Influence of the xyloadenosine analogue of 2',5'-oligoriboadenylate on poly(A)-specific, 2',5'-oligoriboadenylate degrading 2',3'-exoribonuclease and further enzymes involved in poly(A)(+)mRNA metabolism

Homologies between different forms of 2-5A synthetases

Sequence analyses of 2-5A synthetases of class I (M(r) 40,000-46,000) revealed high homology among them. The cDNA coding for the M(r) 69,000 2-5A synthetase of class II displayed in the second half a likewise high homology to the complete sequences of class I enzymes. This high degree of conservation of the 2-5A synthetases supports the assumption that these enzymes play important roles during virus infection (Williams et al. 1979; Coccia et al. 1990) and in the control of growth and differentiation of mammalian cells (Williams and Silverman 1985).

The 2-5A system and HIV infection

2',5'-Oligoadenylates (2-5A) have an essential role in the establishment of the antiviral state of a cell exposed to virus infection. The key enzymes of the 2-5A system are the 2-5A forming 2',5'-oligoadenylate synthetase (2-5OAS), the activity of which depends on the presence of viral or cellular double-stranded RNA (dsRNA), and the 2-5A-activated ribonuclease (RNase L). Basic research in recent years has shown that the 2-5A system is a promising target for anti-HIV chemotherapy, particularly due to its interaction with double-stranded segments within HIV RNA. Two new strategies have been developed which yield a selective antiviral effect of 2-5A against HIV-1 infection: (1) development of 2-5A analogues displaying a dual mode of action (activation of RNase L and inhibition of HIV-1 RT) and (2) intracellular immunization of cells against HIV-1 infection by application of the HIV-1-LTR--2-5OAS hybrid gene. A further strategy is the inhibition of DNA topoisomerase I by longer 2-5A oligomers.

(2'-5')Oligoadenylate and intracellular immunity against retrovirus infection

1. The double-stranded RNA-dependent 2',5'-oligoadenylate (2-5A) synthetase/ribonuclease L (RNase L) system plays an essential role in the establishment of the antiviral state of a cell exposed to virus infection. 2. Until recently, the application of 2-5A derivatives to reinforce this system seemed to be limited mainly due to the low specificity of RNase L for viral RNA. 3. Two new strategies have been developed which yield a selective antiviral effect of 2-5As at least against human immunodeficiency virus-1 (HIV-1) infection: (i) an "intracellular immunization" approach using 2-5A synthetase cDNA linked to HIV trans-acting response element (TAR) and (ii) inhibition of retroviral reverse transcriptase activity by 2-5A analogues.

Alteration of nuclear (2'-5')oligoriboadenylate synthetase and nuclease activities preceding replication of human immunodeficiency virus in H9 cells

After infection of the respective target cells with the human immunodeficiency virus (HIV-1) viral progeny is produced only after a short temporary delay of some days, depending on cell type. After this period of time a sudden onset of HIV-1 protein synthesis with a dramatic increase in virus release occurs. (2'-5')Oligoriboadenylates [(2'-5')A], capable to activate a latent ribonuclease (RNase L) degrading both mRNA and rRNA, are known mediators involved in the early response of cells to virus infection. Here we show that the (2'-5')A-synthesizing (2'-5')A synthetase, which is inducible by interferon and activated by double-stranded RNA, as well as a (2'-5')A nuclease (2',3'-exoribonuclease) are associated with the nuclear matrix of uninfected and infected H9 cells, also in the absence of interferon. Infection of H9 cells with HIV-1 was found to cause a strong (7.7-fold) enhancement of (2'-5')A synthetase activity and a smaller (2-fold) increase of 2',3'-exoribonuclease activity. Simultaneously the concentration of synthesized (2'-5')A increased 5 to 10 times in isolated nuclei. After incubation for 2 to 3 days both enzyme activities reached a maximum and then dropped below their initial values. Concomitantly a drastic increase in virus production occurred, as judged by reverse transcriptase activity in the culture fluid. These results suggest that the (nuclear matrix-associated) (2'-5')A system might be important during the initial stage of HIV infection, also by destructing matrix-bound viral messengers.

Induction of gamma-interferon by avarol in human peripheral blood lymphocytes

Avarol is a cytostatic and anti-human immunodeficiency virus (HIV) agent. In this study, the avarol caused induction of gamma-interferon (IFN-gamma) in buffy coat cells (human peripheral blood lymphocytes) is demonstrated by immunological and molecular biological techniques. IFN-gamma production was detected after a 24-hr incubation period with avarol; maximal production was obtained after 5 days in the presence of the optimal avarol concentration of 0.75 microgram/ml. Blotting experiments using human IFN-gamma cDNA and beta-actin cDNA containing plasmids showed that in the absence of avarol no IFN-gamma transcripts were present in lymphocytes. Already after a 24-hr incubation with avarol, IFN-gamma gene induction was detected, and maximal induction was found after a 5-day incubation period. The enhanced IFN-gamma production seems to be caused by a change at the transcriptional and/or post-transcriptional level, but not during subsequent nucleocytoplasmic transport of mRNA. This molecular event is specific, at least in relation to the expression of the beta-actin gene. Our studies demonstrate that avarol displays, besides its potential anti-tumor and anti-HIV activity, a potential immunomodulating effect.