Antiviral actions of interferon. Interferon-regulated cellular proteins and their surprisingly selective antiviral activities.

Considerable progress has been made in the understanding of the molecular biology of the human interferon system. The genes encoding the interferons, their receptors, and the proteins that mediate many of their biological effects have been molecularly cloned and characterized. The availability of complete cDNA clones of components of the interferon systems has contributed significantly to our understanding of both the biology and the biochemistry of the antiviral actions of interferons. At the biological level, the antiviral effects of interferon may be viewed to be virus-type nonspecific. That is, treatment of cells with one type or even subspecies of interferon often leads to the generation of an antiviral state effective against a wide array of different RNA and DNA animal viruses. However, at the biochemical level, the antiviral action of interferon is often virus-type selective. That is, the apparent molecular mechanism which is primarily responsible for the inhibition of virus replication may differ considerably between virus types, and even host cells. For example, the IFN-regulated Mx protein selectively inhibits influenza virus but not other viruses when constitutively expressed in mouse cells. The IFN-regulated 2',5'-oligoadenylate synthetase selectively inhibits EMC and mengo viruses, two picornaviruses, but not viruses of other families when constitutively expressed in transfected cells. Some viruses are typically insensitive to the antiviral effects of interferon, both in cell culture and in intact animals. This lack of sensitivity to IFN may result from a virus-mediated direct antagonism of the interferon system. For example, in the case of adenovirus, the activation of the IFN-regulated RNA-dependent P1/elF-2 protein kinase is blocked by the virus-associated VA RNA. The relative sensitivity to interferon of different animal viruses varies appreciably. All three of the basic components required to measure an antiviral response may play a role in determining the relative effectiveness of the antiviral response: the species of interferon administered; the kind of cell treated; and, the type of virus used to challenge the interferon-treated host cell. Thus, the relative sensitivity to interferon observed for a particular interferon-cell-virus combination is likely the result of the equilibrium between the many agonists and antagonists which contribute to the overall response. That is, the relative sensitivity of a virus to the inhibitory action of IFN is governed by the qualitative nature and quantitative amount of the individual IFN-regulated cell proteins that may collectively contribute to the inhibition of virus replication.(ABSTRACT TRUNCATED AT 400 WORDS)     

Molecular regulation of interferon antiviral response in fish

Interferon (IFN) response is the first line of host defense against virus infection. The recent years have witnessed tremendous progress in understanding of fish IFN antiviral response. Varied number of IFN genes has been identified in different fish species but obviously, they do not show a one-to-one orthologous relationship with mammalian IFN homologs. These genes are divided into two groups with different abilities to induce downstream gene expression through binding to different receptor complexes. Consistently, some fish IFN-stimulated genes such as Mx and PKR have been confirmed for their antiviral effects. In this review, we focus on how fish cells respond to IFNs and how fish IFNs are triggered through TLR pathway and RLR pathway. We highlight the roles of IRF3 and IRF7 in activation of fish IFN response. In addition, the unique mechanisms underlying IRF3/7-dependent fish IFN response and auto-regulation of fish IFN gene expression are discussed.     

Inhibition by estrone of the antiviral protection and interferon elicited by interferon inducers in mice

The susceptibility of mice to infection with MM virus is markedly increased after treatment with the sex hormone estrone. Studies were undertaken to determine if either suppression of production or interference with the action of interferon was involved in this phenomenon. The protection of mice against MM virus infection by several interferon-inducing agents was partially impeded by estrone treatment either 24 hr before or 24 hr after the administration of the inducing agent. The titers of circulating interferon induced by each of the agents were lower in estrone-pretreated animals than in untreated controls. The protection of mice by exogenous L cell interferon was blocked only when the hormone was given prior to the interferon. It is concluded that the adverse activity of estrone is related to its ability to interfere with the action of interferon.     

Effect of thymosin on interferon production and antiviral resistance in mice

The 5th and 6th fractions of thymosin, a hormone of the thymus gland, stimulated interferon production both in vivo (experiments in white and CBA mice) and in vitro in CBA mouse splenocytes when different interferon inducers were used (phage dsRNA, poly(G): poly(C), NDV, and mitogens). The highest stimulating effect in vivo was observed with interferon induction 6-8 hours after thymosin administration. An increase in production of both alpha/beta and gamma interferons under the influence of thymosin was observed. Thymosin alone induced no interferon synthesis.     

人新型干扰素K的基因克隆、表达、纯化及其抗病毒活性的初步研究

目的制备人干扰素κ(hIFN-κ)并初步研究其生物学活性.方法克隆hIFN-κ的cDNA并根据大肠埃希菌的密码子偏好性人工合成了hIFN-κ基因,在大肠埃希菌DH5α中高效表达、纯化后测定了rhIFN-κ的多种生物学活性,包括抗病毒活性、抗细胞增殖活性、种属特异性以及NK细胞调节活性.结果成功地获得了高纯度的rhIFN-κ,纯度在90%以上.利用WISH-VSV系统检测rhIFN-κ的抗病毒活力为2.0×106 IU/mg.与rhIFN-α2b的比较发现,rhIFN-κ无论在抗病毒活性、细胞生长抑制,还是在促NK细胞活性方面均弱于前者.结论rhIFN-κ在不同种属来源细胞上的抗病毒活性因种属来源而异,不同的病毒对rhIFN-κ的敏感性是不同的.     

Human herpesvirus portal proteins: Structure,function, and antiviral prospects

Herpesviruses (Herpesvirales) and tailed bacteriophages (Caudovirales) package their dsDNA genomes through an evolutionarily conserved mechanism. Much is known about the biochemistry and structural biology of phage portal proteins and the DNA encapsidation (viral genome cleavage and packaging) process. Although not at the same level of detail, studies on HSV‐1, CMV, VZV, and HHV‐8 have revealed important information on the function and structure of herpesvirus portal proteins. During dsDNA phage and herpesviral genome replication, concatamers of viral dsDNA are cleaved into single length units by a virus‐encoded terminase and packaged into preformed procapsids through a channel located at a single capsid vertex (portal). Oligomeric portals are formed by the interaction of identical portal protein monomers. Comparing portal protein primary aa sequences between phage and herpesviruses reveals little to no sequence similarity. In contrast, the secondary and tertiary structures of known portals are remarkable. In all cases, function is highly conserved in that portals are essential for DNA packaging and also play a role in releasing viral genomic DNA during infection. Preclinical studies have described small molecules that target the HSV‐1 and VZV portals and prevent viral replication by inhibiting encapsidation. This review summarizes what is known concerning the structure and function of herpesvirus portal proteins primarily based on their conserved bacteriophage counterparts and the potential to develop novel portal‐specific DNA encapsidation inhibitors.     

Tunicamycin treatment inhibits the antiviral activity of interferon in mice

Earlier we reported that tunicamycin (TM) treatment of L cells in vitro significantly enhances the antiviral activity of interferon (IFN) against viruses (such as vesicular stomatitis, Sindbis, and herpes simplex) which bud from membranes. However, no such enhancement of the antiviral activity of IFN by TM was observed against encephalomyocarditis virus (EMCV) (nonbudding). We were interested to know whether TM would similarly enhance the antiviral activity of IFN and IFN inducers in vivo against Semliki Forest virus (SFV) and EMCV infections in mice. It was observed that TM alone (0.001 to 5.0 micrograms per mouse) did not protect mice against infections of SFV and EMCV; instead, TM-treated mice died with virus-specific paralytic symptoms earlier than untreated animals. The enhanced mortality in TM-treated and SFV- or EMCV-infected mice was associated with the concomitant increase in virus titer in brain tissue. IFN significantly protected mice against SFV and EMCV infections. The antiviral protection of mice by IFN against both the viruses was markedly inhibited by TM administration. IFN inducers (polyinosinic acid-polycytidylic acid, 6-MFA [a mixture of proteins, polysaccharides, and double-stranded DNA isolated from Aspergillus ochraceus ATCC 28706]) protected a significant number of mice against SFV infection. However, no such protection was observed in mice injected with a combination of TM and IFN inducer. These results indicate that TM treatment inhibits the antiviral action of IFN or IFN inducers in vivo.     

The interferon in TLR signaling: more than just antiviral

The Toll-like receptor (TLR) system is responsible for the recognition of infectious agents leading to initiation of the primary innate, and later adaptive, immune response. Genetic technologies have enabled the discovery of new factors involved in these systems, their genetic manipulation and the global analyses of their effects on gene expression. Furthermore, this increased understanding has resulted in the need to reassess our preconceptions about the functions of well-known molecules. For example, type I interferons (IFNs), which were discovered as antiviral proteins, are now known to be produced in response to TLR activation by many pathogens, including bacteria. Should we be surprised? Has the inflammatory response unexpectedly highjacked the body's antiviral system? Or are we too easily blinkered by preconceptions from how a compound was discovered?     

Mouse genes influence antiviral action of interferon in vivo.

BALB/c mice are more sensitive to the antiviral effect of interferon than C57BL/6 mice, as demonstrated by experiments involving protection against lethal infection with encephalomyocarditis virus. This greater sensitivity of the BALB/c genotype to interferon action is in accord with previous observations that the bone marrow-derived erythroid precursors and macrophages of BALB/c mice are more sensitive to the anti-proliferative action of interferon than those of C57BL/6 mice. An analysis of the loci involved in the modulation of the activity of interferon against encephalomyocarditis virus infection was carried out in (BALB/c x C57BL/6)F1 progeny and in six recombinant inbred lines originally derived from a BALB/c x C57BL/6 cross. The antiviral effect of exogenous interferon in the F1 progeny was comparable to the effect in BALB/c mice, indicating dominance of the greater sensitivity to interferon action. The results obtained with the six recombinant inbred lines suggested a multifactorial influence. In vitro, interferon pretreatment of encephalomyocarditis virus-infected BALB/c and C57BL/6 fibroblast cultures did not reveal a difference in sensitivity between the two mouse genotypes. This finding demonstrates that it is not always possible to extrapolate from in vitro to in vivo when sensitivity to interferon action is studied.     

Comparative analysis of interferon and antiviral protein messenger RNAs.

A comparative analysis of interferon and antiviral protein messenger RNAs was carried out. Differences in their biological activities and sedimentation coefficients were found. In RNA preparations from superinduced cells (cells treated with poly(I).poly(C) and antimetabolites) and from cells treated with interferon, messenger RNAs possesing interferon and antiviral activities were detected. The results suggest the existence of two types of mRNA (for interferon and antiviral protein, respectively) and support the hypothetic model of interferon action via an antiviral protein.     

Oromucosal interferon therapy: marked antiviral and antitumor activity.

Oromucosal administration of murine interferon-alpha/beta (IFN-alpha/beta) or individual recombinant species of murine IFN-alpha, IFN-beta, or IFN-gamma or recombinant human IFN-alpha1-8, which is active in the mouse, exerted a marked antiviral activity in mice challenged systemically with a lethal dose of encephalomyocarditis virus (EMCV), vesicular stomatitis virus (VSV), or varicella zoster virus (VZV). The effects observed were dose dependent and similar in magnitude to those observed following parenteral administration of the same dose of IFN. No antiviral activity was observed after oromucosal administration of murine IFN-alpha/beta in animals in which the IFN receptor had been inactivated by homologous recombination. In contrast to parenteral treatment, oromucosal IFN therapy was found to be ineffective when IFNs were administered before virus infection. Oromucosal administration of IFN-alpha also exerted a marked antitumor activity in mice injected i.v. with highly malignant Friend erythroleukemia cells or other transplantable tumors, such as L1210 leukemia, which has no known viral etiology, the EL4 tumor, or the highly metastatic B16 melanoma. These results show that high doses of IFN can be administered by the oromucosal route apparently without ill effect, raising the possibility that the oromucosal route will prove to be an effective means of administering high doses of IFN that are clinically effective but poorly tolerated.     

人新型干扰素κ的基因克隆、表达、纯化及其抗病毒活性的初步研究

目的制备人干扰素κ(hIFNκ)并初步研究其生物学活性。方法克隆hIFNκ的cDNA并根据大肠埃希菌的密码子偏好性人工合成了hIFNκ基因,在大肠埃希菌DH5α中高效表达、纯化后测定了rhIFNκ的多种生物学活性,包括抗病毒活性、抗细胞增殖活性、种属特异性以及NK细胞调节活性。结果成功地获得了高纯度的rhIFNκ,纯度在90%以上。利用WISHVSV系统检测rhIFNκ的抗病毒活力为2.0×106IU/mg。与rhIFNα2b的比较发现,rhIFNκ无论在抗病毒活性、细胞生长抑制,还是在促NK细胞活性方面均弱于前者。结论rhIFNκ在不同种属来源细胞上的抗病毒活性因种属来源而异,不同的病毒对rhIFNκ的敏感性是不同的。