Inhibition of hepatitis B virus production associated with high levels of intracellular viral DNA intermediates in iron-depleted HepG2.2.15 cells.

BACKGROUNDS/AIMS: The effects of iron-depletion on hepatitis B virus (HBV) replication were examined in HepG2.2.15 cells. METHODS: Proliferating cells were iron-depleted with desferrioxamine (DFO), at 20 or 100 microM for 48 h. Levels of viral mRNAs, cytoplasmic DNA replicative intermediates and virion production were examined. A comparative study was performed with hydroxyurea, a specific inhibitor of ribonucleotide reductase. RESULTS: In desferrioxamine treated cells, virion production is dramatically decreased, while viral replicative intermediates accumulate in the cytoplasm. DFO, like hydroxyurea, blocks cell cycle progression in the G1/S transition or S phase with a corresponding 2-fold increase of viral mRNAs. As expected, hydroxyurea leads to a strong reduction of virion production associated with low levels of intracellular replicative intermediates. CONCLUSIONS: These results strongly suggest that iron depletion affects the HBV life cycle indirectly through the cell cycle arrest and directly through the inhibition of the viral DNA secretion. They also indicate the need to re-evaluate with caution the iron depletion protocols on HBV infected patients since a decrease of viral markers in the serum following iron-depletion may not reflect a decrease of viral replicative forms, but on the contrary, could be associated with active viral DNA synthesis.

Dynamic changes in the functions of Odd-skipped during early Drosophila embryogenesis.

Although many of the genes that pattern the segmented body plan of the Drosophila embryo are known, there remains much to learn in terms of how these genes and their products interact with one another. Like many of these gene products, the protein encoded by the pair-rule gene odd-skipped (Odd) is a DNA-binding transcription factor. Genetic experiments have suggested several candidate target genes for Odd, all of which appear to be negatively regulated. Here we use pulses of ectopic Odd expression to test the response of these and other segmentation genes. The results are complex, indicating that Odd is capable of repressing some genes wherever and whenever Odd is expressed, while the ability to repress others is temporally or spatially restricted. Moreover, one target gene, fushi tarazu, is both repressed and activated by Odd, the outcome depending upon the stage of development. These results indicate that the activity of Odd is highly dependent upon the presence of cofactors and/or overriding inhibitors. Based on these results, and the segmental phenotypes generated by ectopic Odd, we suggest a number of new roles for Odd in the patterning of embryonic segments. These include gap-, pair-rule- and segment polarity-type functions.