Abstract Topic: 20. Lymphoma Biology & Translational Research
Background: Adult T-cell leukemia/ lymphoma (ATL) is derived from mature T-cells transformed by human T-cell lymphotropic virus type 1 (HTLV-1). It takes several decades for carriers to develop ATL after HTLV-1 infection. HTLV-1–infected T-cells accumulate genetic and epigenetic, which possibly drives leukemogenesis. Trimethylation at histone H3Lys27 (H3K27me3) accumulates aberrantly in HTLV-1-infected T-cells and an inhibitor of enhancer of zeste homolog (EZH), which catalyze trimethylation of H3K27, has been recently approved for the treatment of relapsed/refractory ATL in Japan. On the other hand, we have reported that regional DNA hypermethylation correlated with ATL development and progression, and DNA demethylating agents suppressed tumor cell growth (Blood 2020, 136: 871-884). Taken together, epigenetic abnormalities, especially hypermethylation of DNA and histone H3K27, are functionally important for ATL leukemogenesis and represent effective therapeutic targets.
Aims: Since the epigenetic reprogramming that drives T-cell differentiation and proliferation was recently shown to be regulated by extracellular methionine, here, we aimed to reveal the involvement of methionine metabolism in regulation of epigenetic modification in ATL cells.
Methods: HTLV-1-infected cell lines were cultured in RPMI-1640 medium containing 100 μM methionine (control) or modified RPMI-1640 medium with a reduced concentration of methionine. In xenograft mouse model, MT-2 cells were inoculated into immunodeficient Balb/c Rag-2-/- Jak3-/- mice. Methionine restricted feed (10% fat, 0.12% methionine) and control feed (10% fat, 0.86% methionine) were from Research Diets, Inc. Genome-wide DNA methylation and H3K27me3 status were determined by using Infinium MethylationEPIC Bead Chips and H3K27me3 ChIP-seq assay, respectively. The expression of SLC7A5 protein in tissue samples of patients with ATL was determined by immunohistochemical staining.
Results: Methionine restriction suppressed the growth of HTLV-1-infected cell lines in vitro. In a xenograft mouse model, dietary methionine restriction also suppressed growth of tumor cells inoculated into immunodeficient mice. MT-2 cells cultured methionine restricted condition for 8 days were analyzed by C-SCOPE at Human Metabolome Technologies, Inc. The metabolome analysis showed that intracellular methionine and S-adenosylmethionine were dramatically decreased under methionine restriction condition. Furthermore, in the genome-wide DNA methylation analysis, we found that DNA methylation at highly methylated regions was significantly reduced in MT-2 cells cultured methionine restricted condition (Fig. A). Similarly, ChIP-seq analysis revealed a reduction in H3K27me3 at transcription start site (TSS) regions under methionine restricted condition (Fig. B). The integrated analysis of data from transcriptome, DNA methylome and H3K27me3 ChIP-seq identified several genes, whose expression was changed due to epigenetic reprogramming under methionine restricted condition (Fig. C). It is important to note that the expression of SLC7A5 which acts as a methionine transporter, in tissue samples such as bone marrow, lymph node, and subcutis from patients with aggressive ATL tended to be high compared with that with indolent ATL (Fig. D).
Summary/Conclusion: Based on these results, epigenetic abnormalities in HTLV-1-infected cells were shown to be regulated by methionine metabolism. Targeting methionine incorporation or metabolism to could be an alternative therapeutic strategy for the treatment of ATL.
Keywords: Methylation, Epigenetic, Oncogenesis, ATL