Activation of the human beta-interferon gene requires an interferon-inducible factor

Investigating Functional Roles for Positive Feedback and Cellular Heterogeneity in the Type I Interferon Response to Viral Infection

Secretion of type I interferons (IFN) by infected cells mediates protection against many viruses, but prolonged or excessive type I IFN secretion can lead to immune pathology. A proper type I IFN response must therefore maintain a balance between protection and excessive IFN secretion. It has been widely noted that the type I IFN response is driven by positive feedback and is heterogeneous, with only a fraction of infected cells upregulating IFN expression even in clonal cell lines, but the functional roles of feedback and heterogeneity in balancing protection and excessive IFN secretion are not clear. To investigate the functional roles for feedback and heterogeneity, we constructed a mathematical model coupling IFN and viral dynamics that extends existing mathematical models by accounting for feedback and heterogeneity. We fit our model to five existing datasets, reflecting different experimental systems. Fitting across datasets allowed us to compare the IFN response across the systems and suggested different signatures of feedback and heterogeneity in the different systems. Further, through numerical experiments, we generated hypotheses of functional roles for IFN feedback and heterogeneity consistent with our mathematical model. We hypothesize an inherent tradeoff in the IFN response: a positive feedback loop prevents excessive IFN secretion, but also makes the IFN response vulnerable to viral antagonism. We hypothesize that cellular heterogeneity of the IFN response functions to protect the feedback loop from viral antagonism. Verification of our hypotheses will require further experimental studies. Our work provides a basis for analyzing the type I IFN response across systems.

Live Cell Analysis and Mathematical Modeling Identify Determinants of Attenuation of Dengue Virus 2'-O-Methylation Mutant

Dengue virus (DENV) is the most common mosquito-transmitted virus infecting ~390 million people worldwide. In spite of this high medical relevance, neither a vaccine nor antiviral therapy is currently available. DENV elicits a strong interferon (IFN) response in infected cells, but at the same time actively counteracts IFN production and signaling. Although the kinetics of activation of this innate antiviral defense and the timing of viral counteraction critically determine the magnitude of infection and thus disease, quantitative and kinetic analyses are lacking and it remains poorly understood how DENV spreads in IFN-competent cell systems. To dissect the dynamics of replication versus antiviral defense at the single cell level, we generated a fully viable reporter DENV and host cells with authentic reporters for IFN-stimulated antiviral genes. We find that IFN controls DENV infection in a kinetically determined manner that at the single cell level is highly heterogeneous and stochastic. Even at high-dose, IFN does not fully protect all cells in the culture and, therefore, viral spread occurs even in the face of antiviral protection of naïve cells by IFN. By contrast, a vaccine candidate DENV mutant, which lacks 2’-O-methylation of viral RNA is profoundly attenuated in IFN-competent cells. Through mathematical modeling of time-resolved data and validation experiments we show that the primary determinant for attenuation is the accelerated kinetics of IFN production. This rapid induction triggered by mutant DENV precedes establishment of IFN-resistance in infected cells, thus causing a massive reduction of virus production rate. In contrast, accelerated protection of naïve cells by paracrine IFN action has negligible impact. In conclusion, these results show that attenuation of the 2’-O-methylation DENV mutant is primarily determined by kinetics of autocrine IFN action on infected cells.

Dengue virus (DENV) infection is a global health problem for which no selective therapy or vaccine exists. The magnitude of infection critically depends on the induction kinetics of the interferon (IFN) response and the kinetics of viral countermeasures. Here we established a novel live cell imaging system to dissect the dynamics of this interplay. We find that IFN controls DENV infection in a kinetically determined manner. At the single cell level, the IFN response is highly heterogeneous and stochastic, likely accounting for viral spread in the presence of IFN. Mathematical modeling and validation experiments show that the kinetics of activation of the IFN response critically determines control of virus replication and spread. A vaccine candidate DENV mutant lacking 2’-O-methylation of viral RNA is profoundly attenuated in IFN-competent cells. This attenuation is primarily due to accelerated kinetics of IFN production acting on infected cells in an autocrine manner. In contrast, accelerated protection of naïve cells by paracrine IFN action has negligible impact. Thus, attenuation of the 2’-O-methylation DENV mutant is primarily determined by kinetics of autocrine IFN action on infected cells.

Toll-like receptors' pathway disturbances are associated with increased susceptibility to infections in humans

Toll-like receptors (TLRs) sense microbial products and play an important role in innate immunity. Currently, 11 members of TLRs have been identified in humans, with important function in host defense in early steps of the inflammatory response. TLRs are present in the plasma membrane (TLR1, TLR2, TLR4, TLR5, TLR6) and endosome (TLR3, TLR7, TLR8, TLR9) of leukocytes. TLRs and IL-1R are a family of receptors related to the innate immune response that contain an intracellular domain known as the Toll-IL-1R (TIR) domain that recruits the TIR-containing cytosolic adapters MyD88, TRIF, TIRAP and TRAM. The classical pathway results in the activation of both nuclear factor κB and MAPKs via the IRAK complex, with two active kinases (IRAK-1 and IRAK-4) and two non-catalytic subunits (IRAK-2 and IRAK-3/M). The classical pro-inflammatory TLR signaling pathway leads to the synthesis of inflammatory cytokines and chemokines, such as IL-1β, IL-6, IL-8, IL-12 and TNF-α. In humans, genetic defects have been identified that impair signaling of the TLR pathway and this may result in recurrent pyogenic infections, as well as virus and fungi infections. In this review, we discuss the main mechanisms of microbial recognition and the defects involving TLRs.

Model-based simulation and prediction of an antiviral strategy against influenza A infection

There is a strong need to develop novel strategies in using antiviral agents to efficiently treat influenza infections. Thus, we constructed a rule-based mathematical model that reflects the complicated interactions of the host immunity and viral life cycle and analyzed the key controlling steps of influenza infections. The main characteristics of the pandemic and seasonal influenza strains were estimated using parameter values derived from cells infected with Influenza A/California/04/2009 and Influenza A/NewCaledonia/20/99, respectively. The quantitative dynamics of the infected host cells revealed a more aggressive progression of the pandemic strain than the seasonal strain. The perturbation of each parameter in the model was then tested for its effects on viral production. In both the seasonal and pandemic strains, the inhibition of the viral release (k_C), the reinforcement of viral attachment (k_V), and an increased transition rate of infected cells into activated cells (k_I) exhibited significant suppression effects on the viral production; however, these inhibitory effects were only observed when the numerical perturbations were performed at the early stages of the infection. In contrast, combinatorial perturbations of both the inhibition of viral release and either the reinforcement of the activation of infected cells or the viral attachment exhibited a significant reduction in the viral production even at a later stage of infection. These results suggest that, in addition to blocking the viral release, a combination therapy that also enhances either the viral attachment or the transition of the infected cells might provide an alternative for effectively controlling progressed influenza infection.

Biphasic RLR-IFN-β response controls the balance between antiviral immunity and cell damage

In RNA virus-infected cells, retinoic acid-inducible gene-I-like receptors (RLRs) sense foreign RNAs and activate signaling cascades to produce IFN-α/β. However, not every infected cell produces IFN-α/β that exhibits cellular heterogeneity in antiviral immune responses. Using the IFN-β-GFP reporter system, we observed bimodal IFN-β production in the uniformly stimulated cell population with intracellular dsRNA. Mathematical simulation proposed the strength of autocrine loop via RLR as one of the contributing factor for biphasic IFN-β expression. Bimodal IFN-β production with intracellular dsRNA was disturbed by blockage of IFN-α/β secretion or by silencing of the IFN-α/β receptor. Amplification of RLRs was critical in the generation of bimodality of IFN-β production, because IFN-β(high) population expressed more RLRs than IFN-β(low) population. In addition, bimodality in IFN-β production results in biphasic cellular response against infection, because IFN-β(high) population was more prone to apoptosis than IFN-β(low) population. These results suggest that RLR-mediated biphasic cellular response may act to restrict the number of cells expressing IFN-β and undergoing apoptosis in the infected population.

Stochastic expression of the interferon-β gene

The analysis of stochastic interferon-beta gene expression in virus-infected mammalian cells reveals that the levels of components required for virtually every step in the virus induction pathway are limiting.

Virus infection of mammalian cells induces the production of high levels of type I interferons (IFNα and β), cytokines that orchestrate antiviral innate and adaptive immunity. Previous studies have shown that only a fraction of the infected cells produce IFN. However, the mechanisms responsible for this stochastic expression are poorly understood. Here we report an in depth analysis of IFN-expressing and non-expressing mouse cells infected with Sendai virus. Mouse embryonic fibroblasts in which an internal ribosome entry site/yellow fluorescent protein gene was inserted downstream from the endogenous IFNβ gene were used to distinguish between the two cell types, and they were isolated from each other using fluorescence-activated cell sorting methods. Analysis of the separated cells revealed that stochastic IFNβ expression is a consequence of cell-to-cell variability in the levels and/or activities of limiting components at every level of the virus induction process, ranging from viral replication and expression, to the sensing of viral RNA by host factors, to activation of the signaling pathway, to the levels of activated transcription factors. We propose that this highly complex stochastic IFNβ gene expression evolved to optimize both the level and distribution of type I IFNs in response to virus infection.

Eukaryotic cells can respond to extracellular signals by triggering the activation of specific genes. Viral infection of mammalian cells, for example, induces a high level of expression of type I interferons (IFNα and β), proteins required for antiviral immunity that protects cells from the infection. Previous studies have shown that the expression of the IFNβ gene is stochastic, and under optimal conditions only a fraction of the infected cells express the IFNβ gene. At present neither the mechanisms nor functions of this interesting phenomenon are well understood. We have addressed this question by analyzing IFN-expressing and non-expressing mouse cells that were infected with the highly transmissible Sendai virus. We show that stochastic IFNβ gene expression is a consequence of cell-to-cell differences in limiting levels and/or activities of virus components at every level of the virus induction process, from viral replication to expression. These differences include the sensing of viral RNA by host factors, the activation of the signaling pathway, and the levels of activated transcription factors. Our findings reveal the complexity of the regulatory mechanisms controlling stochastic IFNβ gene expression. We propose that the stochastic expression of IFN allows for an even distribution of IFN, thus avoiding over-expression of IFN in infected cells.

Activation of the beta interferon promoter by paramyxoviruses in the absence of virus protein synthesis

Conflicting reports exist regarding the requirement for virus replication in interferon (IFN) induction by paramyxoviruses. Our previous work has demonstrated that pathogen-associated molecular patterns capable of activating the IFN-induction cascade are not normally generated during virus replication, but are associated instead with the presence of defective interfering (DI) viruses. We demonstrate here that DIs of paramyxoviruses, including parainfluenza virus 5, mumps virus and Sendai virus, can activate the IFN-induction cascade and the IFN-β promoter in the absence of virus protein synthesis. As virus protein synthesis is an absolute requirement for paramyxovirus genome replication, our results indicate that these DI viruses do not require replication to activate the IFN-induction cascade.

Failure to activate the IFN-β promoter by a paramyxovirus lacking an interferon antagonist

It is generally thought that pathogen-associated molecular patterns (PAMPs) responsible for triggering interferon (IFN) induction are produced during virus replication and, to limit the activation of the IFN response by these PAMPs, viruses encode antagonists of IFN induction. Here we have studied the induction of IFN by parainfluenza virus type 5 (PIV5) at the single-cell level, using a cell line expressing GFP under the control of the IFN-β promoter. We demonstrate that a recombinant PIV5 (termed PIV5-VΔC) that lacks a functional V protein (the viral IFN antagonist) does not activate the IFN-β promoter in the majority of infected cells. We conclude that viral PAMPs capable of activating the IFN induction cascade are not produced or exposed during the normal replication cycle of PIV5, and suggest instead that defective viruses are primarily responsible for inducing IFN during PIV5 infection in this system.

Heterocellular induction of interferon by negative-sense RNA viruses

The infection of cells by RNA viruses is associated with the recognition of virus PAMPs (pathogen-associated molecular patterns) and the production of type I interferon (IFN). To counter this, most, if not all, RNA viruses encode antagonists of the IFN system. Here we present data on the dynamics of IFN production and response during developing infections by paramyxoviruses, influenza A virus and bunyamwera virus. We show that only a limited number of infected cells are responsible for the production of IFN, and that this heterocellular production is a feature of the infecting virus as opposed to an intrinsic property of the cells.

TLR3 and TLR4 are innate antiviral immune receptors in human microglia: role of IRF3 in modulating antiviral and inflammatory response in the CNS

In the CNS, microglia are the primary targets of HIV infection. In this study, we investigated the effect of activation of the innate antiviral receptors TLR3 and TLR4 on HIV infection of primary human microglia, as well as microglial cell signaling and gene expression. Ligands for both TLR3 and TLR4 potently inhibited HIV replication in microglia through a pathway requiring IRF3. Surprisingly, a remarkably similar pattern of cell signaling and gene expression was observed in TLR3- and TLR4-activated microglia, suggesting a relatively minor role for MyD88 following TLR4 activation in these cells. HIV did not activate IRF3 but rather decreased IRF3 protein, indicating that HIV does not activate TLR3 or RIG-like helicases in microglia. Taken together, these results indicate that activation of TLR3 or TLR4 will elicit antiviral immunity, in addition to inducing proinflammatory responses. We suggest that a balanced expression between inflammatory and innate immune genes might be achieved by IRF3 over-expression.

Virus Infection Induces NF-kappaB-dependent interchromosomal associations mediating monoallelic IFN-beta gene expression

Transcriptional activation of the IFN-beta gene by virus infection requires the cooperative assembly of an enhanceosome. We report that the stochastic and monoallelic expression of the IFN-beta gene depends on interchromosomal associations with three identified distinct genetic loci that could mediate binding of the limiting transcription factor NF-kappaB to the IFN-beta enhancer, thus triggering enhanceosome assembly and activation of transcription from this allele. The probability of a cell to express IFN-beta is dramatically increased when the cell is transfected with any of these loci. The secreted IFN-beta protein induces high-level expression of the enhanceosome factor IRF-7, which in turn promotes enhanceosome assembly and IFN-beta transcription from the remaining alleles and in other initially nonexpressing cells. Thus, the IFN-beta enhancer functions in a nonlinear fashion by working as a signal amplifier.

The Npro product of classical swine fever virus and bovine viral diarrhea virus uses a conserved mechanism to target interferon regulatory factor-3

Classical swine fever virus (CSFV) is a member of the genus Pestivirus in the family Flaviviridae. The N(pro) product of CSFV targets the host's innate immune response and can prevent the production of type I interferon (IFN). The mechanism by which CSFV orchestrates this inhibition was investigated and it is shown that, like the related pestivirus bovine viral diarrhea virus (BVDV), this involves the N(pro) protein targeting interferon regulatory factor-3 (IRF-3) for degradation by proteasomes and thus preventing IRF-3 from activating transcription from the IFN-beta promoter. Like BVDV, the steady-state levels of IRF-3 mRNA are not reduced markedly by CSFV infection or N(pro) overexpression. Moreover, IFN-alpha stimulation of CSFV-infected cells induces the antiviral protein MxA, indicating that, as in BVDV-infected cells, the JAK/STAT pathway is not targeted for inhibition.

Further studies of the distribution of CDF/LIF mRNA

Differentiation choices in the haemopoietic and nervous systems are controlled in part by instructive factors. The cholinergic differentiation factor (CDF, also known as leukaemia inhibitory factor, LIF) affects the development of cultured cells from both systems. To understand the role of CDF/LIF during normal development in vivo, we have begun to localize its mRNA in the late fetal and postnatal rat. Application of reverse transcriptase-polymerase chain reaction and RNase protection methods reveals that CDF/LIF mRNA levels are developmentally modulated in both haemopoietic and neural tissues. A target tissue of cholinergic sympathetic neurons, the footpads that contain the sweat glands, express high levels of this mRNA (relative to mRNA for actin and beta 2-microglobulin). Levels in targets of noradrenergic neurons are lower, but do undergo significant changes during development. Signals are also detected in selective regions of the adult brain, and in embryonic skeletal muscle. This finding in muscle may be significant for motor neurons, because CDF/LIF is a trophic factor for these neurons in culture. Embryonic liver, neonatal thymus and postnatal spleen express CDF/LIF mRNA, and expression in gut is the highest of all tissues examined. The selective tissue distribution and developmental modulation of CDF/LIF mRNA expression support a role for this factor in the normal development of several organ systems.

A possible role of autogenous IFN-beta for cytokine productions in human fibroblasts

It has been already known that human diploid fibroblasts are able to produce not only high levels of IFN-beta but also various kinds of cytokines by poly rI: poly rC, and some inflammatory cytokines are induced by IFN-beta gene activation. We also obtained similar results. However, in our system, cytokine productions were extremely enhanced by treating the cells with a low dose of type 1 IFN and the priming effects on cytokine productions were blocked by cycloheximide similar to those on IFN-beta productions. Most of cytokines were produced later than IFN-beta and synthesis patterns of their mRNA showed the same phenomena. We made clear that cytokine productions by poly rI: poly rC are mediated by secreted IFN-beta at a protein level using a monoclonal antibody against human IFN-beta. Further, it was shown that intra-cellular IFN-beta which is not secreted might also participate in cytokine productions. Meanwhile, IL-1beta induced various kinds of cytokines in human fibroblasts and production time courses of these cytokines were similar to those of poly rI: poly rC induced cytokines. Although secreted IFN-beta was not detected in IL-1beta stimulated culture, expression of IFN-beta mRNA was augmented. These results showed that priming effects of type 1 IFN on cytokine productions by poly rI: poly rC might not be the direct action, but successive IFN-beta production might be essential in the production processes of other cytokines. Further, it was suggested that inducible IFN-beta might also take part in IL-1beta-induced cytokine productions.

Induction of genes involved in cell cycle progression by interleukin-4

Interleukin-4 (IL-4) can elicit diverse cellular responses, including differentiation, fusion, and proliferation, and these are all critical to establishment of an effective immune response. In this report, we provide evidence that IL-4 induces the proliferation of T lymphocytes with the coordinate transcriptional induction of the cell cycle regulatory genes encoding Cdc25A and the minichromosome maintenance (MCM) family. This specific gene induction appears to be due to activation of the signal transducer and activator of transcription, Stat6, and in part to phosphatidylinositol 3-kinase (PI3K). The function of another family of transcription factors, E2F, is known to induce cell cycle-regulated gene expression by binding to specific DNA target sites. We demonstrate that IL-4-activated Stat6 dimers can bind to a subset of E2F target sites and stimulate gene expression by binding to these DNA elements. Our results support a role for the Stat6 signal pathway in regulating a subset of E2F-responsive genes. In addition, activation of PI3K may play a complementary role in the induction of cell cycle-regulated genes in response to IL-4.

PACT-mediated enhancement of reporter gene expression at the translational level

The cellular protein, PACT, can directly activate protein kinase (PKR) in vitro by the interaction of PACT domain 3 with PKR. In contrast, in vivo, PACT-mediated PKR activation and concomitant inhibition of protein synthesis require additional cellular stresses. We observed that without such stresses, cotransfection of a PACT expression vector with various reporter genes enhances their levels of expression. This effect was promoter and inducer-independent and PACT specific and mediated by PACT domains 1 and 2. PACT did not increase the level of the reporter mRNA but enhanced its translation by suppressing phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) caused by the transfection process. To further examine the phenomenon, we generated cell lines expressing a PACT mutant containing only domains 1 and 2. Reporter gene expression was higher and eIF2alpha phosphorylation was lower in such cell lines compared with the corresponding control cells. Thus, different domains of PACT can either promote or inhibit translation by appropriately modulating the status of eIF2alpha phosphorylation.

Age and diet act through distinct isoforms of the class II transactivator gene in mouse intestinal epithelium

BACKGROUND & AIMS

Normal weaning induces class II major histocompatibility complex (Ia) and invariant chain (Ii) expression in the mouse intestinal epithelium. Because the class II transactivator protein (CIITA) induces Ia and Ii in most cell types, we hypothesized that diet-induced expression of these genes was through CIITA.

METHODS

Mouse litters were split and weaned onto an elemental diet or a normal (complex) chow diet. On days 24, 31, and 45, epithelial cells were isolated from small intestine with EDTA, and the RNA was extracted from both wild-type and interferon (IFN)-gamma receptor knockout mice. Messenger RNA (mRNA) was measured by Northern blotting, RNase protection assay, and real-time polymerase chain reaction and Ia localized by immunohistochemistry.

RESULTS

By day 31, CIITA mRNA was induced in the intestinal epithelium of normally weaned wild-type mice, and this mirrored the expression of Ii chain mRNA. Mice weaned onto an elemental diet did not exhibit Ii mRNA or increased CIITA mRNA in the intestinal epithelium by day 31, but low levels of Ii mRNA were detectable by day 45. Of the 3 isoforms of CIITA, weaning onto a complex diet induced only CIITA IV by day 31. Mice deficient in the IFN-gamma receptor expressed Ia in the epithelium and they also accumulated Ii mRNA (at low levels) by day 45, irrespective of diet. CIITA III mRNA accumulation mirrored the dietary-independent changes of Ii mRNA.

CONCLUSIONS

Two mechanisms regulate Ii in the mouse intestinal epithelium: a rapid one, which is diet-induced acting through CIITA IV; and a slower, dietary-independent pathway, acting through CIITA III.

Alcoholic liver injury in the rat is associated with reduced expression of peroxisome proliferator-alpha (PPARalpha)-regulated genes and is ameliorated by PPARalpha activation

Alcoholic liver disease is associated with a state of hepatic fatty acid overload. We examined the effect of ethanol and different types of dietary fat on the expression of mRNA for liver fatty acid binding protein (L-FABP), peroxisome proliferator-activated receptor-alpha (PPARalpha), and peroxisomal fatty acyl CoA oxidase (FACO). Four groups of rats (n = 5) were fed intragastrically, a liquid diet with or without ethanol (10-16 g/kg/day) for 4 weeks. Pair-fed controls received isocaloric amounts of dextrose. The source of fat was either corn oil or fish oil. Ethanolfed rats developed fatty liver, necrosis, and inflammation; the changes were more severe in the fish oil-ethanol (FE) rats. PPARalpha mRNA levels were not different between groups, although there was a trend toward increased levels in ethanol-fed rats. We calculated L-FABP/PPARalpha and FACO/PPARalpha ratios as a measure of FACO and L-FABP up-regulation relative to PPARalpha expression. Both FACO/PPARalpha and L-FABP/PPARalpha ratios were significantly decreased in FE rats. However, only L-FABP/PPARalpha was decreased in corn oil plus ethanol rats. Also, the level of L-FABP/mRNA correlated inversely with the degree of fatty liver in ethanol-fed rats. Since expression of PPARalpha response genes was impaired in ethanol-fed rats, we determined whether activation of PPARalpha would normalize the PPARalpha response and prevent the pathological changes in ethanol-fed rats. Treatment with clofibrate, a PPARalpha-activating ligand, led to a marked decrease in fatty liver and complete abrogation of necroinflammatory changes in FE rats. Also, nuclear factor kappaB activation and up-regulation of tumor necrosis factor-alpha and cyclooxygenase-2 was also abolished in clofibrate-treated rats. We conclude that adaptive gene regulation of FACO and L-FABP by PPARalpha is impaired in ethanol-fed rats and that treatment with clofibrate, a PPARalpha ligand, prevents alcohol-induced pathological liver injury, possibly by reversing the above changes.

Activation of the TGFalpha autocrine loop is downstream of IGF-I receptor activation during mitogenesis in growth factor dependent human colon carcinoma cells

The inappropriate expression of TGFalpha in growth arrest contributes to malignant progression in human colon carcinoma cells. Early stage, non-progressed colon tumor cells show a down-regulation of TGFalpha in growth arrest and require both nutrients and growth factors for re-entry into the cell cycle. In contrast, highly progressed cells up-regulate TGFalpha during growth arrest and require only nutrients for re-entry. Given the importance of TGFalpha in malignant progression, this work addressed the regulation of TGFalpha expression in the early stage colon carcinoma cell line, FET. Growth-arrested FET cells down-regulated the expression of TGFalpha, EGFr and, in turn, EGFr activation. These quiescent cells continued to express high levels of IGF-IR protein, but IGF-IR activation was undetectable. Cell cycle re-entry required exogenous growth factor activation of the IGF-IR by insulin or IGF-I. This IGF-IR activation resulted in S phase re-entry and was accompanied by an approximate threefold induction of TGFalpha expression along with EGFr activation at 1 h following release from growth arrest. Activation of IGF-IR occurred within 5 min of cell-cycle re-entry. Previously identified DNA binding proteins which bind to a unique TGFalpha/EGF response element within the TGFalpha promoter were similarly induced following IGF-IR activation. The addition of EGFr neutralizing antibodies abolished the activated IGF-IR stimulated S phase re-entry. Moreover, disruption of the growth arrest associated down-regulation of TGFalpha in FET cells by constitutive TGFalpha expression abrogated the requirement for IGF-IR activation for cell cycle re-entry. Consequently, this study indicates, for the first time, that IGF-IR activation up-regulates components of the TGFalpha autocrine loop resulting in TGFalpha-mediated EGFr activation which was critical for IGF-IR mediated re-entry into the cell cycle from the growth-arrested state.

Vascular endothelial growth factor-165 overexpression stimulates angiogenesis and induces cyst formation and macrophage infiltration in human ovarian cancer xenografts

Vascular endothelial growth factor (VEGF) is suggested to be an important regulator of angiogenesis in ovarian cancer. We have evaluated the effects of VEGF overexpression on the histology and growth rate of human ovarian cancer xenografts. OVCAR-3 human ovarian cancer cells were stably transfected with an expression vector encoding the 165-amino acid isoform of VEGF. As subcutaneous xenografts, moderately and highly VEGF(165)-overexpressing OVCAR-3 cells formed tumors with large cysts. Immunohistochemistry demonstrated an increase in the number of CD31-positive microvessels, some of which were larger in diameter than those in the parental tumors, as well as extensive vascular rimming around the cysts. Weakly VEGF(165)-overexpressing tumors also contained an increased number of CD31-positive microvessels and occasional vascular rimming, but cysts were not present. Immunohistochemistry further revealed the presence of monocytes and macrophages in both parental and VEGF(165)-overexpressing xenografts. Interestingly, the number of monocytes/macrophages was greatly increased in moderately and highly VEGF(165)-overexpressing xenografts and large areas populated with monocytes/macrophages were detected within the tumor stroma. Although the higher number of CD31-positive cells would suggest a better vascularization pattern in VEGF(165)-overexpressing xenografts, tumor growth rates were not increased when compared with that of parental xenografts. These data provide functional evidence for a role of VEGF(165) in cyst formation and monocyte/macrophage infiltration.

Function and factor interactions of a locus control region element in the mouse T cell receptor-alpha/Dad1 gene locus

Locus control regions (LCRs) refer to cis-acting elements composed of several DNase I hypersensitive sites, which synergize to protect transgenes from integration-site dependent effects in a tissue-specific manner. LCRs have been identified in many immunologically important gene loci, including one between the TCRdelta/TCRalpha gene segments and the ubiquitously expressed Dad1 gene. Expression of a transgene under the control of all the LCR elements is T cell specific. However, a subfragment of this LCR is functional in a wide variety of tissues. How a ubiquitously active element can participate in tissue-restricted LCR activity is not clear. In this study, we localize the ubiquitously active sequences of the TCR-alpha LCR to an 800-bp region containing a prominent DNase hypersensitive site. In isolation, the activity in this region suppresses position effect transgene silencing in many tissues. A combination of in vivo footprint examination of this element in widely active transgene and EMSAs revealed tissue-unrestricted factor occupancy patterns and binding of several ubiquitously expressed transcription factors. In contrast, tissue-specific, differential protein occupancies at this element were observed in the endogenous locus or full-length LCR transgene. We identified tissue-restricted AML-1 and Elf-1 as proteins that potentially act via this element. These data demonstrate that a widely active LCR module can synergize with other LCR components to produce tissue-specific LCR activity through differential protein occupancy and function and provide evidence to support a role for this LCR module in the regulation of both TCR and Dad1 genes.

Gene repression by coactivator repulsion

We show that the IRF-2 oncoprotein represses virus-induced IFN-beta gene transcription via a novel mechanism. Virus infection induces recruitment of IRF-2 to some of the endogenous IFN-beta enhancers as part of the enhanceosome. Enhanceosomes bearing IRF-2 cannot activate transcription, due to the presence of a domain in IRF-2 that prevents enhanceosome-dependent recruitment of the CBP-Pol II holoenzyme complex. As a consequence, IRF-2 incorporation into enhanceosomes restricts the number of IFN-beta promoters directing transcription. Remarkably, deletion of the IRF-2 gene increases IFN-beta expression by expanding the number of cells capable of inducing IFN-beta gene transcription in response to virus infection.

Evaluating limited specificity of drug pumps reduced relative resistance in human MDR phenotypes

In the parallel paper, we developed a property to characterize drug efflux pumps, i.e. the reduced relative resistance (RRR). Using this RRR, we here investigate whether the observed diversity in human multidrug resistance (MDR) phenotypes might be due to variable levels of P-glycoprotein encoded by MDR1. We analyzed resistance phenotypes of various human cell lines in which either one, or both, classical human multidrug resistance genes, MDR1 and MDR3, are overexpressed. In addition, RRR values were calculated for MDR phenotypes presented in the literature. The results suggest that more than a single mechanism is required to account for the observed phenotypic diversity of classical multidrug resistance. This diversity is only partly due to differences in plasma membrane permeabilities between cell line families. It is discussed whether the alternative MDR phenotypes might be MDR1 phenotypes modified by other factors that do not themselves cause MDR. The method we here apply may also be useful for other nonspecific enzymes or pumps.

The EGF/TGFalpha response element within the TGFalpha promoter consists of a multi-complex regulatory element

Autocrine TGFalpha is an important growth effector in the transformed phenotype. Growth stimulation of some colon cancer cells as well as other types of cancer cells is effected by activation of the epidermal growth factor receptor. Importantly, this receptor activation leads to further stimulation of TGFalpha transcription and increased peptide synthesis. However, the molecular mechanism by which TGFalpha transcription is activated is poorly understood. In this paper, we describe the localization of a cis-sequence within the TGFalpha promoter which mediates this stimulation. This region contains parallel cis-acting elements which interact to regulate both basal and EGF-induced TGFalpha expression. The well differentiated colon carcinoma cell line designated FET was employed in these studies. It produces autocrine TGFalpha but requires exogenous EGF in the medium for optimal growth. Addition of EGF to FET cells maintained in the absence of EGF resulted in a 2 - 3-fold increase of both TGF promoter activity and endogenous TGFalpha mRNA at 4 h. This addition of EGF also stimulated protein synthesis. The use of deletion constructs of the TGFalpha promoter in chimeras with chloramphenicol acetyl transferase localized EGF-responsiveness to between -247 and -201 within the TGFalpha promoter. A 25 bp sequence within this region conferred EGF-responsiveness to heterologous promoter constructs. Further use of deletion/mutation chimeric constructs revealed the presence of at least two interacting cis-elements, one binding a repressor activity and the other, an activator. Gel shift studies indicate the presence of distinct complexes representing activator and repressor binding, which are positively modulated by EGF. The type and amount of complexes formed by these proteins interact to regulate both the basal activity and EGF-responsiveness of the TGFalpha promoter. The interaction of an activator protein with an EGF-responsive repressor may serve to regulate the level of this progression-associated, transforming protein within tight limits.

A novel element upstream of the Vgamma2 gene in the murine T cell receptor gamma locus cooperates with the 3' enhancer to act as a locus control region

Transgenic expression constructs were employed to identify a cis-acting transcription element in the T cell receptor (TCR)-gamma locus, called HsA, between the Vgamma5 and Vgamma2 genes. In constructs lacking the previously defined enhancer (3'E(Cgamma1)), HsA supports transcription in mature but not immature T cells in a largely position-independent fashion. 3'E(Cgamma1), without HsA, supports transcription in immature and mature T cells but is subject to severe position effects. Together, the two elements support expression in immature and mature T cells in a copy number-dependent, position-independent fashion. Furthermore, HsA was necessary for consistent rearrangement of transgenic recombination substrates. These data suggest that HsA provides chromatin-opening activity and, together with 3'E(Cgamma1), constitutes a T cell-specific locus control region for the TCR-gamma locus.

Genes differentially expressed in medulloblastoma and fetal brain

Serial analysis of gene expression (SAGE) was used to identify genes that might be involved in the development or growth of medulloblastoma, a childhood brain tumor. Sequence tags from medulloblastoma (10229) and fetal brain (10692) were determined. The distributions of sequence tags in each population were compared, and for each sequence tag, pairwise chi2 test statistics were calculated. Northern blot was used to confirm some of the results obtained by SAGE. For 16 tags, the chi2 test statistic was associated with a P value < 10(-4). Among those transcripts with a higher expression in medulloblastoma were the genes for ZIC1 protein and the OTX2 gene, both of which are expressed in the cerebellar germinal layers. The high expression of these two genes strongly supports the hypothesis that medulloblastoma arises from the germinal layer of the cerebellum. This analysis shows that SAGE can be used as a rapid differential screening procedure.

Tumor necrosis factor-alpha signals to the IFN-gamma receptor complex to increase Stat1alpha activation

We describe a novel mechanism of signaling interaction through which tumor necrosis factor-alpha (TNF-alpha) treatment augments interferon-gamma (IFN-gamma)-induced Stat1alpha DNA-binding complexes and transcriptional activation of a Stat-binding element. In TNF-alpha-treated cells, IFN-gamma-induced phosphorylation of Jak2 kinase is increased, Jak2 kinase activity is enhanced, and genetic studies indicate that TNF-alpha requires Jak2 kinase activity to enhance Stat1alpha tyrosine phosphorylation. Increased Jak2 and Stat1alpha phosphorylation are observed within minutes of coexposure to TNF-alpha/IFN-gamma, suggesting a direct signaling interaction. IFN-gamma receptor chain 1 (IFNGR-1) tyrosine phosphorylation is markedly enhanced in cells treated with TNF-alpha/IFN-gamma without alteration in receptor levels. Thus, there exists a direct signaling interaction between TNF-alpha and IFN-gamma, independent of cooperating enhancer elements, that may be relevant for cytokine action during immune-mediated host defense and inflammatory processes.

Endothelial cells express a novel, tumor necrosis factor-alpha-regulated variant of HOXA9

The expression of the class 1 homeobox (HOX) family of "master control" transcription factors has been studied principally in embryogenesis and neoplasia in which HOX genes play a critical role in cell proliferation, migration, and differentiation. We wished to test whether HOX family members were also involved in a differentiation-like process occurring in normal, diploid adult cells, that is, cytokine-induced activation of endothelial cells (EC). Screening of a human EC cDNA library yielded several members of the A and B groups of HOX transcription factors. One clone represented a novel, alternatively spliced variant of the human HOXA9 gene containing a new exon and the expression of which was driven by a novel promoter. This variant termed HOXA9EC appeared restricted to cells of endothelial lineage, i.e. expressed by human EC from multiple sources, but not by fibroblasts, smooth muscle cells, or several transformed cell lines. HOXA9EC mRNA was rapidly down-regulated in EC in response to tumor necrosis factor-alpha due to an apparent reduction in transcriptional rate. Reporter construct studies showed that the 400 base pairs of genomic DNA directly 5' to the transcription initiation site of HOXA9EC contained the information required for both up-regulation in response to cotransfection with a HOXA9EC expression vector and tumor necrosis factor-alpha-dependent down-regulation of this gene. These results provide evidence of a novel HOX family member that may participate in either the suppression or the genesis of EC activation.

Transcriptional induction of the p69 isoform of 2',5'-oligoadenylate synthetase by interferon-beta and interferon-gamma involves three regulatory elements and interferon-stimulated gene factor 3

The 2',5'-oligoadenylate synthetases are key enzymes that mediate antiviral actions of interferon (IFN). The mRNAs for the intermediate isoforms (p69) of human 2',5'-oligoadenylate synthetase are rapidly induced 10- to 20-fold in HT1080 glioma cells by IFN-beta and induced 3-fold at 24 h by IFN-gamma. Induction is mediated by three regulatory elements, an IFN-stimulated response element and two identical sites resembling interferon response factor binding sites that are located within 300 bp of the transcriptional start site. Maximal induction requires all three elements, yet mutation in the most distal IRF-1-like site diminishes transcription only slightly. Mutation in the ISRE substantially decreases constitutive expression but does not abrogate the response to IFNs. Simultaneous mutation in all three elements abolishes responsiveness to both IFN-beta and IFN-gamma. Both constitutive and IFN-beta-induced expression from the p69 promoter is blocked in mutant cell lines deficient in components of the transcription factor, interferon-stimulated gene factor 3, suggesting that it is the primary factor controlling IFN-beta induced expression of this gene.

Induction of interferon synthesis and activation of interferon-stimulated genes by liposomal transfection reagents

Liposome-mediated transfection is a widely used technique for the introduction of exogenous DNA into mammalian cells. We observed a significant induction of endogenous interferon (IFN)-stimulated genes (ISGs) in cells treated with the liposomal reagents, lipofectamine and DOSPER, in the absence of DNA. Liposome treatment induced expression of reporter constructs driven by IFN-responsive promoter elements, demonstrating a generalized effect on ISG expression. The kinetics of ISG induction were markedly delayed in response to liposome as compared with IFN or double-stranded RNA. ISG induction could be transferred to naive cells with conditioned medium from liposome-treated cells, suggesting that a secreted factor was responsible for this activity. A cell line defective in IFN signaling was refractory to liposome-induced ISG expression, indicating a role for IFN in this induction. Indeed, liposome treatment directly induced IFN-beta gene expression and, thus, represents a novel IFN inducer. IFN induction by liposomal reagents and its potential effects on transgene expression should be considered in the choice of transfection reagent. The ability of liposomal gene delivery reagents to induce IFN synthesis in the host may prove useful in gene therapy approaches to viral and neoplastic diseases.

Type I interferon gene expression: differential expression of IFN-A genes induced by viruses and double-stranded RNA

The family of interferon regulatory transcription factors (IRF) participates in the virus-induced and dsRNA-stimulated transcriptional regulation of either type I IFN genes or a definite set of genes which can also be activated by IFN. In this review, we place emphasis on the role of IRF-3 that associates with the coactivators CBP and/or p300, together or not with IRF-7. These complexes bind to the PRDI, PRDI-like domains or to a number of ISRE sequences located in the promoter of these virus-inducible genes. We also discuss the involvement of the IRF-3-related complexes in the differential regulation of IFN-A genes.

Hair defects and pup loss in mice with targeted deletion of the first cut repeat domain of the Cux/CDP homeoprotein gene

CDP, a ubiquitous homeoprotein homologous to Drosophila cut, is implicated as a transcriptional repressor in several developmental systems. It contains four independent DNA binding domains: three "cut repeats" plus the homeodomain. The murine Cux/CDP gene spans more than 200 kb and is composed of at least 21 exons. We designed a targeting construct to replace the first cut repeat with a neomycin resistance cassette, introducing a nonsense mutation after position 1319 of the 4.5-kb reading frame of Cux/CDP. We expected to generate a truncated product of approximately 60 kDa with this construct, but instead we obtained mice expressing a mutant form of the protein, with an internal deletion of 246 amino acids encompassing cut repeat 1, but intact in the C-terminal region. Ribonuclease protection assays and direct sequencing of mutant cDNA obtained by RT-PCR demonstrate skipping of exons 10 and 11 in the mutant. Homozygous mutant mice, designated Cux/CDPDeltaCR1, display a phenotype characterized by curly vibrissae and wavy hair. We also observed a high degree of pup loss in litters born to mutant females, most likely on a nutritional basis. The mutant protein is present at levels slightly greater than wild-type, but exhibits the same tissue distribution as wild-type protein, and has approximately normal affinity for known target sequences (though no DNA targets identified to date require the first cut repeat for binding). These results support the hypothesis that the different DNA binding domains of the ubiquitous Cux/CDP protein are responsible for regulation of different genes in diverse tissues during development.

Immortalization of rat embryo fibroblasts by a 3'-untranslated region

We have exploited a cross-species expression screen to search for cellular immortalizing activities. A newt blastemal cDNA expression library was transfected into rat embryo fibroblasts and immortal cell lines were selected. This identified a 1-kb cDNA fragment which has a low representation in the cDNA library and is derived from the 3'-UTR of an alpha-glucosidase-related mRNA. Expression of this sequence in rat embryo fibroblasts has shown that it is active in promoting colony formation and immortalization. It is also able to cooperate with an immortalization-defective deletion mutant of SV40 T antigen, indicating that it can exert its growth-stimulatory activity in the pathway activated by a viral immortalizing oncogene. This is the first example of an immortalizing activity mediated by an RNA sequence, and further analysis of its mechanism should provide new insights into senescence and immortalization.

Aberrant regulation of transforming growth factor-alpha during the establishment of growth arrest and quiescence of growth factor independent cells

Autocrine transforming growth factor alpha (TGFalpha) is an important positive growth effector in malignant cells and plays a significant role in generating the growth factor-independent phenotype associated with malignant progression. However, the molecular mechanisms by which TGFalpha confers a growth advantage in progression is poorly understood. The highly tumorigenic cell line HCT116 up-regulates TGFalpha mRNA expression during growth arrest, whereas the poorly tumorigenic growth factor-dependent FET cell line down-regulates TGFalpha mRNA expression as it becomes quiescent. We have identified a 25-bp sequence at -201 to -225 within the TGFalpha promoter which mediates the differential regulation of TGFalpha expression during quiescence establishment in these two cell lines. This same sequence confers TGFalpha promoter responsiveness to exogenous growth factor or autocrine TGFalpha. The abberant upregulation of TGFalpha mRNA in quiescent HCT116 cells may allow them to return to the dividing state under more stringent conditions (nutrient replenishment alone) then quiescent FET cells (requires nutrients and growth factors). Antisense TGFalpha approaches showed that the dysregulated TGFalpha expression in quiescent HCT116 cells is a function of the strong TGFalpha autocrine loop (not inhibited by blocking antibodies) in these cells.

The growing family of interferon regulatory factors

Interferons (IFN) exert their multiple biological effects through the induction of expression of over 30 genes encoding proteins with antiviral, antiproliferative and immunomodulatory functions. Among the many IFN-inducible proteins are the Interferon Regulatory Factors (IRFs), a family of transcription regulators, originally consisting of the well-characterized IRF-1 and IRF-2 proteins; the family has now expanded to over 10 members and is still growing. The present review provides a detailed description of recently characterized IRF family members. Studies analyzing IRF-expressing cell lines and IRF knockout mice reveal that each member of the IRF family exerts distinct roles in biological processes such as pathogen response, cytokine signalling, cell growth regulation and hematopoietic development. Understanding the molecular mechanisms by which the IRFs affect these important cellular events and IFN expression will contribute to a greater understanding of events leading to various viral, immune and malignant disease states and will suggest novel strategies for antiviral and immune modulatory therapy.

Hepatocyte nuclear factor-4 prevents silencing of hepatocyte nuclear factor-1 expression in hepatoma x fibroblast cell hybrids

Hepatocyte nuclear factors-1alpha (HNF1alpha) and -4 (HNF4) are components of a liver-enriched transcription activation pathway which is thought to play a critical role in hepatocyte-specific gene expression, including activation of alpha1-antitrypsin gene expression. HNF1alpha, HNF4 and alpha1-antitrypsin (alpha1AT) genes are extinguished in hepatoma/fibroblast somatic cell hybrids, suggesting that fibroblasts contain a repressor-like activity. To determine the molecular basis for silencing of these genes in cell hybrids, ectopic expression of HNF1alpha and HNF4 was used. Results show that constitutive expression of HNF4 prevents extinction of HNF1alpha gene expression in hepatoma/fibroblast hybrids. In contrast, forced HNF1alpha expression failed to prevent extinction of the HNF4 locus in cell hybrids. Likewise, the alpha1AT gene remained silent in the presence of both HNF1alpha and HNF4. These results suggest that extinction of HNF1alpha is a simple lack-of-activation phenotype, whereas extinction of HNF4 andalpha1AT loci is more complex, perhaps involving negative regulation.

Chemotherapeutic purine analogs alter the level of interferon-beta mRNA induced by poly I-poly C in cultured osteosarcoma cells

The purine nucleoside analogs fludarabine, 2-chlorodeoxyadenosine, and 2'-deoxycoformycin exhibit impressive activity in lymphoproliferative malignancies of adults and children. Their mechanism of action is not clear. Studies have suggested that their use is associated with significant myelosuppression, immunosuppression, and in some circumstances, increased infection with viral and opportunistic pathogens. Because interferons (IFNs) are known to have immunomodulatory activity as well as potent antiproliferative and antiviral activity, we examined whether the chemotherapeutic purine nucleoside analogs alter interferon-beta (IFN-B) gene expression in MG63 in human osteosarcoma cells. Northern blot analysis showed a dose-dependent inhibition of IFN-B mRNA accumulation in response to a known inducer (Poly I-Poly C) all three purine analogs. Hybridization analysis also revealed that inhibition of IFN-beta mRNA accumulation by the purine analogs is not a result of decreased mRNA stability. Further analysis of gene expression by PCR differential display indicated that the effect of the purine analogs was restricted to only a limited number of inducible genes. The data suggest that these molecules alter the signaling process involved in regulating the expression of specific genes, including IFN-beta. These findings predict that the use of purine nucleoside analogs may reduce IFN production in vivo and thereby abrogate host defenses against infectious pathogens.

Selective loss of the hepatic phenotype due to the absence of a transcriptional activation pathway

Liver-enriched trans-acting factors hepatocyte nuclear factor-1 alpha (HNF1 alpha) and -4 (HNF4) are components of a transcriptional activation pathway that is thought to play a major role in hepatic gene activation. We previously described the isolation and characterization of distinct classes of hepatoma variants which lack the HNF4-->HNF1 alpha pathway (1). In order to determine the influence of the HNF4-->HNF1 alpha pathway on hepatic gene expression, genetic rescue experiments were done using hepatoma variant line H11 as a model system. Results suggest that this pathway is required for basal expression of a number of endogenous hepatocyte-specific genes. Complementation groups were established by fusion of H11 cells with other variant lines. Lastly, introduction of human chromosome 20 (containing the HNF4 locus) or randomly-marked human chromosomes into H11 cells failed to rescue the hepatic phenotype, suggesting that what appears to be a 'simple' defect may involve multiple genetic loci.

Stat2 is a transcriptional activator that requires sequence-specific contacts provided by stat1 and p48 for stable interaction with DNA

Transcriptional responses to interferon (IFN) are mediated by tyrosine phosphorylation and nuclear translocation of transcription factors of the signal transducer and activator of transcription (Stat) family. The Stat1 protein is required for all transcriptional responses to IFN (both type I and type II). Responses to type I IFN (alpha and beta) also require Stat2 and the IFN regulatory factor family protein p48, which form a heterotrimeric transcription complex with Stat1 termed ISGF3. Stat1 homodimers formed in response to IFN-gamma treatment can also interact with p48 and function as transcriptional activators. We now show that Stat2 is capable of forming a stable homodimer that interacts with p48, can be recruited to DNA, and can activate transcription, raising a question of why Stat1 is required. Analysis of the transcriptional competence, affinity, and specificity of Stat2-p48 complexes compared with other Stat protein-containing transcription factor complexes suggests distinct roles for each component. Although Stat2 is a potent transactivator, it does not interact stably with DNA in complex with p48 alone. Adding Stat1 increases the affinity and alters the sequence selectivity of p48-DNA interactions by contacting a half-site of its palindromic recognition motif adjacent to a p48 interaction sequence. Thus, ISGF3 assembly involves p48 functioning as an adaptor protein to recruit Stat1 and Stat2 to an IFN-alpha-stimulated response element, Stat2 contributes a potent transactivation domain but is unable to directly contact DNA, while Stat1 stabilizes the heteromeric complex by contacting DNA directly.

Dexamethasone induces posttranslational degradation of GLUT2 and inhibition of insulin secretion in isolated pancreatic beta cells. Comparison with the effects of fatty acids

GLUT2 expression is strongly decreased in glucose-unresponsive pancreatic beta cells of diabetic rodents. This decreased expression is due to circulating factors distinct from insulin or glucose. Here we evaluated the effect of palmitic acid and the synthetic glucocorticoid dexamethasone on GLUT2 expression by in vitro cultured rat pancreatic islets. Palmitic acid induced a 40% decrease in GLUT2 mRNA levels with, however, no consistent effect on protein expression. Dexamethasone, in contrast, had no effect on GLUT2 mRNA, but decreased GLUT2 protein by about 65%. The effect of dexamethasone was more pronounced at high glucose concentrations and was inhibited by the glucocorticoid antagonist RU-486. Biosynthetic labeling experiments revealed that GLUT2 translation rate was only minimally affected by dexamethasone, but that its half-life was decreased by 50%, indicating that glucocorticoids activated a posttranslational degradation mechanism. This degradation mechanism was not affecting all membrane proteins, since the alpha subunit of the Na+/K+-ATPase was unaffected. Glucose-induced insulin secretion was strongly decreased by treatment with palmitic acid and/or dexamethasone. The insulin content was decreased ( approximately 55 percent) in the presence of palmitic acid, but increased ( approximately 180%) in the presence of dexamethasone. We conclude that a combination of elevated fatty acids and glucocorticoids can induce two common features observed in diabetic beta cells, decreased GLUT2 expression, and loss of glucose-induced insulin secretion.

Concomitant downregulation of IgH 3' enhancer activity and c-myc expression in a plasmacytoma x fibroblast environment: implications for dysregulation of translocated c-myc

Regulation of immunoglobulin heavy chain (IgH) gene expression is controlled by a B cell-specific promoter, intronic enhancer and additional B cell-specific enhancer elements identified recently in the 3' end of the IgH locus. One of the latter elements, the IgH 3' enhancer, is of particular interest: (1) it is B cell-specific and active only in late B cell development; (2) in rodent plasmacytomas and in some human Burkitt's lymphomas it is part of a locus control region (LCR) that is involved in deregulation of the c-myc oncogene as a result of translocation into the IgH locus; and (3) it has been implicated in the mechanisms that control Ig gene class switch recombination. We have used a somatic cell hybridization approach to genetically analyse regulation of the activity of the IgH 3' enhancer. When mouse MPC11 plasmacytoma cells, in which the IgH 3' enhancer is active, are fused with fibroblasts, Ig expression is extinguished at the level of transcription. Here we show that in a MPC11 plasmacytoma x fibroblast environment, the IgH 3' enhancer is transcriptionally inactive. Furthermore, we demonstrate that binding of several B cell-specific transcription factors, essential for IgH 3' enhancer activity, is lacking, which may explain 3' enhancer inactivity, although the binding of repressors cannot be excluded. Moreover, the high expression level of c-myc, characteristic of the parental MPC11 cells carrying the t(12;15) translocation, is down-regulated in the hybrids to that in unfused fibroblasts. Therefore, inactivation of the IgH 3' enhancer is a multifactorial process affecting several transcription factors that control the cell-specific and developmental activity of the enhancer.

Identification of a (CUG)n triplet repeat RNA-binding protein and its expression in myotonic dystrophy

Myotonic dystrophy (DM) is an autosomal dominant neuromuscular disease that is associated with a (CTG)n repeat expansion in the 3'-untranslated region of the myotonin protein kinase (Mt-PK) gene. This study reports the isolation and characterization of a (CUG)n triplet repeat pre-mRNA/mRNA binding protein that may play an important role in DM pathogenesis. Two HeLa cell proteins, CUG-BP1 and CUG-BP2, have been purified based upon their ability to bind specifically to (CUG)8 oligonucleotides in vitro. While CUG-BP1 is the major (CUG)8-binding activity in normal cells, nuclear CUG-BP2 binding activity increases in DM cells. Both CUG-BP1 and CUG-BP2 have been identified as isoforms of a novel heterogeneous nuclear ribonucleoprotein (hnRNP), hNab50. The CUG-BP/hNab50 protein is localized predominantly in the nucleus and is associated with polyadenylated RNAs in vivo. In vitro RNA-binding/photocrosslinking studies demonstrate that CUG-BP/hNab50 binds to RNAs containing the Mt-PK 3'-UTR. We propose that the (CUG)n repeat region in Mt-PK mRNA is a binding site for CUG-BP/hNab50 in vivo, and triplet repeat expansion leads to sequestration of this hnRNP on mutant Mt-PK transcripts.

Gene expression of DNA topoisomerases I, II alpha and II beta and response to cisplatin-based chemotherapy in advanced ovarian carcinoma

DNA topoisomerases, nuclear enzymes that regulate DNA topology, are recognized as the primary targets of effective anti-tumor drugs. These enzymes may also have a role in the repair of DNA damage induced by alkylating agents and platinum compounds; therefore, their expression may be a determinant of tumor response to chemotherapy. Our study was undertaken in an attempt to establish a correlation between the enzyme expression and response of ovarian cancer to cisplatin-based chemotherapy. The expression of topoisomerase I, II alpha and II beta genes was assessed by RNase protection assay in tumor specimens obtained from 37 untreated patients with advanced epithelial ovarian cancer at initial surgery and from 13 pre-treated patients at subsequent laparotomy. The expression levels were compared with those found in 5 specimens from benign ovarian tissue and 5 specimens from normal ovarian tissue. The expression levels in untreated patients were used to establish a correlation with response to high-dose cisplatin therapy. A significant intertumor variability of mRNA expression was noted for all the genes examined. However, a comparison of median values indicated a remarkable increase of expression in malignant tumors over benign or normal tissues only for topoisomerase II alpha. This change is not related to alterations or amplification of topoisomerase II alpha gene. Interestingly, a correlation was found between tumor response to chemotherapy and the expression level of the isoform alpha (but not of topoisomerase II beta and topoisomerase I). The observed correlation suggests a contribution of the enzyme in determining tumor sensitivity. Alternatively, increased expression levels of the alpha isoenzyme gene in responsive tumors might reflect higher fractions of proliferating tumor cells that may be more drug-sensitive than resting cells.

Developmental differences in the expression of the cholera toxin sensitive subunit (Gs alpha) of adenylate cyclase in the rat small intestine

BACKGROUND

The stimulatory guanosine triphosphate (GTP) binding protein alpha subunit (Gs alpha) of adenylate cyclase is the target protein for cholera toxin.

AIMS/METHODS

The expression of this signal transducer was analysed in the small intestine of developing rats by RNA transfer (northern blot) analysis by immunoblotting, and by ADP-ribosylation of membrane proteins.

RESULTS

Intestinal Gs alpha mRNA (about 1.9 kb) was increased in the neonate compared with the adult rat. Two isoforms of Gs alpha proteins, a 45,000 and a 52,000 form, were expressed in the small intestinal epithelial cell and both were ADP-ribosylated by cholera toxin. A significant increase in the larger isoform (52,000) and in its ribosylation was noted in the 2 week old suckling compared with post-weaned older animals. The protein content or ribosylation of the smaller form (45,000) did not significantly change with age.

CONCLUSION

These data show that a developmental decline of intestinal Gs alpha expression seems to be, in part, regulated at the mRNA level. An increased Gs alpha expression in the immature intestine may help to explain a previously reported, dose dependent increased adenylate cyclase response and an increase in fluid secretion to cholera toxin in neonates compared with adults.

A novel vitamin D analog with two double bonds in its side chain. A potent inducer of osteoblastic cell differentiation

EB 1089 (1 alpha,25-dihydroxy-22,24-diene-24,26,27-trihomovitamin D3) is a novel, synthetic analog of calcitriol, characterized by two extra double bonds in its side chain. It is less potent than calcitriol in its calcemic action, but is an order of magnitude more potent in its antiproliferative action. The aim of this study was to determine the ability of EB 1089 to induce the well-known biological effects of calcitriol in MG-63 human osteosarcoma cells (i.e. by inhibiting cell proliferation and by induction of differentiation). Both calcitriol and EB 1089 significantly decreased cell growth after 2 days in culture. At 5 days, however, Eb 1089 was more potent than the natural hormone in inhibiting the proliferation of MG-63 cells. Potent effects of EB 1089 on cell differentiation were also seen in the stimulation of alkaline phosphatase activity, cellular vitamin D receptor mRNA levels, and medium osteocalcin synthesis. EB 1089 was clearly more effective than calcitriol in stimulating alkaline phosphatase activity and osteocalcin synthesis. In gel shift assays, the binding of vitamin D receptor to the composite AP-1 plus vitamin-D responsive promoter region of the human osteocalcin gene after EB 1089 treatment was stronger and longer-lasting than after calcitriol treatment.

Induction of interleukin-8 messenger RNA in heart and skeletal muscle during pediatric cardiopulmonary bypass

BACKGROUND

Interleukin-8 (IL-8), the major neutrophil chemoattractant factor, contributes to inflammatory tissue injury by activating neutrophils and promoting their migration into tissue. IL-8 levels increase in serum of patients undergoing cardiopulmonary bypass (CPB). The purpose of this study was to determine if IL-8 gene expression is activated in tissues subjected to CPB with or without hypothermic arrest.

METHODS AND RESULTS

IL-8 transcript levels were measured by ribonuclease protection in samples of human atrium and skeletal muscle from children before and after CPB for repair of congenital heart defects. Results were quantified by PhosphorImager. Atrial IL-8 mRNA levels increased during CPB in 14 of 16 patients tested (median increase, 2.9-fold; P = .0029). In skeletal muscle, IL-8 mRNA increased in 11 of 12 patients (median, 12-fold; P = .012). Degree of IL-8 induction in atrium and muscle was not directly associated with total support time or cross-clamp time. Transcript increase in skeletal muscle occurred with or without a period of circulatory arrest, suggesting that the stimulus of CPB alone was sufficient to induce message production. Baseline values for IL-8 mRNA varied widely among patients in atrium and skeletal muscle. In situ hybridization analysis revealed diffuse increase in IL-8 mRNA throughout the tissue after CPB, with striking increase in some small veins.

CONCLUSIONS

We conclude that production of IL-8 mRNA occurs in most patients during CPB in both myocardium and skeletal muscle. This may result in high local IL-8 concentrations, contributing to the tissue injury after CPB.

Characterization of specific DNA-binding factors activated by double-stranded RNA as positive regulators of interferon alpha/beta-stimulated genes

Viral infection results in transcriptional activation of the cellular interferon alpha/beta-stimulated genes (ISGs) independent of the autocrine action of interferon alpha/beta (IFN-alpha/beta). Induction of ISG expression by virus appears to be mediated through production of viral double-stranded RNA (dsRNA). Previously, we identified two novel dsRNA-activated factors (DRAFs) that bind to the interferon-stimulated response element (ISRE), the DNA sequence that mediates transcriptional activation by IFN-alpha/beta. In this report we define sequences that flank the classical ISRE to be necessary for DRAF1 binding. More significantly, it is shown that the sequences required to bind DRAF1 correlate with the ability to mediate ISG induction by virus. These results strongly suggest that DRAF1 is a positive regulator of ISG transcription. DRAF1 is shown to bind selectively to the promoters of those ISGs which are strongly induced by viral infection, again suggesting the functional significance of this factor. UV cross-linking experiments indicate that DRAF1 and DRAF2 share a common DNA-binding subunit of approximately 70 kDa which is referred to as the DRAF binding component (DRAFB). DRAFB is shown to preexist in the cytoplasm of unstimulated cells. Consistent with this observation, both DRAF1 and DRAF2 are activated in the cytoplasm prior to nuclear translocation.