MAML1, a human homologue of Drosophila Mastermind, is a transcriptional co-activator for NOTCH receptors

Abstract

Notch receptors are involved in cell-fate determination in organisms as diverse as flies, frogs and humans. In Drosophila melanogaster , loss-of-function mutations of Notch produce a 'neurogenic' phenotype in which cells destined to become epidermis switch fate and differentiate to neural cells. Upon ligand activation, the intracellular domain of Notch (ICN) translocates to the nucleus, and interacts directly with the DNA-binding protein Suppressor of hairless (Su(H)) in flies, or recombination signal binding protein Jkappa (RBP-Jkappa) in mammals, to activate gene transcription. But the precise mechanisms of Notch-induced gene expression are not completely understood. The gene mastermind has been identified in multiple genetic screens for modifiers of Notch mutations in Drosophila. Here we clone MAML1, a human homologue of the Drosophila gene Mastermind, and show that it encodes a protein of 130 kD localizing to nuclear bodies. MAML1 binds to the ankyrin repeat domain of all four mammalian NOTCH receptors, forms a DNA-binding complex with ICN and RBP-Jkappa, and amplifies NOTCH-induced transcription of HES1. These studies provide a molecular mechanism to explain the genetic links between mastermind and Notch in Drosophila and indicate that MAML1 functions as a transcriptional co-activator for NOTCH signalling.

The Notch signaling pathway: Transcriptional regulation at Notch target genes

“…S4 is the C-terminal phosphorylation site, important for Notch turnover (see below: CycC/ Cdk8 and phosphorylation of Notch receptor and Mastermind/p300. Mastermind is a member of the Mastermind-like (MAML) family of coactivators [101,102], originally identified in genetic screens in Drosophila [2]. Recently, the first detailed view of the coactivator complex was provided by the determination of the structure of full-length RBP-J bound to DNA in combination with a truncated form of NICD and the interacting part of MAML [103] and reviewed in [104,105].…”

“…In Drosophila, the mastermind gene codes for a glutamine-rich protein, indicative for an transcriptional activators. Mammalian MAML was shown to stabilize the RBP/NICD bound to DNA during activation of target genes [102]. In vivo, the importance of MAML has been impressively demonstrated with dominant-negative MAML, which completely blocks all Notch-mediated transcriptional activation [106].…”

Altered LKB1/CREB-regulated transcription co-activator (CRTC) signaling axis promotes esophageal cancer cell migration and invasion

“…Preparation of whole cell lysates and western blotting analysis were performed as described previously (Wu et al, 2000). Nuclear protein fractions were isolated using a Nuclear Extract Kit (Active motif).…”

“…Cell staining and reporter assays Cell staining and luciferase-based reporter assays were performed as previously described (Wu et al, 2000).…”

Generation and characterization of a Notch1 signaling‐specific reporter mouse line

“…The last cleavage liberates the intracellular domain of Notch (NIC), which translocates to the nucleus (Struhl and Adachi, 1998). Once in the nucleus, NIC associates with the DNA binding protein CSL/ RBPJj (Fortini and Artavanis-Tsakonas, 1994;Jarriault et al, 1995) thereby recruiting other coactivators and initiates the formation of a functional transcription activation complex driving target gene expression (Kurooka and Honjo, 2000;Oswald et al, 2001;Wallberg et al, 2002;Wu et al, 2000).…”