Department of Molecular and Medical Genetics, School of Medicine, and the OHSU Knight Cancer Institute, Oregon Health & Science University, Portland, Oregon.
Cancer Res Commun. 2024 Oct 1;4(10):2835-2845. doi: 10.1158/2767-9764.CRC-24-0312.
Ribosome biogenesis is a highly regulated cellular process requiring a large cohort of accessory factors to ensure the accurate production of ribosomes. Dysregulation of ribosome biogenesis is associated with the development of various human diseases, including cancer. The Las1L-Nol9 endonuclease-kinase complex is essential for the cleavage of the rRNA internal transcribed spacer 2 (ITS2), the phosphorylation of the 5'-hydroxyl end of the resulting precursor, and, thus, the maturation of the 60S ribosome. However, how the Las1L-Nol9 complex is regulated in cells is unclear. In this study, we report that the nucleolar ubiquitin-specific protease USP36 is a novel regulator of the Las1L-Nol9 complex. USP36 interacts with both Las1L and Nol9 and regulates their stability via deubiquitination. Intriguingly, USP36 also mediates the SUMOylation of Las1L, mainly at lysine (K) 565. Mutating K565 to arginine (R) does not affect the levels of Las1L and the formation of the Las1L-Nol9 complex, but abolishes its function in ITS2 processing, as unlike wild-type Las1L, the K565R mutant failed to rescue the defects in the ITS2 processing induced by the knockdown of endogenous Las1L. These results suggest that USP36-mediated Las1L SUMOylation is critical for ITS2 processing and that USP36 plays a critical role in ribosome biogenesis by regulating the Las1L-Nol9 complex.
This study identifies USP36 as a deubiquitinating and small ubiquitin-like modifier ligase dual-function enzyme to mediate Las1L deubiquitination and SUMOylation. Las1L SUMOylation at K565 plays a critical role in pre-rRNA ITS2 processing. Thus, our study reveals a novel downstream pathway for USP36-regulated ribosome biogenesis.
核糖体生物发生是一个高度调控的细胞过程，需要大量辅助因子来确保核糖体的准确产生。核糖体生物发生的失调与各种人类疾病的发展有关，包括癌症。Las1L-Nol9 内切核酸酶-激酶复合物对于 rRNA 内部转录间隔区 2（ITS2）的切割、切割产物的 5'-羟基末端的磷酸化以及 60S 核糖体的成熟是必不可少的。然而，Las1L-Nol9 复合物在细胞中是如何被调节的尚不清楚。在这项研究中，我们报告核仁泛素特异性蛋白酶 USP36 是 Las1L-Nol9 复合物的一种新型调节剂。USP36 与 Las1L 和 Nol9 相互作用，并通过去泛素化调节它们的稳定性。有趣的是，USP36 还介导 Las1L 的 SUMO 化，主要在赖氨酸（K）565 上。将 K565 突变为精氨酸（R）不会影响 Las1L 的水平和 Las1L-Nol9 复合物的形成，但会使其在 ITS2 加工中的功能丧失，因为与野生型 Las1L 不同，K565R 突变体不能挽救内源性 Las1L 敲低引起的 ITS2 加工缺陷。这些结果表明，USP36 介导的 Las1L SUMO 化对于 ITS2 加工至关重要，并且 USP36 通过调节 Las1L-Nol9 复合物在核糖体生物发生中发挥关键作用。
本研究鉴定 USP36 为一种去泛素化和小泛素样修饰酶双重功能酶，可介导 Las1L 的去泛素化和 SUMO 化。Las1L 在 K565 的 SUMO 化在 pre-rRNA ITS2 加工中起关键作用。因此，我们的研究揭示了 USP36 调节的核糖体生物发生的一个新的下游途径。
