GRIM-19 mutations fail to inhibit v-Src-induced oncogenesis

The non-receptor tyrosine kinase Src is a major player in multiple physiological responses including growth, survival and differentiation. Overexpression and/or oncogenic mutation in the Src gene have been documented in human tumors. The v-Src protein is an oncogenic mutant of Src, which promotes cell survival, migration, invasion and division. GRIM-19 is an anti-oncogene isolated using a genome-wide knockdown screen. GRIM-19 binds to transcription factor STAT3 and ablates its pro-oncogenic effects while v-Src activates STAT3 to promote its oncogenic effects. However, we found that GRIM-19 inhibits the pro-oncogenic effects of v-Src independently of STAT3. Here, we report the identification of functionally inactivating GRIM-19 mutations in a set of Head and Neck cancer patients. While wild-type GRIM-19 strongly ablated v-Src-induced cell migration, cytoskeletal remodeling and tumor metastasis, the tumor-derived mutants (L⁷¹P, L⁹¹P and A⁹⁵T) did not. These mutants were also incapable of inhibiting the drug resistance of v-Src-transformed cells. v-Src down regulated the expression of Pag1, a lipid raft-associated inhibitor of Src, which was restored by wild-type GRIM-19. The tumor-derived mutant GRIM-19 proteins failed to upregulate Pag1. These studies show a novel mechanism that deregulates Src activity in cancer cells.

Targeted therapy via oral administration of attenuated Salmonella expression plasmid-vectored Stat3-shRNA cures orthotopically transplanted mouse HCC

The development of RNA interference-based cancer gene therapies has been delayed due to the lack of effective tumor-targeting delivery systems. Attenuated Salmonella enterica serovar Typhimurium (S. Typhimurium) has a natural tropism for solid tumors. We report here the use of attenuated S. Typhimurium as a vector to deliver shRNA directly into tumor cells. Constitutively activated signal transducer and activator of transcription 3 (Stat3) is a key transcription factor involved in both hepatocellular carcinoma (HCC) growth and metastasis. In this study, attenuated S. Typhimurium was capable of delivering shRNA-expressing vectors to the targeted cancer cells and inducing RNA interference in vivo. More importantly, a single oral dose of attenuated S. Typhimurium carrying shRNA-expressing vectors targeting Stat3 induced remarkably delayed and reduced HCC (in 70% of mice). Cancer in these cured mice did not recur over 2 years following treatment. These data demonstrated that RNA interference combined with Salmonella as a delivery system may offer a novel clinical approach for cancer gene therapy.

Enhanced tumor suppression in vitro and in vivo by co-expression of survivin-specific siRNA and wild-type p53 protein

The development of malignant prostate cancer involves multiple genetic alterations. For example, alterations in both survivin and p53 are reported to have crucial roles in prostate cancer progression. However, little is known regarding the interrelationships between p53 and survivin in prostate cancer. Our data demonstrate that the expression of survivin is inversely correlated with that of wtp53 protein (r(s)=0.548) in prostate cancer and in normal prostate tissues. We have developed a therapeutic strategy, in which two antitumor factors, small interfering RNA-survivin and p53 protein, are co-expressed from the same plasmid, and have examined their effects on the growth of PC3, an androgen-independent prostate cancer cell line. When p53 was expressed along with a survivin-specific short hairpin RNA (shRNA), tumor cell proliferation was significantly suppressed and apoptosis occurred. In addition, this combination also abrogated the expression of downstream target molecules such as cyclin-dependent kinase 4 and c-Myc, while enhancing the expression of GRIM19. These changes in gene expression occurred distinctly in the presence of survivin-shRNA/wtp53 compared with control or single treatment groups. Intratumoral injection of the co-expressed construct inhibited the growth and survival of tumor xenografts in a nude mouse model. These studies revealed evidence of an interaction between p53 and survivin proteins plus a complex signaling network operating downstream of the wtp53-survivin pathway that actively controls tumor cell proliferation, survival and apoptosis.

GRIM-19 associates with the serine protease HtrA2 for promoting cell death

We have isolated a novel interferon (IFN)-retinoid regulated cell death regulatory protein genes associated with retinoid-IFN-induced mortality (GRIM)-19 earlier. To understand its mechanism of action, we have employed a yeast-two-hybrid screen and identified serine protease HtrA2 as its binding partner. GRIM-19 physically interacts with HtrA2 and augments cell death in an IFN/all-trans retinoic acid (RA)-dependent manner. In the presence of GRIM-19, the HtrA2-driven destruction of the antiapoptotic protein X-linked inhibitor of apoptosis (XIAP) is augmented. These interactions were disrupted by an human herpes virus-8 (HHV-8)-coded oncoprotein, vIRF1, and conferred resistance to IFN/RA-induced cell death. These data show a critical role of HtrA2 in a cytokine-induced cell death response for the first time and its inhibition by a viral protein.

A proteomic analysis reveals the loss of expression of the cell death regulatory gene GRIM-19 in human renal cell carcinomas

Gene associated with retinoid interferon-induced mortality (GRIM)-19, an inhibitor of transcription factor STAT3, was originally identified as a critical regulatory protein in a genetic screen that was designed to identify the gene products necessary for Interferon (IFN)-beta- and retinoic acid-induced cell death. Over expression of GRIM-19 activates cell death. Conversely, inactivation of its expression promotes cell growth. STAT3 is a transcription factor that regulates gene expression in response to multiple extra cellular growth factors. In contrast to its normal feedback inhibition, a constitutive activation of STAT3 has been documented in several tumors. Although many STAT3-inhibitors are described, their relevance to human cancer is unclear. In an attempt to define the molecular alterations associated with human renal cell carcinoma (RCC) using mass spectrometry, we have discovered that expression of GRIM-19 is lost or severely depressed in a number of primary RCC and in some urinogenital tumors. Using an RCC cell line, we show that down regulation of GRIM-19 promotes tumor growth via an augmentation of STAT3-dependent gene expression. These studies for the first time show a tumor-suppressor like activity of GRIM-19.

Modulation of p53 dependent gene expression and cell death through thioredoxin-thioredoxin reductase by the Interferon-Retinoid combination

We have shown earlier that the IFN-beta and all-trans retinoic acid (RA) combination, but not the single agents, induces death in several tumor cell lines. Employing a genetic technique we have identified several Genes associated with Retinoid-IFN induced Mortality (GRIM). One of the GRIMs was human thioredoxin reductase (TR), a redox enzyme. Since the overexpressed TR augments IFN/RA stimulated cell death, we explored the mechanisms of TR-mediated death. Here we show that TR augments cell death by upregulating the transcriptional activity of p53 tumor suppressor. This process does not involve a physical increase in levels of p53. Using redox inactive mutants of TR and its substrate, thioredoxin (Trx), we demonstrate that IFN/RA-induced regulation of p53 dependent gene expression requires TR and Trx. In contrast-over-expression of wildtype TR or Trx augment the p53 dependent gene expression in response to IFN/RA treatment. Consistent with these results an increased DNA binding activity of p53 was noted in the presence of TR. These studies identify a novel mechanism of p53 mediated cell death regulation involving redox enzymes.

Regulation of interferon and retinoic acid-induced cell death activation through thioredoxin reductase

Interferons (IFNs) and retinoids are potent biological response modifiers. The IFN-beta and all-trans-retinoic acid combination, but not these single agents individually, induces death in several tumor cell lines. To elucidate the molecular basis for these actions, we have employed an antisense knockout approach to identify the gene products that mediate cell death and isolated several genes associated with retinoid-IFN-induced mortality (GRIMs). One of the GRIM cDNAs, GRIM-12, was identical to human thioredoxin reductase (TR). To define the functional relevance of TR to cell death and to define its mechanism of death-modulating functions, we generated mutants of TR and studied their influence on the IFN/RA-induced death regulatory functions of caspases. Wild-type TR activates cell death that was inhibited in the presence of caspase inhibitors or catalytically inactive caspases. A mutant TR, lacking the active site cysteines, inhibits the cell death induced by caspase 8. IFN/all-trans-retinoic acid-induced cytochrome c release from the mitochondrion was promoted in the presence of wild type and was inhibited in the presence of mutant TR. We find that TR modulates the activity of caspase 8 to promote death. This effect is in part caused by the stimulation of death receptor gene expression. These studies identify a new mechanism of cell death regulation by the IFN/all-trans-retinoic acid combination involving redox enzymes.

IFN-gamma inhibits lipopolysaccharide-induced interleukin-1 beta in primary murine macrophages via a Stat1-dependent pathway

Interleukin-1 (IL-1) plays an important role in host defenses against microbial pathogens. Excessive production of this cytokine, however, may be responsible in part for the lethality observed during sepsis. Our studies show that interferon-gamma (IFN-gamma) downregulates lipopolysaccharide (LPS)-induced interleukin-1beta (IL-1beta) transcription in primary macrophages. This phenomenon does not occur in splenocytes or bone marrow-derived macrophages from signal transducer and activator of transcription (Stat1)-deficient mice, suggesting that Stat1, a transcription factor involved in IFN signaling, plays a critical role in this process. Moreover, nitric oxide (NO) was also involved in the downregulation of LPS-induced IL-1 by IFN, as addition of the inducible nitric oxide synthase (iNOS) inhibitor L-N(6)-(1-iminoethyl)lysine (NIL) negated the effect. Kinetic analysis of IL-1 and IFN levels in LPS-treated mice in vivo suggests that IFN-mediated inhibition of IL-1 might be an important negative feedback mechanism for limiting IL-1 generation in vivo.

Thioredoxin participates in a cell death pathway induced by interferon and retinoid combination

Interferons (IFNs) and retinoids are potent tumor growth suppressors. We have shown earlier that the IFN-beta and all-trans retinoic acid combination, but not the single agents, induces death in several tumor cell lines. Employing a genetic approach we have recently identified several Genes associated with Retinoid-IFN induced Mortality (GRIM) that mediate the cell death effect of IFN/RA combination. One of the GRIMs, GRIM-12, was identical to human thioredoxin reductase (TR), an enzyme that controls intracellular redox state. To define the participants of TR mediated death pathway we have examined the role of thioredoxin (Trx), its downstream substrate, and its influence on IFN/RA-induced death regulation. Inhibition of the thioredoxin expression by antisense RNA suppressed cell death. Similarly, a mutant Trx1 lacking the critical cysteine residues blocked cell death. In contrast, overexpression of wildtype thioredoxin augmented cell death. This effect of Trx1 was in part due to its ability to augment cell death via caspase-8. The redox inactive Trx1 mutant inhibits the cell death induced by caspase-8 but not caspase-3. These studies identify a novel mechanism of cell death regulation by IFN/RA combination involving redox enzymes.

Activation of Rac1 and the p38 mitogen-activated protein kinase pathway in response to all-trans-retinoic acid

Several signaling pathways are activated by all-trans-retinoic acid (RA) to mediate induction of differentiation and apoptosis of malignant cells. In the present study we provide evidence that the p38 MAP kinase pathway is activated in a RA-dependent manner in the NB-4, acute pro-myelocytic leukemia, and the MCF-7, breast carcinoma, cell lines. RA treatment of cells induces a time- and dose-dependent phosphorylation of p38, and such phosphorylation results in activation of its catalytic domain. p38 activation is not inducible by RA in a variant NB-4 cell line, NB-4.007/6, which is resistant to the effects of RA, suggesting a role for this pathway in the induction of RA responses. Our data also demonstrate that the small G-protein Rac1 is activated by RA and functions as an upstream regulator of p38 activation, whereas the MAPKAPK-2 serine kinase is a downstream effector for the RA-activated p38. To obtain information on the functional role of the Rac1/p38/MAPKAPK-2 pathway in RA signaling, the effects of pharmacological inhibition of p38 on RA-induced gene transcription and cell differentiation were determined. Our results indicate that treatment of cells with the SB203580 inhibitor does not inhibit RA-dependent gene transcription via retinoic acid response elements or induction of Stat1 protein expression. However, treatment with SB203580 or SB202190 strongly enhances RA-dependent induction of cell differentiation and RA-regulated growth inhibitory responses. Altogether, our findings demonstrate that the Rac1/p38 MAP kinase pathway is activated in a RA-dependent manner and exhibits negative regulatory effects on the induction of differentiation.

Mechanism of repression of squamous differentiation marker, SPRR1B, in malignant bronchial epithelial cells: role of critical TRE-sites and its transacting factors

The overexpression of SPRR1B in bronchial epithelium is a marker for early metaplastic changes and the loss of its expression is associated with an irreversible malignant transformation. In the present study, we have used a model system consisting of normal and malignant bronchial epithelial (BE) cells to elucidate the differential transcriptional control of SPRR1B. SPRR1B expression is either detectable or PMA (phorbol 13-myristate 12-acetate) -inducible in several malignant BE cells including squamous, adeno, small and large cell carcinomas. Loss of SPRR1B expression is correlated well with the lack of strong in vivo protein-DNA interactions at the -152 bp promoter, which contains two functional TRE sites. Even though the basal level AP-1 protein DNA binding pattern is different between normal and malignant cells, PMA significantly enhances Jun and Fos binding to the consensus TRE site in both cell types. Intriguingly, the composition of AP-1 protein binding to the -152 to -86 bp SPRR1B promoter is quite different. In untreated cells, SPRR1B promoter is predominantly occupied by JunD and Fra2. PMA significantly induced binding of JunB and Fra1 in normal cells, while JunB and Fra2 bound to TREs in the malignant cells. Overexpression of fra1 in malignant cells significantly enhanced SPRR1B promoter activity. In contrast, overexpression of fra2, but not fra1, strongly reduced both basal and PMA-inducible promoter activities in normal cells. Together, these results indicate that either temporal expression and/or differential activation of AP-1 proteins, especially Fra1 and Fra2, might contribute to the dysregulation of terminal differentiation marker, SPRR1B, expression in various BE cells.

ERK1 and ERK2 activate CCAAAT/enhancer-binding protein-beta-dependent gene transcription in response to interferon-gamma

Interferons (IFNs) regulate the expression of a number of cellular genes by activating the JAK-STAT pathway. We have recently discovered that CCAAAT/enhancer-binding protein-beta (C/EBP-beta) induces gene transcription through a novel IFN response element called the gamma-IFN-activated transcriptional element (Roy, S. K., Wachira, S. J., Weihua, X., Hu, J., and Kalvakolanu, D. V. (2000) J. Biol. Chem. 275, 12626-12632. Here, we describe a new IFN-gamma-stimulated pathway that operates C/EBP-beta-regulated gene expression independent of JAK1. We show that ERKs are activated by IFN-gamma to stimulate C/EBP-beta-dependent expression. Sustained ERK activation directly correlated with C/EBP-beta-dependent gene expression in response to IFN-gamma. Mutant MKK1, its inhibitors, and mutant ERK suppressed IFN-gamma-stimulated gene induction through the gamma-IFN-activated transcriptional element. Ras and Raf activation was not required for this process. Furthermore, Raf-1 phosphorylation negatively correlated with its activity. Interestingly, C/EBP-beta-induced gene expression required STAT1, but not JAK1. A C/EBP-beta mutant lacking the ERK phosphorylation site failed to promote IFN-stimulated gene expression. Thus, our data link C/EBP-beta to IFN-gamma signaling through ERKs.

Identification of GRIM-19, a novel cell death-regulatory gene induced by the interferon-beta and retinoic acid combination, using a genetic approach

We show here that the combination of interferon-beta (IFN-beta) and all-trans-retinoic acid (RA) induces the death of tumor cells. To understand the molecular basis for synergistic growth-suppressive action and to identify the gene products that participate in this process, we have employed an antisense knock-out technique. This approach permits the isolation of cell death-associated genes based on their selective inactivation by overexpression of antisense cDNAs. Because the antisense mRNA inactivates gene expression of death-specific genes, transfected cells survive in the presence death inducers. Several Genes associated with Retinoid-IFN-induced Mortality (GRIM) were identified using this approach. Here we report the isolation of a novel GRIM gene, GRIM-19. This 552-base pair cDNA encodes a 16-kDa protein. Antisense expression of GRIM-19 confers a strong resistance against IFN/RA-induced death by reducing the intracellular levels of GRIM-19 protein. Overexpression of GRIM-19 enhances cell death in response to IFN/RA. GRIM-19 is primarily a nuclear protein whose expression is induced by the IFN/RA combination. Together, our studies identify a novel cell death-regulatory molecule.

Phorbol ester-induced expression of airway squamous cell differentiation marker, SPRR1B, is regulated by protein kinase Cdelta /Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway

The transcriptional induction of SPRR1B by phorbol 12-myristate 13-acetate (PMA) is mainly mediated by the first -152-base pair 5'-flanking region containing two functional AP-1 sites. In this study, we have analyzed the signaling pathways that mediate the induction in tracheobronchial epithelial cells. PKC inhibitor ablated PMA-stimulated expression of endogenous SPRR1B and reporter gene expression driven by SPRR1B promoter. PKC activator promoted the transcription. The dominant negative protein kinase Cdelta (dn-PKCdelta) and rottlerin (PKCdelta inhibitor) completely suppressed PMA-stimulated promoter activity. dn-Ras or dn-MEKK1 inhibited PMA-stimulated promoter activity, while their corresponding constitutively active mutants augmented it. dn-c-Raf-1 did not have any effect on reporter gene expression. Since MEKK1 activates multiple parallel pathways, we examined involvement of JNK/SAPK, p38, and MKK1 in promoter regulation. Co-expression of the dominant negative forms of MKK4, MKK7, JNK/SAPK, MKK3, MKK6, or p38alpha did not suppress PMA-stimulated reporter gene expression. However, MKK1 inhibitors UO126 and PD98095 suppressed gene expression. Consistent with this, expression of dn-MKK1 strongly suppressed PMA-stimulated promoter activity, while the constitutively active MKK1 augmented it. However, MKK1-mediated induction of SPRR1B probably does not depend on extracellular signal-regulated kinases 1 and 2, suggesting the requirement of another kinase(s). dn-c-Jun mutants abolished PMA-stimulated expression supporting an important role for AP-1 proteins in SPRR1B expression. Together, these results suggest that a PKCdelta/Ras/MEKK1/MKK1-dependent/AP-1 pathway regulates the PMA-inducible expression of the SPRR1B in tracheobronchial epithelial cells.

Chromosomal localization of human GRIM-19, a novel IFN-beta and retinoic acid-activated regulator of cell death

Apoptosis is a tightly regulated mechanism that controls the proliferation of cells in metazoans. In mammals, multiple genes are required to regulate cell death. We have employed a gene expression knockout technique to isolate cell death-related genes. One such gene, gene associated with retinoid-interferon-induced mortality-19 (GRIM-19), is essential for tumor cell death induced by interferon-beta (IFN-beta) and retinoic acid (RA). Here, we describe the localization of GRIM-19 to human chromosome 19p13.2. This region is essential for prostate tumor suppression. Together with its death-inductive role in the IFN-retinoid-regulated pathways and the tumor-suppressive function of this locus, the data suggest that GRIM-19 may be a novel tumor suppressor.

Interleukin-6 modulates interferon-regulated gene expression by inducing the ISGF3 gamma gene using CCAAT/enhancer binding protein-beta(C/EBP-beta)

Although interleukin-6 (IL-6) alone does not induce the expression of IFN stimulated genes (ISG), a low dose priming of cells with IL-6 strongly enhances the cellular responses to interferon-alpha (IFN-alpha). This effect of IL-6 is not due to superstimulation of the JAK-STAT pathway. Rather, IL-6 induces expression of ISGF3 gamma (p48), a subunit of the multimeric transcription factor ISGF3. As a result IFN-alpha robustly activates gene transcription in IL-6 primed cells. We have shown earlier that the transcription of ISGF3 gamma gene is regulated through a novel element GATE (gamma-IFN activated transcriptional element). We show here IL-6 induces the ISGF3 gamma gene through GATE. Transcription factor C/EBP-beta is required for inducing ISGF3 gamma gene expression through GATE. A mutant C/EBP-beta inhibits the IL-6 inducible ISGF3 gamma gene expression through GATE. Together, these results establish a molecular basis for the synergy between IFNs and IL-6.

CCAAT/enhancer-binding protein-beta regulates interferon-induced transcription through a novel element

We have described previously a novel interferon (IFN)-responsive cis-acting enhancer element called gamma-IFN-activated transcriptional element (GATE). GATE is distinct from the known IFN-stimulated elements and binds to novel transacting factors. To identify the gamma-IFN-responsive transacting factors that interact with GATE, we have screened a cDNA expression library derived from IFN-gamma-stimulated murine macrophage cell line and isolated three different cDNAs. Among these is a gene coding for the pleiotropic transcription factor, CCAAT/enhancer-binding protein-beta (C/EBP-beta). We report here that the gene for C/EBP-beta binds to GATE and induces gene expression. A mutant C/EBP-beta interferes with the IFN-gamma-stimulated transcription of the ISGF3gamma (p48) promoter. Other members of the C/EBP family do not cause these effects. Interestingly, the expression of C/EBP-beta, not the other members of its family, is induced by IFN-gamma. These studies thus identify a novel role for C/EBP-beta in the IFN-signaling pathways.

The interferon-beta and tamoxifen combination induces apoptosis using thioredoxin reductase

Interferons (IFNs) suppress cell growth by inducing cellular genes. The anti-estrogen tamoxifen (Tam), binds to estrogen receptor and inhibits transcription of estrogen stimulated genes. In cells resistant to IFN-induced growth suppression, IFN/Tam combination causes cell death. We previously reported that the combination of IFN-beta and Tam was a more potent growth suppressor of human tumor xenografts than either agent alone. The IFN/Tam combination acts in a manner similar to the IFN/retinoic acid combination. Using a genetic technique, we have recently identified several genes associated with retinoid-IFN-induced mortality (GRIM). One such gene, GRIM-12, was identical to human thioredoxin reductase (TR). In the present study we have examined whether the IFN/Tam combination also requires GRIM-12 for inducing cell death. We report here that GRIM-12 is necessary for mediating the cell death effects of IFN/Tam, and its expression is induced by IFN/Tam at a post-transcriptional stage. Repression of GRIM-12 levels either by antisense expression or by dominant negative inhibitors caused resistance to IFN/Tam induced death and promoted cell growth. Overexpression of GRIM-12 increased IFN/Tam induced apoptosis. Thus, these studies have identified a critical role for GRIM-12 (TR) in apoptosis.

Interferons and cell growth control

Cytokines modulate cell growth, differentiation, and immune defenses in the vertebrates. Interferons (IFNs) are a unique class of cytokines that stimulate antiviral, antitumor and antigen presentation by inducing the expression of several cellular genes. Recent studies have identified a novel gene regulatory pathway activated by IFNs, which serves as a paradigm for most cytokine signal transduction pathways. A number of genes induced by IFNs participate in cell growth regulation and apoptosis. These include novel tumor suppressor genes. Although discovered as IFN-regulated factors, deletions of these genes cause leukemias in experimental models and in human patients. Genetic approaches have identified several novel regulators of apoptosis. Studies on the mechanism of action of these growth regulatory molecules are not only useful in identifying novel targets for the development of therapeutics but also help understand the molecular basis for loss of cell growth control and resistance to IFNs. This review focuses on the functions and roles of IFN regulated factors in cell growth control and mechanisms of disruption of IFN action in cancer cells.

RNase-L-dependent destabilization of interferon-induced mRNAs. A role for the 2-5A system in attenuation of the interferon response

The 2-5A system is an interferon-regulated RNA degradation pathway with antiviral, growth-inhibitory, and pro-apoptotic activities. RNase-L mediates the antiviral activity through the degradation of viral RNAs, and the anticellular effects of the 2-5A system are thought to be similarly mediated through the degradation of cellular transcripts. However, specific RNase-L-regulated cellular RNAs have not been identified. To isolate candidate RNase-L substrates, differential display was used to identify mRNAs that exhibited increased expression in RNase-L-deficient N1E-115 cells as compared with RNase-L-transfected cells. A novel interferon-stimulated gene encoding a 43-kDa ubiquitin-specific protease, designated ISG43, was identified in this screen. ISG43 expression is induced by interferon and negatively regulated by RNase-L. ISG43 induction is a primary response to interferon treatment and requires a functional JAK/STAT signaling pathway. The kinetics of ISG43 induction were identical in wild type and RNase-L knock-out fibroblasts; however, the decline in ISG43 mRNA following interferon treatment was markedly attenuated in RNase-L knock-out fibroblasts. The delayed shut-off kinetics of ISG43 mRNA corresponded to an increase in its half-life in RNase-L-deficient cells. ISG15 mRNA also displayed RNase-L-dependent regulation. These findings identify a novel role for the 2-5A system in the attenuation of the interferon response.

Virus interception of cytokine-regulated pathways

Cytokines regulate host antiviral, immune and antitumor responses. Viruses combat the host-imposed inhibitory pathways to survive and spread the infection. Some viruses have evolved molecules that override apoptotic programs to promote cell survival until virus assembly is complete, persistence is established or cellular transformation occurs.

Gamma interferon augments macrophage activation by lipopolysaccharide by two distinct mechanisms, at the signal transduction level and via an autocrine mechanism involving tumor necrosis factor alpha and interleukin-1

When given in the presence of gamma interferon (IFN-gamma), otherwise nontoxic doses of lipopolysaccharide (LPS or endotoxin) become highly lethal for mice. The mechanisms of this synergistic toxicity are not known. We considered the possibility that an interaction between the LPS-induced NF-kappaB and IFN-gamma-induced JAK-STAT pathways at the pretranscriptional level may enhance the LPS-induced signals. To test this hypothesis, we incubated murine macrophage RAW 264.7 cells with IFN-gamma for 2 h before addition of different doses of LPS. Consistent with the synergistic induction of inducible nitric oxide synthase mRNA and nitric oxide production by a combination of LPS and IFN-gamma, IFN-gamma strongly augmented LPS-induced NF-kappaB activation and accelerated the binding of NF-kappaB to DNA to as early as 5 min. In agreement with this, IFN-gamma pretreatment promoted rapid degradation of IkappaB-alpha but not that of IkappaB-beta. Inhibition of protein synthesis during IFN-gamma treatment suppressed LPS-initiated NF-kappaB binding. A rapidly induced protein appeared to be involved in IFN-gamma priming. Preincubation of cells with antibodies to tumor necrosis factor alpha or the interleukin-1 receptor partially reduced the priming effect of IFN-gamma. In a complementary manner, LPS enhanced the activation of signal-transducing activator of transcription 1 by IFN-gamma. These data suggest novel mechanisms for the synergy between IFN-gamma and LPS by which they cross-regulate the signal-transducing molecules. Through this mechanism, IFN-gamma may transform a given dose of LPS into a lethal stimulus capable of causing sepsis. It may also serve a beneficial purpose by enabling the host to respond quickly to relatively low doses of LPS and thereby activating antibacterial defenses.

Regulation of interferon-alpha/beta-stimulated gene expression through the gamma-activated transcriptional element

Interferons (IFNs) stimulate gene expression to mediate their biological actions. A multimeric transcription factor consisting of STAT1, STAT2 and p48, a DNA binding protein, regulates IFN-alpha/beta stimulated gene expression. Since the cellular level of p48 is also increased by pre-treatment of cells with IFN-gamma, it is also known as ISGF3gamma. To understand how IFN-gamma regulates the expression of the p48 gene, we have previously isolated and characterized the promoter of murine p48 gene and identified a novel gamma-IFN activated transcriptional element (GATE). In this study using several mutant constructs of p48 promoter we have determined that the same element responds to IFN-alpha/beta treatment. Relatively high doses of IFN-alpha/beta compared to IFN-gamma are required for the induction of p48 promoter. This ability of IFN-alpha/beta to regulate GATE dependent gene expression is linked to the activation of a factor induced by IFN-alpha. However, IFN-gamma induces the binding of two gamma-IFN inducible factors (GIFs) to GATE. The IFN-alpha inducible GATE binding factor is not recognized by specific antibodies raised against the known IFN-regulated factors. It is likely IFN-gamma is a stronger inducer of this gene because it activates two GIFs. GATE-like elements present in hither to undefined IFN-stimulated genes may control IFN-responses in a unique manner.

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.

Thioredoxin reductase mediates cell death effects of the combination of beta interferon and retinoic acid

Interferons (IFNs) and retinoids are potent biological response modifiers. By using JAK-STAT pathways, IFNs regulate the expression of genes involved in antiviral, antitumor, and immunomodulatory actions. Retinoids exert their cell growth-regulatory effects via nuclear receptors, which also function as transcription factors. Although these ligands act through distinct mechanisms, several studies have shown that the combination of IFNs and retinoids synergistically inhibits cell growth. We have previously reported that IFN-beta-all-trans-retinoic acid (RA) combination is a more potent growth suppressor of human tumor xenografts in vivo than either agent alone. Furthermore, the IFN-RA combination causes cell death in several tumor cell lines in vitro. However, the molecular basis for these growth-suppressive actions is unknown. It has been suggested that certain gene products, which mediate the antiviral actions of IFNs, are also responsible for the antitumor actions of the IFN-RA combination. However, we did not find a correlation between their activities and cell death. Therefore, we have used an antisense knockout approach to directly identify the gene products that mediate cell death and have isolated several genes associated with retinoid-IFN-induced mortality (GRIM). In this investigation, we characterized one of the GRIM cDNAs, GRIM-12. Sequence analysis suggests that the GRIM-12 product is identical to human thioredoxin reductase (TR). TR is posttranscriptionally induced by the IFN-RA combination in human breast carcinoma cells. Overexpression of GRIM-12 causes a small amount of cell death and further enhances the susceptibility of cells to IFN-RA-induced death. Dominant negative inhibitors directed against TR inhibit its cell death-inducing functions. Interference with TR enzymatic activity led to growth promotion in the presence of the IFN-RA combination. Thus, these studies identify a novel function for TR in cell growth regulation.

The polyoma virus T antigen interferes with interferon-inducible gene expression

Murine polyoma virus (MPyV) is a small DNA virus that induces tumors in multiple tissues of infected host. In this investigation, we show that cell lines derived from wild type virus-induced breast tumors are resistant to the growth inhibitory action of interferon beta (IFN-beta). Furthermore, replication of heterologous viruses such as vesicular stomatitis virus and encephalomyocarditis virus was not inhibited by IFN-beta in these cells. This effect was due to inhibition of IFN-stimulated gene expression by viral T antigen. Activation of IFN-stimulated gene factor 3 was inhibited in cells derived from a tumor induced by wild-type MPyV but not those from a mutant that lacks the pRB binding site of the large T antigen. Similarly IFN-gamma-inducible gene expression was also inhibited in cells transformed by wild-type virus. The levels of components of IFN-stimulated gene factor 3 and signal transducing Janus tyrosine kinases were comparable between the cells transformed by the wild-type and mutant viruses. The viral large T antigen bound to Janus tyrosine kinase 1 and inactivated signaling through IFN receptors. Thus, these studies identify a mechanism of viral resistance to IFN action.

The interferon-inducible murine p48 (ISGF3gamma) gene is regulated by protooncogene c-myc

p48 protein is an integral component of the multimeric interferon (IFN)-regulated transcription factor, ISGF3. We have shown earlier that this gene is regulated by a novel IFN-gamma-regulated element. In addition to the IFN-regulated element, a myc-max binding site is also present in this promoter. In this investigation we have studied the role of this site in the regulation of the p48 gene. In serum-induced quiescent cells Myc up-regulated the expression of p48 mRNA. We show that the protooncogene Myc regulates the expression of p48 through the element CACGTG. Mutations in this motif abolish Myc-inducibility of the reporter genes carrying p48 promoter elements. Purified Myc and Max proteins interact with the Myc-stimulated element of the p48 promoter. We also show that cells lacking p48 expression are highly susceptible to the cytocidal action of anticancer drugs. Taken together these data suggest that p48 may function as an anti-stress cell survival factor.

Increasing effectiveness of interferon-alpha for malignancies

Alpha-interferons (IFN-alphas) have been shown to be effective agents in inducing the regression of various malignancies, including leukemias and lymphomas as well as solid tumors, and are the first human therapeutic proteins to result in increased survival in cancer patients. Based on their pleiotropic activities, IFNs have the potential for interacting synergistically with other anticancer agents. For example, preclinical in vitro and animal data suggest a synergistic antitumor interaction between IFN-alpha2 and the antiestrogens toremifene and tamoxifen. Further studies are required to elucidate the molecular basis for such synergistic interactions, particularly with respect to IFN-stimulated genes.

Synergistic antitumor effects of a combination of interferons and retinoic acid on human tumor cells in vitro and in vivo

Solid tumors are relatively resistant to growth inhibition by IFNs. To enhance sensitivity, we assessed combinations of IFNs with all-trans-retinoic acid (RA). Antiproliferative studies in vitro suggested that the growth of three human breast carcinomas (MCF-7, MDA-MB-231, and MDA-MB-468), an ovarian carcinoma (NIH-OVCAR-3), and a malignant melanoma (SK-MEL-1) was inhibited to a greater degree by combination treatment with human IFN-beta and RA compared to single agents. Some of these cell lines were resistant to 10-100 IU/ml human IFN-alpha2b or IFN-beta or to 0.1-1.0 microM RA. Growth was inhibited significantly by combinations of IFNs and RA in all cell lines tested, and in some cases, cytotoxicity was observed. Sequential treatment of MCF-7 cells with RA followed by IFN-beta was more effective at inhibiting growth than treatment with IFN-beta followed by RA, suggesting that RA modulated the anticellular response of IFN-beta rather than the converse. In nude mice, the growth of MCF-7 and NIH-OVCAR-3 tumors was suppressed completely when combination treatment was started 2 days after tumor inoculation. Established, 6-week-old NIH-OVCAR-3 tumors underwent regression when treated with the combination of IFN-beta and RA but not with single-agent therapy. Together with our recent studies that demonstrated enhancement of IFN-stimulated gene expression by RA pretreatment in IFN-resistant cells, these data suggest that combination treatment with RA and IFNs may increase IFN-stimulated gene expression in IFN-resistant tumors, leading to augmented antitumor effects.

Modulation of interferon action by retinoids. Induction of murine STAT1 gene expression by retinoic acid

We have previously demonstrated that up-regulation of STAT1 protein by all-trans-retinoic acid (RA) in interferon (IFN)-unresponsive cells permits growth inhibition by IFNs. Here, we show that the promoter of STAT1 directly responds to retinoic acid treatment. Sequence and functional analysis of the murine STAT1 promoter have identified a direct repeat motif that serves as a retinoic acid response element. Mutagenesis of this element resulted in a loss of response to RA. This element is activated by RA receptors alpha, beta, and gamma. In vivo, RA receptor beta and retinoid X receptor alpha preferentially interacted with this element. Thus, these data define a molecular basis for the synergy between IFNs and retinoids in tumor growth inhibition.

Tamoxifen enhances interferon-regulated gene expression in breast cancer cells

The molecular basis for the enhanced growth inhibition of MCF-7 human breast cancer xenografts by a combination of human interferon-beta (IFN-beta) and tamoxifen was investigated. Treatment of MCF-7, MDA-MB-231, and BT-20 cells with the combination of IFN-beta and tamoxifen resulted in enhanced antiproliferative effects in vitro. Treatment with the combination of IFN-beta and tamoxifen enhanced the expression of several IFN-beta-inducible genes in human breast carcinoma cell lines relative to levels induced by IFN-beta alone. Tamoxifen alone did not induce transcription of IFN-stimulated genes (ISGs). Augmentation of ISG expression by the combination of IFN-beta and tamoxifen was noted in breast tumor cell lines irrespective of their functional estrogen receptor (ER) status or their dependence on estradiol for growth, suggesting that upregulation of ISGs was independent of ER status. Enhancement of IFN-stimulated gene expression by tamoxifen occurred at the transcriptional level. Expression of transfected reporter genes under the control of IFN-alpha/beta regulated promoters was also enhanced in IFN-beta and tamoxifen-treated cells. Similarly, transcriptional induction of chimeric reporter plasmids driven by an IFN-gamma inducible promoter (GAS; IFN-gamma activated site) was also enhanced by the combination of IFN-gamma and tamoxifen. In tamoxifen treated cells, IFN-beta and IFN-gamma readily activated transcription factors ISGF-3 and GAF, respectively. Therefore, augmentation of ISG expression by tamoxifen is an early event in the antitumoral activity of this drug combination.

Interferon gamma-induced transcription of the murine ISGF3gamma (p48) gene is mediated by novel factors

In this investigation, we show that the gene encoding p48, a subunit of transcription factor ISGF3, is transcriptionally induced by interferon gamma (IFN-gamma). We have identified a novel IFN-gamma-activated response element in the p48 gene promoter. This motif, notated as gamma-activated transcriptional element (GATE), has no significant resemblance to either pIRE (palindromic IFN-response element) or GAS (the IFN-gamma-activated sequence) but has partial homology to ISRE (IFN-stimulated response element). When fused to a neutral promoter, GATE, a 24-bp element, induced the expression of reporter genes following IFN-gamma treatment. In murine RAW cells, two IFN-gamma-inducible factors (GIF) bind to GATE. Binding of these factors to GATE is inhibited by cycloheximide and staurosporine. Although p48 gene induction is dependent on STAT1 and JAK1, activated STAT1 does not bind to GATE. Thus, GIFs appear to be novel trans-acting factors in the IFN-signaling pathway.

Modulation of interferon (IFN)-inducible gene expression by retinoic acid. Up-regulation of STAT1 protein in IFN-unresponsive cells

Interferons (IFN) and retinoids failed to inhibit the growth of a number of breast tumor cell lines. However, a combination of these two biological response modifiers significantly suppressed the cell growth at pharmacologically achievable doses. The molecular basis for such enhancement was investigated in MCF-7, a breast tumor cell line resistant to growth inhibition by IFN-beta. Pretreatment of cells with retinoic acid (RA) for 16 h followed by IFN-beta, but not the converse, induced cytotoxic effects in the cells. Continuous presence of RA was not necessary, although it enhanced the degree of cell death when present. Further analyses revealed that IFN-beta failed to activate IFN-stimulated gene transcription. However, IFN-beta strongly up-regulated the gene expression in RA-pretreated cells. Both IFN-beta- and IFN-gamma-inducible gene expression were enhanced via a modulation of the transcriptional factor IFN-stimulated gene factors-3 and GAF binding to respective cognate regulatory elements. STAT1 was undetectable in these cells prior to RA treatment. RA increased the levels of this crucial regulator, thereby restoring IFN responses. Thus, RA augmentation of STAT1 may be an early step in the cooperative anti-tumor effects of IFN and RA.

Retinoids and interferons in non-melanoma skin cancer

Retinoids alone and in combination with interferon-alpha are the best systemic agents to study in the reversal of skin carcinogenesis and in the treatment of advanced squamous cell carcinoma of the skin. This article reviews the major laboratory advances in the mechanistic study of retinoids and interferons alone and in combination. Recent data in several cancer cell lines suggest that retinoic acid can potentiate the interferon signal-transduction pathway. Also reviewed is the current status of clinical studies of systemic retinoids and interferon in (i) skin cancer prevention (as single agents) and (ii) treatment of advanced squamous cell carcinoma (as single agents and in combination). Future clinical studies with translational laboratory correlates are necessary to determine the roles of retinoids and interferons in the prevention and treatment of skin cancer.

Transcriptional induction of genes by IFN-beta in mouse cells is regulated by a transcription factor similar to human ISGF-3

Previous studies of IFN-stimulated transcription factors in murine cells have identified a variety of trans-acting factors that bind to the IFN-stimulated response element (ISRE) whose role in gene expression remain unclear. The present investigation was undertaken to delineate the signal transduction pathway as well as to identify the transcription factors regulated by murine IFN-beta in L929 cells. Tyrosine kinase inhibitor, Genistein, abrogated gene induction and activation of transcription factors by IFN-beta. As early as 5 min after IFN-beta treatment, a transcription factor was activated in the cytoplasm which subsequently migrated into the nucleus. Anti-phosphotyrosine antibodies detected a specific transcription factor induced by mIFN-beta. Antibodies raised against human ISGF-3 subunit proteins p48, p84, p91 and p113 recognized this factor in the cytoplasm as well as in the nucleus of IFN-beta-treated L929 cells. An antibody raised against an oligopeptide of human p113 (residues 435-450) recognized the ISGF-3 complexes both in human and murine cells. However, a different antibody against the C-terminus of human p113 (residues 671-806) did not recognize the ISGF-3 like complex in mouse cells, indicating differences in the primary sequence of these proteins.

Retinoic acid and interferon in human cancer: mechanistic and clinical studies

Various combinations of retinoids, metabolic and synthetic derivatives of vitamin A, and interferons (IFNs) have demonstrated synergistic antiproliferative, differentiating, and antiangiogenic activity in some human hematologic and solid-tumor systems. This synergistic antitumor activity may be due to enhanced gene expression. In several cell systems, the actions of IFNs are enhanced by differentiation of cells with retinoic acid (RA). Combined RA-IFN effects have been correlated with the induction of higher levels of IFN-stimulated genes than the levels induced by either agent alone. Natural and synthetic retinoids have been found to augment the antiproliferative activity of IFNs in several squamous cell carcinoma (SCC) and breast tumor cell lines. Results of recent clinical trials indicate substantial activity of 13-cis-RA (13cRA) combined with IFN against advanced SCC of the skin and cervix, and possibly against other solid tumors. Two phase II trials have confirmed activity against locally advanced SCC of the cervix. Successful integration of this regimen with radiotherapy appears to be the most probable means of optimizing clinical outcome. Further studies are needed to determine the mechanistic details of the RA-IFN interaction.

Transcription factor GATA-4 regulates cardiac muscle-specific expression of the alpha-myosin heavy-chain gene

The alpha-myosin heavy-chain (alpha-MHC) gene is the major structural protein in the adult rodent myocardium. Its expression is restricted to the heart by a complex interplay of trans-acting factors and their cis-acting sites. However, to date, the factors that have been shown to regulate expression of this gene have also been found in skeletal muscle cells. Recently, transcription factor GATA-4, which has a tissue distribution limited to the heart and endodermally derived tissues, was identified. We recently found two putative GATA-binding sites within the proximal enhancer of the alpha-MHC gene, suggesting that GATA-4 might regulate its expression. In this study, we establish that GATA-4 interacts with the alpha-MHC GATA sites to stimulate cardiac muscle-specific expression. Mutation of the GATA-4-binding sites either individually or together decreased activity by 50 and 88% in the adult myocardium, respectively. GATA-4-dependent enhancement of activity from a heterologous promoter was mediated through the alpha-MHC GATA sites. Coinjection of an alpha-MHC promoter construct with a GATA-4 expression vector permitted ectopic expression in skeletal muscle but not in fibroblasts. Thus, the lack of alpha-MHC expression in skeletal muscle correlates with a lack of GATA-4. GATA-4 DNA binding activity was significantly up-regulated in triiodothyronine- or retinoic acid-treated cardiomyocytes. Putative GATA-4-binding sites are also found in the regulatory regions of other cardiac muscle-expressed structural genes. This indicates a mechanism whereby triiodothyronine and retinoic acid can exert coordinate control of the cardiac phenotype through a trans-acting regulatory factor.

Differentiation-dependent activation of interferon-stimulated gene factors and transcription factor NF-kappa B in mouse embryonal carcinoma cells

We have recently shown that the adenovirus E1A gene products block interferon-alpha-induced signal transduction and transcription factor NF-kappa B-mediated gene induction. Here we report that the same responses are also blocked in undifferentiated F9 teratocarcinoma cells. The block was removed upon cellular differentiation and regained upon the introduction of viral E1A into the differentiated cells. In undifferentiated cells, interferon-beta failed to induce the transcription of interferon-responsive genes because of a lack of activation of the cognate trans-acting factors. As a result, in these cells, virus replication was not inhibited by interferon. Similarly, in undifferentiated but not in differentiated F9 cells, tumor necrosis factor alpha failed to stimulate NF-kappa B-mediated transcription of a reporter gene because of a failure in the activation of NF-kappa B trans-acting factor. These results suggest that a cellular E1A-like activity, present in undifferentiated F9 cells, and adenoviral E1A use similar mechanisms for repressing the expression of specific cellular genes.

Transcriptional repression of interleukin-6 gene by adenoviral E1A proteins

Transcription of interleukin-6 (IL-6) gene in human HepG2 and HeLa cells was induced by treatment with interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), phorbol 12-myristate 13-acetate, or dibutyryl cyclic AMP. These agents enhanced the expression of chloramphenicol acetyltransferase (CAT) activity in cells transfected with chimeric CAT genes driven by the transcriptional regulatory regions of human IL-6 gene. Both induced and basal levels of CAT expression were severely repressed upon co-transfection of expression vectors encoding the adenoviral E1A289R or E1A243R protein. The conserved region 1 of E1A proteins was required for this activity. IL-6-CAT expression could also be induced by co-transfecting expression vectors containing cDNAs of the catalytic subunit of protein kinase A or c-jun. E1A repressed transcriptional induction by these agents as well. Similar inhibition was observed when a CAT gene driven by the NF kappa B element of the IL-6 gene was used as a reporter plasmid. In a cell line stably transfected with the E1A gene, IL-1 or TNF-alpha failed to induce IL-6 mRNA. Electrophoretic mobility shift assays were carried out with nuclear extracts of these cells using, as probes, the NF kappa B element or the multiple regulatory element of the IL-6 gene. With either probe, additional faster migrating DNA-protein complexes were formed in the extracts of E1A-expressing cells as compared with the extracts of the corresponding control cells. Experiments with NF kappa B antibody revealed differences between the different DNA-protein complexes formed in the extract of E1A-expressing cells. These observations suggest that E1A represses IL-6 gene transcription by interfering with the formation of appropriate DNA-protein complexes.

Adenovirus E1A represses the cyclic AMP-induced transcription of the gene for phosphoenolpyruvate carboxykinase (GTP) in hepatoma cells

Adenovirus infection of hepatoma cells inhibited transcription of the phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) gene and virtually eliminated transcription of a chimeric gene which contained the PEPCK promoter linked to the structural gene for chloramphenicol acetyltransferase (CAT). This effect is due to the viral protein E1A, since adenovirus containing a deletion in the E1A gene did not repress transcription from the PEPCK promoter. Both the 243R and 283R products of the E1A gene were effective. The conserved region 1 (CR-1) domain of E1A was required for this effect. Treatment of hepatoma cells with 8-bromo-cAMP or transfection with plasmids coding for the catalytic subunit of protein kinase A, CAAT/enhancer binding protein alpha (C/EBP), or Jun, all potent inducers of PEPCK gene transcription, did not relieve the inhibition caused by E1A. This inhibition does not appear to be mediated by major enhancer elements and in the PEPCK gene since transcription from the PEPCK promoter containing block mutations in binding domains for C/EBP and cAMP regulatory element binding protein (CREB) was also inhibited by E1A. Transcription of chimeric genes containing two copies each of the major cAMP response domains (CRE-1 and P-3) linked to a neutral promoter and fused to the CAT structural gene was stimulated by the catalytic subunit of protein kinase A, but this effect was totally inhibited by E1A. The strong repressive effect of E1A on PEPCK gene transcription seems to involve an interruption of an obligatory interaction between factors which bind to the cAMP response element in the PEPCK promoter and the TATA box.

Inhibition of interferon-inducible gene expression by adenovirus E1A proteins: block in transcriptional complex formation

Infection with wild-type adenovirus 5, but not with a mutant lacking the E1A gene, prevented the induction by interferon (IFN) alpha of chloramphenicol acetyltransferase (CAT) activity in HeLaM cell lines that had been permanently transfected with chimeric CAT reporter genes driven by the transcriptional regulatory regions of the IFN-responsive genes 561 and 6-16. Similar inhibition of IFN-inducible CAT activity was observed in cells that were cotransfected with the same reporter genes and plasmids expressing either the E1A 289- or 243-amino acid protein. These proteins also prevented the induction of CAT activity by IFN-gamma from a cotransfected HLA-DR alpha-CAT gene. Experiments with E1A mutants mapped the inhibitory activity to amino acid residues 38-65 of these proteins. In a HeLa cell line permanently expressing the E1A 289-amino acid protein, the replication of vesicular stomatitis virus and encephalomyocarditis virus was not inhibited by IFN-alpha, suggesting a global blockade of IFN responses. In accord with this theory, induction of 561, 1-8, and (2'-5')oligoadenylate synthetase mRNAs by IFN was blocked in these cells at the transcriptional level. The observed transcriptional inhibition could be attributed to the lack of formation of the crucial IFN-stimulated gene factor 3 (ISGF3) transcriptional complex. As shown by mobility shift assays, this complex was not formed in the nuclear extracts of IFN-treated adenovirus-infected cells or IFN-treated E1A-producing cells. These nuclear extracts were deficient in both ISGF3 alpha and ISGF3 gamma subunits. However, they did not block the formation of ISGF3 complex from exogenously added components.

Preparation and characterization of immunoliposomes for targeting of antiviral agents

Antibodies specific to avian myeloblastosis virus envelope glycoprotein gp80 were raised. Immunoliposomes were prepared using anti-avian myeloblastosis virus envelope glycoprotein gp80 antibody. The antibody was palmitoylated to facilitate its incorporation into lipid bilayers of liposomes. The fluorescence emission spectra of palmitoylated IgG have exhibited a shift in emission maximum from 330 to 370 nm when it was incorporated into the liposomes. At least 50% of the incorporated antibody molecules were found to be oriented towards the outside in the liposomes. The average size of the liposome was found to be 300 A, and on an average, 15 antibody molecules were shown to be present in a liposome. When adriamycin encapsulated in immunoliposomes was incubated in a medium containing serum for 72 h, about 75% of the drug was retained in liposomes. In vivo localization studies, revealed an enhanced delivery of drug encapsulated in immunoliposomes to the target tissue, as compared to free drug or drug encapsulated in free liposomes. These data suggest a possible use of the drugs encapsulated in immunoliposomes to deliver the drugs in target areas, thereby reducing side effects caused by antiviral agents.

Enhancement of expression of exogenous genes by 2-aminopurine. Regulation at the post-transcriptional level

In human and mouse cell lines, expression of exogenous genes was enhanced by treatment with 2-aminopurine (2-AP). Chloramphenicol acetyltransferase (CAT) and neomycin phosphotransferase activities were increased by up to 50-fold upon 2-AP treatment of cells permanently transfected with genes encoding these enzymes. Neomycin phosphotransferase activity was also increased by this treatment in cells infected with a retroviral vector carrying the neomycin phosphotransferase gene. 2-AP-mediated increase in CAT activity was observed in various cell lines which had been permanently transfected with chimeric CAT genes containing transcriptional regulatory elements of the interferon-inducible genes 6-16 and 561, SV40 early genes, mouse mammary tumor viral gene, or metallothionein II gene. The increase in the cellular CAT enzymatic activity was due to an elevated level of CAT protein. The 2-AP-mediated enhancement of CAT expression was operative at the translational level; the rate of transcription of CAT mRNA or its steady-state level was affected only marginally. The translational up-regulation by 2-AP was restricted to the genes introduced from outside; there was no gross change in the rate of synthesis of other cellular proteins.

Gene induction by interferons: functional complementation between trans-acting factors induced by alpha interferon and gamma interferon

HeLaM is a variant cell line in which the transcriptional induction of many genes by alpha interferon has special characteristics (Tiwari et al., Mol. Cell. Biol. 8:4289-4294, 1988). The same characteristics were also displayed for induced transcription of a permanently transfected chimeric gene containing the interferon-stimulated response element of gene 561. For understanding the molecular basis of the special requirements of HeLaM cells, an analysis of the interferon-stimulated gene factors (ISGF) was undertaken. By using gel shift assays, it was shown that the activation of ISGF3 by alpha interferon treatment of HeLaM cells had characteristics identical to those of induced transcription: inhibition by 2-aminopurine and the need for ongoing protein synthesis which was obviated by pretreating the cells with gamma interferon. Upon mixing in vitro the cytoplasmic fraction of gamma interferon-treated HeLaM cells with that of cells treated with alpha interferon and cycloheximide, active ISGF3 was reconstituted, presumably through complementation of two components, ISGF3 gamma and ISGF3 alpha, present in the two respective fractions. Because, unlike other cells, untreated HeLaM cells did not contain detectable levels of either component, we could induce them individually and study their independent properties. Induction of ISGF3 gamma but not of ISGF3 alpha needed ongoing protein synthesis and was blocked by 2-aminopurine. Once induced, ISGF3 gamma was active for 24 h and was present in both the nuclear and cytoplasmic fractions. Activated ISGF3 alpha, on the other hand, did not translocate to the nucleus in the absence of ISGF3 gamma, and in the cytoplasm its activity decayed within 2 h of its activation. In reference to our working model, all of the above observations indicate that ISGF3 gamma is the product of signal 1 and ISGF3 alpha is the product of signal 2.