A phospho-dependent mechanism involving NCoR and KMT2D controls a permissive chromatin state at Notch target genes

Abstract

The transcriptional shift from repression to activation of target genes is crucial for the fidelity of Notch responses through incompletely understood mechanisms that likely involve chromatin-based control. To activate silenced genes, repressive chromatin marks are removed and active marks must be acquired. Histone H3 lysine-4 (H3K4) demethylases are key chromatin modifiers that establish the repressive chromatin state at Notch target genes. However, the counteracting histone methyltransferase required for the active chromatin state remained elusive. Here, we show that the RBP-J interacting factor SHARP is not only able to interact with the NCoR corepressor complex, but also with the H3K4 methyltransferase KMT2D coactivator complex. KMT2D and NCoR compete for the C-terminal SPOC-domain of SHARP. We reveal that the SPOC-domain exclusively binds to phosphorylated NCoR. The balance between NCoR and KMT2D binding is shifted upon mutating the phosphorylation sites of NCoR or upon inhibition of the NCoR kinase CK2β. Furthermore, we show that the homologs of SHARP and KMT2D in Drosophila also physically interact and control Notch-mediated functions in vivo. Together, our findings reveal how signaling can fine-tune a committed chromatin state by phosphorylation of a pivotal chromatin-modifier.

Inhibition of Notch signaling rescues cardiovascular development in Kabuki Syndrome

“…Rbpj is the major transcriptional effector of Notch signaling (64). Recent studies in Drosophila demonstrated that KMT2D binds nuclear Notch co-activator complex (65), establishing a strong precedent of a regulatory link between Notch pathway and KMT2D (66). This report is consistent with our findings that loss of kmt2d produces a misbalance of Notch signaling at the level of transcription factor regulation.…”

The Canonical Notch Signaling Pathway: Structural and Biochemical Insights into Shape, Sugar, and Force

“…The investigators found that NCor does not bind to Mint/SHARP/SPEN unless it is phosphorylated by CKII on a conserved LSDSD motif; once phosphorylated, NCor effectively compete with Kmt2D for Mint/SHARP/SPEN binding. The recruitment of NCor represses transcription whereas the recruitment of the MLL4 complex to RBPj-bound regions enhances the retention of transcription-ready chromatin (Oswald et al, 2016), reminiscent of reports that Mint enhanced transcription mediated by Runx2 (Sierra et al, 2004). …”

“…A recent study explored the Mint/SHARP/SPEN repression complex in some detail and reported a surprising observation (Figure 2C,D; (Oswald et al, 2016)). The C-terminal SPOC domain of the Mint/SHARP/SPEN protein bound to the MLL4 activator complex via Kmt2D, a H3K4 methyltransferase that generates H3K4me3 marks.…”

PHF3 regulates neuronal gene expression through the new Pol II CTD reader domain SPOC

“…These residues are required for the SPOC-containing protein SHARP to interact with the co-repressor complex SMRT/NCoR (Ariyoshi and Schwabe, 2003). Serine phosphorylation of the LSD motif within SMRT or NCoR increases their binding affinity for the conserved Arg within the SHARP SPOC domain, suggesting that the SPOC domain is a phospho-serine binding module (Mikami et al, 2014;Oswald et al, 2016).…”