Function and Mechanism of METTL5-mediated translation in multiple myeloma

The abnormal expression of m6A methyltransferase is a significant factor in the occurrence and progression of tumors. The 18S ribosomal RNA (rRNA) m6A methyltransferase Methyltransferase-like 5 (METTL5) is upregulated in various cancers, leading to adverse prognosis by abnormally regulating protein translation in tumor cells. However, the functionality and molecular mechanisms of METTL5 in the progression of multiple myeloma (MM) remains unknown. In this study, we demonstrate that the expression of METTL5 in the bone marrow (BM) of newly diagnosed MM patients is significantly higher than in healthy individuals and patients in remission following treatment. Importantly, we found that MM patients with upregulated METTL5 expression had a poorer prognosis. Additionally, we show that METTL5 plays a key role in promoting MM progression both in vitro and in a orthotopical xenograft model. Mechanistically, the depletion of METTL5 expression mediates a decrease in overall translation efficiency and selenium metabolism-related signaling pathway levels. We further revealed that the reduction in selenophosphate synthetase 2 (SEPHS2) translation efficiency mediated by METTL5 depletion can lead to diminished synthesis of selenoprotein and lead to increased reactive oxygen species (ROS), thereby inducing apoptosis in MM. Salvianolic Acid C (SAC) was identified as a potential METTL5 inhibitor, demonstrating significant pro-apoptotic effects during the treatment of MM both in vitro and in vivo. In summary, our research highlights the critical role of METTL5 in the progression of MM cells. Our data indicate METTL5's function is to influence the overall translation efficiency and reprogram selenium metabolism to inhibit apoptosis. Overall design: RNA-seq and Ribo-seq were used to study the differential translated genes in the METTL5 knockout and control cells.

N⁶-甲基腺嘌呤（m⁶A）甲基转移酶的异常表达是肿瘤发生与进展的关键驱动因素。18S核糖体RNA（ribosomal RNA, rRNA）的m⁶A甲基转移酶——甲基转移酶样5（Methyltransferase-like 5, METTL5）在多种癌症中呈高表达状态，通过异常调控肿瘤细胞的蛋白质翻译过程，进而导致不良预后。然而，METTL5在多发性骨髓瘤（multiple myeloma, MM）进展中的生物学功能与分子机制仍有待阐明。

本研究证实，初诊多发性骨髓瘤患者骨髓（bone marrow, BM）中的METTL5表达水平显著高于健康个体以及治疗后达到缓解的患者。值得注意的是，METTL5表达上调的多发性骨髓瘤患者往往预后更差。此外，本研究证明METTL5可在体内外环境中促进多发性骨髓瘤的进展，相关实验包括体外细胞实验与原位异种移植模型实验。

从分子机制层面分析，敲低METTL5的表达可同时降低细胞整体翻译效率与硒代谢相关信号通路的活性。本研究进一步揭示，METTL5敲低介导的硒磷酸合成酶2（selenophosphate synthetase 2, SEPHS2）翻译效率下降，会导致硒蛋白合成量减少，并引发活性氧（reactive oxygen species, ROS）水平升高，最终诱导多发性骨髓瘤细胞凋亡。

本研究筛选得到丹酚酸C（Salvianolic Acid C, SAC）作为潜在的METTL5抑制剂，其在体内外治疗多发性骨髓瘤的过程中均表现出显著的促凋亡效果。

综上，本研究明确了METTL5在多发性骨髓瘤细胞进展中的关键作用。研究数据表明，METTL5可通过影响整体翻译效率、重编程硒代谢通路来抑制肿瘤细胞凋亡。

整体实验设计：本研究采用RNA测序（RNA-seq）与核糖体测序（Ribo-seq）技术，分析METTL5敲除细胞与对照细胞中的差异翻译基因。