Background: ␤-Arrestin-1 is present in the nucleus but lacks an identifiable nuclear localization signal. Results: Using sequence comparison and mutagenesis, we found Lys 157 is critical to ␤-arrestin-1 nuclear localization and its regulation of NF-B activation. Conclusion: ␤-Arrestin-1 uses a novel basic sequence for its entry into the nucleus. Significance: This work provides a structural basis for the nuclear function of ␤-arrestin-1.

A mounting body of evidence has shown the importance of βArrestin1 in the nucleus, however the mechanism of how βArrestin1 enters the nucleus to mediate its functions is not known. Despite a high homology between the two members of the βarrestin family, they do not localize to the same subcellular compartments. βarrestin1 can be seen ubiquitously throughout the cell while βarrestin2 is excluded from the nucleus by a functional NES in its C terminus. While no nuclear import signal has been identified in either βarrestin, it has been noted that an intact N‐terminal domain is required for nuclear localization of both members. To explore this further, we visualized the localization of full‐length βarrestin1 as well as N‐terminal domain truncation and deletion mutants. Based on the results, a seven‐residue candidate nuclear localization sequence was found in βarrestin1. Mutation of these residues led to a loss of βarrestin1 nuclear localization by inhibiting its binding to the nuclear import machinery. Functionally, expression of wild type βArrestin1 is able to enhance the transcriptional activity of NF‐κB following bradykinin stimulation and the nuclear localization of βArrestin1 is critical for this effect. Loss of nuclear localization of βArrestin1 led to an inhibition of NF‐κB mediated gene transcription by affecting the post‐translational modification profile of p65/RelA following bradykinin stimulation, which led to a decrease in effective promoter binding. In conclusion, this study identifies structural determinants for the nuclear localization of βArrestin1, and demonstrates its role in regulating NF‐κB activation.