Identification of a Nuclear Localization Sequence in Beta-Arrestin1:Implications in NF- kB Activation

A mounting body of evidence suggests that beta-arrestin1 plays important roles in the nucleus, but how beta-arrestin1 enters the nucleus remains unclear since no nuclear import signal has been identified in the -arrestins. We sought to characterize the cellular localization of wild type beta-arrestin1 and a series of N domain mutants to determine the structural basis and functional implications of beta-arrestin1 nuclear localization. A seven-residue candidate nuclear localization sequence (NLS) was identified based on sequence analysis. Mutation of the NLS led to a loss of beta-arrestin1 nuclear localization in transfected cells. Exogenous expression of wild type beta-arrestin1 enhanced the transcriptional activity of nuclear factor kappaB (NF-kappaB) induced by bradykinin, while mutation of the NLS reduced this effect by two thirds relative to wild type controls. Loss of beta-arrestin1 nuclear localization was accompanied by reduced recruitment of the CREB binding protein and altered post-translational modification profile of p65/RelA. Further mutational analysis identified Lys157 within the putative NLS as being critical to nuclear localization of beta-arrestin1. Substitution of Lys157 to Ala led to reduced nuclear localization, decreased promoter binding by p65/RelA and decreased IL-1beta gene transcription. These results demonstrate a critical role for beta-arrestin1 nuclear localization in scaffolding and transcriptional regulation.