Structure and expression in Escherichia coli of canine interferon-alpha genes

Interferon therapies in small animals

Interferons (IFNs) are cytokines that play an important role in the immune response of animals and humans. A number of studies reviewed here have evaluated the use of human, canine and feline IFNs as treatments for infectious, inflammatory and neoplastic disease in dogs and cats. Recombinant canine IFN-γ is deemed an efficacious therapy for canine atopic dermatitis. Recombinant feline IFN-ω is effective against canine parvoviral enteritis and has also been recommended for canine atopic dermatitis. Based on limited evidence, recombinant canine IFN-α could be a topical treatment option for dogs with gingivitis and keratoconjunctivitis sicca. Conclusive evidence is lacking for other diseases and large randomised controlled trials are needed before IFNs can be recommended for other indications.

In vitro Effect of Recombinant Feline Interferon-Ω (rFeIFN-Ω) on the Primary CanineTransmissible Venereal Tumor Culture

Background: Interferons (IFNs), signaling proteins produced by host cells, are secreted in response to pathogen activity as well as to tumor cells, and display antiviral, antiproliferative, and immunomodulatory effects. Recombinant feline interferon omega (rFeIFN-ω) has in vitro growth inhibition activities on various canine and feline tumor cell lines. Canine transmissible venereal tumor (CTVT) is used as an animal model for immunotherapy due to its specific growth phase. Previous studies have usually focused on the interaction between tumor infiltrating lymphocytes (TILs) and CTVT cells. However, the specific effects of rFeIFN-ω on CTVT cells remains poorly defined.

Aims: The aims of this study, therefore, were to evaluate the in vitro effect of rFeIFN-ω on primary CTVT cells and to study the mRNA expression of apoptotic genes and drug resistance genes.

Materials and Methods: Purified CTVT cells were treated with various concentrations of rFeIFN-ω and the viability of the cultured cells was ascertained at 24, 48, and 72 h post treatment (hpt) and a dose-response curve plotted. The mRNA expression of apoptotic (BAX and BCL-2) and drug resistance (ABCB1 and ABCG2) genes was performed by reverse transcription quantitative real-time PCR at 72 hpt.

Results: rFeIFN-ω displayed an effect against CTVT cell viability, which decreasing viability in a dose-dependent manner within 72 hpt. The relative mRNA expression of BCL-2 was upregulated only at a rFeIFN-ω concentration of 10⁴ IU/100 μl. However, higher concentrations of rFeIFN-ω gave a higher level of relative mRNA expression of ABCB1 transporter gene.

Conclusion: This study provided the information of in vitro effect of rFeIFN-ω on CTVT cell viability in a dose dependent manner, as well as, the alteration of BCL-2 and ABCB1 gene expression after treatment. These results encourage future in vivo studies to evaluate the potential efficacy of this treatment in CTVT cases.

Type I interferons in the pathogenesis and treatment of canine diseases

Type I interferons (IFNs) such as IFN-α, IFN-β, IFN-ε, IFN-κ, and IFN-ω represent cytokines, which are deeply involved in the regulation and activation of innate and adaptive immune responses. They possess strong antiviral, antiproliferative, and immunomodulatory activities allowing their use in the therapy of different viral diseases, neoplasms, and immune-mediated disorders, respectively. Initially, treatment strategies were based on nonspecific inducers of type I IFNs, which were soon replaced by different recombinant proteins. Drugs with type I IFNs as active agents are currently used in the treatment of hepatitis B and C virus infection, lymphoma, myeloid leukemia, renal carcinoma, malignant melanoma, and multiple sclerosis in humans. In addition, recombinant feline IFN-ω has been approved for the treatment of canine parvovirus, feline leukemia virus, and feline immunodeficiency virus infections. However, the role of type I IFNs in the pathogenesis of canine diseases remains largely undetermined so far, even though some share pathogenic mechanisms and clinical features with their human counterparts. This review summarizes the present knowledge of type I IFNs and down-stream targets such as Mx and 2',5'-oligoadenylate synthetase proteins in the pathogenesis of infectious and immune-mediated canine diseases. Moreover, studies investigating the potential use of type I IFNs in the treatment of canine lymphomas, melanomas, sarcomas, and carcinomas, canine distemper virus, parvovirus, and papillomavirus infections as well as immune-mediated keratoconjunctivitis sicca and atopic dermatitis are presented. A separate chapter is dedicated to the therapeutic potential of IFN-λ, a type III IFN, in canine diseases. However, further future studies are still needed to unravel the exact functions of the different subtypes of type I IFNs and their target genes in healthy and diseased dogs and the full potential action of type I IFNs as treatment strategy.

Functional characterization of canine interferon-lambda

In this study, we provide the first comprehensive annotation of canine interferon-λ (CaIFN-λ, type III IFN). Phylogenetic analysis based on genomic sequences indicated that CaIFN-λ is located in the same branch with Swine IFN-λ1 (SwIFN-λ), Bat IFN-λ1 (BaIFN-λ), and human IFN-λ1 (HuIFN-λ1). CaIFN-λ was cloned, expressed in Escherichia coli, and purified to further investigate the biological activity in vitro. The recombinant CaIFN-λ (rCaIFN-λ) displayed potent antiviral activity on both homologous and heterologous animal cells in terms of inhibiting the replication of the New Jersey serotype of vesicular stomatitis virus (VSV), canine parvovirus, and influenza virus A/WSN/33 (H1N1), respectively. In addition, we also found that rCaIFN-λ exhibits a significant antiproliferative response against A72 canine tumor cells and MDCK cells in a dose-dependent manner. Furthermore, CaIFN-λ activated the JAK-STAT signaling pathway. To evaluate the expression of CaIFN-λ induced by virus and the expression of IFN-stimulated genes (ISGs) induced by rCaIFN-λ in the MDCK cells, we measured the relative mRNA level of CaIFN-λ and ISGs (ISG15, Mx1, and 2'5'-OAS) by quantitative real-time PCR and found that the mRNA level of CaIFN-λ and the ISGs significantly increased after treating the MDCK cells with viruses and rCaIFN-λ protein, respectively. Finally, to evaluate the binding activity of rCaIFN-λ to its receptor, we expressed the extracellular domain of the canine IFN-λ receptor 1 (CaIFN-λR1-EC) and determined the binding activity via ELISA. Our results demonstrated that rCaIFN-λ bound tightly to recombinant CaIFN-λR1-EC (rCaIFN-λR1-EC).

Molecular and functional characterization of canine interferon-epsilon

In this study, we provide the first comprehensive annotation of the entire family of canine interferons (IFNs). Canine IFN-ε (IFNE), IFN-κ (IFNK), and IFN-λ (IFNL) were discovered for the first time. Ten functional and 2 truncated IFN-α (IFNA) pseudogenes were found in the genome, which also enriched the existing knowledge about canine IFNA. The canine type I IFN genes are clustered on chromosome 11, and their relative arrangements are illustrated. To further investigate the biological activity of canine IFNE, it was expressed and purified in Escherichia coli. Recombinant canine IFNE (rCaIFN-ε) displayed potent antiviral activity on both homologous and heterologous animal cells in vitro, indicating that rCaIFN-ε has more broad cross-species activity than recombinant canine IFNA (rCaIFN-α). The antiviral activities of rCaIFN-ε and rCaIFN-α7 against different viruses on MDCK cells were also evaluated. The antiviral activities of recombinant canine IFNK and IFNL were demonstrated using a VSV-MDCK virus-target cell system. rCaIFN-ε exhibited a significant anti-proliferative response against A72 canine tumor cells and MDCK canine epithelial cells in a dose-dependent manner. rCaIFN-α7 was approximately 16-fold more potent than rCaIFN-ε in promoting natural killer cell cytotoxicity activity. Further, rCaIFN-ε can activate the JAK-STAT signaling pathway.

Enrichment and characterization of glycopeptide epitopes from complex mixtures

Antigen posttranslational modifications, including glycosylation, are recognized by the innate and adaptive arms of the immune system. Analytical approaches, including mass spectrometry and allied techniques, have allowed advances in the enrichment and identification of glyco-antigens, particularly T-cell epitopes. Similarly, major advances have been made in the identification, isolation, and detailed characterization of prokaryotic and eukaryotic glycoproteins and glycopeptides. In particular, peptide centric approaches are now capable of enriching low level glycopeptides from highly complex peptide mixtures. Similarly, advanced mass spectrometry methods allow identification of glycopeptides, characterization of glycans, and mapping of modification sites. Herein, we describe methods developed in our laboratory for the broad study of glycopeptides and illustrate how these approaches can be exploited to further our understanding of the identity and nature of glycopeptide epitopes in various diseases or auto immune disorders.

Ability of orally administered IFN-α4 to inhibit naturally occurring gingival inflammation in dogs

It has been reported that type I interferons (IFN-α/β) play an important role in innate immune responses against viral and bacterial infections. In this study, we used and examined naturally occurred canine periodontal disease to show the therapeutic efficacy of low dose oral administration (LDOA) of canine IFN-α subtype 4 (CaIFN-α4). We administered purified recombinant CaIFN-α4 expressed in a baculovirus system to dogs with or without gingival inflammation. We found that LDOA of CaIFN-α4 reduce periodontopathic bacterial counts. LDOA induced improvement of naturally occurring gingival inflammation, and reduction of the stress marker responses was also observed after LDOA. These results suggest that LDOA of CaIFN-α4 has effectiveness for improvement of naturally occurring gingival inflammation in dogs.

Efficient production of canine interferon-alpha in silkworm Bombyx mori by use of a BmNPV/Bac-to-Bac expression system

We exploited the silkworm Bombyx mori for the production of recombinant canine interferon-alpha (CaIFN-alpha). The recombinant baculovirus harboring canine interferon gene was rapidly generated by the BmNPV/Bac-to-Bac system that was recently developed. In B. mori-derived cell lines, the expression of the recombinant protein reached maximal levels around 72-96 h post-infection. For the isolation of the expressed recombinant protein from B. mori larvae, the whole bodies of the infected larvae were homogenized, and the expressed protein was purified by affinity chromatography. Based on the fact that the recombinant CaIFN-alpha showed two bands on the sodium dodecyl sulfate polyacrylamide gel electrophoresis pattern, the expressed protein was thought to be glycosylated. The rCaIFN-alpha yield was about 528 microg per larva, showing that the expression in silkworm was successful. Furthermore, the recombinant protein was proven to be able to inhibit the infection of Madin-Darby canine kidney cells by the vesicular stomatitis virus, indicating that it is biologically active in vitro. The method established in this study provides an efficient way to produce a large amount of CaIFN-alpha and paves the way for further utilization of this protein as a therapeutic agent or vaccine adjuvant in dogs.

Cloning and expression of canine interferon-alpha genes in Escherichia coli

We cloned five new subtypes of cDNA encoding canine interferon-alpha (CaIFN-alpha) from a canine epithelial cell line. CaIFN-alphas were divided into two groups by amino acid sequences and a molecular phylogenic tree. Two subtypes of them were expressed in Escherichia coli, and IFN proteins were purified. Recombinant CaIFN-alphas were highly species-specific and showed antiviral activity against Vesicular stomatitis New Jersey virus and canine adenovirus-1 , but not against canine herpesvirus-1.

High Level Expression of Biologically Active Canine Interferon-.ALPHA. Subtype 4 Using a Baculovirus

In this study, a high amount of bioactive recombinant canine interferon-alpha subtype 4 (CaIFN-alpha4) was expressed in a baculovirus system. For easy purification, it was expressed as a CaIFN-alpha4 bearing histidine hexamer at the C-terminal region, designated CaIFN-alpha4His. CaIFN-alpha4His was detected in culture supernatants of insect cells infected with the recombinant virus using sodium dodecyl sulfate-polyarcylamide gel electrophoresis (SDS-PAGE) and Coomassie Brilliant Blue staining. The level of expression was very high, and approximately 1 mg of purified protein, with 5.0 x 10(7) units/mg, was obtained from 300 ml of culture supernatant. The purified product showed antiviral activity against Vesicular stomatitis virus on canine tumor cell line A72 and chicken embryo fibroblast cells.

Cloning of cDNAs encoding multiple subtypes of feline interferon-alpha from the feline epitherial cell line

Mammalian interferon (IFN)-alpha consists of a 23-amino acid signal peptide and a 166-amino acid mature protein. Feline (Fe) IFN-alpha has an extra unique molecule consisting of a 171-amino acid mature protein with a 5-amino acid insertion. We cloned eight new subtypes of cDNA encoding FeIFN- alpha from a feline epithelial cell line. Among all the FeIFN-alpha subtypes, including six that have previously been reported, the variations were found to be far less than those of IFN-alphas of other animals.

Treatment of canine parvoviral enteritis with interferon-omega in a placebo-controlled challenge trial

Canine parvoviral enteritis continues to cause significant morbidity and mortality in dogs worldwide, and efficacious antiviral therapies are lacking. The present trial was aimed at evaluating the therapeutic efficacy of a recombinant feline interferon (type omega) preparation in the treatment of parvoviral enteritis in dogs. A double-blind, placebo-controlled challenge trial was performed in beagle pups (8-9 weeks); clinical signs, body weight, hematologic parameters, and mortality were monitored for a period of 14 days after challenge. Fourteen animals were inoculated with virulent canine parvovirus; 10 animals that developed clinical signs thereby meeting the inclusion criteria were admitted to the treatment phase in two randomly selected groups (placebo and IFN) of equal size. The IFN group received daily intravenous injections of rFeIFN-omega (2.5 MU/kg) for three consecutive days. The placebo group received daily injections of saline without IFN. Both groups of animals received individual supportive treatment consisting of adjusted diet and electrolyte solution. All five dogs in the placebo group developed fulminating enteritis with typical clinical signs and died within 10 days post-inoculation (or 6 days post-treatment). In the IFN-treated group, one animal died on day 2 after the treatment was started, whereas the other four dogs survived the challenge and gradually recovered. Our data confirm that the rFeIFN-omega can exert a significant therapeutic effect on dogs with parvoviral enteritis by improving clinical signs and reducing mortality.

Cloning, expression, purification, and biological activity of five feline type I interferons

Type I interferons (IFN) are important mediators of the host defense against viral infections in mammals. In humans multiple subtypes of IFN-alpha exist, most of which possess antiviral activity. Little is known about the type I IFN genes in cats and the role they may play in feline immunological responses to viruses. We have isolated cDNAs encoding five feline IFN-alpha (feIFN) subtypes that share from 95 to 99% amino acid sequence identity. FeIFN-alpha5 has five additional amino acids inserted at position 139, which are not present in the other four subtypes. Sequence identity of the feIFN proteins encoded by the five clones compared to human IFN-alpha2 is approximately 60%. Unlike most of the human subtypes, each of the five feline IFN sequences has an N-glycosylation recognition site. Expression of all five feIFN-alpha subtypes in Chinese hamster ovary (CHO) cells was confirmed by Western blot analysis, and all resulting proteins were glycosylated. The antiviral activity of each feIFN-alpha subtype produced in transiently transfected CHO cell cultures was tested in vitro. In addition, subtype feIFN-alpha6 was expressed in the yeast, Pichia pastoris. The resulting secreted mature recombinant protein was purified and demonstrated significant antiviral activity and induction of 2',5'-oligoadenylate synthetase activity in vitro.

Evaluation of a short interspersed nucleotide element in the 3' untranslated region of the defective dystrophin gene of dogs with muscular dystrophy

OBJECTIVES

To determine the distribution of a 231-base pair (bp) element in the dystrophin gene 3' untranslated region (UTR) in a colony of Golden Retrievers with muscular dystrophy and other unrelated dogs and to estimate the frequency of recombination for the canine dystrophin gene.

ANIMALS

77 dogs from the Golden Retriever Muscular Dystrophy (GRMD) colony at the Murdoch Veterinary School and 30 unrelated dogs from the Murdoch University Veterinary Clinic.

PROCEDURE

Samples of blood or hair from dogs were used for amplification of DNA, using primers to the canine dystrophin 3' UTR.

RESULTS

The DNA from affected dogs generated a larger PCR product than that obtained from clinically normal dogs. Products were cloned and sequenced, and the difference in size was found to be attributable to a 231-bp short interspersed nucleotide element (SINE). The SINE was found in all affected dogs in the colony but not in most unaffected puppies in the colony. Eighteen of 19 dogs in the colony were heterozygous for the GRMD mutation, and 7 of 30 unrelated dogs also were heterozygous for the SINE.

CONCLUSION AND CLINICAL RELEVANCE

Evidence of recombination between the GRMD mutation and the SINE was observed in only 4 dogs (2 sets of littermates) in the GRMD colony. Incidence of this SINE in a few unrelated dogs suggests that this particular insertion into the dystrophin gene may have been a recent event. The SINE in the dystrophin 3' UTR did not have an apparent influence on dystrophin mRNA concentrations.

The evolution of the type I interferons

There are five recognized subtypes within the type I interferons (IFN), IFN-alpha, IFN-beta, IFN-delta, IFN-omega, and IFN-tau, although others may remain to be described, and the IFN-omega may have to be subdivided further because of their evident structural complexity. Together, they constitute an ancient family of intronless genes, possibly present in all vertebrates. THe IFNA/IFNB genes originated by duplication of a progenitor after the divergence of birds, most probably about 250 million years ago (MYA). The avian gene itself proceeded to duplicate to form a series of independent subtypes. The IFND, to date described only in the pig, arose from the IFNA lineage before the emergence of mammals about 180 MYA and might, therefore, be generally distributed in present day species. The IFNB, which occurs as a single gene in primates and rodents, have been duplicated in some other orders. Recent events have produced 10 or more genes in bovid species. The IFNA, which are clustered with the IFNW in humans and cattle, exist as multiple genes in all mammals so far examined as a result of a series of duplication events, some of which occurred recently and, therefore, independently in separate mammalian lineages. The IFNW diverged from the IFNA approximately 130 MYA, just prior to the emergence of mammals, and have continued to duplicate since then. The IFNT, which play a role in reproduction of ruminants, arose from an IFNW within the Artiodactyla suborder about 36 MYA and are found only in the suborder Ruminantia. These genes have also continued to duplicate to form an extensive family. Consequently, their involvement in early pregnancy is a feature of ruminants and not of other mammalian species.

Clinical effects of the recombinant feline interferon-omega on experimental parvovirus infection in beagle dogs

The clinical effects of recombinant feline interferon-omega (rFeIFN-omega), produced in silkworm by recombinant baculovirus, were examined in 3-4 month-old beagle dogs given an experimental canine parvovirus type-2 (CPV-2) infection. Clinical symptoms, such as pyrexia, vomiting, anorexia and diarrhea, were observed on day 4 after oral inoculation of 10(7) TCID50 of CPV-2 (cc 238 strain) in almost all the inoculated dogs. From day 4, rFeIFN-omega (1 mega units/kg/day) or physiological saline was administered intravenously to infected dogs for 3 consecutive days. Seven out of 17 dogs treated with physiological saline showed hemorrhagic diarrhea and continuously expressed severe clinical enteritis; one dog died with a large amount of hemorrhagic rice-water stool on day 6 after viral exposure. In contrast, 4 out of 12 dogs treated with rFeIFN-omega showed severe clinical enteritis associated with intermittent diarrhea. Scoring of fecal condition revealed that treatment with rFeIFN-omega significantly shifted the enteritis from a severe to mild form. Furthermore, rFeIFN-omega administered in the morning decreased the number of dogs expressing clinical enteritis in the evening suggesting a rapid effect. Vomiting and anorexia were also improved by treatment with rFeIFN-omega. These results suggest that rFeIFN-omega can reduce severe enteritis caused by CPV-2 infection in dogs.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

Cloning and expression of the canine interferon-beta gene

We isolated the canine interferon-beta (IFN-beta) gene from dog liver chromosomal DNA by the polymerase chain reaction (PCR). The coding region encodes a predicted protein of 197 amino acids, consisting of a signal sequence of 32 amino acids and a mature IFN-beta of 165 amino acids. In the IFN-beta sequence, there are five potential N-glycosylation sites and four cysteine residues. Canine IFN-beta has 44% and 60% amino acid sequence homology with murine and human IFN-beta, respectively, whereas it has only 28% homology with canine IFN-alpha. The canine IFN-beta gene was expressed in insect cells under the control of the polyhedrin promoter in a recombinant baculovirus. After infecting Sf21 cells with the recombinant baculovirus, IFN activity was detected in the culture medium, indicating that it is secreted from the cells. This activity was stable from pH 2 to 12 for 18 h at 4 degrees C. Southern blot analysis indicated that the gene for canine IFN-beta is a single gene in the dog haploid chromosome.

A type I ovine interferon with limited similarity to IFN-alpha, IFN-omega and IFN-tau: gene structure, biological properties and unusual species specificity

A gene encoding a 195 amino-acid (a.a.) polypeptide with a putative 23 a.a. signal sequence that had about 60% a.a. sequence identity to ovine interferon-omega (OvIFN-omega) and 55% or less identity to BoIFN-tau, OvIFN-tau and all known IFN-alpha and -beta has been identified from an ovine genomic DNA library. Surprisingly, it shared almost complete identity to genes for rabbit IFN-omega within its coding sequence and proximal promoter region, although the two were different in their 3'-ends. This IFN (tentatively termed ovine IFN-omega variant, OvIFN-omegav), purified in recombinant form from E. coli, had normal antiviral activity when tested on sheep fetal tongue and brain cells and rabbit kidney cells, but very low activity towards bovine, goat and human cells. It competed with 125I-labeled BoIFN-tau for binding to IFN receptors on ovine cells. Expression of OvIFN-omegav was not detected by reverse transcription-PCR either in ovine peripheral blood leukocytes infected with Sendai virus, or in any other tissues examined. OvIFN-omegav may represent a previously unrecognized, non-virally inducible type I subtype distinct from IFN-alpha, -beta, -omega and -tau. The presence of a conserved gene in rabbit and sheep could reflect a recent interspecies transfer.

Chicken interferon gene: cloning, expression, and analysis

A gene encoding chicken interferon (ChIFN) was cloned from a cDNA library made from primary chick embryo cells that had been "aged" in vitro so as to produce copious amounts of IFN upon induction. The coding region is predicted to produce a signal peptide of 31 amino acids and a mature protein of 162 amino acids with a molecular weight of 18,957. There are four potential N-glycosylation sites and six cysteine residues. Three disulfide bonds are possible, with two being common to most mammalian type I IFNs. A motif of 10 amino acids surrounding Cys-137 is highly conserved: It shows 80% homology with mammalian type I IFNs, but only 30% with a reported fish IFN. The T-rich 3' UTR displays the canonical element AATAAA required for polyadenylation, and contains six repeats of the octamer CTATTTAT that may be involved in down-regulating translation. Northern blots demonstrate that the accumulation of ChIFN mRNA correlates with induction of ChIFN determined by bioassay. Biologically active protein was synthesized in transfected mouse L cells using mRNA prepared in vitro from the cloned sequence. This activity was neutralized by a monoclonal antibody prepared against purified ChIFN. The ChIFN gene shows sequence identity at the amino acid/nucleotide level with consensus mammalian IFNs as follows: alpha (24/23%), beta (20/24%), omega (23/43%), tau (20/43%), gamma (3/31%), and with flatfish IFN (16/35%). The conserved features of the predicted ChIFN protein and the general similarity of predicted secondary structure suggest a molecule that fits the five alpha-helix three-dimensional topology reported for type I mammalian IFNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and structural analysis of four genes encoding interferon-omega in rabbit

By using an ovine interferon-tau (IFN-tau) cDNA probe, four recombinant phages were isolated from a rabbit genomic library and sequenced from nucleotides -450 to 1,300 relative to the CAP site. Each of the four rabbit genes contains an open reading frame of 595 nucleotides and code for proteins that exhibit structural characteristics of the interferon-omega (IFN-omega) family. They display more than 98% identity in their coding regions. The deduced amino acid sequences share > 96% sequence similarity. In contrast, the 5' and 3' noncoding regions have diverged considerably (approximately 50% identity). Amino acid comparisons of rabbit IFN-omega with IFN-omega of other species reveal the highest degree of identity with human (72%), followed by porcine (68%) IFN-omega. Rabbit IFN-omega displays only 57% sequence similarity with ovine IFN-tau. The coding regions of the four genes subcloned in a cytomegalovirus eukaryotic expression vector and transfected in monkey COS-7 cells direct the production of proteins that protect bovine and rabbit cells against vesicular stomatitis virus infection, thus demonstrating that these genes encode fully active IFN proteins. The expression of these genes was studied in Sendai-induced rabbit leukocytes. A single band of poly(A)+RNA hybridized with a rabbit IFN-omega probe under stringent conditions, whereas no IFN-omega transcript was detected with RNA isolated from uninduced leukocytes. Southern blot analysis suggest the existence of at least eight IFN-omega genes or pseudogenes in the rabbit genome.

Genes for the trophoblast interferons in sheep, goat, and musk ox and distribution of related genes among mammals

The trophoblast interferons (IFNs) are a family of Type 1 IFN found in domestic ruminants that are most closely related to the little-studied 172-amino-acid IFN-omega. They are produced in massive amounts by the preimplantation conceptus at a time coincident with maternal recognition of pregnancy, and are implicated in playing an important role in this process. Here we report the characterization of four distinct members of the ovine trophoblast IFN (oTP-1) gene family, and demonstrate that they, along with previously characterized bovine trophoblast (bTP-1) genes, possess distinctive promoter sequences when compared to ovine and bovine IFN-omega genes. Genomic Southern blot analysis of numerous mammalian species (zoo blots) indicate that, whereas the IFN-omega are widely distributed among mammals, genes for the trophoblast IFN appear to be limited to ruminant species within the Artiodactyla order. Further polymerase chain reaction (PCR) analysis of trophoblast IFN genes in these ruminant species has permitted isolation of genes for goat and musk ox trophoblast IFN. These data suggest that the trophoblast IFNs are a distinct family of IFN with a limited distribution among mammals.

A highly repetitive DNA sequence possibly unique to canids

A short interspersed nucleotide (nt) element (SINE) was cloned from the genomic DNA of the domestic dog, Canis familiaris. Southern-blot analysis of canine DNA digested with four restriction endonucleases indicated that the SINE is widely dispersed throughout the genome. Hybridizations also indicated that the element may be unique to canids and is absent in a variety of other mammals, including members of four closely-related carnivore families. Three examples of the SINE have been located and sequenced. The 130-bp SINE contains putative RNA polymerase III transcriptional control sequences. The SINE is flanked at the 3' end by a (TC)8-repeat region followed by a poly(A) tract of 35-65 nt. Computer database searches located two homologous sequences with approx. 80% identity to the SINE. These sequences were located in untranslated regions of the canine genes encoding interferon-omega and clotting factor IX.

The porcine family of interferon-omega: cloning, structural analysis, and functional studies of five related genes

We report the molecular characterization of the porcine IFN-omega multigenic family which appears to comprise six to seven loci. Five of these loci were cloned and sequenced, revealing two pseudogenes (psi PoIFN-omega 1 and -omega 2) and three genes with an intact reading frame (PoIFN-omega 3, -omega 4, and -omega 5) that could encode preproteins of 179-190 amino acids including a putative signal peptide of 23 residues. By comparison of porcine IFN-omega coding sequences to those of known mammalian counterparts, it appeared that porcine sequences contain an in-frame five-codon deletion (between positions 113 and 117) in a region of relatively high sequence variability. In vitro transcription and translation of the three potentially functional reading frames gave rise to proteins with antiviral activity, showing that the porcine-specific deletion does not abolish the biological activity. Comparative analysis of flanking sequences revealed unique features of the 3' untranslated region of IFN-omega 4 gene: It contained a consensus estrogen-responsive element (ERE) in the vicinity of an extensive A-T-rich sequence known to serve a specific regulatory role in the expression of many genes involved in the inflammatory response. This finding suggests that the expression of the functional members of the porcine IFN-omega family may be mediated through different mechanisms. The expression of these genes was studied by Northern blot analysis of mRNAs from pig conceptus (days 14-20). Five bands of poly(A)+ RNAs hybridized with an IFN-omega probe provided the stringency was low, suggesting that a distinct family of IFN-omega-related genes were expressed by porcine trophoblastic cells during early gestation.

Human interferon omega 1: isolation of the gene, expression in Chinese hamster ovary cells and characterization of the recombinant protein

A gene encoding human interferon omega-1 (IFN-omega 1) was isolated from a cosmid library, sequenced and expressed in Chinese hamster ovary (CHO) cells under the control of an SV40-derived promoter/enhancer sequence. Culture supernatants of stably transfected cell clones contained biologically active IFN-omega 1 at concentrations up to 10 micrograms/l. Amplification of the expression vector containing a dhfr gene under methotrexate selection pressure resulted in yields up to 200 micrograms/l. Production of IFN-omega 1 was further enhanced 2- to 3-fold by propagation of the cells in the presence of n-butyrate. IFN-omega 1 was purified from culture supernatants by monoclonal antibody affinity chromatography. The resulting protein was at least 95% pure as determined by reverse-phase HPLC and size-exclusion HPLC. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed two bands of about the same intensity with apparent molecular masses of 24.5 and 22.5 kDa. Upon treatment with peptide:N-glycosidase F, both bands were shifted to lower molecular masses (20.5 and 18.5 kDa), indicating that CHO cell-derived IFN-omega 1 is glycosylated; Asn-78 was identified as the glycosylation site. Analysis of the carbohydrate moiety using glycosidases and lectins revealed the presence of biantennary complex oligosaccharides containing neuraminic acid. Amino acid sequencing showed that only about 40% of the molecules have the expected N-terminus, whereas the others carry two additional amino acids derived from the signal sequence. C-terminal amino acid sequencing using carboxypeptidase P demonstrated that the smaller form of the protein lacks nine amino acids. Disulfide bridges were shown to connect Cys residues 1 and 99 as well as 29 and 139, respectively, as in IFN-alpha. The specific antiviral activity of recombinant, glycosylated human IFN-omega 1 on human cells was 2.6 x 10(8) IU/mg, not significantly different from that of the authentic, human leukocyte-derived protein.

Constitutive and trophoblast-specific expression of a class of bovine interferon genes

The early conceptus in sheep and cattle secretes a low molecular weight protein called ovine and bovine trophoblast protein 1 (TP-1) that is critical for establishment of pregnancy. TP-1 is a type I interferon (IFN) and is most related to IFN-omega. Here we have determined if TP-1 genes are regulated similarly to other type I IFNs. Single day 18 bovine conceptuses secrete approximately 10(5) units of IFN antiviral activity per hour in culture, amounts approximately 300 times higher than those produced by Sendai virus-induced leukocytes. Although conceptuses express mRNA for IFN-alpha, IFN-omega, and TP-1, TP-1 constitutes greater than 99% of the IFN produced. In contrast, leukocytes produced predominantly IFN-alpha, although TP-1 mRNA is inducible by Sendai virus to very low levels. TP-1 mRNA is detectable by Northern analysis in conceptuses from early pregnancy but is absent in late gestation placenta and several adult tissues. Transfected bovine TP-1 genes are expressed in human choriocarcinoma (JAR) cells in the absence of any specific stimulus, whereas these cells do not secrete antiviral activity constitutively or after transfection with a bovine IFN-omega gene. The transfected TP-1 gene is not expressed in nontrophoblast cells (mouse L929 and hamster Chinese hamster ovary), however. The 5' promoter region of the TP-1 gene is sufficient to direct trophoblast-specific expression onto a human growth hormone reporter gene in JAR cells. Deletion of the promoter from -450 to -126 results in a 4- to 5-fold decrease in expression. Together these data demonstrate that the genes for TP-1 are inducible by virus but are expressed preferentially in trophoblast cells and are functionally distinct from IFN-omega genes.

Cloning and structural analysis of two distinct families of ovine interferon-alpha genes encoding functional class II and trophoblast (oTP) alpha-interferons

Ovine trophoblast protein (oTP) is a polypeptide secreted by ovine trophectoderm from day 11 to 21, which plays a key role in maternal recognition of pregnancy. Structural analyses established that oTP shares extensive homology with class II alpha-interferon (IFN-alpha II) subfamily. Previous screening of an ovine genomic DNA library probed with an oTP cDNA incidently resulted in the isolation of a functional IFN-alpha II gene and two relevant pseudogenes, as shown by sequence analysis and study of expression in eukaryotic COS cells. The expected oTP gene together with a cognate pseudogene was successfully isolated from the series of clones selected from another genomic library probed with the oTP cDNA, using two specific oligonucleotides, each one complementary to a region of oTP cDNA with little homology with the IFN-alpha II gene and related pseudogenes. Southern blotting of ovine genomic DNA indicated the existence of at least five trophoblast IFN-alpha genes or pseudogenes. Nucleotide sequence comparisons showed that the oTP gene exhibits a higher homology (90%) with bovine trophoblast IFN gene (Stewart et al. (1990) J. Mol. Endocrinol. 4, 275-282) than with oIFN-alpha II gene (70%), thus providing evidence that embryonic IFNs constitute a distinct subfamily of IFN-alpha s.

Unique features of the trophoblast interferons

The trophoblast interferons (IFN) are Type I IFN with about 50% amino acid sequence identity to the leukocyte IFN (IFN-alpha). They are the major secretory products of the trophoblast of ruminant ungulate species during pregnancy in the period immediately preceding attachment and implantation when they have been implicated in the phenomenon known as maternal recognition of pregnancy. The trophoblast IFN have antiviral and antiproliferative activities typical of other Type I IFN, but unlike IFN-alpha, -beta and -omega are poorly responsive to viral induction and have a highly restricted pattern of expression. Nevertheless, a recombinant bovine IFN-alpha can mimic many of the properties of the trophoblast IFN and has been used pharmacologically to improve pregnancy success in sheep. It still remains unclear, however, whether the trophoblast IFN have unique biological properties or whether they are unusual merely by virtue of the location, magnitude and temporal nature of their expression at a critical time during pregnancy.

Recombinant equine interferon-beta 1: purification and preliminary characterization

Equine interferon-beta 1 (EqIFN-beta 1) was purified from extracts of recombinant Escherichia coli by sequential chromatography on hydroxylapatite, anion-, and cation-exchangers. The resulting protein was greater than 98% pure as determined by sodium dodecylsulfate gel electrophoresis, gel permeation HPLC, and reverse-phase HPLC. Amino-terminal amino acid sequencing revealed that essentially all molecules contained an additional amino-terminal methionine. The specific antiviral activity of EqIFN-beta 1 determined on equine dermal fibroblasts challenged with vesicular stomatitis virus (VSV) was approximately 5 X 10(8) U/mg. Less than 0.001% of this activity was observed in antiviral assays using human (A549), murine (L-M), ovine (SCP), or bovine (MDBK and BT) cells challenged with VSV or encephalomyocarditis virus. A series of monoclonal murine IgG antibodies were developed which neutralize the antiviral activity of EqIFN-beta 1. None of these antibodies nor rabbit antiserum to EqIFN-beta 1 were able to neutralize human IFN-beta; antiserum to human IFN-beta did not neutralize EqIFN-beta 1. Two of the monoclonal antibodies were used to establish a rapid one-step solid-phase enzyme immunoassay for EqIFN-beta 1.

Existence and unique N-terminal sequence of alpha II (omega) interferon in natural leukocyte interferon preparation

Human alpha interferon produced in Sendai virus-stimulated leukocytes was purified by immunosorbent affinity chromatography and subjected to subtype analysis. All subtypes in leukocyte culture supernatant were confirmed in purified preparation. One of these subtypes was reactive in Western blotting with antibody specific to alpha II (omega). N-terminal amino acid sequence analysis of this particular subtype showed addition of two amino acids to the N-terminus of alpha II predicted through cDNA studies. The apparent cleavage site for leader sequence of alpha II was different from the site common to all other alpha subtypes. This is the first report on the isolation of natural alpha II and its unique N-terminal amino acid sequence.

Monoclonal antibodies and enzyme immunoassays specific for human interferon (IFN) omega 1: evidence that IFN-omega 1 is a component of human leukocyte IFN

Four hybridoma cell lines secreting monoclonal IgG antibodies to human interferon (IFN) omega 1 (= IFN-alpha II 1) were developed, using spleen cells of mice immunized with IFN-omega 1 and/or a novel hybrid interferon, IFN-omega 1/alpha 2. All antibodies (OMG-2, -4, -5, and -7) neutralize the antiviral activity of IFN-omega 1 and show distinct patterns of reactivity with the hybrid proteins, IFN-omega 1/alpha 2 and IFN-alpha 2c/omega 1. However, none of the antibodies is able to neutralize human IFN-alpha, confirming earlier observations that IFN-omega 1 and IFN-alpha are antigenically unrelated. The epitope specificities of the antibodies were further characterized in direct and competitive enzyme immunoassays (ELISAs). All binary antibody combinations were tested for their suitability for a two-site ("sandwich") ELISA for IFN-omega 1, using horse radish peroxidase as the marker enzyme. A configuration employing OMG-2 for antigen capture and OMG-7 as the detector antibody resulted in the highest assay sensitivity (approximately 10 pg IFN-omega 1/ml) and was studied further. This one-step assay is highly specific for IFN-omega 1 and does not recognize human IFN-alpha, -beta, and -gamma, thus allowing for determination of IFN-omega 1 levels in natural mixtures of human IFNs. Using this ELISA, it was found that IFN-omega 1 is present in IFN preparations derived from virus-induced human peripheral blood leukocytes and may constitute as much as 15% of the total leukocyte IFN activity. IFN-omega 1 was also detected at somewhat lower levels in preparations of human "lymphoblastoid" IFN.