Human Notch-1 Inhibits NF-κB Activity in the Nucleus Through a Direct Interaction Involving a Novel Domain

Abstract

Notch participates in diverse cell fate decisions throughout embryonic development and postnatal life. Members of the NF-κB/Rel family of transcription factors are involved in the regulation of a variety of genes important for immune function. The biological activity of the NF-κB transcription factors is controlled by IκB proteins. Our previous work demonstrated that an intracellular, constitutively active form of human Notch-1/translocation-associated Notch homologue-1 (NotchIC) functions as an IκB molecule with specificity for the NF-κB p50 subunit and physically interacts with NF-κB in T cells. In the current study, we investigated the roles of different domains of NotchIC in the regulation of NF-κB-directed gene expression and NF-κB DNA binding activity. We found that NotchIC localizes to the nucleus and that a region in the N-terminal portion of NotchIC, not the six ankyrin repeats, is responsible for the inhibitory effects of Notch on NF-κB-directed gene expression and NF-κB DNA binding activity. The N-terminal portion of NotchIC inhibited p50 DNA binding and interacted specifically with p50 subunit, not p65 of NF-κB. The interaction between Notch and NF-κB indicates that in addition to its role in the development of the immune system, Notch-1 may also have critical functions in the immune response, inflammation, viral infection, and apoptosis through control of NF-κB-mediated gene expression.