Epigenetic drug library screening reveals targeting DOT1L abrogates NAD plus synthesis by reprogramming H3K79 methylation in uveal melanoma

Uveal melanoma (UM) is the most frequent and life-threatening ocular malignancy in adults. Aberrant histone methylation contributes to the abnormal transcriptome during oncogenesis. However, a comprehensive understanding of histone methylation patterns and their therapeutic potential in UM remains enigmatic. Herein, using a systematic epi-drug screening and a high-throughput transcriptome profiling of histone methylation modifiers, we observed that disruptor of telomeric silencing-1-like (DOT1L), a methyltransferase of histone H3 lysine 79 (H3K79), was activated in UM, especially in the high-risk group. Concordantly, a systematic epi-drug library screening revealed that DOT1L inhibitors exhibited salient tumor-selective inhibitory effects on UM cells, both in vitro and in vivo. Combining Cleavage Under Targets and Tagmentation (CUT&Tag), RNA sequencing (RNA-seq), and bioinformatics analysis, we identified that DOT1L facilitated H3K79 methylation of nicotinate phosphoribosyltransferase (NAPRT) and epigenetically activated its expression. Importantly, NAPRT served as an oncogenic accel-erator by enhancing nicotinamide adenine dinucleotide (NAD+) synthesis. Therapeutically, DOT1L inhi-bition epigenetically silenced NAPRT expression through the diminishment of dimethylation of H3K79 (H3K79me2) in the NAPRT promoter, thereby inhibiting the malignant behaviors of UM. Conclusively, our findings delineated an integrated picture of the histone methylation landscape in UM and unveiled a novel DOT1L/NAPRT oncogenic mechanism that bridges transcriptional addiction and metabolic reprogramming.(c) 2022 The Author(s). Published by Elsevier B.V. on behalf of Xi'an Jiaotong University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Uveal melanoma (UM) is a common and dangerous ocular malignancy in adults, and aberrant histone methylation plays a role in its development. This study identified that DOT1L, a methyltransferase of histone H3 lysine 79 (H3K79), was activated in UM, especially in high-risk cases. DOT1L inhibitors showed tumor-selective inhibitory effects on UM cells. The study also revealed that DOT1L facilitated H3K79 methylation of NAPRT, which enhanced NAD+ synthesis and contributed to oncogenesis. DOT1L inhibition silenced NAPRT expression and inhibited the malignant behaviors of UM. These findings provide insights into the histone methylation landscape in UM and uncover a novel oncogenic mechanism involving DOT1L and NAPRT.