S6K1 phosphorylation-dependent degradation of Mxi1 by β-Trcp ubiquitin ligase promotes Myc activation and radioresistance in lung cancer.
S6K1 phosphorylation-dependent degradation of Mxi1 by β-Trcp ubiquitin ligase promotes Myc activation and radioresistance in lung cancer.
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β-Trcp 泛素连接酶对 Mxi1 的 S6K1 磷酸化依赖性降解促进肺癌中 Myc 激活和放射抗性
作者：
Huang Y;Hu K;Zhang S;Dong X;Yin Z;Meng R;Zhao Y;Dai X;Zhang T;Yang K;Liu L;Huang K;Shi S;Zhang Y;Chen J;Wu G;Xu S
Mxi1被认为是一种潜在的肿瘤抑制蛋白，可拮抗原癌基因Myc的转录活性。然而，Mxi1在肺癌中的调节的临床意义和潜在机制仍然知之甚少。方法：采用质谱分析和免疫沉淀法研究蛋白质间的相互作用。通过体外激酶测定评估Mxi 1的磷酸化。通过体内泛素化测定检测Mxi 1的多聚泛素化。稳定表达野生型Mxi1或Mxi1-S160A的肺癌细胞用于功能分析。采用免疫组化法检测肺癌组织及癌旁正常肺组织中Mxi 1和S6 K1的表达水平。结果：肺癌组织中Mxi 1表达下调，与预后不良相关。利用串联亲和纯化技术，我们提供了β-Trcp E3泛素连接酶与Mxi1相互作用并促进其泛素化和降解的证据。此外，我们证明了Mxi1在S160位点被蛋白激酶S6K1磷酸化，随后通过泛素连接酶β-Trcp降解。此外，不能被S6K1和β-Trcp降解的Mxi1的磷酸化突变形式（Mxi1-S160A）在抑制肺癌细胞中Myc的转录活性和辐射抗性方面更加稳定和有效。更重要的是，在人肺癌组织中观察到S6K1和Mxi1表达之间的强负相关。结论：我们的研究结果不仅建立了mTOR/S6K1信号通路和Myc激活之间的串扰，而且还表明靶向S6K1/Mxi1通路是治疗肺癌的有希望的治疗策略。
Rationale: Mxi1 is regarded as a potential tumor suppressor protein that antagonizes the transcriptional activity of proto-oncogene Myc. However, the clinical significances and underlying mechanisms by which Mxi1 is regulated in lung cancer remain poorly understood. Methods: Mass spectrometry analysis and immunoprecipitation assay were utilized to detect the protein-protein interaction. The phosphorylation of Mxi1 was evaluated by in vitro kinase assays. Poly-ubiquitination of Mxi1 was examined by in vivo ubiquitination assay. Lung cancer cells stably expressing wild-type Mxi1 or Mxi1-S160A were used for functional analyses. The expression levels of Mxi1 and S6K1 were determined by immunohistochemistry in lung cancer tissues and adjacent normal lung tissues. Results: We found that Mxi1 is downregulated and correlated with poor prognosis in lung cancer. Using tandem affinity purification technology, we provided evidence that β-Trcp E3 ubiquitin ligase interacts with and promotes the ubiquitination and degradation of Mxi1. Furthermore, we demonstrated that Mxi1 is phosphorylated at S160 site by the protein kinase S6K1 and subsequently degraded via the ubiquitin ligase β-Trcp. Moreover, a phosphorylation mutant form of Mxi1 (Mxi1-S160A), which cannot be degraded by S6K1 and β-Trcp, is much more stable and efficient in suppressing the transcriptional activity of Myc and radioresistance in lung cancer cells. More importantly, a strong inverse correlation between S6K1 and Mxi1 expression was observed in human lung cancer tissues. Conclusion: Our findings not only establish a crosstalk between the mTOR/S6K1 signaling pathway and Myc activation, but also suggest that targeting S6K1/Mxi1 pathway is a promising therapeutic strategy for the treatment of lung cancer.
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影响因子：
16
作者：
Dehan, Elinor;Bassermann, Florian;Guardavaccaro, Daniele;Vasiliver-Shamis, Gaia;Cohen, Michael;Lowes, Kym N.;Dustin, Michael;Huang, David C. S.;Taunton, Jack;Pagano, Michele
通讯作者：
Pagano, Michele
影响因子：
10.3
作者：
Ougolkov, A;Zhang, B;Minamoto, T
通讯作者：
Minamoto, T
影响因子：
64.8
作者：
Arif A;Terenzi F;Potdar AA;Jia J;Sacks J;China A;Halawani D;Vasu K;Li X;Brown JM;Chen J;Kozma SC;Thomas G;Fox PL
通讯作者：
Fox PL
影响因子：
64.8
作者：
Schreiber-Agus, N;Meng, Y;DePinho, RA
通讯作者：
DePinho, RA
影响因子：
11.5
作者：
Sahin, F;Kannangai, R;Torbenson, M
通讯作者：
Torbenson, M