell death pathways, the IL-3-dependent cells 32D.3 and FL5.12 were stably transfected with expression plasmids encoding an activated form (38 Glycine-->Valine) of R-Ras protein. R-Ras(38V)-producing 32D.3 and FL5.12 cells experienced increased rates of apoptotic cell death relative to control transfected cells when deprived of IL-3. Analysis of several independent clones of transfected 32D.3 cells revealed a correlation between higher levels of R-Ras protein and faster rates of cell death upon withdrawal of IL-3 from cultures. 32D.3 cells cotransfected with R-Ras(38V) and Bcl-2 exhibited prolonged cell survival in the absence of IL-3, equivalent to 32D.3 cells transfected with Bcl-2 expression plasmids alone. R-Ras(38V) also increased rates of cell death in serum-deprived NIH-3T3 cells, and Bcl-2 again abrogated most of this effect. The ratio of GTP and GDP bound to R-Ras(38V) was not significantly different in control 32D.3 cells vs those that overexpressed Bcl-2, indicating that Bcl-2 does not abrogate R-Ras-mediated effects on cell death by altering R-Ras GDP/GTP regulation. Moreover, purified Bcl-2 protein had no effect on the GTPase activity of recombinant wild-type R-Ras in vitro. When expressed in Sf9 cells using recombinant baculoviruses, R-Ras(38V) bound to and induced activation of Raf-1 kinase irrespective of whether Bcl-2 was coproduced in these cells, suggesting that Bcl-2 does not nullify R-Ras effects by interfering with R-Ras-mediated activation of Raf-1 kinase. Taken together, these findings suggest that R-Ras enhances the activity of a cell death pathway in growth factor-deprived cells and imply that Bcl-2 acts downstream of R-Ras to promote cell survival.

Neuron-specific regulation of major histocompatibility complex class I, interferon-beta, and anti-viral state genes

The regulation of major histocompatibility complex (MHC) class I, interferon (IFN)-beta, and anti-viral state expression in neurons was analyzed. Treatment of neurons with either double-stranded RNA (poly I: poly C) or virus, but not IFNs, induced high levels of IFN-beta, but not MHC class I genes. However, neurons treated with IFN-beta established an anti-viral state. Transfection of neurons with IFN-beta constructs showed that a region containing PRDI (IRF-E site) and PRDII (kappa B site) mediated induction, but closely related sites in a MHC class I construct did not. Gel mobility shift assays indicated that transcription factors containing the RelA (p65) component of NF-kappa B, but not p50, bound to PRDII. PRDI, however, bound to transcriptional antagonist IRF-2. Unique selective induction of these transcription factors is likely to mediate non-coordinate expression of IFN-beta, MHC class I, and anti-viral state genes in neurons.

FAS-induced apoptosis is mediated via a ceramide-initiated RAS signaling pathway

Fas receptor-induced apoptosis plays critical roles in immune homeostasis. However, most of the signal transduction events distal to Fas ligation have not been elucidated. Here, we show that Ras is activated following ligation of Fas on lymphoid lines. The activation of Ras is a critical component of this apoptotic pathway, since inhibition of Ras by neutralizing antibody or a dominant-negative Ras mutant interfered with Fas-induced apoptosis. Furthermore, ligation of Fas also resulted in stimulation of the sphingomyelin signalling pathway to produce ceramides, which, in turn, are capable of inducing both Ras activation and apoptosis. This suggests that ceramides acts as second messengers in Fas signaling via Ras. Thus, ligation of the Fas molecule on lymphocyte lines induces activation of Ras via the action of ceramide, and this activation is necessary, but not sufficient, for subsequent apoptosis.

Mouse and human chromosomal assignments of mortalin, a novel member of the murine hsp70 family of proteins

Mortalin has been shown to exhibit differential distributions in cells with mortal and immortal phenotypes. In the present study, we report mot-2 cDNA cloning from RS-4 cells--an immortal clone from CD1-ICR mouse embryonic fibroblasts--and the chromosomal assignments of mortalin related genes to mouse chromosomes 18 and X by fluorescence in situ hybridization. Similar analysis assigned the gene to chromosome 5q31.1 in human.

Possible involvement of the transcription factor ISGF3 gamma in virus-induced expression of the IFN-beta gene

Two virus-inducible transcription factors, IRF-1 and IRF-2 have been identified as an activator and a repressor, respectively, of the type I interferon (IFN) genes. Recent studies with mice carrying null mutations for the IRF-1 or IRF-2 alleles have revealed the existence of IRF-1-dependent and -independent pathways mediating IFN-beta gene induction. Here we report that the expression of an IRF family member ISGF3 gamma is induced upon viral infection in IRF-1-/-, IRF-2-/- embryonic fibroblasts. Furthermore, ISGF3 gamma can bind to a virus-inducible promoter element in the IFN-beta gene. These results suggest that ISGF3 gamma or complex containing ISGF3 gamma is involved in the IRF-1-independent pathway mediating IFN-beta gene regulation.

The Janus protein tyrosine kinase family and its role in cytokine signaling

During the past 2 years, research from quite divergent areas has converged to provide the first insights into the mechanisms by which cytokines that utilize receptors of the cytokine receptor superfamily function. On the one hand, the obscure Jak family of cytoplasmic protein tyrosine kinases was independently implicated in IFN and hematopoietic growth factor signaling. Recent studies have expanded these initial observations to demonstrate that Jaks are critical to the functioning of all the receptors of the cytokine receptor superfamily. A variety of questions remain to be explored regarding the structure and function of Jaks and their interaction with receptors. It will also be important to pursue additional approaches to determine if the Jaks are necessary for various biological responses, particularly for mitogenic responses. The second major area of convergence has been the demonstration that members of the Stat family of transcription factors, initially identified in IFN-regulated gene expression, are generally involved in cytokine signaling. Clearly, a number of Stat-like activities remain to be cloned and it can be anticipated that the family contains additional members. Although a variety of genes are known to be regulated by the Stats association with IFN responses, much less is known concerning the genes regulated by the new Stats in cytokine signaling. Of particular importance is information relating to their potential contribution to mitogenic responses. From a biochemical standpoint, the Stats represent a remarkable family of proteins with regard to the ability of the modification of a single tyrosine residue to so dramatically affect cellular localization and DNA binding activity. Studies to identify the domains involved, and associated proteins that might contribute to either property, will be of considerable interest. More generally, it can hypothesized that Jaks and Stats, if important for proliferation and differentiation, may be the targets for malignant transformation. Although none of the genes map to chromosomal breakpoints that have been implicated in transformation, gain of function mutations is a likely mechanism that needs to be explored. Similarly, the Jak-Stat pathway would appear to be an excellent target for the development of drugs that affect a variety of cytokine functions.

p53 status and the efficacy of cancer therapy in vivo

The therapeutic responsiveness of genetically defined tumors expressing or devoid of the p53 tumor suppressor gene was compared in immunocompromised mice. Tumors expressing the p53 gene contained a high proportion of apoptotic cells and typically regressed after treatment with gamma radiation or adriamycin. In contrast, p53-deficient tumors treated with the same regimens continued to enlarge and contained few apoptotic cells. Acquired mutations in p53 were associated with both treatment resistance and relapse in p53-expressing tumors. These results establish that defects in apoptosis, here caused by the inactivation of p53, can produce treatment-resistant tumors and suggest that p53 status may be an important determinant of tumor response to therapy.

The Bcl-2 family of proteins: regulators of cell death and survival

The Bcl-2 protein inhibits apoptosis induced by a variety of signals, in a range of cell types and in diverse organisms, and it is implicated in both normal development and oncogenesis. Despite this central role, the mechanism of action of Bcl-2 is not yet clear. Recent studies have uncovered a number of Bcl-2-related gene products that regulate apoptosis either negatively or positively, and Bcl-2 forms heterodimers with at least one of these proteins, Bax. This article discusses the role of the Bcl-2 family of proteins in the light of these findings.

Involvement of the IRF-1 transcription factor in antiviral responses to interferons

The mechanisms underlying interferon (IFN)-induced antiviral states are not well understood. Interferon regulatory factor-1 (IRF-1) is an IFN-inducible transcriptional activator, whereas IRF-2 suppresses IRF-1 action. The inhibition of encephalomyocarditis virus (EMCV) replication by IFN-alpha and especially by IFN-gamma was impaired in cells from mice with a null mutation in the IRF-1 gene (IRF-1-/- mice). The IRF-1-/- mice were less resistant than normal mice to EMCV infection, as revealed by accelerated mortality and a larger virus titer in target organs. The absence of IRF-1 did not clearly affect replication of two other types of viruses. Thus, IRF-1 is necessary for the antiviral action of IFNs against some viruses, but IFNs activate multiple activation pathways through diverse target genes to induce the antiviral state.