PRMT6-CDC20 facilitates glioblastoma progression via the degradation of CDKN1B

PRMT6, a type I arginine methyltransferase, di-methylates the arginine residues of both histones and non-histones asymmetrically. Increasing evidence indicates that PRMT6 plays a tumor mediator involved in human malignancies. Here, we aim to uncover the essential role and underlying mechanisms of PRMT6 in promoting glioblastoma (GBM) proliferation. Investigation of PRMT6 expression in glioma tissues demonstrated that PRMT6 is overexpressed, and elevated expression of PRMT6 is negatively correlated with poor prognosis in glioma/GBM patients. Silencing PRMT6 inhibited GBM cell proliferation and induced cell cycle arrest at the G0/G1 phase, while overexpressing PRMT6 had opposite results. Further, we found that PRMT6 attenuates the protein stability of CDKN1B by promoting its degradation. Subsequent mechanistic investigations showed that PRMT6 maintains the transcription of CDC20 by activating histone methylation mark (H3R2me2a), and CDC20 interacts with and destabilizes CDKN1B. Rescue experimental results confirmed that PRMT6 promotes the ubiquitinated degradation of CDKN1B and cell proliferation via CDC20. We also verified that the PRMT6 inhibitor (EPZ020411) could attenuate the proliferative effect of GBM cells. Our findings illustrate that PRMT6, an epigenetic mediator, promotes CDC20 transcription via H3R2me2a to mediate the degradation of CDKN1B to facilitate GBM progression. Targeting PRMT6-CDC20-CDKN1B axis might be a promising therapeutic strategy for GBM. Overall design: To test the effect of suppression of PRMT6 on the gene expression, U87 cells were transfected with PRMT6 Scramble shRNA (NC) or PRMT6 shRNA. PRMT6-knockdown U87 cells were compared to control cells.

PRMT6作为I型精氨酸甲基转移酶（type I arginine methyltransferase），可对组蛋白与非组蛋白的精氨酸残基进行不对称双甲基化修饰。越来越多的研究证据表明，PRMT6是参与人类恶性肿瘤发生发展的肿瘤调控因子。本研究旨在阐明PRMT6在促进胶质母细胞瘤（glioblastoma, GBM）增殖过程中的核心作用及其潜在分子机制。对胶质瘤组织中PRMT6的表达水平进行检测后发现，PRMT6在胶质瘤组织中呈高表达状态，且其表达上调与胶质瘤/GBM患者的不良预后呈显著负相关。沉默PRMT6可抑制GBM细胞增殖，并诱导细胞周期阻滞于G0/G1期；而过表达PRMT6则会产生完全相反的生物学效应。进一步研究证实，PRMT6可通过促进CDKN1B的降解，降低其蛋白稳定性。后续机制探究显示，PRMT6通过激活组蛋白甲基化标记H3R2me2a，维持CDC20的转录水平；且CDC20可与CDKN1B相互作用并使其去稳定化。拯救实验（rescue experiment）结果证实，PRMT6可通过CDC20介导CDKN1B的泛素化降解，进而促进细胞增殖。本研究还验证了PRMT6抑制剂EPZ020411可显著减弱GBM细胞的增殖能力。综上，本研究揭示PRMT6作为一种表观遗传调控介质，通过H3R2me2a激活CDC20的转录，进而介导CDKN1B的降解，最终促进GBM的进展。靶向PRMT6-CDC20-CDKN1B信号轴有望成为GBM潜在的治疗策略。实验设计概述：为探究PRMT6沉默对基因表达的影响，将U87细胞分别转染PRMT6阴性对照短发卡RNA（NC）与PRMT6短发卡RNA（shRNA），以PRMT6敲低的U87细胞与对照细胞进行对比分析。