NUCLEAR EXPORT SIGNAL OF I-KAPPA-B-ALPHA INTERFERES WITH THE REV-DEPENDENT POSTTRANSCRIPTIONAL REGULATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE

De novo synthesized I kappa B alpha accumulates transiently in the nuc leus where it inhibits NF-kappa B-dependent transcription and reduces nuclear NF-kappa B content, A sequence present in the C-terminal domai n of I kappa B alpha and homologous to the HIV-1 Rev nuclear export si gnal (NES) has been recently defined as a functional NES conferring on I kappa B alpha the ability to export I kappa B alpha/NF-kappa B comp lexes. Rev utilises its RNA-binding activity and NES sequence to promo te specifically the transport of unspliced and monospliced viral RNAs to the cytoplasm, The object of this work was to determine if nuclear I kappa B alpha could interfere with Rev-dependent transport of viral RNA from the nucleus to the cytoplasm, We report that accumulation of I kappa B alpha in the cell nucleus blocks viral replication, This eff ect could be dissociated from the capacity of I kappa B alpha to inhib it NF-kappa B-DNA-binding activity and required a functional I kappa B alpha NES motif, Indeed, mutation of the NES abrogated the capacity o f I kappa B alpha to inhibit Rev-dependent mechanisms involved in the replication of either wild-type or NF-kappa B-mutated HIV-1 molecular clones, Nuclear accumulation of a reporter protein tagged with a nucle ar localization signal (NLS) and fused to the I kappa B alpha NES moti f (NLS-PK-NES) was sufficient to inhibit HIV-1 replication at a post-t ranscriptional level by specifically blocking the expression of a Rev- dependent gene, Furthermore, in cells pulsed with TNF, a treatment whi ch favors nuclear accumulation of newly synthesized I kappa B alpha, N LS-PK-NES expression promoted sustained accumulation of nuclear NF-kap pa B lacking DNA-binding activity. This NES-mediated accumulation of i nactive nuclear NF-kappa B is likely the consequence of interference i n the I kappa B alpha-mediated export of NF-kappa B. These findings in dicate that I kappa B alpha and Rev compete for the same nuclear expor t pathway and suggest that nuclear accumulation of I kappa B alpha, wh ich would occur during normal physiological cell activation process, m ay interfere with the Rev-NES-mediated export pathway of viral RNAs, t hus inhibiting HIV-1 replication.