Structure and expression in Escherichia coli of a cloned rat interferon-alpha gene

Recombinant expression of bioactive peptide lunasin in Escherichia coli

Lunasin, a cancer-preventive peptide, was isolated from soybean, barley, and wheat. Previous studies showed that this 43-amino acid peptide has the ability to suppress chemical carcinogen-induced transformation in mammalian cells and skin carcinogenesis in mice. In this study, we attempted to use the Escherichia coli T7 expression system for expression of lunasin. The lunasin gene was synthesized by overlapping extension polymerase chain reaction and expressed in E. coli BL21(DE3) with the use of vector pET29a. The recombinant lunasin containing his-tag at the C-terminus was expressed in soluble form which could be purified by immobilized metal affinity chromatography. After 4 h, the expression level is above 4.73 mg of recombinant his-tagged lunasin/L of Luria-Bertani broth. It does not affect the bacterial growth and expression levels. This is the first study that successfully uses E. coli as a host to produce valuable bioactive lunasin. The result of in vitro bioassay showed that the purified recombinant lunasin can inhibit histone acetylation. Recombinant lunasin also inhibits the release of pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, and nitric oxide production). Compared with other research methods on extraction or chemical synthesis to produce lunasin, our method is very efficient in saving time and cost. In the future, it could be applied in medicine and structure-function determination.

Differential expression of tapasin and immunoproteasome subunits in adenovirus type 5- versus type 12-transformed cells

Adenovirus type 12 (Ad12)-transformed baby rat kidney (BRK) cells are oncogenic in syngeneic immunocompetent rats in contrast to adenovirus type 5 (Ad5)-transformed BRK cells, which are not oncogenic in these animals. A significant factor contributing to the difference in oncogenicity may be the low levels of major histocompatibility complex (MHC) class I membrane expression in Ad12-transformed BRK cells as compared with those in Ad5-transformed BRK cells, which presumably results in escape from killing by cytotoxic T lymphocytes. Here we show that, in addition to the decreased levels of expression of the MHC class I heavy chain and the peptide transporter Tap-2, the expression levels of the chaperone Tapasin and the immunoproteasome components MECL-1, PA28-alpha, and PA28-beta also are much lower in Ad12- than in Ad5-transformed BRK cells. The low expression levels of these proteins may contribute to the escape from killing by cytotoxic T lymphocytes, because the generation of optimal peptides and loading of these peptides on MHC class I require these components. Increased levels of phosphorylated signal transducer and activator of transcription-1 protein and expression of IFN regulatory factor-7 were found in Ad5- versus Ad12-transformed BRK cells. Therefore, the critical alteration leading to the plethora of differences may be an interferon (-related) effect.

Cloning and expression of flatfish (Paralichthys olivaceus) interferon cDNA

Fish interferon (IFN) cDNA was first cloned from the cDNA library of immortalized flatfish leukocytes. The clone contains an open reading frame that encodes a 138 amino acid polypeptide including a glycosylation site and a signal peptide containing 30 amino acids. BHK-21 cells transfected with the INF-expression plasmid produced active recombinant IFN (about 16 kDa) which was then purified by WGA agarose affinity chromatography. This recombinant IFN inhibited infection of fish cells with the Hirame (flatfish) rhabdovirus.

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.

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.

Assignment of 12 loci to rat chromosome 5: evidence that this chromosome is homologous to mouse chromosome 4 and to human chromosomes 9 and 1 (1p arm)

Twelve loci have been assigned to rat chromosome 5: aldolase B (ALDOB), atrial natriuretic factor (ANF = pronatriodilatin, PND), D4RP1, DSI1, galactosyltransferase (GGTB2), glucose transporter (GLUT1), interferon alpha 1 and related interferon alpha (INFA), interferon beta (INFB), lymphocyte-specific protein-tyrosine kinase (LCK), oncogene MOS, alpha 2U-globulin (major urinary protein, MUP), and orosomucoid (ORM, also called alpha 1-acid glycoprotein, AGP). Among these, the interferon alpha and beta genes map in the q22-23 region, which also contains a transformation suppressor gene (SAI1). The other loci reside outside this region. This study also indicated that the rat genome contains 2 LCK genes, unlike the human and murine genomes. These new assignments on rat chromosome 5 demonstrate that this chromosome is highly homologous to mouse chromosome 4 and carries synteny groups conserved on human chromosome 9 (interferon alpha and beta, galactosyltransferase, orosomucoid, and aldolase B genes) and on the short arm of human chromosome 1 (MYCL, glucose transporter, protein kinase LCK, and atrial natriuretic factor genes).

From cloning to a commercial realization: human alpha interferon

Recent applications of recombinant DNA techniques have enabled the cloning of several interesting human genes, leading to the production of rare biologicals in abundant quantities. We review here the discovery, early characterization, cloning, and expression of Interferon Alfa-2B (IFN alpha-2b or Intron A) as a therapeutic at Schering-Plough Research. IFN alpha-2a is marketed by Hoffman LaRoche under the trade name Roferon. The studies on the expression, purification, biology, and clinical aspects of this interferon offer a plethora of information on one of the earliest recombinant DNA based drugs to reach the market place.

Expression of the rat interferon-alpha 1 gene in Escherichia coli controlled by the secondary structure of the translation-initiation region

A synthetic ribosome-binding site (RBS) containing a 7-nucleotide-long Shine-Dalgarno (SD) sequence was placed ahead of the rat interferon (IFN)-alpha 1 coding region. The translational efficiency of this construct was extremely low. Structural probing of transcripts with RNases T1 and U2 combined with computer predictions revealed the presence of a stable hairpin in which the SD region was base-paired to codons 3, 4 and 5 of the IFN mRNA. Each mutation in this stem changing an A-U to an A.C or a G-C a G.U pair increased translational efficiency about fourfold and this effect could be reversed by a compensating stabilizing substitution in the other strand of the stem. We conclude that the strength of an RBS is to a major degree determined by its involvement in secondary structure. We also show that the negative effect of secondary structure on the efficiency of an RBS can be overcome by allowing upstream translation to terminate within the base-paired region. In our clones, termination-dependent restarts occur at a frequency comparable to that taking place in constructs containing destabilized hairpins.

Translational reinitiation in the presence and absence of a Shine and Dalgarno sequence

The process of translational reinitiation in Escherichia coli was studied in a two cistron system where expression of the downstream reporter gene was dependent on translation of an upstream reading frame. The dependence was almost absolute. Upstream translation increased expression of the downstream gene by two to three orders of magnitude. This large difference allowed us to quantitate restarts in a meaningful manner. In the absence of a Shine and Dalgarno (SD) region reinitiation occurred but its efficiency was about 10% of that found in the SD carrying counterpart. We discuss three ways by which translational coupling between neighboring cistrons can be enforced.

The cysteines in position 1 and 86 of rat interferon-alpha 1 are indispensable for antiviral activity

The human, bovine, murine and rat interferon (IFN)-alpha families contain 4 conserved cysteines located at positions 1, 29, 99 and 139 that are involved in disulfide bridges. Rat and murine IFN-alpha subspecies carry a fifth Cys (Cys-86) which is not conserved in bovine and human IFN-alpha subspecies except for human IFN-alpha 1. Changing Cys-86 in rat IFN-alpha 1 into Ser or Tyr virtually abolished antiviral activity. As shown by others, the substitution of Cys-86 to Ser in human IFN-alpha 1 had no pronounced effect on activity. This suggests that in contrast to human and bovine IFN-alpha, Cys-86 in rodent IFN-alpha plays a crucial role in receptor binding. Changing Cys-1 to Gly in rat IFN-alpha 1 also destroyed activity, in agreement with results obtained in the human IFN-alpha 1 system.

A family of interferon-induced Mx-related mRNAs encodes cytoplasmic and nuclear proteins in rat cells

Mouse Mx protein, an interferon (IFN)-induced nuclear protein, confers selective resistance to influenza virus. We show here that, as with influenza virus-resistant Mx+ mouse embryo cells, influenza virus mRNA accumulation and protein synthesis are strongly inhibited in rat embryo cells treated with IFN-alpha/beta. IFN-alpha/beta induced in rat cells the synthesis of Mx-related mRNAs migrating on Northern (RNA) gels as two bands of about 3.5 and 2.5 kilobases which directed the synthesis of three electrophoretically distinct proteins called rat Mx proteins 1, 2, and 3. The three rat proteins were antigenically related to the mouse Mx protein but differed in molecular weight and intracellular location. Rat Mx protein 1 was found predominantly in the nucleus and, on the basis of several criteria, resembled the nuclear mouse Mx protein. It was induced by IFN-alpha/beta in all 28 inbred rat strains tested. Rat Mx proteins 2 and 3 differed from protein 1 at the carboxy terminus and were predominantly cytoplasmic like the human Mx homolog. Sequence data of partial cDNA clones indicate that three Mx-related genes, rather than one, exist in the rat.

Chemical mutagenesis of human interferon-beta: construction, expression in E. coli, and biological activity of sodium bisulfite-induced mutations

A series of modified human interferon-beta (IFN-beta) genes was produced by sodium bisulfite treatment of the IFN-beta gene cloned in M13. A library of mutated sequences was generated from which subgenomic fragments containing one or a small number of coding alterations were isolated and substituted into the IFN-beta gene in an E. coli expression vector. A number of modified genes and their expression products were evaluated. In several instances levels of expression and biological activity profiles are altered compared to the parental gene product. A number of key amino acids can be identified, whose substitutions have marked effects on biological activity of IFN-beta.

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

Using a human interferon-alpha (IFN-alpha) cDNA probe, several recombinant phages containing type I IFN genes were isolated from a canine genomic library. One of these phages contains two complete CaIFN-alpha genes with identical coding sequences, and a second one a slightly different IFN-alpha gene. The IFN-alpha protein sequences contain six cysteine residues as well as two or three potential N-glycosylation sites. Expression of mature CaIFN-alpha 1 in E. coli results in antiviral activity on dog cells. Genomic analysis using an equine IFN-omega probe and DNA sequencing suggests the deletion of IFN-omega genes from canine genome.

Antiviral and antiproliferative activities of interferon-alpha 1: the role of cysteine residues

Site-specific in vitro mutagenesis was used to direct serine for cysteine substitutions within the sequence of human interferon-alpha 1 (IFN-alpha 1). Antiviral specific activities and antiproliferative activities of IFN-alpha 1 analogs, expressed in M13 as fusion proteins, were assessed following purification by monoclonal antibody affinity chromatography. Based on analysis of IFN-alpha 2, IFN-alpha 1 contains two disulfide bridges between cysteine residues 29 and 139 and cysteine residues 1 and 99. IFN-alpha 1 also contains a fifth cysteine residue at position 86. The series of serine for cysteine substitutions performed indicated that IFN-alpha 1 molecules unable to form the residue 29 to residue 139 disulfide bridge have substantially reduced antiviral and antiproliferative activities, IFN-alpha 1 molecules unable to form the residue 1 to residue 99 disulfide bridge have only marginally altered antiviral and antiproliferative activities, the low antiviral activity of IFN-alpha 1 compared with other human IFN-alpha subtypes is not due to the formation of nonnative disulfide bridges involving the fifth cysteine residue at position 86, which the other subtypes lack, and (iv) the reduced biological activities of certain analogs may be due to the formation of nonnative disulfide bridges.

The hepatitis delta (delta) virus possesses a circular RNA

Hepatitis delta (delta) virus (HDV), a satellite virus of the hepatitis B virus (HBV), causes a severe form of viral hepatitis in humans. Here we present evidence based on electron microscopy and electrophoretic behaviour that HDV contains a single stranded circular RNA molecule. This is the first animal virus identified with a circular RNA genome. Circular RNAs have only been found in plant viruses. We have obtained a partial complementary DNA clone representing approximately 25% of the total genome of HDV. Analysis of this cDNA revealed similarity to two plant viruses that may explain the origin of the virus.

Molecular cloning and expression in Escherichia coli of equine type I interferons

Using human interferon-alpha 2 (IFN-alpha 2) and IFN-beta DNA to probe an equine genomic library we isolated recombinant phages containing genes for equine interferon-alpha (EqIFN-alpha), interferon-beta (EqIFN-beta), and interferon-omega (EqIFN-omega). Sequence and hybridization analyses of these genes reveal that the equine genome contains gene families of each of these three type I interferon classes. The mature proteins of EqIFN-alpha are 71-77% homologous to human IFN-alpha polypeptides, and, when expressed in E. coli, possess antiviral activity on both equine and human cells. By contrast, EqIFN-beta is only 59% homologous to its human counterpart and shows activity only on equine cells.

Molecular cloning and sequencing of a gene encoding biologically active porcine alpha-interferon

Nine distinct genomic clones containing human alpha 1-interferon (IFN-alpha 1) related sequences were isolated from a porcine genomic library constructed in phage lambda. Restriction mapping and Southern blot analysis revealed that these clones contained a total of 10 potential porcine IFN-alpha genes or pseudogenes belonging to a multigene family of at least 12 members. One of these genes was subcloned in plasmid pUC8 and the recombinant plasmid obtained was shown to direct the synthesis of a low but detectable IFN-alpha activity in Escherichia coli JM103. The sequence of this porcine IFN-alpha gene (Po IFN-alpha 1) was determined. As expected, it contained no introns and encoded a 189-amino-acid-long preprotein with a putative signal peptide of 23 residues. The homology to human (Hu)IFN-alpha 1 was 78.5% at the nucleotide level and 64% at the amino acid level.

Structure and expression of a new murine interferon-alpha gene: MuIFN-alpha I9

A new murine alpha interferon gene, MuIFN-alpha I9, isolated from a BALB/c genomic clone, was characterized. It encodes a mature polypeptide of 167 amino acids (aa), presenting from 77 to 86% homology with the seven other MuIFN-alpha I aa sequences previously described. When compared to the latter, pre-IFN-alpha I9 has 13 distinctive aa, and, remarkably, ten of these occur in pairs. The coding region, fused to the SV40 early promoter and introduced into COS monkey cells, directed the transient secretion of an acid-stable functional IFN of 18-21 kDa. The production in this system reached levels of 300 000 units per 0.15 ml. A comparison of the aa sequence of different murine, rat, bovine, and human alpha and beta IFNs revealed certain common features allowing us to propose a putative secondary structure of the IFN proteins. A detailed analysis of results previously published by us and by others showed that the MuIFN-alpha I9 gene is, together with a least twelve other MuIFN-alpha I genes, located on chromosome 4.

Cloning and expression of the chromosomal immune interferon gene of the rat

The chromosomal immune interferon gene of the rat (IFN-gamma) was identified by screening a recombinant rat lambda phage library with a human IFN-gamma cDNA probe. In contrast to the genes of other rat IFNs, this rat IFN-gamma chromosomal gene contains introns and its structural organization closely resembles that of the human and murine IFN-gamma genes. The rat IFN-gamma gene encodes a signal sequence of 19 amino acids followed by the mature IFN-gamma protein of 137 amino acids. The gene was expressed under control of the simian virus 40 (SV40) early promoter in Chinese hamster ovary (CHO) cells deficient in dihydrofolate reductase (DHFR) after co-transformation with a plasmid containing the mouse DHFR gene. Initial transformants with a DHFR+ phenotype produced IFN-gamma titres ranging from 20 to 1600 units/ml. After stepwise increases in the concentration of methotrexate (MTX) in the growth medium of transformed CHO cells, MTX-resistant clones producing 80 000-100 000 units per ml were isolated. Protein analysis of supernatants of these MTX-resistant cells by polyacrylamide gel electrophoresis revealed a product with an apparent mol. wt. of 18 000 daltons which was not detectable in the growth medium of DHFR+ transformants that did not produce IFN. The product was identified as rat IFN-gamma and constituted approximately 5% of the proteins excreted from these cells.