Dimerization-dependent NOTCH receptor transactivation unveils a class of highly selective NOTCH signalling inhibitors

The NOTCH pathway is an ancient, ubiquitously expressed cell signalling system that is essential for embryonic and postembryonic cell fate control and tissue growth. It is activated via intercellular interactions between receptors and ligands expressed by neighbouring cells. This releases the latent transcription-promoting potential of the receptor through proteolytic cleavage of the intracellular domain, which translocates to the nucleus and directly stimulates target gene expression as part of a DNA-bound transcription activation complex. To date, it has been assumed that this process involves interactions between ligand homomers and receptor homomers. In this study, we present several lines of evidence in support of the view that NOTCH receptor dimerization/oligomerization (hereafter referred to as dimerization) could be necessary for the transactivation of receptor signalling. We show that (1) NOTCH receptors can efficiently self-associate, which is mediated via a short motif found in the negative regulatory region (NRR) of the extracellular domain; (2) deletion of this motif ablates receptor homodimerization and blocks receptor transactivation; and (3) short peptides specifically targeting the dimerization motif similarly block receptor dimerization and receptor transactivation. Since the NOTCH pathway is corrupted in a wide range of disorders, the newly identified mechanism of NOTCH receptor transactivation presented here, and the discovery of a unique class of NOTCH signalling inhibitors, potentially reveals new therapeutic avenues to treating these diseases. In this light, a proof-of-concept study centred on T-cell acute lymphoblastic leukaemia (T-ALL) is presented.