Physiological expression of the 2',5'-oligoadenylate synthetase gene in mouse intestine

Ribonuclear inclusions in skeletal muscle in myotonic dystrophy types 1 and 2

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are caused by genomic expansions of CTG or CCTG repeats. When transcribed, these mutations give rise to repeat expansion RNAs that form nuclear inclusions and compromise the function of myonuclei. Here, we have used in situ hybridization and immunofluorescence to compare DM1 and DM2 and search for proteins that associate with the RNA nuclear (ribonuclear) inclusions. Although muscle disease is generally more severe in DM1, the ribonuclear inclusions were 8- to 13-fold more intense in DM2, implying greater amounts of repeat expansion RNA. Expression of repeat expansion RNA in myoblasts has been implicated in the pathogenesis of congenital DM1. However, we found that repeat expansion RNA is also expressed in myoblasts in DM2, a disorder that has not been associated with a congenital phenotype. Of 10 putative CUG binding proteins tested for colocalization with mutant RNA, only proteins in the muscleblind family were recruited into ribonuclear inclusions. Previous studies have shown activation of the protein kinase, PKR, by expanded CUG repeats in vitro. However, breeding experiments utilizing PKR knockout mice indicate that this kinase is not required for disease pathogenesis in a transgenic mouse model of DM1. We conclude that ribonuclear inclusions are a key feature of the muscle pathology in DM and that sequestration of muscleblind proteins may have a direct role in the disease process.

High Level Activity of 2', 5'-Oligoadenylate Synthetase in Dog Serum

Most animal cells that are exposed to interferon (IFN) experience an increase in the activity of 2', 5'-oligoadenylate synthetase (OAS), which is an important effector of IFN's antiviral action. OAS activity has been widely used in clinical chemistry as an indicator of IFN activity. In this study, we found that OAS activity in canine serum is 46.0 +/- 40.4 nmol/dl/hr, which is 10- to 100-fold higher than in other animals such as the cat (1.9 +/- 2.1), rabbit (4.0 +/- 1.1), and guinea pig (0.3 +/- 0.6). The canine OAS protein was detected by Western blotting using a 68M-10 monoclonal anti-murine OAS antibody, and was found to be composed of at least three distinct molecular species of p40 class OAS. Among these, the 40 and 42 kDa components were determined to be the major species in serum and fibroblast cell lines, respectively.

Relationship between 24-hour rhythm in antiviral effect of interferon-beta and interferon-alpha/beta receptor expression in mice

The influence of interferon-beta (IFN-beta) dosing time on antiviral activity was investigated in ICR male mice under light-dark cycle conditions (lights on at 07:00, off at 19:00) with food and water available ad libitum. There was a significant dosing time-dependent change in 2',5'-oligoadenylate synthetase (2',5'-OAS) activities, as an index of antiviral activity, in liver at 12 h after IFN-beta (15 MIU/kg, i.v.) injection. IFN-beta-induced 2',5'-OAS activity was more potent after the drug injection during the late dark phase. The higher antiviral effect of IFN-beta was observed when the interferon-alpha/beta receptor (IFNAR) expression in the liver increased, and the lower effect was observed when its expression decreased. IFN-beta-induced fever was more serious after IFN-beta injection from the late dark phase to the early light phase. A significant dosing time-dependent change was demonstrated for plasma IFN-beta concentrations, which showed a higher level during the light phase and a lower level during the dark phase. The dosing time-dependent change of plasma IFN-beta concentrations was not associated with that of the antiviral effect or fever induced by IFN-beta. These results suggest that selecting the most suitable dosing time of IFN-beta, associated with the 24-h rhythm of IFNAR expression in the liver, may be important to increase effectively the antiviral activity of the drug in experimental and clinical situations.

Liver targeting of human interferon-beta with pullulan based on metal coordination

Although interferon (IFN)-beta is widely used for the elimination of hepatitis C virus in patients with chronic liver disease, its clinical efficacy is unsatisfactory. Targeting IFN-beta to the liver might enhance its efficacy without increasing its side effects. The objective of the present study was to target IFN-beta to the liver to enhance its biological activity and reduce its side effects. A chelating residue, diethylenetriaminepentaacetic acid (DTPA), was introduced to pullulan, a water-soluble polysaccharide with a high affinity to the liver (DTPA-pullulan) and natural human IFN-beta was coordinately conjugated with the DTPA-pullulan by mixing in an aqueous solution containing zinc ions (Zn(2+)). Intravenous injection of the IFN-beta-DTPA-pullulan conjugate with Zn(2+) coordination into mice enhanced induction of an antiviral enzyme, 2',5'-oligoadenylate synthetase (2-5AS), specifically in the liver to a significantly greater extent than free natural IFN-beta. The enhanced 2-5AS level in the liver depended on the molar mixing ratio of IFN-beta, DTPA residue of the DTPA-pullulan, and Zn(2+). Moreover, the duration of the liver 2-5AS induction by the IFN-beta-DTPA-pullulan conjugate was longer than that by free natural IFN-beta. Thus, human IFN-beta-DTPA-pullulan conjugate appears to be applicable for clinical use, which is promising for treatment of patients with chronic hepatitis C.

Genomic structure of the mouse 2',5'-oligoadenylate synthetase gene family

2',5'-Oligoadenylate synthetase (2-5OAS) is one of the interferon (IFN)-induced proteins and mediates the antiviral action of IFN. In human, three classes of 2-5OAS genes (OAS1, OAS2, and OAS3) and one OAS-like gene (OASL) are reported. In mice, however, OAS genes corresponding to human OAS2 and OAS3 have not been identified. In this report, we identified six novel OAS family genes in mice by screening mouse genomic library and expressed sequence tag (EST) database. These genes include three homologs of the human OAS1 and each homologous gene of the human OAS2, OAS3, and OASL, respectively. Each gene displays 52%-65% amino acid identity to the corresponding human homologs. Nine 2-5OAS genes, except for two OASL genes, locate within the 210-kb genomic region and form a cluster. Each novel 2-5OAS gene showed a characteristic expression pattern among different tissues, and all of them were induced by polyinosinic-polycytidylic acid. Biochemical analyses using recombinant proteins produced in Escherichia coli showed that all the novel mouse 2-5OAS molecules have double-stranded RNA (dsRNA) binding ability, but they do not have 2-5OAS activity except for the OAS2 and OAS3 mouse homologs. These results show that there are at least 11 OAS genes, which are classified into four groups, in the mouse.

Cloning of a novel 2',5'-oligoadenylate synthetase-like molecule, Oasl5 in mice

The 2',5'-oligoadenylate synthetase (2-5OAS) is a enzyme that catalyzes synthesis of 2',5'-oligoadenylates (2-5A) in a dsRNA-dependent manner, and known as a major component of the IFN-induced host defense mechanisms against microbial infections. Here, we report the presence of a novel 2-5OAS-like molecule, termed Oasl5, in mice. The size of Oasl5 cDNA was about 2 kb and encoded a protein consisting of 362 aa. The amino acid sequence showed 76% similarity to the mouse 2-5OAS, however, several motifs being important for the enzyme activity were not conserved. The Oasl5 mRNA was most significantly expressed in the brain, and relatively weak expression was found in other organs such as the spleen, kidney, ovary and testis. It was also expressed in embryonic stem (ES) cells. The Oasl5 mRNA expression in ES cells was elevated 5-fold after treatment with IFN and about 2-fold in the brain when stimulated with IFN inducer, polyinosinic-polycytidylic acid (poly[I:C]). In situ hybridization analysis revealed that Oasl5 is expressed in neurons in the central nervous system in adult mice. When Oasl5 was expressed in E. coli, it yielded 42 kDa protein that binds to dsRNA, but it did not show oligoadenylate synthetase activity. These findings suggest a novel function of Oasl5, which are independent of oligoadenylate synthetase activity, in the brain and developing embryos.

2',5'-oligoadenylate synthetase gene in chicken: gene structure, distribution of alleles and their expression

We have cloned the gene for chicken 2',5'-oligoadenylate synthetase (ChOAS) by the method of polymerase chain reaction with use of ChOAS cDNA sequence. The ChOAS gene is composed of five introns and six exons containing all of the sequence of the ChOAS cDNA from the start to the stop codon. The first five exons of ChOAS gene which encode the OAS catalytic domain have a similar structure to HuOAS1 gene including the exon-intron boundaries. However, the length of introns of ChOAS gene is only 1/7 of those of HuOAS1 gene. The sixth exon of the ChOAS gene encodes the ubiquitin-like (UbL) domain of two consecutive sequence (UbL1 and UbL2) homologous to ubiquitin. ChOAS encoded in a single copy gene has at least two alleles, OAS(*)A and OAS(*)B. The differences between these two alleles are in the sixth exon of the gene; a 96-nucleotide sequence in the UbL1 portion of OAS(*)A is deleted from OAS(*)B. No OAS(*)B gene was detected in nine lines of chickens tested other than Leghorns. Almost the same levels of ChOAS-A and -B proteins induced physiologically in erythrocytes were detected in infant chickens (2-week-old), but in grown-up chickens (6-month-old) the level of erythrocyte OAS-B was markedly reduced in most of B/B chickens. Thus, the UbL domain of ChOAS is responsible for the maintenance of the OAS level in the tissue.

Effects of specific mutations in active site motifs of 2',5'-oligoadenylate synthetase on enzymatic activity

2',5'-Oligoadenylate synthetase (2',5'-OAS) is a double-stranded RNA-dependent nucleotidyl-transferase induced by interferon (IFN). Several 2',5'-OAS cDNA have been cloned from human, pig, rat, mouse, and chicken. A P-loop motif followed by an Asp-containing sequence (referred to as D-box) and a region with a high content of Lys and Arg (KR-rich region) are well conserved in 2',5'-OAS. The sequence 196DFLKQR201 of 40-kDa human 2',5'-OAS, to which 8-azido-ATP binds (N. Kon and R.J. Suhadolnik, J. Biol. Chem. 271, 19983-19990, 1996), is included in the KR-rich region. We introduced several site-directed mutations into these active motifs of 42-kDa murine 2',5'-OAS. Each mutant enzyme studied bound to poly(I):poly(C) to the same extent as wild-type enzyme. Both K67R, a P-loop mutant, and K200R, a KR-rich region mutant, exhibited a reduced but considerable rate of enzymatic activities. The activity of the double mutant K67R/K200R was about 10% of the wild type. On the other hand, the activities of both K67M and K200M were not more than 2% of the wild-type enzyme, and no activity was detected in another P-loop mutant, G62A/G63A. The binding of Mg2+ to a D-box mutant D76N/D78N was markedly reduced, and only a very low level of enzymatic activity was detected in this mutant. These results demonstrate that the P-loop, the D-box that binds Mg2+, and the KR-rich region are important for the enzymatic activities of 2',5'-OAS.

Effects of oral administration of interferon-alpha on antibody production in mice with induced tolerance

In vivo systemic effects and the immunomodulating potential of the oral administration of murine interferon-alpha (IFN-alpha) were investigated through mRNA expression of both IFN-alpha-inducible factors, interferon regulatory factor-1 (IRF-1) and 2,5-adenylate synthetase [2-5(A) synthetase] and 2-5(A) synthetase enzymatic activity in spleen and antibody production. The daily administration of IFN-alpha (0.1, 1, 10, and 100 IU/body) for 1 week augmented IRF-1 and 2-5(A) synthetase mRNA expression levels, as well as 2-5(A) synthetase enzymatic activity in spleen cells but not in cervical lymph nodes. The in vivo immunomodulating potential of the oral administration of IFN-alpha was also evaluated through antibody production in mice with induced tolerance. Ovalbumin (OVA) was administered intraperitoneally (i.p.) to induce systemic antibody production on day 0 when OVA feeding was initiated. The OVA was fed every 2-3 days for a total of 14 doses to suppress serum antibody levels. Oral administration of murine IFN-alpha was initiated on day 0 and was continued for 5 consecutive days weekly for 5 weeks (24 doses). On every sampling date (days 10, 17, 24, and 32), specific antibody levels in the IFN-alpha-administered groups were significantly higher than those in the control (nonadministered) group. This was especially noted in early phases (days 10 and 17) of antibody production when the levels of antibody in serum from the IFN-alpha-administration groups were equivalent to those of the nontolerance group. Altogether, it is suggested that oral use of IFN-alpha can elicit immunomodulating actions (e.g., antibody levels) by affecting the systemic immune system(s).

Interferon action in triply deficient mice reveals the existence of alternative antiviral pathways

Antiviral proteins encoded by the interferon (IFN)-stimulated genes provide a front-line defense against viral infections. In particular, PKR, RNase L, and Mx are considered to be the principal proteins through which IFNs mount an antiviral state. To determine whether alternative antiviral pathways exist, RNase L-/- mice and PKR-/- mice were crossed onto an Mx1(-/-) background to generate a strain of triply deficient (TD) mice. After infections with encephalomyocarditis virus, the TD mice died 3-4 days earlier than infected, wild-type mice. However, there was an IFN dose-dependent increase in survival times after encephalomyocarditis virus infections for both the TD and wild-type mice. Mice that were deficient for PKR or RNase L showed intermediate survival times between those of the TD and wild-type mice. Surprisingly, cultured embryonic fibroblasts lacking RNase L, PKR, or both proteins were still able to mount a substantial residual antiviral response against encephalomyocarditis virus or vesicular stomatitis virus after IFN-alpha treatments. These results confirm the antiviral functions of RNase L and PKR in vivo but also provide unequivocal evidence for the existence of novel, innate immune pathways against viruses.

Simple mixing of IFN with a polysaccharide having high liver affinity enables IFN to target to the liver

Interferon (IFN) therapy is only one method that is clinically effective in controlling disease activity in patients with chronic hepatitis. A chelating residue (diethylenetriamine pentaacetic acid, DTPA) was introduced to pullulan, which is a polysaccharide with high liver affinity. This DTPA-pullulan could conjugate with IFN through Zn2+ coordination on mixing these three components. Intravenous injection of the IFN-DTPA-pullulan conjugate with Zn2+ coordination induced activity in the liver of an antiviral enzyme. 2',5'-oligoadenylate synthetase at IFN doses lower than those used for free IFN injection. In addition, synthetase induction by the conjugate continued for a longer time than did induction by free IFN. Liver targeting of IFN by this conjugation technique based on Zn2+ coordination opens a new method of IFN therapy.

Production of immunoreactive 2',5'-oligoadenylate synthetase in p48-deficient mice

2',5'-Oligoadenylate synthetase (2'5'OAS), an enzyme induced by interferon (IFN), is physiologically produced in IFN-untreated normal healthy mice. The enzyme is localized mainly in the epithelium of the digestive tract, reproductive organs, and the choroid plexus in the brain. 2'5'OAS is also detected in oocytes in the ovary and in neurons and glial cells of both the telencephalon and cerebellum. Here, we examined the role of p48 (ISGF3gamma), a component of IFN-stimulated gene factor 3 (ISGF3), in the physiologic production of 2'5'OAS using p48-deficient mice generated by gene targeting. In the p48-deficient mice, the physiologic production of 2'5'OAS localized in the following cells was severely impaired: hepatocytes, Kupffer cells, splenocytes, epithelium of the large intestine, oviduct, and uterus, and neurons and glial cells in both the telencephalon and cerebellum. The results show that 2'5'OAS in these cells is induced physiologically through a pathway including p48. However, the production of 2'5'OAS in oocytes was not affected in the p48-deficient mice, indicating that oocyte 2'5'OAS is produced through a p48-independent pathway. A possible function of the GAS sequence found in the promoter region of the 2'5'OAS gene to which Stat6 may bind also is discussed.

The target cells of injected type I interferons in mouse liver

Type I interferons (IFNs) have been used for the treatment of viral hepatitis, but it is unclear which cells in the liver are affected by injected IFN. The effects of IFN have been studied by the production of 2',5'-oligoadenylate synthetase (2'5'OAS), an IFN-inducible enzyme. Here, we studied the distribution of 2'5'OAS in mouse liver after injection of natural mouse IFN-alpha/beta by Western blotting and immunohistochemistry using a monoclonal antibody specific to mouse 42-kDa 2'5'OAS. Injection of IFN-alpha/beta increased the levels of liver 2'5'OAS and enhanced the intensities of immunohistochemical staining for this enzyme in both hepatocytes and Kupffer cells. In IFN-untreated normal mice, hepatocytes were lightly stained, but some of the Kupffer cells showed rather strong staining. The 2'5'OAS-positive Kupffer cells comprised approximately 60% of those in normal liver, whereas this increased to approximately 90% following IFN-alpha/beta injection. Thus, hepatocytes and Kupffer cells were the targets of injected IFN.

Liver targeting of interferon through pullulan conjugation

PURPOSE

The purpose of this study was to actively target interferon (IFN) to the liver through its chemical conjugation with pullulan, a water-soluble polysaccharide with a high affinity for the liver.

METHODS

Chemical conjugation of IFN with pullulan was achieved by a cyanuric chloride method. Following intravenous injection of the conjugates to mice, their body distribution and the activity of an IFN-induced enzyme, 2', 5'-oligoadenylate (2-5A) synthetase in the liver and other organs, were evaluated.

RESULTS

The cyanuric chloride method enabled us to prepare an IFN-pullulan conjugate that retained approximately 7-9% of the biological activity of IFN. Pullulan conjugation enhanced the liver accumulation of IFN and the retention period with the results being reproducible. When injected intravenously to mice, the IFN-pullulan conjugate enhanced the activity of 2-5A synthetase in the liver. The activity could be induced at IFN doses much lower than those of free IFN injection. In addition, the liver 2-5A synthetase induced by conjugate injection was retained for 3 days, whereas it was lost within the first day for the free IFN-injected mice.

CONCLUSIONS

IFN-pullulan conjugation was promising for IFN targeting to the liver with efficient exertion of its antiviral activity therein.

Biological effects of the interferons and other cytokines

There were seven workshops that primarily concerned the biological effects of the interferons and the other cytokines. These were: Workshop 6, The refractory state in the response to interferons (IFNs) and antibodies in treated patients; Workshop 7, IFNs, multiple sclerosis, and the nervous system; Workshop 9, Viral inhibition of the response to IFNs and other cytokines; Workshop 10, Cell growth inhibition by IFNs and other cytokines; Workshop 12, Cytokines and cell death; Workshop 13, Interactions between cytokines; and, Workshop 14, Cytokine gene therapy. Summaries of each of these sessions follow.

Distribution of immunoreactive 2',5'-oligoadenylate synthetase in mouse digestive tract

2',5'-Oligoadenylate synthetase (2-5OAS), an enzyme induced by interferon (IFN), has also been found in various "normal" animals that had not been treated with IFN. The distribution of this enzyme in the digestive tracts of normal healthy mice was studied by western blotting and by an immunohistochemical method using a specific monoclonal antibody. On western blotting, the antibody to 42 kD 2-5OA synthetase reacted with extracts from the stomach and intestines (small and large intestine), but not with extracts from the esophagus. Immunohistochemically, the 42 kD 2-5OAS was localized on the following cells: surface mucous and parietal cells of fundic glands in the stomach; surface epithelial cells in the intestines; and some enteric nervous cells in the esophagus, stomach, and intestines. Treatment with IFN- alpha/beta did not essentially change the distribution of the enzyme in the tissues, although a small amount of the enzyme was detected in the esophagus by western blotting. Expression of the 42 kD 2-5OAS in the digestive tract may be responsible for the prevention of viral infections.