Nuclear Translocation of IFN-γ Is an Intrinsic Requirement for Its Biologic Activity and Can Be Driven by a Heterologous Nuclear Localization Sequence

We have previously identified a nuclear localization sequence (NLS) in interferon-γ (IFN-γ). This NLS functions intracellularly by forming a complex with its transcription factor Stat1α and the nuclear importer of Stat1α, the importin-α analog NPI-1. The stability of this complex and the subsequent nuclear translocation of the complexed Stat1α are dependent on the integrity of this NLS, showing that Stat1α nuclear import is mediated by the IFN-γ NLS. In this study, to directly evaluate the intrinsic requirement of nuclear IFN-γ toward its biologic activities, we engineered a chimeric in which the IFN-γ NLS has been substituted by a heterologous NLS, namely, the prototypical NLS of the SV40 large T antigen, which would drive nuclear translocation of IFN-γ in a sequence-nonspecific manner. The chimeric, IFN-γ-SV, was equally active in antiviral and antiproliferative assays as the wild-type IFN-γ. Interestingly, IFN-γ-SV was also translocated to the nucleus and was also recovered intracellularly as a complex...