Assembly of a Notch Transcriptional Activation Complex Requires Multimerization

Notch transmembrane receptors direct essential cellular processes, such as proliferation and differentiation, through direct cell-to-cell interactions. Inappropriate release of the intracellular domain of Notch (N-ICD) from the plasma membrane results in the accumulation of deregulated nuclear N-ICD that has been linked to human cancers, notably T-cell acute lymphoblastic leukemia (T-ALL). Nuclear N-ICD forms a transcriptional activation complex by interacting with the coactivator protein Mastermind-like 1 and the DNA binding protein CSL (for CBF-1/Suppressor of Hairless/Lag-1) to regulate target gene expression. Although it is well understood that N-ICD forms a transcriptional activation complex, little is known about how the complex is assembled. In this study, we demonstrate that N-ICD multimerizes and that these multimers function as precursors for the stepwise assembly of the Notch activation complex. Importantly, we demonstrate that the assembly is mediated by N-ICD multimers interacting with Skip and Mastermind. These interactions form a preactivation complex that is then resolved by CSL to form the Notch transcriptional activation complex on DNA.