Human notch and mastermind proteins activate target genes differently depending on combination used

Abstract

Notch signaling plays a crucial role in cell development and proliferation. The Notch receptor is an inducible transcription factor found on the cell surface which is cleaved resulting in the release of the intracellular domain (NICD). The NICD enters the nucleus and complexes with CBF1 and Mastermind (MAM) to activate target genes. In humans, there are four Notch receptors and three Mastermind proteins. We wish to understand if all NICD and MAM proteins contribute equally to transcriptional activation of target genes and if all MAM proteins are capable of degrading the different NICD's. Various combinations of NICD and MAM constructs result in different activation of the HES1 and HES5 promoters depending on the combination used. HES5 was much stronger in activation than HES1. NICD3 and NICD4 paired with any MAM protein weakly activated both HES1 and HES5 promoters. The strongest activation of promoters occurred in the presence of MAM2 with NICD1 and 2. NICD degradation occurred by over‐expression of all three MAM's with the exception of NICD4 which was weakly degraded by the different MAM's. Taken together these results suggest that promoter activation depends strongly on the context of the combination of proteins used and degradation may not necessarily be the deciding factor in strength of promoter activation. Support of research was through NSF‐REU and HHMI‐SCRIBE Programs at San Jose State University to TMB.