The tetracycline-responsive promoter contains functional interferon-inducible response elements

Tetracycline (tet)-responsive expression vectors allow controlled inducible expression of proteins in mammalian cells. This system is widely used for experimental research both in vivo and in vitro, in our attempts to use thi s system to study the antiviral effect of IFN alpha on hepatitis B virus, w e discovered an unexpected feature of the tet-responsive promoter (tet prom oter) of the currently available expression vectors. IFNa was found to stim ulate tet promoter activity after transient transfection in a dose- and cel l type-dependent manner. By sequence inspection, an IFN alpha-stimulated re sponse element (ISRE)-like sequence was identified in the linker regions lo cated between the heptameric tet operator sequences. Gel shin assays reveal ed binding of IFN-stimuiated gene factors to these sequences, indicating th at they mediate the IFN alpha-mediated promoter stimulation. These data dem onstrate an unexpected feature of the tet-responsive expression system whic h needs to be taken into acount when using this system for analysis of cyto kine functions in vitro and in vivo. The data also imply that the tet promo ter-based expression system can be rendered non-responsive to IFN alpha by mutagenesis of the ISREs and this may be essential when considering gene th erapy in vivo.