Synthesis, antiviral activity, and conformational characterization of mouse-human alpha-interferon hybrids

Reconstitution of virus-mediated expression of interferon alpha genes in human fibroblast cells by ectopic interferon regulatory factor-7

Type I interferons constitute an important part of the innate immune response against viral infection. Unlike the expression of interferon (IFN) B gene, the expression of IFNA genes is restricted to the lymphoid cells. Both IFN regulatory factor 3 and 7 (IRF-3 and IRF-7) were suggested to play positive roles in these genes expression. However, their role in the differential expression of individual subtypes of human IFNA genes is unknown. Using various IFNA reporter constructs in transient transfection assay we found that overexpression of IRF-3 in virus infected 2FTGH cells selectively activated IFNA1 VRE, whereas IRF-7 was able to activate IFNA1, A2, and A4. The binding of recombinant IRF-7 and IRF-3 to these VREs correlated with their transcriptional activation. Nuclear proteins from infected and uninfected IRF-7 expressing 2FTGH cells formed multiple DNA-protein complexes with IFNA1 VRE, in which two unique DNA-protein complexes containing IRF-7 were detected. In 2FTGH cells, virus stimulated expression of IFNB gene but none of the IFNA genes. Reconstitution of IRF-7 synthesis in these cells resulted, upon virus infection, in the activation of seven endogenous IFNA genes in which IFNA1 predominated. These studies suggest that IRF-7 is a critical determinant for the induction of IFNA genes in infected cells.

Low-dose oral type I interferons reduce early virus replication of murine cytomegalovirus in vivo

Immunity to viral infections involves both innate and antigen-specific immune responses. The antiviral properties of interferons (IFNs) are part of the innate immune response. Low doses of type I IFNs (IFN-alpha and IFN-beta) administered daily (10 IU per mouse) by the oral route significantly reduced the early replication of murine cytomegalovirus (MCMV) in both the spleen and liver of MCMV-infected susceptible BALB/c mice. Significant inhibition of virus replication was observed for two different inoculum doses of virus (2 x 10(4) pfu per mouse [0.6 LD50] and 2 x 10(4.12) pfu per mouse [0.8 LD50]). Analysis of IFN retention, using [35S]-labeled IFN-alpha1 compared with the nonreceptor binding mutant IFN-alpha1 (R33M) administered orally to mice, revealed binding of wild-type IFN-alpha1 to several tissues. In particular, IFN was retained by tissues proximal to lymphoid regions, including the posterior nasal cavity, posterior tongue, small intestine, and rectum. These findings suggest that type I IFNs may inhibit MCMV replication by distal binding of the orally administered IFN to various tissues, which in turn augment the primary immune response to virus infection.

Structure-activity of type I interferons

Type I IFNs constitute a family of proteins exhibiting high homology in primary, secondary, and tertiary structures. They interact with the same receptor and transmit signals to cellular nucleus through a similar mechanism, eliciting roughly homogeneous biological activity. Nevertheless, the members of that family, IFN alpha species, IFN beta and IFN omega, due to local differences in the structure sometime show distinct properties. From the reported data it results that even minute changes or differences in the primary sequences could be responsible for a significant variety of biological actions, thus inducing to the hypothesis that Type I IFNs, rather than to be the result of a redundant replication during the evolution play definite roles in the defense of living organisms to foreign agents.

Role of interferon-stimulated gene ISG-15 in the interferon-omega-mediated inhibition of human immunodeficiency virus replication

Interferon-alpha (IFN-alpha) inhibits human immunodeficiency virus (HIV) replication in vivo and in vitro. In this study, we show that IFN-omega (IFN-omega) is also a potent inhibitor of HIV replication in vitro and that both laboratory and primary isolates of HIV-1 are more sensitive to IFN-omega than to IFN-alpha 2. Like IFN-alpha 2, IFN-omega inhibited proviral synthesis in acutely infected cells, but in contrast to IFN-alpha 2, IFN-omega did not alter the levels of HIV-1 unspliced messages. Yet, inhibition of HIV protein synthesis was greater in IFN-omega-treated than in IFN-alpha 2-treated cells. Whereas expression of IFN-stimulated genes was transient in IFN-alpha 2-treated cells, their expression was sustained in IFN-omega-treated cells. Expression of ISG-15 in particular was higher on treatment with IFN-omega than with IFN-alpha 2. Overexpression of ISG-15 in IFN-alpha 2-treated cells mimicked the effects of IFN-omega. In untreated cells, it resulted in the trapping of HIV unspliced RNA in the nucleus and a decrease in cytoplasmic HIV transcripts and HIV protein synthesis. These findings suggest that the sustained induction of IFN-stimulated genes by IFN-omega and that of ISG-15 in particular may confer a higher therapeutic index to IFN-omega in controlling HIV infection.

Interferon-alpha hybrids

The alpha-interferons (IFN-alpha) belong to a family of polypeptides comprising several subtypes. Using recombinant DNA technology, it has been possible to create IFN hybrids that provide novel combinations of the amino acid residues from the parental protein sequences. They have been used to study structure-activity relationships of IFN-alpha and interactions with the IFN-alpha receptor, and to create analogs of natural IFNs with novel properties for potential therapeutic application. The biological data obtained with these hybrids are now evaluated in terms of the published structural and homology models of IFN-beta and -alpha.

Structure/function studies with interferon tau: evidence for multiple active sites

A novel interferon (IFN), called IFN-tau (IFN-tau), has recently been discovered and has been shown to be a pregnancy recognition hormone. Unlike known IFNs, however, IFN-tau exhibits high antiviral and antiproliferative activity without cytotoxicity. The structural basis for IFN-tau function has been examined using six overlapping synthetic peptides corresponding to the entire ovine (Ov) IFN-tau sequence. Four peptides representing amino acids 1-37, 62-92, 119-150, and 139-172 inhibited OvIFN-tau antiviral activity in a dose-dependent manner. Polyclonal antipeptide antisera directed against the same four peptides blocked OvIFN-tau binding and antiviral activity, confirming the specificity of the peptide competitions. Because IFN-tau and IFN-alpha both interact with the type I IFN receptor, peptide inhibition of bovine and human IFN alpha activity was also determined. Of importance, only three peptides, OvIFN-tau (62-92), (119-150), and (139-172) inhibited IFN-alpha antiviral activity. The amino-terminal IFN-tau peptide, OvIFN-tau(1-37), was not inhibitory. These data suggest that the internal and carboxy-terminal reactive domains of IFN-tau may interact with a common type I IFN site on the receptor, while the amino terminus interacts with a site that elicits activity unique to OvIFN-tau. Finally, the antiproliferative activity of OvIFN-tau was localized primarily to the broad carboxy-terminal region, with OvIFN-tau(119-150) being the most effective inhibitor of OvIFN-tau-induced reduction of cell proliferation. Thus, multiple domains of IFN-tau have functional significance.(ABSTRACT TRUNCATED AT 250 WORDS)

A homology model of human interferon alpha-2

An atomic coordinate five alpha-helix three-dimensional model is presented for human interferon alpha-2 (HuIFN alpha 2). The HuIFN alpha 2 structure was constructed from murine interferon beta (MuIFN beta) by homology modeling using the STEREO and IMPACT programs. The HuIFN alpha 2 model is consistent with its known biochemical and biophysical properties including epitope mapping. Lysine residues predicted to be buried in the model were primarily unreactive with succinimidyl-7-amino-4-methylcoumarin-3-acetic acid (AMCA-NHS), a lysine modification agent, as shown by mass spectrometric analysis of tryptic digests. N-terminal sequence analysis of polypeptides generated by limited digestion of HuIFN alpha 2 with endoproteinase Lys-C demonstrated rapid cleavage at K31, which is consistent with the presence of this residue in a loop in the proposed HuIFN alpha 2 model. Based on this model structure potential receptor binding sites are identified.

Structural, functional and evolutionary implications of the three-dimensional crystal structure of murine interferon-beta

The crystal structure of recombinant murine interferon-beta as elucidated by Senda et al. (Proc. Jap. Acad. 66B: 77-80 (1990); EMBO J. 11: 3193-3201 (1992)) appears to represent the basic structural framework of all Type I interferons including interferons-beta and all subtypes of interferons-alpha of various mammalian origin. Now the huge accumulated data on the structure-activity relationship of Type I interferons using various chemical and genetic techniques can be systematically evaluated in terms of the three-dimensional structure. Structural comparison with other cytokines, for which three-dimensional structures have been established, including interferon-gamma and considerations on the evolution of cytokines and cytokine receptors are also given.

Definition of receptor binding domains in interferon-alpha

Earlier studies from this laboratory had identified three regions in interferon-alpha (IFN-alpha) that influence the active conformation of the molecule. These domains are associated with the amino acid residues 10-35, 78-107, and 123-166. In this report, we define these domains more accurately by identifying their critical clusters of amino acids. Using a panel of IFN-alpha 2a variants in antiviral, growth inhibitory, and receptor binding studies, we are able to show that these three domains, defined by residues 29-35, 78-95, and 123-140, are likely located on the surface of the molecule, with domains 29-35 and 123-140 in close spatial proximity. We conclude that the 29-35 and 123-140 domains are responsible for IFN-alpha receptor binding interactions and constitute receptor recognition sites in IFN-alpha. Extrapolating from our biological activity data, in the context of a number of predictive algorithms that provide insights into the hydrophobicity/hydrophilicity, surface probability, and flexibility of amino acid clusters, we infer that the residues 29-35 influence the active configuration of IFN-alpha most significantly. This region likely represents a loop structure that is relatively rigid in configuration. The carboxy-terminally located strategic domain, 123-140, is comprised of two clusters of amino acid residues, one that forms part of a rigid alpha-helix, the other a more flexible loop structure. Similarly, the 78-95 domain comprises a portion of an alpha-helical structure that is followed by a loop structure. Close examination of the amino acid sequences in all three regions among the different species of IFN-alpha s and human IFN-beta indicate that the 29-35 and 123-140 domains are most highly conserved, yet some variance is apparent in the 78-95 domain. We propose that the 78-95 region influences species specificity among the murine and human IFN-alpha s and determines the differential specificity of action between human IFN-alpha and human IFN-beta.

Intermolecular homologies of human interferon-alpha

Human interferon-alpha 2 (IFN) was analyzed by homology search computer program with the use of protein primary structures data bases. Results indicate that four domains with heightened ability to form homology pairs with different proteins exist in the IFN molecule. These domains occupy regions 35-56, 72-85, 97-110 and 124-136, mainly between the alpha-helical cylinders on the tertiary structure models. Additionally, results show in IFN structure the presence of amino-acid motifs that create the opportunity for this cytokine to influence directly the processes of DNA functioning in cell nuclei.

Structure/function studies of murine interferon-alpha 1 using site-directed mutagenesis followed by in vitro synthesis

Site-directed in vitro mutagenesis followed by in vitro transcription and translation has been used to study structure/function relationships for murine interferon-alpha 1 (MuIFN-alpha 1). The mature form of the MuIFN-alpha 1 protein was expressed as well as analogue forms with amino acid substitutions at positions 33, 71, 72, 123 and 133. These positions were chosen on the basis of known human interferon-alpha structure/function relationships. Biological assays for antiviral activity on murine cells and natural killer cell activation have been performed for each of the proteins produced. The data obtained have been interpreted in the light of previous human and murine interferon-alpha structure/function work and the recently published three-dimensional structure of murine type I interferon.

Structure-function relationships of the hematopoietic growth factors

The hematopoietic growth factors are a family of glycoproteins involved in the production of blood cells from their bone marrow precursors and in the activation of mature blood cells. Much has been learned about the structural features of these molecules responsible for their characteristic biological activities. Most studies have been based upon mutagenesis strategies of intact polypeptides and on epitope mapping of informative monoclonal antibodies to the growth factors. A more limited amount of physical data is available. This review will summarize these findings, highlight the growing body of evidence suggesting that many of these proteins share common evolutionary origins and structural elements, and hopefully point to the directions being taken for further investigations of these scientifically informative and clinically useful group of proteins.

Cytokine conformations: predictive studies

The amino acid sequences of human and murine haemopoietins have been analysed using algorithms predictive for secondary structure. The results for 19 of these proteins (human and murine interleukins 2, 3, 4, 5, 6, 7 and granulocyte, macrophage and granulocyte macrophage-colony stimulating factors as well as human erythropoietin) suggest that they each contain a 4-alpha-helical bundle, ca 25 A long, as a common conformational feature. The most important predictive indicator was considered to be the occurrence of quasi-repeating sequences of seven amino acids of the form (a-b-c-d-e-f-g), with apolar side chains (usually leucine) lying alternately three and four residues apart in the a and d positions. As with other proteins of known secondary structure this periodicity favours the formation of alpha-helical elements, each with an apolar external strip, which interdigitate closely with one another when tested appropriately. Molecular models based on these putative 4-alpha-helical bundles are presented--with special reference to human granulocyte macrophage-colony stimulating factor. The extent to which such models are consistent with experiments designed to delineate receptor binding sites is discussed.

Relative antiviral activity of in vitro-synthesized murine interferon-alpha 4 and -alpha 1

Murine interferon-alpha 4 (MuIFN-alpha 4) is notable among the MuIFN-alpha subtypes because it lacks 5 amino acids corresponding to positions 103-107 of the other subtypes, yet is the most highly expressed subtype. Site-directed in vitro mutagenesis has been used to modify the genes coding for MuIFN-alpha 4 and MuIFN-alpha 1. The modifications have allowed (i) the in vitro expression of the mature form of each MuIFN-alpha subtype and (ii) the insertion of five amino acids, corresponding to amino acid positions 103-107 of MuIFN-alpha 1, into the MuIFN-alpha 4 sequence. In contrast to previously published data MuIFN-alpha 4 and MuIFN-alpha 1 show only a twofold difference in antiviral activity, with MuIFN-alpha 4 being the more active subtype. In keeping with this observation, it was also found that insertion of the five "missing" amino acids into MuIFN-alpha 4 resulted in an analogue MuIFN-alpha with antiviral activity equivalent to MuIFN-alpha 1. It may be inferred from this work that the deletion of amino acids 103-107 (QVGVQ) is solely responsible for the difference in antiviral activity between MuIFN-alpha 4 and MuIFN-alpha 1.

Identification of a decapeptide region of human interferon-alpha with antiproliferative activity and homology to an immunosuppressive sequence of the retroviral transmembrane protein P15E

We have identified a 10-amino acid sequence (amino acid, 9-18) from interferon-alpha (IFN-alpha) that when presented as a synthetic peptide inhibits both the proliferation of the Daudi lymphoblastoid cell line and the antigen receptor-stimulated proliferation of fresh human T lymphocytes. This sequence, which was identified by virtue of its sequence similarity (70% identity) to the immunosuppressive sequence of the retroviral transmembrane protein p15E, represents the smallest fragment of IFN-alpha that has been shown to date to be biologically active.

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.

The biological activity of interferon alpha is influenced by two distinct regions in the protein

With the aim to assign differences in activity between murine interferon-alpha 1 and -alpha 4 to specific amino acids, we have constructed hybrid genes and analysed the antiviral properties of the corresponding hybrid proteins. The hybrid genes were constructed by means of homologous recombination between the alpha 1 and alpha 4 genes in Escherichia coli. Hybrids in which the N-terminal part is derived from alpha 1 show that two regions have a major effect on the activity: amino acid 10-20 and 55-67. When comparing hybrids with N-terminal alpha 4 sequences, transitions in activity are found in the same regions. Interestingly, the curves for the two sets of hybrids are exactly each others mirror image.

Conformational homologies among cytokines: interleukins and colony stimulating factors

Some 30 cytokine amino acid sequences (mainly interleukins, colony stimulating factors and tumor necrosis factors) have been examined for evidence of secondary structure as well as longer-range interactions of a type likely to lead to stable alpha-helical bundles. Most, though not all, of the cytokines examined have a high predicted alpha-helical content (40-60%) and quasi-repeating heptads containing i/i + 3 apolar periodicities. This major subset of the cytokines is predicted to be characterized by molecules in which 4-alpha-helical bundles with an average length of 25A are the most marked conformational features. Based on these conclusions, we suggest structures for huG-CSF, huGM-CSF and muIL-5 in which defined loop segments at the ends of helical bundles are the most likely sites for binding and recognition by specific cell receptors. As such, they provide a means for testing or refining the three working models we have defined, using currently available methods of site-directed substitution and deletion mutagenesis, as well as synthetic peptides corresponding to the proposed loop sequences and the use of monoclonal antibodies of defined epitopic specificity. The structure arrived at for huGM-CSF is consistent with the limited data currently available concerning the residues which are important for binding and activity.