FBXW11介导NF90泛素化参与结直肠癌血管生成的分子机制研究

A growing number of evidence suggest that dysregulation of nuclear factor 90 (NF90) promotes cancer progression, including angiogenesis. We have found that the expression of NF90 was aberrantly up-regulated in colorectal cancer (CRC) tissues compared with normal controls and NF90 promoted angiogenesis of CRC. However, the mechanism of how NF90 protein is regulated in CRC remains unknown. FBXW11 is a well characterized E3 ligase of ubiquitination, which is a major protein modification that controls protein stability. Herein, we found that a), the protein expression between FBXW11 and NF90 was negatively correlated; b), FBXW11 interacted with NF90; c), overexpression of FBXW11 significantly reduced the endogenous NF90 protein level while MG132, a potent inhibitor of ubiquitin-protosome system, could effectively reversed the phenomenon; d), knocking down FBXW11 promoted tumor progression in an xenograft model. Therefore, we hypothesize that FBXW11 serving as an E3 ligase, promotes NF90 ubiquitination, thus regulating CRC angiogenesis. We intend to test our hypothesis from “phenomenon-mechanism-function” by applying techniques such as target gene transfection, immunoprecipitation, angiogenesis model etc. The present study will provide novel therapeutic strategies and targets for anti-angiogenesis based treatment of CRC.

越来越多的证据表明失调的细胞核因子90（NF90）在包括血管生成等肿瘤的发生、进展中发挥重要作用。我们前期研究发现，NF90在结直肠癌组织中异常高表达并促进结直肠癌的血管生成，但其自身蛋白水平的调控机制不详。泛素化是一种重要的蛋白修饰，控制蛋白稳定性，而FBXW11是泛素化过程中经典的E3连接酶。在预实验中，我们发现：1、FBXW11蛋白表达与NF90呈负相关；2、FBXW11与NF90存在结合；3、过表达FBXW11降低NF90蛋白水平，泛素-蛋白酶体抑制剂（MG132）逆转这一现象；4、敲除FBXW11促进裸鼠移植瘤生长。因此，我们推测：FBXW11作为NF90的特异性E3连接酶，介导后者发生泛素化降解，从而影响结直肠癌血管生成。我们拟应用目的基因转染、免疫共沉淀、血管生成模型等技术，从现象-机制-功能层次证明我们的假说。此研究将为抗结直肠癌血管生成的相关治疗手段提供新思路和新靶点。

泛素化作为一种重要的蛋白质翻译后修饰作用，深刻影响蛋白质的代谢和功能，广泛参与细胞生命活动的调控，与肿瘤的发生和进展关系密切。我们前期研究发现，NF90在结直肠癌组织中异常高表达并促进结直肠癌的血管生成，但其自身蛋白水平的调控机制不详。为此，我们试验证实FBXW11可特异性与NF90结合，介导其发生多聚泛素化，并且发现该泛素化修饰依赖于GSK3β对NF90特异性氨基酸序列的磷酸化作用，从而使得NF90蛋白质发生降解，最终导致结直肠癌血管生成能力下降。此外我们对课题进行了延伸，发现泛素化及去泛素化过程影响肿瘤的代谢重编程，尤其是嘌呤代谢的从头合成过程。试验结果显示CLK3作为磷酸激酶，可磷酸化去泛素化酶USP13，增强嘌呤代谢中关键分子c-Myc蛋白稳定性，最终促进肿瘤进展。我们通过小分子药物库筛选出盐酸他克林可抑制CLK3活性，达到抑制肿瘤生长的效果。总之，本课题试验结果将为以泛素化为靶点的相关治疗手段提供新的理论依据和新的潜在药物选择。

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