FIG. 6.

High-level expression of NICD is required for LEF-1 activation. (A) Low levels of NICD stimulate a CSL reporter but do not potentiate LEF-1. Fold induction of CSL-luc, with increasing amounts of NICD expression plasmid, is shown relative to the reporter alone (left graph). Stimulation of LEF-1 in the presence of increasing amounts of NICD compared to the LEF-OT reporter and LEF-1 alone is shown (right graph). (B) Excess CSL inhibits NICD's ability to stimulate LEF-1 activity. Neuro-2A cells were transfected with the LEF-OT reporter and the indicated expression vectors. Results are given as fold induction relative to the reporter alone. (C) Activity of NICD in the presence of endogenous LEF-1. Jurkat cells were transfected with reporters containing wild-type (LEF-OT) or mutant (LEF-OF) LEF-1 binding sites, plus or minus an expression vector for NICD as indicated. Data are represented as fold induction relative to LEF-OF alone.