A helicase-independent role of DHX15 promotes MYC stability and acute leukemia cell survival. A helicase-independent role of DHX15 promotes MYC stability and acute leukemia cell survival

DHX15 has been implicated in RNA splicing and ribosome biogenesis, primarily functioning as an RNA helicase. To systematically assess the cellular role of DHX15, we conducted proteomic analysis to investigate the landscape of DHX15 interactome, and identified MYC as a binding partner. DHX15 co-localizes with MYC in cells and directly interacts with MYC in vitro. Importantly, DHX15 contributes to MYC protein stability at the post-translational level and independent of its RNA binding capacity. Mechanistic investigation reveals that DHX15 interferes the interaction between MYC and FBXW7, thereby preventing MYC polyubiquitylation and proteasomal degradation. Consequently, abrogation of DHX15 drastically inhibits MYC-mediated transcriptional output. While DHX15 depletion blocks T-cell development and leukemia cell survival as we recently reported, overexpression of MYC significantly rescues the phenotypic defects. These findings shed light on the essential role of DHX15 in mammalian cells and suggest that maintaining sufficient MYC expression is a significant contributor to DHX15-mediated cellular functions. Overall design: To confirm the pivotal role of MYC as a significant downstream target of DHX15, we performed the transcriptome analysis in DHX15-depleted KOPTK1 cells while MYC was restored.

DHX15 已被证实参与RNA剪接与核糖体生物发生过程，其主要功能为RNA解旋酶（RNA helicase）。为系统评估DHX15的细胞生物学功能，我们开展蛋白质组学分析以探究DHX15的互作组图谱，并鉴定出MYC为其结合伴侣。DHX15可在细胞内与MYC共定位，并在体外与MYC直接相互作用。重要的是，DHX15可在翻译后水平增强MYC蛋白的稳定性，且该功能不依赖于其RNA结合能力。机制研究揭示，DHX15可干扰MYC与FBXW7之间的相互作用，从而抑制MYC的多泛素化与蛋白酶体降解。因此，DHX15的功能缺失会显著抑制MYC介导的转录输出。正如我们近期所报道的，DHX15敲低会阻断T细胞发育与白血病细胞存活，而MYC过表达可显著挽救该表型缺陷。上述研究结果阐明了DHX15在哺乳动物细胞中的关键作用，并提示维持充足的MYC表达是DHX15介导的细胞功能的重要贡献因素。总体实验设计：为验证MYC作为DHX15关键下游靶点的核心作用，我们在DHX15敲低的KOPTK1细胞中恢复MYC表达，并开展了转录组学分析。