Abstract 3567: Cancer-epigenetic mouse models for medulloblastoma

Abstract

Abstract Medulloblastoma (MB) is the most common childhood brain tumors (up to 20% of all childhood brain tumors) and occurs mainly in children (<15 years old. MB is located in the cerebellum in the brain and can spread to the spine or to other parts of brain. Because MB growth is very fast, MB is categorized as a type of high-grade malignant primary tumors. MB development is often associated with the dysregulation of signaling pathways, such as the wingless (WNT) and sonic hedgehog (SHH). Methylated histone H3 lysine 4 (H3K4) is a major methylation mark. Trimethyl H3K4 (H3K4me3) occupies as much as 75% of all human gene promoters. We previously reported that the H3K4 methyltransferase KMT2D (also called MLL4, MLL2, and ALR; a transcriptional coactivator, is required for neuronal differentiation of human neuron-lineage NT2/D1 stem cells. Interestingly, our analysis of several databases has shown that Kmt2d is the most frequently mutated epigenetic modifier (8%‒10%) in medulloblastoma (MB). Recently, we showed that brain-specific knockout of Kmt2d alone induces spontaneous MB in mice. Kmt2d loss highly upregulated several oncogenic signaling programs and downregulated tumor suppressive genes. In this study, we sought to determine whether Kmt2d loss cooperates with another oncogenic event in MB genesis. Particularly, PTCH (also known as PTCH1) is one of the most frequently mutated genes in MB, and KMT2D is known to be a shared driver gene mutation in MB. For these reasons, we examined the effect of Kmt2d loss on of Ptch+/−-driven MB genesis. A heterozygous loss of Kmt2d increased the incidence and progression of Ptch+/−-driven MB genesis. We have shown that Kmt2d loss reduces epigenomic signals for super-enhancers/enhancers and broad H3K4me3 in 4-month-old cerebella. In addition, we determine the effect of heterozygous Kmt2d loss on cell proliferation by comparing the Nes-Cre Kmt2dfl/+ Ptch+/- (KP) cerebella to Ptch+/- cerebella at 2- & 4-month-old time points using IHC staining of Ki-67 (a proliferation marker). MB’s from KP mice showed two different mechanisms by activating oncogenic cellular signaling kinases (e.g., phospho [p]-AKT and p-p38) levels as well as MYCN signaling pathway. Our transcriptomic analysis revealed several tumor suppressive and transcriptional corepressor genes to be downregulated such as Ncor2 and Dnmt3a. We found Ncor2 depletion in Ptch-/+ neurospheres shows upregulation of similar oncogenic genes as in KP mice tumors. Kmt2d loss reduced cerebellar granule cell differentiation. Our analysis for oncogenic kinases may provide a basis for a novel MB treatment plan involving the use of cellular kinase inhibitors. As KMT2D is among the most often mutated genes in human MBs, this mouse model may be useful for future preclinical therapeutic experiments for the treatment of MB patients. KMT2D in medulloblastoma genesis using mouse models will provide epigenetic and mechanistic insights into how heterozygous KMT2D loss promotes medulloblastoma. Citation Format: Shilpa S. Dhar, Ali S. Rizvi, Lauren Reed, Calena Brown, Min Gyu Lee. Cancer-epigenetic mouse models for medulloblastoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3567.