RESUMEN
BACKGROUND: In airway epithelia, the kinetics of recombinant adeno-associated virus (AAV) transgene expression is slow. This has negative practical implications for research, as well as for translation into therapy. The DNA minor groove-binding agent Hoechst-33342 has been shown to enhance AAV transgene expression. In the present study, we investigated the mechanism of Hoechst-related augmentation of AAV-mediated transgene expression. METHODS: We investigated the effect of Hoechst-33342 on HT1080, COS-7, mouse and human airway epithelia transduced with different AAV serotypes encoding enhanced green fluorescent protein (eGFP). We exposed cells to increasing concentrations of Hoechst-33342 at different time points. We evaluated the effect on second-strand DNA synthesis using AAV with a self-complementary genome. We also investigated the effect on expression from transfected plasmids with and without AAV2 inverted terminal repeats (ITRs). RESULTS: We found that Hoechst-33342 significantly accelerated AAV transgene expression for all serotypes tested. Hoechst-33342 only had an effect when the treatment was given during or after transduction, even 120 days post-transduction, suggesting an effect on transgene expression regulation. Hoechst-33342 increased transgene expression when cells were transduced with a self-complementary AAV with the cytomegalovirus promoter, although there was no effect on cells transduced with conventional single-stranded AAV encoding the Rous sarcoma virus promoter. Finally, Hoechst-33342 increases gene expression from transfected plasmids regardless of the presence of AAV2 ITRs. CONCLUSIONS: Hoechst dramatically augments and accelerates AAV-mediated transgene expression in airway epithelia without altering AAV-mediated gene transfer. Hoechst activation of the cytomegalovirus promoter is seen in plasmids, although it is drastically enhanced in the context of AAV.
