Inhibitory effects of interferon on the expression of genes regulated by platelet-derived growth factor

Temporal expression of type I interferon receptor in the peri-implantation ovine extra-embryonic membranes: demonstration that human IFNalpha can bind to this receptor

Interferon-tau (IFNtau), produced by the trophectoderm of ruminant ungulates, binds to the type I IFN receptor (IFNAR) located at the uterine endometrium in a paracrine manner. Since IFNtau attenuates the secretory pattern of an endometrial luteolysin, prostaglandin F2alpha, IFNtau has been considered as a conceptus factor implicated in the process of maternal recognition of pregnancy. Here we report the presence of IFNAR subunit (IFNAR1) in ovine conceptuses during the period of peri-implantation development and demonstrate that 125I-human (h) IFNalpha binds to membrane preparations from ovine corpus luteum and conceptus. Using an antibody against hIFNAR1, immunohistochemical analysis revealed that IFNAR1 protein was present in day 14 and 16 conceptuses (day 0 = day of estrus) and luminal and glandular epithelia of the endometrium. Conceptus membrane proteins analyzed by western blot with the same antibody displayed immunoreactive bands at 95, 60 and 55 kDa while endometrial membrane proteins showed bands at 200, 95 and 55 kDa. Northern blot analysis revealed that IFNAR1 mRNA was present in days 15-19 conceptuses and day 18-19 allantoic membranes. Receptor binding studies indicated that 125I-hIFNalpha binding to day 16, but not earlier, conceptus membrane proteins could be displaced with hIFNalpha or ovine IFNtau. Based on Scatchard analysis, day 16 conceptus membranes contained 28 fmol IFNAR/mg protein with a dissociation constant of 300 pM. Cross-linking experiments demonstrated that 125I-hIFNalpha-receptor complex migrated at 120 kDa, indicating that the receptor component(s) was approximately 100 kDa. These data provide evidence that although the binding does not occur until day 16, ovine conceptuses possess IFNAR1 near or at the time of implantation, suggesting that IFNtau, a factor produced by the trophectoderm of ruminant ungulates, could act on the conceptus in an autocrine manner. In addition to functioning as an antiluteolytic factor, therefore, IFNtau may have a direct effect on conceptus development.

Apoptosis and cell growth inhibition as antitumor effector functions of interferons

Since their introduction to the clinic some 30 yr ago, interferons (IFNs) have become standard therapy for a range of disorders, including malignant and benign tumors as well as various viral diseases. Although IFNs will induce remissions in some patients with cancer, they are of no benefit or, at best, lead only to minor improvements in the great majority of patients with malignant disease. One of the great challenges of IFN research is to understand the multiple ways by which IFNs influence the behavior of tumor cells and to identify the factors that underlie the resistance of some tumors to IFNs. This review is written with a focus on two anticellular effects of IFN, inhibition of proliferation and induction of apoptosis, possible mechanisms underlying the antitumor action of IFN. In addition, possible reasons for IFN tumor cell resistance are also discussed.

The role of STATs in transcriptional control and their impact on cellular function

The STAT proteins (Signal Transducers and Activators of Transcription), were identified in the last decade as transcription factors which were critical in mediating virtually all cytokine driven signaling. These proteins are latent in the cytoplasm and become activated through tyrosine phosphorylation which typically occurs through cytokine receptor associated kinases (JAKs) or growth factor receptor tyrosine kinases. Recently a number of non-receptor tyrosine kinases (for example src and abl) have been found to cause STAT phosphorylation. Phosphorylated STATs form homo- or hetero-dimers, enter the nucleus and working coordinately with other transcriptional co-activators or transcription factors lead to increased transcriptional initiation. In normal cells and in animals, ligand dependent activation of the STATs is a transient process, lasting for several minutes to several hours. In contrast, in many cancerous cell lines and tumors, where growth factor dysregulation is frequently at the heart of cellular transformation, the STAT proteins (in particular Stats 1, 3 and 5) are persistently tyrosine phosphorylated or activated. The importance of STAT activation to growth control in experiments using anti-sense molecules or dominant negative STAT protein encoding constructs performed in cell lines or studies in animals lacking specific STATs strongly indicate that STATs play an important role in controlling cell cycle progression and apoptosis. Stat1 plays an important role in growth arrest, in promoting apoptosis and is implicated as a tumor suppressor; while Stats 3 and 5 are involved in promoting cell cycle progression and cellular transformation and preventing apoptosis. Many questions remain including: (1) a better understanding of how the STAT proteins through association with other factors increase transcription initiation; (2) a more complete definition of the sets of genes which are activated by different STATs and (3) how these sets of activated genes differ as a function of cell type. Finally, in the context of many cancers, where STATs are frequently persistently activated, an understanding of the mechanisms leading to their constitutive activation and defining the potential importance of persistent STAT activation in human tumorigenesis remains. Oncogene (2000).

Regulation of c-myc expression by IFN-gamma through Stat1-dependent and -independent pathways

Interferons (IFNs) inhibit cell growth in a Stat1-dependent fashion that involves regulation of c-myc expression. IFN-gamma suppresses c-myc in wild-type mouse embryo fibroblasts, but not in Stat1-null cells, where IFNs induce c-myc mRNA rapidly and transiently, thus revealing a novel signaling pathway. Both tyrosine and serine phosphorylation of Stat1 are required for suppression. Induced expression of c-myc is likely to contribute to the proliferation of Stat1-null cells in response to IFNs. IFNs also suppress platelet-derived growth factor (PDGF)-induced c-myc expression in wild-type but not in Stat1-null cells. A gamma-activated sequence element in the promoter is necessary but not sufficient to suppress c-myc expression in wild-type cells. In PKR-null cells, the phosphorylation of Stat1 on Ser727 and transactivation are both defective, and c-myc mRNA is induced, not suppressed, in response to IFN-gamma. A role for Raf-1 in the Stat1-independent pathway is revealed by studies with geldanamycin, an HSP90-specific inhibitor, and by expression of a mutant of p50(cdc37) that is unable to recruit HSP90 to the Raf-1 complex. Both agents abrogated the IFN-gamma-dependent induction of c-myc expression in Stat1-null cells.

Basic fibroblast growth factor stimulates cytosolic phospholipase A2, phospholipase C-gamma1 and phospholipase D through distinguishable signaling mechanisms

Fibroblast growth factors (FGFs) stimulate proliferation, differentiation and motility of different cell types. The cellular effects of FGF are transduced by its interaction with any one of four members of a family of high affinity, cell surface FGF receptors (FGFRs) that have autophosphorylating tyrosine kinase activity. Activation of FGFR causes release of various low molecular weight signaling molecules which are required for the pleotropic effects of FGFs. We report here that basic FGF plays critical role in membrane phospholipid hydrolysis in NIH 3T3 cells that are stably transfected with FGFR1. Upon binding to FGFR1, basic FGF stimulates cytosolic form of phospholipase A2 (cPLA2), phospholipase C-gamma1 (PLC-gamma1) and phospholipase D (PLD), the key enzymes for the production of various lipid second messengers, in a tyrosine kinase-dependent manner. In addition to tyrosine phosphorylation, cPLA2 catalytic activation requires serine phosphorylation by p42 mitogen-activated protein (MAP) kinase and possibly pertussis toxin-sensitive G-protein coupling. On the other hand, phosphatidyl inositol 4,5 bisphosphate (PIP2) hydrolysis requires direct phosphorylation at tyrosine residue of the PLC-gamma1 isozyme. The activation of PLD needs direct or indirect receptor tyrosine kinase and protein kinase C (PKC) activities. Additionally, it also requires botulinum toxin C-sensitive Rho-like G-protein activation. All these results suggest that the pleotropic effects of FGF are exerted through its tyrosine kinase receptors and individual effectors are activated via distinguishable signaling mechanisms according to the cell's need.

Consensus-interferon and platelet-derived growth factor adversely regulate proliferation and migration of Kaposi's sarcoma cells by control of c-myc expression

Platelet-derived growth factor-B (PDGF-B) is a potent paracrine-acting mitogen in Kaposi's sarcoma (KS) lesions. Interferon-alpha is widely used for clinical treatment of KS. Here we show that platelet-derived growth factor-B activates proliferation and migration of cultivated AIDS-KS spindle cells whereas interferon-alpha acts as an inhibitor. At the molecular level, these opposite activities of platelet-derived growth factor-B and interferon-alpha converged onto the adverse regulation of the c-myc gene expression. Platelet-derived growth factor-B induced c-myc mRNA and protein synthesis in cultivated AIDS-KS spindle cells whereas interferon-alpha inhibited these processes. Using c-myc-specific phoshothioate antisense oligodeoxynucleotides, we demonstrated that down-regulation of c-myc expression is sufficient to inhibit proliferation and migration of KS spindle cells in vitro. This indicated that c-Myc protein may be an important regulatory molecule of KS spindle cell proliferation and migration. High amounts of the c-Myc protein were detected in the nuclei of KS spindle cells in histological sections of AIDS-KS biopsies. This suggested that the c-myc gene may also regulate proliferation and migration of AIDS-KS spindle cells in vivo. In this case, c-myc may play an important role in the focus of major pathogenic and therapeutic pathways of KS.

Why do so many cancer patients fail to respond to interferon therapy?

Since their first use in the clinic some 25 years ago, interferons (IFNs) have become accepted therapy in a range of cancer forms. However, although in some patients they induce remission, in the great majority they are of no benefit or, at best, lead only to minor improvements. This review considers possible reasons for these failures.

Interferon alfa and gamma inhibit proliferation and collagen synthesis of human Ito cells in culture

During the course of ongoing liver fibrogenesis, Ito cells acquire myofibroblastic features, proliferate, and synthesize increased amounts of extracellular matrix components. Interferon (IFN) alfa and IFN gamma have been shown to elicit antiproliferative and/or antifibrogenic effects in various cell cultures of mesenchymal origin. The aim of this study was to investigate the effects of IFN-alpha and IFN-gamma on cultured human myofibroblastic Ito cells (MFBIC) proliferation and collagen synthesis and secretion. Serum-stimulated incorporation of [3H]-thymidine into DNA of MFBIC was dose-dependently decreased by both cytokines. IFN-alpha (10(4) U/mL) and IFN-gamma (10(3) U/mL) decreased DNA synthesis by 69% and 66%, respectively. Inhibition of cell proliferation was confirmed by cell counting. Similar results were observed when cell growth was stimulated with platelet-derived growth factor (PDGF-BB, PDGF-AA) or transforming growth factor (TGF)-beta 1. Collagen secretion per cell was inhibited by both cytokines, as assessed by [3H]-hydroxyproline incorporation. After a 6-day treatment, IFN-gamma showed a greater potency than IFN-alpha in inhibiting secretion of newly synthetized collagen (41% and 4% of control in the presence of 10(2) U/mL of IFN-gamma and 10(4) U/mL of IFN-alpha, respectively). Both IFN-alpha and IFN-gamma concurrently decreased steady-state expression of type I and type III procollagen messenger RNAs (mRNAs) in quiescent MFBIC. Viability assays ruled out cytotoxic effects of the two molecules. Finally, both IFNs decreased smooth muscle alpha-actin (SM alpha-actin) expression, whether assayed by immunoblotting or by Northern blot analysis. We conclude that IFN-alpha and IFN-gamma inhibit proliferation as well as collagen synthesis in human MFBIC.

Down-regulation of the c-myc proto-oncogene in inhibition of vascular smooth-muscle cell proliferation: a signal for growth arrest?

Vascular smooth muscle (VSM) cell proliferation contributes to the pathogenesis of atherosclerosis, restenosis after angioplasty and vein graft disease. The regulation of genes involved in VSM cell proliferation, particularly by naturally occurring inhibitors, is therefore of some importance. We have investigated the role of the c-myc proto-oncogene in growth arrest of exponentially proliferating rat VSM cells, following mitogen withdrawal, treatment with heparin (50 micrograms/ml), interferon-gamma (IFN-gamma) (100 i.u./ml), or the cyclic nucleotide analogues, 8-bromo-adenosine-3'5'-cyclic monophosphate (8-Br-cAMP; 0.1 mM) and 8-bromoguanosine-3'5'-cyclic monophosphate (8-Br-cGMP; 0.1 mM). Growth arrest was accompanied by down-regulation of c-Myc protein and mRNA following treatment with all inhibitors. Serum withdrawal or IFN-gamma treatment suppressed c-myc expression by more than 50% within 2 h, and this occurred throughout the cell cycle. Platelet-derived growth factor, epidermal growth factor and basic fibroblast growth factor all contributed independently to the maintenance of c-myc expression. Heparin, 8-Br-cAMP or 8-Br-cGMP also suppressed c-myc, but this occurred later, after 24-48 h, and was also observed following arrest by metabolic block. We conclude that c-myc expression is linked to VSM cell growth arrest in response to endogenous regulators and metabolic block. Down-regulation of c-myc expression may thus be an essential part of the arrest programme in VSM cells induced by many pharmacological agents.

Suppression of mitochondrial mRNA levels and mitochondrial function in cells responding to the anticellular action of interferon

A lambda cDNA library prepared from polyadenylated RNA isolated from Daudi cells was differentially screened to isolate cDNAs that recognize mRNA whose levels are reduced following interferon (IFN) treatment. Southern blot and DNA sequence analysis of 20 cDNA clones that were isolated revealed that they represented mitochondrially encoded mRNAs for the following proteins: cytochrome c oxidase subunits II and III, ATPase 6, cytochrome b, and subunit 1 of the NADH dehydrogenase. Northern blot analysis employing these cDNAs and oligonucleotides generated to the remaining mitochondrially encoded mRNAs demonstrated that IFN-alpha treatment of Daudi cells mediates a time-dependent suppression of the level of all of the mitochondrially encoded mRNAs. Study of this IFN-mediated effect reveals that: (i) the suppression of the level of these mRNAs is dependent on protein synthesis, (ii) it can be observed to occur prior to any detectable effect on thymidine incorporation, (iii) the degree of suppression correlates with the sensitivity of the cells to the anticellular action of IFN, and (iv) the suppression of the level of these RNAs appears to result from an effect on the level of transcription rather than on the stability of these mRNAs. A study of the level of cellular respiration in IFN-treated Daudi cells reveals a clear suppression 3 h following IFN treatment.

Deregulated c-fos modulates IgG2b production of B cells mediated by lipopolysaccharide

We have examined effects of the deregulated c-fos protein on IgG2b production of B cells cultured with lipopolysaccharide (LPS) using splenic B cells from a transgenic line carrying the mouse c-fos gene under the control of the interferon alpha/beta (IFN) inducible Mx promoter (Mx-c-fosD). High c-fos expression was induced in the Mx-c-fosD B cells during the first two days of culture. DNA synthesis and IgG2b production were augmented in the culture. When IFN was added together with LPS, the high c-fos expression was prolonged until day 3 of culture. IgG2b production was remarkably suppressed. However, the production was not suppressed by upregulation of c-fos via exogenous IFN on day 4 of culture. These results suggest a regulatory effect of the c-fos protein on the differentiation of B cells to IgG2b producing cells at a distinct period.

Biochemical events accompanying macrophage activation and the inhibition of colony-stimulating factor-1-induced macrophage proliferation by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Agents that can arrest cellular proliferation are now providing insights into mechanisms of growth factor action and how this action may be controlled. It is shown here that the macrophage activating agents tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), and lipopolysaccharide (LPS) can maximally inhibit colony stimulating factor-1 (CSF-1)-induced, murine bone marrow-derived macrophage (BMM) DNA synthesis even when added 8-12 h after the growth factor, a period coinciding with the G1/S-phase border of the BMM cell cycle. This inhibition was independent of autocrine PGE2 production or increased cAMP levels. In order to compare the mode of action of these agents, their effects on a number of other BMM responses in the absence or presence of CSF-1 were examined. All three agents stimulated BMM protein synthesis; TNF alpha and LPS, but not IFN gamma, stimulated BMM Na+/H+ exchange and Na+,K(+)-ATPase activities, as well as c-fos mRNA levels. IFN gamma did not inhibit the CSF-1-induced Na+,K(+)-ATPase activity. TNF alpha and LPS inhibited both CSF-1-stimulated urokinase-type plasminogen activator (u-PA) mRNA levels and u-PA activity in BMM, whereas IFN gamma lowered only the u-PA activity. In contrast, LPS and IFN gamma, but not TNF alpha, inhibited CSF-1-induced BMM c-myc mRNA levels, the lack of effect of TNF alpha dissociating the inhibition of DNA synthesis and decreased c-myc mRNA expression for this cytokine. These results indicate that certain biochemical responses are common to both growth factors and inhibitors of BMM DNA synthesis and that TNF alpha, IFN gamma, and LPS, even though they all have a common action in suppressing DNA synthesis, activate multiple signaling pathways in BMM, only some of which overlap or converge.

A proliferation-related constraint on endogenous and interferon-induced 2-5A synthetase activity in normal and neoplastic Syrian hamster cells

2-5A Synthetase is one of the most extensively characterized enzymes induced by interferon (IFN) and is the central enzyme in a pathway that may be involved in the control of cellular proliferation. We examined the activity of this enzyme in normal diploid Syrian hamster cells (FC13) and their neoplastically transformed derivatives (BP6T); the former cell strain possesses regulated proliferative control, while the latter cell line has escaped from this control. A significant threefold increase in 2-5A synthetase activity was observed in density-arrested versus proliferating FC13 cells, whereas endogenous enzyme activity was uniformly low in BP6T cultures. The increase in enzyme activity in FC13 cultures was not accompanied by the production of IFN at a detectable level, but was parallelled by an increase in the intracellular level of 2',5'-oligoadenylate. IFN treatment resulted in a differential induction of enzyme activity depending on the proliferative state of FC13 cells. After IFN treatment, BP6T cells and subconfluent FC13 cells responded similarly with a fivefold increase in enzyme activity, whereas confluent FC13 cells displayed only a 1.4-fold increase. 2-5A Synthetase enzyme activity reflected steady-state mRNA levels in BP6T and subconfluent FC13 cells. In contrast, a noncoordinate regulation of 2-5A synthetase mRNA expression and enzyme activity was detected in confluent FC13 cells, suggesting that posttranscriptional mechanisms may be involved. The different patterns of endogenous and IFN-induced 2-5A synthetase enzyme activity in FC13 and BP6T cells found in this comparative study may represent an alteration fundamental to the loss of proliferative control in transformed cells.

Lymphocyte-macrophage alveolitis in nonsmoking individuals occupationally exposed to asbestos

A disordered immunologic activity has been observed in humans and animal models of asbestosis and silicosis. To characterize the lung immunologic response following long-term occupational exposure to asbestos, bronchoalveolar lavage (BAL) was performed on 28 nonsmoking individuals. Increased BAL lymphocytes were observed in one third. Lung lymphocytes were predominantly of the CD4+ helper-inducer subtype with increased CD4+/CD8+ ratio and increased surface expression of DR antigen consistent with the activation phenotype. Histologic evaluation of lung tissue from two individuals with lymphocytic-macrophage alveolitis and asbestos exposure revealed an infiltration of alveolar walls with chronic inflammatory mononuclear cells (lymphocytes). Interferon gamma was spontaneously released by BAL cells from 19 (76 percent) of 25 of the individuals with asbestos exposure and only one of ten normal controls. The release of interferon gamma by BAL cells could be further stimulated with concanavalin A and suppressed by cyclosporine. Although asbestosis is characterized by a predominant alveolar macrophage alveolitis, there is a subgroup with lymphocytic alveolitis and activated lymphocytes participating in the inflammatory response, especially in those without respiratory impairment early in the course of the disease process.

Antifibrotic and uveitogenic properties of gamma interferon in the rabbit eye

The feasibility of gamma (gamma)-interferon injection for the treatment of ocular fibrotic conditions was studied in rabbits using recombinant rabbit gamma-interferon and the cell-injection model of tractional detachment. A toxicity study revealed that intravitreal injection of greater than 10(4) units gamma-interferon consistently produced panuveitis. For tractional detachment, 250,000 rabbit dermal fibroblasts were injected intravitreally into 20 eyes; 1 day later, 5 of these eyes received intravitreal injections of 10(4) units gamma-interferon, another 5 were given 10(6) units, and the remaining 10 received balanced salt solution. Slit-lamp examination and fundus photography were performed at regular intervals for 21 days and were graded by a masked observer. The eyes were then enucleated and processed for histology. Doses of 10(4) units gamma-interferon significantly reduced the severity of detachments, but injections of 10(6) units induced panuveitis.

Regulation of bovine bronchial epithelial cell proliferation and proto-oncogene expression by growth factors

The proto-oncogenes are thought to play important roles in the regulation of cellular growth and differentiation. In order to evaluate the role of proto-oncogenes in the regulation of growth of bronchial epithelial cells, we studied steady-state levels of fos, jun, and myc transcripts in response to fetal calf serum, bovine pituitary extract, and insulin. Extensively quiescent populations of bovine bronchial epithelial cells in growth factor-free medium were stimulated to divide by each of these three additives. We observed rapid but transient increases of fos, jun, and myc expression in association with such growth stimulation. There were no changes in tubulin mRNA levels over the same time periods. Other "growth factors" (epidermal growth factor, hydrocortisone, epinephrine, triiodothyronine, and transferrin) were also studied and did not affect either cell growth or expression of fos, jun, or myc. We further examined the effect of transforming growth factor-beta1 (TGF-beta1) on the above stimulatory effects. TGF-beta1 consistently inhibited the growth induced by fetal calf serum, bovine pituitary extract, or insulin and, interestingly, reduced proto-oncogene myc mRNA level without altering that of fos and jun. In conclusion, proto-oncogenes fos, jun, and myc appear to play a role in the regulation of growth response in bovine bronchial epithelial cells. It is also possible that TGF-beta1 exerts its growth inhibitory effect, at least in part, through the processes that involve the regulation of proto-oncogene myc transcription in these cells.

Tumor necrosis factor stimulates ornithine decarboxylase activity in human fibroblasts and tumor target cells

The activity of the polyamine biosynthetic enzyme, ornithine decarboxylase (ODC), has been shown to be rapidly modulated by a variety of growth regulatory molecules. In this report the effect of the growth modulatory peptide, tumor necrosis factor, on ODC activity was examined on two cell lines which express equivalent TNF binding properties, but differ in their growth response when exposed to this factor. TNF treatment of WI-38 fibroblasts stimulated both their growth and induced ODC activity 5-10-fold when measured 6-24 h after TNF incubation. TNF induced cytotoxicity in ME-180 cervical carcinoma cells and, interestingly, stimulated both ODC activity (3-6-fold) and putrescine accumulation when measured prior to the onset of cytotoxicity. Induction of ODC was TNF concentration-dependent and paralleled the concentration-dependency for cytotoxicity. Based upon studies with cycloheximide, de novo protein biosynthesis was required for TNF-mediated ODC induction in ME-180 cells. The effects of other growth inhibitory peptides and growth factors were analyzed for their combined effect on ODC activity in TNF-treated or untreated ME-180 cells. Interferon gamma treatment had no significant effect on basal ODC activity but inhibited TNF-mediated ODC induction by approximately 50%. EGF treatment resulted in a potent stimulation of ODC activity which was not affected by TNF pre-treatment or coadministration on ME-180 cells. These results suggest that TNF has properties which are similar to those of a growth factor and distinct from those of other growth inhibitory peptides. The early growth factor-like actions of TNF occur on both normal fibroblasts and some tumor cells and evidence suggests that these effects are antagonistic to the antiproliferative effects of TNF.

Role of cyclic AMP and polypeptide growth regulators in growth inhibition by interferon in PC-3 cells

Participation of growth factors and intracellular cAMP in direct antiproliferative action of interferon alpha (IFN-alpha) was investigated in PC-3 human prostate carcinoma cell line. IFN-alpha inhibited proliferation of PC-3 cells in a dose-dependent manner in vitro, and the effect was reversible. Fibroblast growth factor, epidermal growth factor and platelet-derived growth factor, when added to the culture medium, showed no effect on growth of PC-3 cells in presence or absence of IFN-alpha. Transforming growth factor beta (TGF-beta) significantly inhibited PC-3 cell growth, and the effect was additived to that of IFN-alpha. TGF-beta content in conditioned medium of PC-3 cells was not affected by treatment with IFN-alpha. On the other hand, IFN-alpha increased intracellular cAMP concentration about 20-fold. Dibutyryl cAMP and reagents which elevated intracellular cAMP level also inhibited PC-3 cell growth. These indicated that direct antiproliferative effect of IFN-alpha on PC-3 cells was at least partly mediated by cAMP, and that neither growth factors nor a growth inhibitor participated in the action of IFN-alpha.

Interferon selectively inhibits the expression of mitochondrial genes: a novel pathway for interferon-mediated responses

As an approach to identifying genes involved in physiological actions of interferons we used differential probes to screen a cDNA library from mouse L-929 cells treated with interferon alpha/beta. We identified two negatively regulated mRNA species which have been examined by analysis of the corresponding mRNAs and by DNA sequencing. Comparison with the GenBank database showed that these cDNA clones corresponded to mitochondrially encoded genes for cytochrome b and subunit I of cytochrome c oxidase. A further cDNA encompassing three mitochondrial genes was used as a probe to show that a third mRNA, NADH dehydrogenase subunit 5, was also down-regulated by interferon while a fourth, NADH dehydrogenase subunit 6, was unaffected. Expression of cytochrome b was also inhibited in mouse NIH 3T3 cells treated with interferon alpha/beta and in human Daudi lymphoblastoid cells treated with interferon alpha. The ability of interferon to reduce mitochondrial mRNA levels could be blocked by cycloheximide suggesting that these effects are mediated by an interferon-responsive nuclear gene which encodes a product capable of regulating mitochondrial gene expression. Analysis of proteins synthesized in the presence of emetine, a specific inhibitor of cytoplasmic translation, showed that the synthesis of several mitochondrial translation products, including cytochrome b, was reduced after treatment with interferon. Our results reveal a novel effect of interferon on cellular physiology which could have important consequences for understanding the effects of interferons as well as suggesting new mechanisms for the regulation of mitochondrial biogenesis and function.

Heparin inhibits c-fos and c-myc mRNA expression in vascular smooth muscle cells

Heparin is a potent inhibitor of vascular smooth muscle cell (VSMC) growth. In this paper we show that heparin suppressed the induction of c-fos and c-myc mRNA in rat and calf VSMC. This effect of heparin is closely associated with its growth-inhibitory activity, as shown by isolating and characterizing a strain of rat VSMC that was resistant to heparin's antiproliferative effect; heparin did not suppress c-fos mRNA induction in these cells. Moreover, neither a nonantiproliferative heparin fragment or other glycosaminoglycans that lack growth-inhibitory activity repressed c-fos or c-myc mRNA levels. The effect of heparin on c-fos mRNA induction was selective for specific mitogens, as heparin inhibited c-fos mRNA induction in phorbol 12-myristate 13-acetate (TPA) stimulated but not epidermal growth factor (EGF) stimulated VSMC. The effect of heparin on gene expression is independent of ongoing protein synthesis, and inhibition of c-fos mRNA is at the transcriptional level. These results suggest that heparin may selectively inhibit a protein kinase C-dependent pathway for protooncogene induction and that this may be one mechanism used by heparin to inhibit cell proliferation.

Posttranscriptional changes in growth factor-inducible gene regulation caused by antiproliferative interferons

Growth factors stimulate quiescent fibroblasts to progress through G0/G1, in part by inducing the expression of genes whose products are necessary or permissive for cell proliferation. Interferons, by contrast, inhibit progress through G0/G1 by mechanisms that are poorly understood. We show, in BALB/c murine 3T3 fibroblasts (A31 cells), that alpha/beta-interferon (IFN) had no effect the growth factor-dependent induction of several messenger ribonucleic acids (mRNAs), including those encoding ornithine decarboxylase (odc), fibronectin and the c-fos and c-myc protooncogenes. However, IFN caused an abnormal accumulation of fibronectin and c-myc mRNA on polysomes and markedly increased the stability of c-myc mRNA. Moreover, despite high, induced levels of mRNA, IFN inhibited the serum-stimulated rise in odc enzyme activity and the increased rate of fibronectin protein synthesis. By contrast, IFN had no effect on c-fos protein synthesis, nor did it affect the synthesis of most, but not all, proteins detectable by two-dimensional gel electrophoresis. The data suggest IFN inhibits proliferation by suppressing the expression of a subset of growth factor-inducible genes through a selective, posttranscriptional mechanism.

Interferon alpha/beta modulation of growth-factor-stimulated mitogenicity in AKR-2B fibroblasts

Growth factor-stimulated mitogenicity in mouse embryo-derived AKR-2B cells was inhibited in a dose-dependent fashion by a mixture of alpha and beta mouse interferons (IFN). A 60% decrease in epidermal growth factor (EGF) and insulin-stimulated DNA synthesis was observed with 10 kU/ml IFN, and half-maximal inhibition was seen at 1 kU/ml. Likewise, the mitogenic effect of 5% fetal bovine serum (FBS) was inhibited by 60% with 10 kU/ml IFN and by 38% with 1 kU/ml IFN. IFN inhibition of DNA synthesis was paralleled by a decrease in monolayer growth of AKR-2B cells by 60% on the 3rd day of culture and by 40% on the 6th day of culture. Soft agar growth of two AKR-2B derived lines, AKR-MCA and AKR-2B (clone 84A), was also inhibited significantly with the addition of 1-10 kU/ml of IFN. The effect of IFN on EGF receptors was also examined. Treatment of AKR-2B cells with 10 kU/ml IFN resulted in a 35% decrease in EGF binding to cell surface receptors. The reduced binding of EGF to cells treated with IFN was due to a loss of EGF receptors as determined by Scatchard analysis. IFN treatment of AKR-2B cells neither altered the affinity of the EGF receptor for its ligand nor affected receptor internalization. Nuclear transcription and actinomycin D decay analysis indicated that within 2 hr, IFN reduced c-myc messenger RNA levels at the level of transcription with no affect on message decay.

Effect of human interferons on morphological differentiation and suppression of N-myc gene expression in human neuroblastoma cells

The activity of human interferons (HuIFNs) to induce morphological changes and the suppression of N-myc gene expression on human neuroblastoma cells (GOTO and KP-N-RT) was evaluated. Morphological differentiation, characterized as the extension and bifurcation of neurites, the formation of multinucleated giant cells and the formation of neurite networks, was induced by treatment with recombinant HuIFN-gamma (rHuIFN-gamma) and also with natural HuIFN-gamma on human neuroblastoma cells (GOTO and KP-N-RT). But recombinant HuIFN-alpha A and recombinant HuIFN-beta did not induce any changes. The rHuIFN-beta and rHuIFN-gamma inhibited the growth of GOTO and KP-N-RT cells more strongly than the rHuIFN-alpha A did. The expression of N-myc gene was suppressed in GOTO cells treated with rHuIFN-gamma. The suppressive effect of rHuIFN-gamma was dependent on the duration of the treatment. However, rHuIFN-alpha A and rHuIFN-beta did not suppress N-myc gene expression. Moreover, both morphological differentiation and the suppressive effect on N-myc gene expression by rHuIFN-gamma were inhibited in the presence of cycloheximide. These results suggest that the morphological changes and N-myc gene expression in neuroblastoma cells are closely related. Furthermore, this decreased N-myc gene expression during the morphological differentiation may be related to the proteins induced by HuIFN-gamma.

The cellular receptor of the alpha-beta interferons

This is a selective review of recent trends in research on the cellular receptor for the alpha-beta interferons. It deals mainly with work published in the last three years (1985-88), and therefore mainly with receptors for the human interferons. The binding characteristics of several human alpha interferons are examined, and the importance of in vitro experimental models for establishing the relationship between receptor binding and the cellular response is emphasized.

Interferon inhibition of bombesin-stimulated mitogenesis in Swiss 3T3 cells occurs without blocking c-fos and c-myc expression

We have investigated the effect of murine interferon-beta on the growth of quiescent Swiss 3T3 cells stimulated by the amphibian tetradecapeptide mitogen bombesin. We found that IFN inhibited mitogenesis in bombesin-stimulated cells in a dose-dependent manner. In addition, bombesin, in common with platelet-derived growth factor (PDGF), was able to reverse the inhibitory effects of IFN in cells stimulated by epidermal growth factor (EGF) and insulin, which elicit a mitogenic response via a distinct signaling pathway. The observation that IFN was as effective in inhibiting DNA synthesis when added 48 h before or as late as 3 h after the mitogen, indicated that a block in one of the early regulatory signals was not essential for the anti-growth effects. Indeed, IFN did not inhibit the increased expression of c-fos and c-myc mRNA induced by bombesin in quiescent Swiss 3T3 cells. The combined data indicate that events occurring late in G1 are more likely targets for IFN action in Swiss 3T3 cells.

Selective inhibition of growth-related gene expression in murine keratinocytes by transforming growth factor beta

Transforming growth factor beta (TGF beta) is a potent inhibitor of epithelial cell proliferation. A nontumorigenic epidermal growth factor (EGF)-dependent epithelial cell line, BALB/MK, is reversibly growth arrested by TGF beta. TGF beta will also abrogate EGF-stimulated mitogenesis of quiescent BALB/MK cells. Increased levels of calcium (greater than 1.0 mM) will induce differentiation in BALB/MK cells; in contrast, TGF beta-mediated growth inhibition does not result in induction of terminal differentiation. In the present study, the effects of TGF beta and calcium on growth factor-inducible gene expression were examined. TGF beta markedly decreased c-myc and KC gene expression in rapidly growing BALB/MK cells and reduced the EGF induction of c-myc and KC in a quiescent population of cells. TGF beta exerted its control over c-myc expression at a posttranscriptional level, and this inhibitory effect was dependent on protein synthesis. TGF beta had no effect on c-fos gene expression, whereas 1.5 mM calcium attenuated EGF-induced c-fos expression in quiescent cells. Expression of beta-actin, however, was slightly increased in both rapidly growing and EGF-restimulated quiescent BALB/MK cells treated with TGF beta. Thus, in this system, TGF beta selectively reduced expression of certain genes associated with cell proliferation (c-myc and KC), and at least part of the TGF beta effect was at a posttranscriptional level.

Recessive genetic deregulation abrogates c-myc suppression by interferon and is implicated in oncogenesis

In a previous study we demonstrated that many hematopoietic tumor cells are resistant to the inhibitory effects that interferon exerts on c-myc mRNA expression without losing other receptor-mediated intracellular responses (M. Einat, D. Resnitzky, and A. Kimchi, Nature [London] 313:597-600). We report here that this partial resistance was overridden in two independent stable somatic cell hybrids prepared by fusion between sensitive and resistant cells. The c-myc mRNA transcribed from the active allele of the resistant parent cell was reduced by interferon within the context of the cell hybrid. It was therefore concluded that changes in the cis-acting sequences of c-myc were not involved in this type of relaxed regulation and that resistance resulted rather from inactivation or loss of postreceptor elements which operate in trans. The growth-stimulating effect that this genetic deregulation might have on cells was tested in experimental systems of cell differentiation in which an autocrine interferon is produced. For that purpose we isolated variant clones of M1 myeloid cells which were partially resistant to alpha and beta interferons and tested their growth behavior during in vitro-induced differentiation. The resistant clones displayed higher proliferative activity on days 2 and 3 of differentiation than did the sensitive clones, which stopped proliferating. The loss of c-myc responses to the self-produced interferon disrupted the normal cessation of growth during differentiation and therefore might lead cells along the pathway of neoplasia.

Effect on platelet-derived growth factor-induced mitogenesis of double-stranded RNA: evidence for an autocrine growth inhibition mediated by interferon-beta

Stimulation of normal human foreskin fibroblasts with platelet-derived growth factor (PDGF) was inhibited by the addition of the synthetic double-stranded RNA polyinosinic-polycytidylic acid (poly-I:C) as measured by incorporation of 3H-thymidine (3H-TdR). Single-stranded polycytidylic or polyinosinic acid had no effect. Double-stranded RNA is an inducer of interferon-beta (IFN-beta) in fibroblasts. On the mRNA level, an expression of IFN-beta 2 but not of IFN-beta 1 was seen after addition of PDGF and/or poly-I:C. The inhibition of PDGF-induced mitogenesis was completely blocked by an antiserum to IFN-beta. Poly-I:C did not interfere with PDGF binding to its receptor, nor did it block protein synthesis, indicating that the inhibition is not due to a nonspecific toxic effect of the double-stranded RNA but rather is mediated by IFN-beta. The present study implies that the IFN-beta system in fibroblasts is a very potent autocrine inhibitory pathway.

Selective inhibition of growth-related gene expression in murine keratinocytes by transforming growth factor beta

Transforming growth factor beta (TGF beta) is a potent inhibitor of epithelial cell proliferation. A nontumorigenic epidermal growth factor (EGF)-dependent epithelial cell line, BALB/MK, is reversibly growth arrested by TGF beta. TGF beta will also abrogate EGF-stimulated mitogenesis of quiescent BALB/MK cells. Increased levels of calcium (greater than 1.0 mM) will induce differentiation in BALB/MK cells; in contrast, TGF beta-mediated growth inhibition does not result in induction of terminal differentiation. In the present study, the effects of TGF beta and calcium on growth factor-inducible gene expression were examined. TGF beta markedly decreased c-myc and KC gene expression in rapidly growing BALB/MK cells and reduced the EGF induction of c-myc and KC in a quiescent population of cells. TGF beta exerted its control over c-myc expression at a posttranscriptional level, and this inhibitory effect was dependent on protein synthesis. TGF beta had no effect on c-fos gene expression, whereas 1.5 mM calcium attenuated EGF-induced c-fos expression in quiescent cells. Expression of beta-actin, however, was slightly increased in both rapidly growing and EGF-restimulated quiescent BALB/MK cells treated with TGF beta. Thus, in this system, TGF beta selectively reduced expression of certain genes associated with cell proliferation (c-myc and KC), and at least part of the TGF beta effect was at a posttranscriptional level.

Recessive genetic deregulation abrogates c-myc suppression by interferon and is implicated in oncogenesis

In a previous study we demonstrated that many hematopoietic tumor cells are resistant to the inhibitory effects that interferon exerts on c-myc mRNA expression without losing other receptor-mediated intracellular responses (M. Einat, D. Resnitzky, and A. Kimchi, Nature [London] 313:597-600). We report here that this partial resistance was overridden in two independent stable somatic cell hybrids prepared by fusion between sensitive and resistant cells. The c-myc mRNA transcribed from the active allele of the resistant parent cell was reduced by interferon within the context of the cell hybrid. It was therefore concluded that changes in the cis-acting sequences of c-myc were not involved in this type of relaxed regulation and that resistance resulted rather from inactivation or loss of postreceptor elements which operate in trans. The growth-stimulating effect that this genetic deregulation might have on cells was tested in experimental systems of cell differentiation in which an autocrine interferon is produced. For that purpose we isolated variant clones of M1 myeloid cells which were partially resistant to alpha and beta interferons and tested their growth behavior during in vitro-induced differentiation. The resistant clones displayed higher proliferative activity on days 2 and 3 of differentiation than did the sensitive clones, which stopped proliferating. The loss of c-myc responses to the self-produced interferon disrupted the normal cessation of growth during differentiation and therefore might lead cells along the pathway of neoplasia.

Modulation of nuclear proto-oncogene expression and cellular growth in myeloid leukemic cells by human interferon alpha

To address the mechanisms that regulate expression of specific growth-related nuclear proto-oncogenes, the transcript levels of the c-fos, c-myc, (2'5')-oligoadenylate synthetase, IFN-alpha 1, and IFN-beta 1 genes have been measured in the human leukemic cell lines KG-1, U937, and HL-60 following growth stimulation by serum, induction of differentiation by tumor-promoting agents, and/or treatment of cells with exogenously supplied alpha interferon (rIFN-alpha 2). Production of fos and myc RNA was measured by S1 mapping, using fos DNA probes which identified either primary unspliced transcripts or steady-state-spliced mRNA levels, and using a myc probe which spanned the two major c-myc start sites, P1 and P2. Pretreatment of a quiescent KG-1 cell population with IFN for 18 hours before serum addition decreased the stimulation of both fos and myc RNA production. In HL-60 and U937 cells, IFN pretreatment had no inhibitory effect on serum-induced fos or myc transcription; however, in U937, rIFN-alpha 2 treatment alone stimulated fos mRNA 11-fold. Expression of 2'5'oligoadenylate synthetase was induced in IFN-treated cultures but not in cells stimulated with serum alone. No serum-induced IFN-alpha 1 or IFN-beta 1 gene expression was observed in KG-1 or U937 cells. These results demonstrate that exogenous rIFN-alpha 2 treatment of quiescent KG-1 cells can antagonize the effect of growth factors by altering expression of nuclear proto-oncogenes, but in general growth inhibition is not obligatorily coupled to inhibition of proto-oncogene transcription.

The biology of interferon actions

The interferons comprise a group of proteins which were first identified by their ability to protect cells against virus infections. They are synthesized and secreted by a variety of cell types in response to various inducers and exert their effects in vivo by interaction with specific cellular receptors. In this sense the interferons are analogous to polypeptide hormones. In recent years it has become clear that the interferons are capable of influencing cellular physiology and behavior in a number of ways. Their effects include antiviral actions, inhibition of cell growth and proliferation, regulation of the expression of specific genes, modulation of cell differentiation and activation of various cell types in the immune system. This review aims to summarize the current state of biology of interferon actions with special emphasis on the hemopoetic system.

Absence of TGF-beta receptors and growth inhibitory responses in retinoblastoma cells

The responses of retinoblastoma tumor cells and normal retinal cells to various growth inhibitory factors were examined. Whereas fetal retinal cells were highly sensitive to the antimitogenic effects of transforming growth factor beta 1 (TGF-beta 1), retinoblastoma tumor cell lines were all resistant to this factor. Binding assays and affinity labeling of these cells with radioiodinated TGF-beta 1 revealed that the cells did not have TGF-beta receptors. The retinoblastoma cells lacked the three affinity-labeled proteins of 65, 95, and 300 kilodaltons typically seen in human cell lines and thus differed from normal retinal cells and from other types of neuroectodermal tumors that display the normal pattern of receptors. Loss of TGF-beta receptors, which is a rare event among tumor cells, may represent one mechanism through which these cells escape from negative control and form retinoblastomas.

Effect of interferon on secretion of proteins by various murine cell lines

The interferons (IFNs) have been shown to be antagonistic to the growth stimulatory effects of mitogens on cultured cells. A report of the interactions of IFN-beta and platelet-derived growth factor on BALB/c-3T3 mouse cells established that IFN itself induced the secretion of a limited number of proteins from this cell line. The present work was undertaken to determine if other murine cell lines treated with homologous IFN-beta also secreted new or additional protein(s) in response to this agent and if this response correlated with other phenotypic properties of the cells. The cell lines examined included L929 cells and two derivatives of this line (GM347 and WDIFN), CAK-TK-, Swiss-3T3, and BALB/c-3T3. Each line was exposed to [35S]methionine in the absence and in the presence of IFN-beta, the supernatant fluids collected, and the radioactive, secreted proteins examined by fluorography after electrophoresis through SDS-containing polyacrylamide gels. Two cell lines (GM347 and Swiss-3T3) did not appear to secrete new or additional proteins after IFN treatment. However, four lines (L929, WDIFN, CAK-TK-, and BALB/c-3T3) did secrete new or additional proteins in response to IFN. Thus IFN-induced secretion of protein appeared to be a common but not universal phenomenon. In addition, although the number and apparent size(s) of the IFN-induced, secreted proteins were different in these various lines, one protein (Mr = 89-90,000) appeared to be secreted by each of them. In this respect it was unique. Moreover the IFN-induced secretion of protein did not appear to correlate with the antiviral or antiproliferative effects of IFN.

Recombinant interferon-gamma inhibits the mitogenic effect of platelet-derived growth factor at a level distal to the growth factor receptor

Highly purified preparations of recombinant human interferons (rIFNs)-alpha A, -beta, and -gamma all inhibited platelet-derived growth factor (PDGF)-induced DNA synthesis in normal human dermal fibroblasts, as monitored by incorporation of [3H]-thymidine into trichloroacetic acid (TCA)-insoluble material. rIFN-gamma was the most potent, since it blocked the PDGF response by 50% at about 10 U/ml or 0.3 ng/ml, whereas with rIFN-alpha A and rIFN-beta 4000 U/ml and 600 U/ml, respectively (10 ng/ml in both cases), were required to achieve the same effect. There was a close parallelism between the ability of these rIFNs to inhibit PDGF mitogenic activity and their capacity to inhibit cell proliferation in serum-containing medium. None of the rIFNs inhibited specific binding of 125I-PDGF to fibroblasts, and none interfered with receptor internalization. The mechanism of action of rIFN-gamma was analyzed further. rIFN-gamma did not inhibit uptake of [3H]-thymidine into these cells. However, it shifted if the time point of initiation of DNA synthesis from about 14 h after stimulation with PDGF to about 18 to 21 h and decreased significantly the rate of the DNA synthesis. rIFN-gamma could be added up to 6 h following stimulation with PDGF with no loss of its inhibitory effect. rIFN-gamma also blocked the mitogenic activity of epidermal growth factor and basic fibroblast growth factor. Taken together these results implicate that rIFN-gamma exerts its antimitogenic effect by inhibiting a process that occurs late in the PDGF signaling pathway and onto which the activity pathways of other mitogens converge. In view of the important role PDGF may play in wound-healing and in the pathogenesis of the proliferative lesions of arteriosclerosis, these data point to a possible role IFN-gamma may play as a regulator of these processes in vivo.

Transcriptional stimulation by CaPO4-DNA precipitates

Genes in human chromosomes that normally require induction by alpha-interferon are activated after calcium phosphate (CaPO4) transfection, but not after DEAE-dextran transfection. The c-fos gene and genes stimulated by gamma-interferon also are affected by CaPO4-DNA precipitates, but the calcium ionophore A23187 stimulates only c-fos among this group. These results suggest caution not only in choosing gene transfer methods, but also in interpreting experiments aimed at understanding the role of second messengers in gene activation.

Induction of c-fos gene expression by interferons

We show that murine interferons (IFNs)-alpha/beta and -gamma induce expression of the protooncogene c-fos in F9 embryonal carcinoma cells, NIH-3T3 cells, and other tissue culture cells. The induction of c-fos mRNA is rapid and transient in that the mRNA appears within 15 min and disappears by 2 h following IFN treatment. The protein synthesis inhibitor cycloheximide (CHX) also stimulates rapid but more stable expression of c-fos mRNA in these cells. Treatment of these cells with a combination of CHX and IFNs results in superinduction of c-fos mRNA. In contrast, IFNs do not affect c-myc mRNA expression in these cells. These results suggest that c-fos gene expression plays a role in signal transduction following binding of IFNs to the receptors.

Identification of a signal for nuclear targeting in platelet-derived-growth-factor-related molecules

The v-vis gene encodes p28sis, the transforming protein of simian sarcoma virus. This gene resulted from a fusion of the env gene of simian sarcoma-associated virus and the woolly monkey gene for the B chain of platelet-derived growth factor (PDGF). Previous work has shown that the v-sis gene product undergoes signal sequence cleavage, glycosylation, dimerization, and proteolytic processing to yield a secreted form of the protein. It transport across the endoplasmic reticulum is blocked by the introduction of a charged amino acid residue within the signal sequence, the protein does not dimerize, is not secreted, and is no longer transforming as assayed by focus-forming ability in NIH 3T3 cells. Instead, this mutant protein localizes to the nucleus as demonstrated by both indirect immunofluorescence and cell fractionation. Using a series of deletion mutations, we delimited an amino acid sequence within this protein which is responsible for nuclear localization. This region is completely conserved in the predicted human c-sis protein, although it lies outside of regions required for transformation by the v-sis gene product. This nuclear transport signal is contained within amino acid residues 237 to 255, RVTIRTVRVRRPPKGKHRK. An amino acid sequence containing these residues is capable of directing cytoplasmic v-sis mutant proteins to the nucleus. This sequence is also capable of directing less efficient nuclear transport of a normally cytoplasmic protein, pyruvate kinase. Pulse-chase experiments indicate that the half-lives of nuclear and cytoplasmic v-sis mutant proteins are approximately 35 min. Using the heat-inducible hsp70 promoter from Drosophila melanogaster, we showed that the nuclear v-sis protein accumulates in the nucleus within 30 min of induction. The identification of a nuclear transport signal in the v-sis gene product raises interesting questions regarding the possibility of some function for PDGF or PDGF-related molecules in the nucleus.