Abstract 4762: Oncogenic over-expression of MED12 is epigenetically fostered in the core-binding factor subgroups of acute myeloid leukemia
Authors: Choudhury Samrat Roy , Bhattacharya Arkajyoti 
Published: April 2023

Mediator (MED) proteins typically assemble and recruit distal coactivators at binding sites of RNA polymerase II to help regulate a gene’s transcriptional output. The MED-kinase module consists of four subunits, MED12/12L, MED13/13L, CDK8/19 and Cyclin C, and reversibly interacts with the MED-core complex to function as a lineage-specific transcriptional activator. In particular, MED12 has been reported to recruit BRD4, FLI/ERG, CBP/p300, and GATA2 transcription factors on H3K27ac-enriched super-enhancer (SE) loci in hematopoietic stem and acute myeloid leukemia (AML) cells to maintain cell fate determination or leukemic growth respectively. Given the regulatory role MED12 in AML, there is a sustained interest in identifying targeted inhibitors against this MED-protein. Herein, we aimed to investigate if the oncogenic over-expression of MED12 is epigenetically regulated in AML. We analyzed the MED12 transcriptomic data in AML patients, belongs to 6 cytogenetic subgroups having chromosomal aberrations such as inv(16) (n=28), t(15;17) (n=37), t(8;21) (n=40), MLL-rearranged (n=38), AML-complex (n=48), and normal karyotype (n=351), compared to normal bone marrow (NBM) mononuclear cells (n=73), from the Microarray Innovations in Leukemia (MILE) study (Stage I). MED12 was found significantly (p&lt;0.01) upregulated in AML subgroups, except for the AML-complex subgroup along 3 probe sets (211342_x_at, 203506_s_at, and 216071_x_at). The highest upregulation of MED12 was observed in the inv(16) subgroup having the mean differential expression of 0.78, followed by 0.57 in t(8;21) and 0.5 in t(15;17) subgroup, compared to NBM. Considering the fact that inv(16) and t(8;21) subgroups showed highest expression of the gene, and are categorized as the core-binding factor (CBF) AML-subgroups, we examined DNA-methylation and chromatin modifications of MED12 in patients [n=3 for inv(16) and n=1 for t(8;21)], based on the whole-genome bisulfite sequencing and chromatin immunoprecipitation sequencing data, as available at the BLUEPRINT epigenome, and DNAse sequencing (K562 cells) data at ENCODE. We observed DNAse hypersensitive peaks at the exon-26 and a region (229 bp) spanning the transcription start site (TSS) and upstream promoter of the gene, indication an open chromatin conformation. The TSS and upstream promoter also contained a broad H3K4me3 domain [1.7 kb in inv(16) and 1.2 kb in t(8;21)], with an overlapping hypomethylated CpG-island. Collectively, our findings suggest that MED12 oncogenic over-expression in CBF AML-subgroups are fostered by an epigenetically active promoter. Future studies will be aimed at understanding the impact of targeted perturbation of MED12 in the enhancer mechanism and sustenance of leukemic growth in CBF AML-subgroups.

Citation Format: Samrat Roy Choudhury, Arkajyoti Bhattacharya. Oncogenic over-expression of MED12 is epigenetically fostered in the core-binding factor subgroups of acute myeloid leukemia. [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 4762.