The mixed lineage leukemia protein-1 (MLL1) belongs to the SET1 family of histone H3 lysine 4 methyltransferases. Recent studies indicate that the catalytic subunits of SET1 family members are regulated by interaction with a conserved core group of proteins that include the WD repeat protein-5 (WDR5), retinoblastoma-binding protein-5 (RbBP5), and the absent small homeotic-2-like protein (Ash2L). It has been suggested that WDR5 functions to bridge the interactions between the catalytic and regulatory subunits of SET1 family complexes. However, the molecular details of these interactions are unknown. To gain insight into the interactions among these proteins, we have determined the biophysical basis for the interaction between the human WDR5 and MLL1. Our studies reveal that WDR5 preferentially recognizes a previously unidentified and conserved arginine-containing motif, called the "Win" or WDR5 interaction motif, which is located in the N-SET region of MLL1 and other SET1 family members. Surprisingly, our structural and functional studies show that WDR5 recognizes arginine 3765 of the MLL1 Win motif using the same arginine binding pocket on WDR5 that was previously shown to bind histone H3. We demonstrate that WDR5's recognition of arginine 3765 of MLL1 is essential for the assembly and enzymatic activity of the MLL1 core complex in vitro.
"Please cite this article in press as: Zhang et al., Evolving Catalytic Properties of the MLL Family SET Domain, Structure (2015), http://dx.doi.org/ 10.1016/j.str.2015.07.018 binds WDR5 (Patel et al., 2008; Zhang et al., 2012). This appears to form a hub that facilitates the recruitment of the other components of the complex (Avdic et al., 2011; Couture and Skiniotis, 2013; Odho et al., 2010; Tremblay et al., 2014). "
"To test this hypothesis, we made a mutation in the WDR5 interacting (Win) motif of MLL ΔSET construct by changing arginine 3765 to alanine. Recent reports have characterized this motif as being sufficient for interaction with WDR5 and point mutation of Arg3765 in this motif abolishes the binding of the whole WRAD complex to MLL (37,38). If WRAD interaction is required for the transcriptional activity of MLL, abolishing the MLL-WDR5 interaction should affect MLL's cell proliferation functions. "
[Show abstract][Hide abstract] ABSTRACT: MLL, the trithorax ortholog, is a well-characterized histone 3 lysine 4 methyltransferase that is crucial for proper regulation
of the Hox genes during embryonic development. Chromosomal translocations, disrupting the Mll gene, lead to aggressive leukemia with poor prognosis. However, the functions of MLL in cellular processes like cell-cycle
regulation are not well studied. Here we show that the MLL has a regulatory role during multiple phases of the cell cycle.
RNAi-mediated knockdown reveals that MLL regulates S-phase progression and, proper segregation and cytokinesis during M phase.
Using deletions and mutations, we narrow the cell-cycle regulatory role to the C subunit of MLL. Our analysis reveals that
the transactivation domain and not the SET domain is important for the S-phase function of MLL. Surprisingly, disruption of
MLL–WRAD interaction is sufficient to disrupt proper mitotic progression. These mitotic functions of WRAD are independent
of SET domain of MLL and, therefore, define a new role of WRAD in subset of MLL functions. Finally, we address the overlapping
and unique roles of the different SET family members in the cell cycle.
Nucleic Acids Research 05/2014; 42(12). DOI:10.1093/nar/gku458 · 9.11 Impact Factor
"Notably, the latter two mutations are located at the region considered to have homology to the Win motif within the pre-SET domain of the mammalian MLL family members. The Win motif is known to affect H3K4 methylation activity of MLL1 through an interaction with WDR5 (human homolog of yeast Swd3) (Patel et al., 2008; Song and Kingston, 2008). These results suggest a conserved role for this region in modulating H3K4 methylation activity of H3K4 methyltransferase members. "
[Show abstract][Hide abstract] ABSTRACT: Past studies have documented a crosstalk between H2B ubiquitylation (H2Bub) and H3K4 methylation, but little (if any) direct evidence exists explaining the mechanism underlying H2Bub-dependent H3K4 methylation on chromatin templates. Here, we took advantage of an in vitro histone methyltransferase assay employing a reconstituted yeast Set1 complex (ySet1C) and a recombinant chromatin template containing fully ubiquitylated H2B to gain valuable insights. Combined with genetic analyses, we demonstrate that the n-SET domain within Set1, but not Swd2, is essential for H2Bub-dependent H3K4 methylation. Spp1, a homolog of human CFP1, is conditionally involved in this crosstalk. Our findings extend to the human Set1 complex, underscoring the conserved nature of this disease-relevant crosstalk pathway. As not all members of the H3K4 methyltransferase family contain n-SET domains, our studies draw attention to the n-SET domain as a predictor of an H2B ubiquitylation-sensing mechanism that leads to downstream H3K4 methylation.
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