T cell leukemia-associated human Notch/translocation-associated Notch homologue has IκB-like activity and physically interacts with nuclear factor-κB proteins in T cells

Abstract

Translocation-associated Notch homologue (TAN-1), a gene originally cloned from the translocation breakpoint of a human T cell leukemia carrying a 9:7(q34.3) translocation, encodes a protein belonging to the Notch/Lin- 12/Glp-1 receptor family. These receptors mediate the specification of numerous cull fates during development in invertebrates and vertebrates. The intracellular portion of Notch/TAN-1 contains six ankyrin repeats that are similar to those found in cytoplasmic IκB proteins. IκB proteins are specific inhibitors of nuclear factor (NF)-κB/Rel transcription factors. Here we show that TAN-1 has functional properties of an IκB-like regulator with specificity for the NF-κB p50 subunit. A recombinant polypeptide corresponding to the cytoplasmic portion of TAN-1 (TAN-1(C)) specifically inhibited the DNA binding of p50-containing NF-κB complexes. When overexpressed in an appropriate cell line, TAN-1(C) prevented κB-dependent transactivation in transient reporter gene assays in a fashion similar to the structurally related protein, Bcl-3. TAN-1(C) could activate κB-dependent gene expression by attenuating the inhibitory effect of an excess of p50 homodimers. Immunoprecipitation experiments showed that the TAN-1 from a T cell line is associated with NF-κB containing p50 and p65 subunits. These observations indicate that TAN-1(C) may directly engage NF-κB transcription factors and modulate nuclear gene expression.