Lytic infection of pseudorabies virus in the presence of spermine, spermidine, or DFMO

Inhibition of lytic infection of pseudorabies virus by arginine depletion

Pseudorabies virus (PRV) is a member of Alphahepesviruses; it is an enveloped virus with a double-stranded DNA genome. Polyamines (such as spermine and spermidine) are ubiquitous in animal cells and participate in cellular proliferation and differentiation. Previous results of our laboratory showed that the PRV can accomplish lytic infection either in the presence of exogenous spermine (or spermidine) or depletion of cellular polyamines. The amino acid arginine is a precursor of polyamine biosynthesis. In this work, we investigated the role of arginine in PRV infection. It was found that the plaque formation of PRV was inhibited by arginase (enzyme catalyzing the conversion of arginine into ornithine and urea) treatment whereas this inhibition can be reversed by exogenous arginine, suggesting that arginine is essential for PRV proliferation. Western blotting was conducted to study the effect of arginine depletion on the levels of structural proteins of PRV in virus-infected cells. Four PRV structural proteins (gB, gE, UL47, and UL48) were chosen for examination, and results revealed that the levels of viral proteins were obviously reduced in long time arginase treatment. However, the overall protein synthesis machinery was apparently not influenced by arginase treatment either in mock or PRV-infected cells. Analyzing with native gel, we found that arginase treatment affected the mobility of PRV structural proteins, suggesting the conformational change of viral proteins by arginine depletion. Heat shock proteins, acting as molecular chaperons, participate in protein folding and translocation. Our results demonstrated that long time arginase treatment could reduce the expression of cellular heat shock proteins 70 (hsc70 and hsp70), and transcriptional suppression of heat shock protein 70 gene promoter was one of the mechanisms involved in this reduced expression.

Regulation of arginase II by interferon regulatory factor 3 and the involvement of polyamines in the antiviral response

The innate antiviral response requires the induction of genes and proteins with activities that limit virus replication. Among these, the well-characterized interferon beta (IFNB) gene is regulated through the cooperation of AP-1, NF-kappaB and interferon regulatory factor 3 (IRF-3) transcription factors. Using a constitutively active form of IRF-3, IRF-3 5D, we showed previously that IRF-3 also regulates an IFN-independent antiviral response through the direct induction of IFN-stimulated genes. In this study, we report that the arginase II gene (ArgII) as well as ArgII protein concentrations and enzymatic activity are induced in IRF-3 5D-expressing and Sendai virus-infected Jurkat cells in an IFN-independent manner. ArgII is a critical enzyme in the polyamine-biosynthetic pathway. Of the natural polyamines, spermine possesses antiviral activity and mediates apoptosis at physiological concentrations. Measurement of intracellular polyamine content revealed that expression of IRF-3 5D induces polyamine production, but that Sendai virus and vesicular stomatitis virus infections do not. These results show for the first time that the ArgII gene is an early IRF-3-regulated gene, which participates in the IFN-independent antiviral response through polyamine production and induction of apoptosis.

Arginine metabolism during macrophage autocrine activation and infection with mouse hepatitis virus 3

In contrast to BALB/c mouse macrophages (Mphi), Mphi from the A/J mouse strain, upon activation by exogenous interferon gamma (IFNgamma), develop an anti-mouse hepatitis virus 3 (MHV3) state which correlates with resistance to virus infection. To investigate the autocrine activation of BALB/c and A/J Mphi, we activated them with interleukin-12 (IL-12) and/or IL-18, and quantified IFNgamma production, the anti-MHV3 state and arginine metabolism. Synergistic activation by IL-12/IL-18 induced the expression of the IFNgamma gene in Mphi from both mouse strains. In bone marrow (BM) or peritoneal (P) Mphi of specific pathogen-free (spf) mice of both strains, IFNgamma synthesis occurred only with a synergistic IL-12/IL-18 activation and showed increasing levels from 24 to 72 h of activation. In contrast, when non-spf mice were used in the assay, their PMphi synthesized higher IFNgamma levels upon activation with only IL-12 or only IL-18 or both. The BALB/c Mphi were always capable of synthesizing higher amounts of IFNgamma than the A/J Mphi. An anti-MHV3 state was observed only in A/J Mphi upon activation with IL-12/IL-18 or IFNgamma regardless of their origin from the peritoneum or bone marrow. Arginine metabolism in activated and/or virus infected BMMphi was investigated through nitric oxide (NO) and arginase induction as well as the consumption of arginine and synthesis of citrulline, ornithine and spermine. The results showed that both BALB/c and A/J BMMphi populations released NO only after activation with IL-12/IL-18 or IFNgamma. Arginase was not induced in BMMphi from both strains by IL-12/IL-18 or IFNgamma but only by IL-4/IL-10. Higher arginine consumption was observed in BMMphi from both strains upon activation with IL-4 or IFNgamma which further increased, in this case, when the cells were infected with MHV3. As a consequence of nitric oxide synthase synthesis and arginine consumption in IFNgamma activated BMMphi, we observed a higher synthesis of citrulline. High levels of ornithine were induced only upon IL-4 activation. Polyamine synthesis was higher in A/J BMMphi than in BALB/c ones, which correlated with the slightly lower levels of ornithine observed. Upon infection with MHV3, we observed a higher synthesis of spermine. IL-12/IL-18 or IFNgamma activation, mainly in MHV3 infected cells, led to a decreased synthesis of polyamines, notably spermine, only in A/J BMMphi. Difluoromethylornithine treatment, which leads to inhibition of polyamine synthesis, induced a decreased MHV3 multiplication in both BALB/c and A/J BMMphi. Altogether these data show the relevance of IFNgamma, from the autocrine or paracrine pathway, and arginine metabolism for the control of MHV3 replication in Mphi of a resistant mouse strain.