Zhu Guoqing, Wang Feng, Li Haojie, Zhang Xiao, Wu Qi, Liu Ya, Qian Mingping, Guo Susu, Yang Yueyue, Xue Xiangfei, Sun Fenyong, Qiao Yongxia, Pan Qiuhui
Department of Clinical Laboratory Medicine, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiaotong University, Shanghai, China.
Department of Gastroenterology, Shanghai Tenth People's Hospital of Tongji University, Shanghai, China.
Front Oncol. 2021 May 31;11:681366. doi: 10.3389/fonc.2021.681366. eCollection 2021.
A tremendous amount of studies have suggested that post-translational modifications (PTMs) play pivotal roles during tumorigenesis. Compared to other PTMs, lipid modification is less studied. Recently, N-myristoylation, one type of lipid modification, has been paid attention to the field of cancer. However, whether and how N-myristoylation exerts its roles in liver tumorigenesis still remains unclear.
Parallel reaction monitoring (PRM) was conducted to evaluate the expression of protein modification enzymes in paired tissues. Liver conditionally knocking NMT1 out mice model was used to assess the critical roles of N-myristoylation during liver tumorigenesis. Proteomics isobaric tags for relative and absolute quantification (iTraq) was performed to identify proteins that changed while NMT1 was knocked down. The click chemistry assay was used to evaluate the N-myristoylation levels of proteins.
Here, N-myristolyation and its enzyme NMT1, but not NMT2, were found to be critical in liver cancer. Two categories of proteins, i.e., N-myristolyation down-regulated proteins (NDP, including LXN, RPL29, and FAU) and N-myristolyation up-regulated proteins (NUP, including AHSG, ALB, and TF), were revealed negatively and positively regulated by NMT1, respectively. Both NDP and NUP could be N-myristolyated by NMT1 indispensable of POTEE. However, N-myristolyation decreased and increased stability of NDP and NUP, respectively. Mechanistically, NDP-specific binding protein RPL7A facilitated HIST1H4H, which has ubiquitin E3 ligase function, to ubiquitinate NDP. By contrast, NUP-specific binding protein HBB prevented NUP from ubiquitination by HIST1H4H. Notably, function of RPL7A and HBB was all NMT1-dependent. Moreover, NDP suppressed while NUP stimulated transformative phenotypes. Clinically, higher levels of NMT1 and NUP with lower levels of NDP had worse prognostic outcome.
Collectively, N-myristolyation by NMT1 suppresses anti-tumorigenic NDP, whereas it stimulates pro-tumorigenic NUP by interfering their ubiquitination to finally result in a pro-tumorigenic outcome in liver cancer. Targeting N-myristolyation and NMT1 might be helpful to treat liver cancer.
大量研究表明，翻译后修饰（PTMs）在肿瘤发生过程中起关键作用。与其他翻译后修饰相比，脂质修饰的研究较少。最近，N-肉豆蔻酰化作为一种脂质修饰类型，已在癌症领域受到关注。然而，N-肉豆蔻酰化在肝癌发生中是否以及如何发挥作用仍不清楚。
采用平行反应监测（PRM）评估配对组织中蛋白质修饰酶的表达。利用肝脏条件性敲除NMT1的小鼠模型评估N-肉豆蔻酰化在肝癌发生中的关键作用。进行蛋白质组学相对和绝对定量等压标签（iTraq）以鉴定NMT1敲低时发生变化的蛋白质。采用点击化学分析法评估蛋白质的N-肉豆蔻酰化水平。
在此研究中，发现N-肉豆蔻酰化及其酶NMT1而非NMT2在肝癌中起关键作用。揭示了两类蛋白质，即N-肉豆蔻酰化下调蛋白（NDP，包括LXN、RPL29和FAU）和N-肉豆蔻酰化上调蛋白（NUP，包括AHSG、ALB和TF），分别受到NMT1的负调控和正调控。NDP和NUP均可被NMT1进行N-肉豆蔻酰化，这是POTEE所必需的。然而，N-肉豆蔻酰化分别降低和增加了NDP和NUP的稳定性。机制上，NDP特异性结合蛋白RPL7A促进具有泛素E3连接酶功能的HIST1H4H对NDP进行泛素化。相比之下，NUP特异性结合蛋白HBB阻止HIST1H4H对NUP进行泛素化。值得注意的是，RPL7A和HBB的功能均依赖于NMT1。此外，NDP抑制而NUP刺激转化表型。临床上，NMT1和NUP水平较高而NDP水平较低的患者预后较差。
总体而言，NMT1介导的N-肉豆蔻酰化通过干扰其泛素化抑制抗肿瘤的NDP，而刺激促肿瘤的NUP，最终导致肝癌的促肿瘤结果。靶向N-肉豆蔻酰化和NMT1可能有助于治疗肝癌。
