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Mol. Cell. Biol., 03 1996, 952-959, Vol 16, No. 3
JJ Hsieh, T Henkel, P Salmon, E Robey, MG Peterson and SD Hayward
The Notch/Lin-12/Glp-1 receptor family participates in cell-cell signaling
events that influence cell fate decisions. Although several Notch homologs
and receptor ligands have been identified, the nuclear events involved in
this pathway remain incompletely understood. A truncated form of Notch,
consisting only of the intracellular domain (NotchIC), localizes to the
nucleus and functions as an activated receptor. Using both an in vitro
binding assay and a cotransfection assay based on the two-hybrid principle,
we show that mammalian NotchIC interacts with the transcriptional repressor
CBF1, which is the human homolog of Drosophila Suppressor of Hairless.
Cotransfection assays using segments of mouse NotchIC and CBF1 demonstrated
that the N- terminal 114-amino-acid region of mouse NotchIC contains the
CBF1 interactive domain and that the cdc10/ankyrin repeats are not
essential for this interaction. This result was confirmed in
immunoprecipation assays in which the N-terminal 114-amino-acid segment of
NotchIC, but not the ankyrin repeat region, coprecipitated with CBF1. Mouse
NotchIC itself is targeted to the transcriptional repression domain (aa179
to 361) of CBF1. Furthermore, transfection assays in which mouse NotchIC
was targeted through Gal4-CBF1 or through endogenous cellular CBF1
indicated that NotchIC transactivates gene expression via CBF1 tethering to
DNA. Transactivation by NotchIC occurs partially through abolition of
CBF1-mediated repession. This same mechanism is used by Epstein-Barr virus
EBNA2. Thus, mimicry of Notch signal transduction is involved in
Epstein-Barr virus-driven immortalization.
Copyright © 1996, American Society for Microbiology
Truncated mammalian Notch1 activates CBF1/RBPJk-repressed genes by a mechanism resembling that of Epstein-Barr virus EBNA2
Department of Pharmacology and Molecular Sciences, The Johns Hopkins University of Medicine, Baltimore, Maryland 21205, USA.
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