KMT2D (lysine (K)-specific methyltransferase 2D), formerly named MLL2 (myeloid/lymphoid or mixed-lineage leukemia 2, also known as ALR/MLL4), is a histone methyltransferase that plays an important role in regulating gene transcription. In particular, it targets histone H3 lysine 4 (H3K4), whose methylations serve as a gene activation mark. Recently, KMT2D has emerged as one of the most frequently mutated genes in a variety of cancers and in other human diseases, including lymphoma, medulloblastoma, gastric cancer, and Kabuki syndrome. Mutations in KMT2D identified thus far point to its loss-of-function in pathogenesis and suggest its role as a tumor suppressor in various tissues. To determine the effect of a KMT2D deficiency on neoplastic cells, we used homologous recombination- and nuclease-mediated gene editing approaches to generate a panel of isogenic colorectal and medulloblastoma cancer cell lines that differ with respect to their endogenous KMT2D status. We found that a KMT2D deficiency resulted in attenuated cancer cell proliferation and defective cell migration. Analysis of histone H3 modifications revealed that KMT2D was essential for maintaining the level of global H3K4 monomethylation and that its enzymatic SET domain was directly responsible for this function. Furthermore, we found that a majority of KMT2D binding sites are located in regions of potential enhancer elements. Together, these findings revealed the role of KMT2D in regulating enhancer elements in human cells and shed light on the tumorigenic role of its deficiency. Our study supports that KMT2D has distinct roles in neoplastic cells, as opposed to normal cells, and that inhibiting KMT2D may be a viable strategy for cancer therapeutics.

Cellular heterogeneity of PCa contributes to hormonal therapy failure, but CXCR2 on neuroendocrine cells is a potential therapeutic target.

Myeloid/lymphoid or mixed-lineage leukemia ( MLL )-family genes encode histone lysine methyltransferases that play important roles in epigenetic regulation of gene transcription. MLL genes are frequently mutated in human cancers. Unlike MLL1, MLL2 (also known as ALR/MLL4) and its homolog MLL3 are not well-understood. Specifically, little is known regarding the extent of global MLL2 involvement in the regulation of gene expression and the mechanism underlying its alterations in driving tumorigenesis. Here we profile the global loci targeted by MLL2. A combinatorial analysis of the MLL2 binding profile and gene expression in MLL2 wild-type versus MLL2 -null isogenic cell lines identified direct transcriptional target genes and revealed the connection of MLL2 to multiple cellular signaling pathways, including the p53 pathway, cAMP-mediated signaling, and cholestasis signaling. In particular, we demonstrate that MLL2 participates in retinoic acid receptor signaling by promoting retinoic acid-responsive gene transcription. Our results present a genome-wide integrative analysis of the MLL2 target loci and suggest potential mechanisms underlying tumorigenesis driven by MLL2 alterations.

Homozygous deletion of methylthioadenosine phosphorylase (MTAP) is one of the most frequent genetic alterations in glioblastoma (GBM), but its pathologic consequences remain unclear. In this study, we report that loss of MTAP results in profound epigenetic reprogramming characterized by hypomethylation of PROM1/CD133–associated stem cell regulatory pathways. MTAP deficiency promotes glioma stem-like cell (GSC) formation with increased expression of PROM1/CD133 and enhanced tumorigenicity of GBM cells and is associated with poor prognosis in patients with GBM. As a combined consequence of purine production deficiency in MTAP-null GBM and the critical dependence of GSCs on purines, the enriched subset of CD133+ cells in MTAP-null GBM can be effectively depleted by inhibition of de novo purine synthesis. These findings suggest that MTAP loss promotes the pathogenesis of GBM by shaping the epigenetic landscape and stemness of GBM cells while simultaneously providing a unique opportunity for GBM therapeutics. Significance: This study links the frequently mutated metabolic enzyme MTAP to dysregulated epigenetics and cancer cell stemness and establishes MTAP status as a factor for consideration in characterizing GBM and developing therapeutic strategies.

Inactivating mutations in the transcriptional repression factor Capicua (CIC) occur in approximately 50% of human oligodendrogliomas, but mechanistic links to pathogenesis are unclear. To address this question, we generated Cic-deficient mice and human oligodendroglioma cell models. Genetic deficiency in mice resulted in a partially penetrant embryonic or perinatal lethal phenotype, with the production of an aberrant proliferative neural population in surviving animals. In vitro cultured neural stem cells derived from Cic conditional knockout mice bypassed an EGF requirement for proliferation and displayed a defect in their potential for oligodendrocyte differentiation. Cic is known to participate in gene suppression that can be relieved by EGFR signal, but we found that cic also activated expression of a broad range of EGFR-independent genes. In an orthotopic mouse model of glioma, we found that Cic loss potentiated the formation and reduced the latency in tumor development. Collectively, our results define an important role for Cic in regulating neural cell proliferation and lineage specification, and suggest mechanistic explanations for how CIC mutations may impact the pathogenesis and therapeutic targeting of oligodendroglioma. Cancer Res; 77(22); 6097–108. ©2017 AACR.

IDH1 mutations occur in the majority of low-grade gliomas and lead to the production of the oncometabolite, D-2-hydroxyglutarate (D-2HG). To understand the effects of tumor-associated mutant IDH1 (IDH1-R132H) on both the neural stem cell (NSC) population and brain tumorigenesis, genetically faithful cell lines and mouse model systems were generated. Here, it is reported that mouse NSCs expressing Idh1-R132H displayed reduced proliferation due to p53-mediated cell-cycle arrest as well as a decreased ability to undergo neuronal differentiation. In vivo, Idh1-R132H expression reduced proliferation of cells within the germinal zone of the subventricular zone (SVZ). The NSCs within this area were dispersed and disorganized in mutant animals, suggesting that Idh1-R132H perturbed the NSCs and the microenvironment from which gliomas arise. In addition, tumor-bearing animals expressing mutant Idh1 displayed a prolonged survival and also overexpressed Olig2, features consistent with IDH1-mutated human gliomas. These data indicate that mutant Idh1 disrupts the NSC microenvironment and the candidate cell-of-origin for glioma; thus, altering the progression of tumorigenesis. In addition, this study provides a mutant Idh1 brain tumor model that genetically recapitulates human disease, laying the foundation for future investigations on mutant IDH1-mediated brain tumorigenesis and targeted therapy. Implications: Through the use of a conditional mutant mouse model that confers a less aggressive tumor phenotype, this study reveals that mutant Idh1 impacts the candidate cell-of-origin for gliomas. Mol Cancer Res; 15(5); 507–20. ©2017 AACR.