Inhibition of EBF function by active Notch signaling reveals a novel regulatory pathway in early B-cell development.

The Notch signaling pathway is involved in several lineage commitment and differentiation events. One of these is fate determination of the common lymphoid progenitor, promoting T-cell development at the expense of B-cell differentiation. It has been suggested that this process relies on Notch's ability to inhibit E proteins, which are crucial for early B-cell development. Here, we report that Notch signaling also modulates the function of the transcription factor, early B-cell factor (EBF). Transient transfection of intracellular Notch1 (Notch1-IC) into a pre-B cell line resulted in the down-regulation of EBF-regulated promoters and diminished the capacity of EBF to activate these promoters in an epithelial cell line. This correlated with a reduction in the ability of EBF to bind DNA. Ligand-induced stimulation of endogenous Notch receptors with Delta4 mimicked the activity of Notch1-IC toward EBF. These data suggest that Notch signaling may affect B-versus T-lineage commitment by the targeting of both EBF and E2A.