Biomedical subjects
J M Leiter
Publications and source records attributed to J M Leiter.
Positive Darwinian evolution in human influenza A viruses.
We earlier suggested that type A human influenza virus genes undergo positive Darwinian selection through immune surveillance. This requires more favorable amino acid replacements fixed in antigenic sites among the surviving lineages than among the extinct lineages. We now show that viral hemagglutinins fix proportionately more amino acid replacements in antigenic sites in the trunk of the evolutionary tree (survivors) than in the branches (nonsurvivors), demonstrating that type A human influenza virus is undergoing positive Darwinian evolution. The hemagglutinin gene is evolving 3 times faster than the nonstructural gene and the average age of the sampled nonsurvivors is only 1.6 years, so that extinction is not only common but rapid.
Inhibition of influenza virus replication by phosphorothioate oligodeoxynucleotides.
Oligodeoxynucleotides (ODNs) were synthesized and tested for their antiviral activity against influenza viruses. ODNs corresponded to the polymerase PB1 gene of either influenza A/WSN/33 virus or influenza C/JJ/50 virus. All compounds were 20 nucleotides long, including control ODNs containing mismatches. The phosphodiester ODNs (O-ODNs) failed to inhibit replication of influenza A and influenza C viruses at concentrations up to 80 microM, possibly due to intracellular nuclease digestion of the unmodified oligomers. By contrast, the phosphorothioate derivatives (S-ODNs) were found to inhibit replication of both influenza A and influenza C virus. The antiviral effect of S-ODNs against influenza A virus was found at concentrations as low as 1.25 microM and was present with mismatched oligomers. In the case of influenza C virus, the S-ODN complementary to the 3' end of the viral RNA of the PB1 gene revealed a sequence-specific antiviral activity at a concentration of 20 microM. (At the same concentration, S-ODNs with one or three mismatches showed little or no antiviral activity.) Reduction in plaque number reached six logarithms when this sequence-specific S-ODN was used at a concentration of 80 microM.
Expression of antisense RNA fails to inhibit influenza virus replication.
Cell lines were constructed which permanently express influenza virus-specific RNA. Two approaches were followed. C127 cells were transformed with bovine papilloma virus (BPV) vectors and the resulting cell lines were found to inhibit the replication of influenza virus at low multiplicity of infection (MOI 0.05). However, examination of cellular RNA using single-stranded probes revealed the presence of both (+)sense and antisense RNA transcripts (45-70 copies per cell). In this BPV-based system the inhibitory activity appeared to be associated with a non-specific, interferon (IFN)-mediated effect. In the second approach, an expression system was used which involved 293 cells, a chimeric human cytomegalovirus (CMV)/human immunodeficiency virus (HIV) promoter, and methotrexate- (Mtx)-mediated gene amplification. Cells were found to express up to 7500 copies of influenza virus-specific RNA per cell at a steady state level. In this system no RNA transcripts of the opposite orientation were found. However, all cell lines permanently expressing either (-)sense or (+)sense viral RNA failed to reduce influenza virus titers in a multi-cycle replication experiment (MOI 0.01).
Increase in histone acetylation and transitions in histone variants during Friend cell differentiation.
Histone acetylation of Murine Erythroleukemia Cells (MELC) has been re-examined. It is demonstrated that sodium butyrate causes hyperacetylation of core histones in inducible as well as non-inducible MELC strains. This indicates that histone hyperacetylation per se is not sufficient to activate genes. However, [3H]acetate incorporation into core histones of the inducible MELC line F4N increases after induction of differentiation with dimethylsulfoxide (DMSO), in contrast to the non-inducible variant F4+. Thus histone acetylation may play a role as an auxiliary mechanism for gene activation (and inactivation). In addition, the appearance of a histone H3 variant during differentiation of MELC is reported.