ZNF479 induced the expression of DNMT1, UHRF1, and mixed-lineage leukemia (MLL) complex proteins (ASH2L and Menin), and increased tri-methylated histone H3 (H3K4me3) levels, but suppressed H3K4 (H3K4me2) di-methylation.
Here we show for the first time that MIs reduced menin protein levels and decreased the half-life of menin protein but have no effect on mRNA level in MLL-FP-expressing leukemia cells, and proteasome or E1 ligase inhibitor rescued the MI-induced menin degradation.
Several studies have shown that both MENIN and LEDGF/p75 are required for efficient MLL-fusion-mediated transformation and for the expression of downstream MLL-regulated genes such as <i>HOXA9</i> and <i>MEIS1</i> In light of developing a therapeutic strategy targeting this complex, understanding the function of LEDGF/p75 in normal hematopoiesis is crucial.
Here, we find that at a subset of gene targets, MLL-AF4 binding spreads into the gene body and is associated with the spreading of Menin binding, increased transcription, increased H3K79 methylation (H3K79me2/3), a disruption of normal H3K36me3 patterns, and unmethylated CpG regions in the gene body.
Our data show that induction of 5-LO promoter activity by SMAD3/4 is MLL-dependent and that knockdown of the MLL complex component MEN1 attenuates the SMAD effect.
Thus, menin by forming a subunit of the mixed lineage leukemia (MLL) complexes that trimethylate histone H3 at lysine 4 (H3K4), facilitates activation of transcriptional activity in target genes such as cyclin-dependent kinase (CDK) inhibitors; and by interacting with the suppressor of variegation 3-9 homolog family protein (SUV39H1) to mediate H3K methylation, thereby silencing transcriptional activity of target genes.
Inactivation of the MEN1 gene, commonly involved in endocrine pancreatic tumors, impairs the association with mixed lineage leukemia involved in histone H3K4me3 methylation.
Although menin acts as an oncogenic cofactor for mixed lineage leukemia (MLL) fusion protein-mediated histone H3 lysine 4 methylation, the precise basis for how menin suppresses gene expression and proliferation of pancreatic beta cells remains poorly understood.
MEN1 and its coactivator, the mixed-lineage leukemia histone methyltransferase, are recruited to the BRCA1, RAD51, and RAD51AP1 promoters by estrogen receptor 1, resulting in increased histone H3-lysine 4 trimethylation and transcription.
Identification of these compounds provides a new tool for better understanding MLL-mediated leukemogenesis and represents a new approach for studying the role of menin as an oncogenic cofactor of MLL fusion proteins.
The menin/WT MLL/MLL-FP hub may also cooperate with several signaling pathways, including Wnt, GSK3, and bromodomain-containing Brd4-related pathways to sustain MLL-FP-induced leukemogenesis, revealing new therapeutic targets to improve the treatment of MLL-FP leukemias.
Based on the menin-MI-2 structure, we developed MI-2-2, a compound that binds to menin with low nanomolar affinity (K(d) = 22nM) and very effectively disrupts the bivalent protein-protein interaction between menin and MLL.
Furthermore, excision of TβRII, a vital component in TGF-β signaling pathway, down-regulated menin expression in MLL-AF9 transformed mouse bone marrow cells.
Silencing MYB in human leukemic cell lines and primary patient material evoked a global decrease in H3K4 methylation, an unexpected decrease in HOXA9 and MEIS1 gene expression, and decreased MLL and menin occupancy in the HOXA9 gene locus.
We demonstrate here that these discordant functions are unified by menin's ability to serve as a molecular adaptor that physically links the MLL (mixed-lineage leukemia) histone methyltransferase with LEDGF (lens epithelium-derived growth factor), a chromatin-associated protein previously implicated in leukemia, autoimmunity, and HIV-1 pathogenesis.
Acute genetic ablation of menin reverses aberrant Hox gene expression mediated by MLL-menin promoter-associated complexes, and specifically abrogates the differentiation arrest and oncogenic properties of MLL-transformed leukemic blasts.