Protumorigenic role of MDM4 in human hepatocarcinogenesis.

肿瘤抑制因子p53编码一种转录因子，在约50%的人类肿瘤中发生突变。由于暴露于外毒素，发展中国家HCC中p53突变的频率很高（>50%），而西方国家则很低（<10-25%）。我们先前已经证明，p53相互作用因子MDM 4在人类肝癌中频繁上调。因此，MDM 4失调可以补充p53的突变失活。另一方面，我们观察到一种p53非依赖性MDM 4功能，这可能会显著影响靶向MDM 4的翻译到人HCC患者的治疗中。该项目的目的是使用CRISPR/Cas9介导的体内特异性敲除来表征促肿瘤发生MDM 4功能的p53依赖性。最近，描述了小分子抑制剂Xi-006通过尚未确定的机制抑制MDM 4转录。因此，我们将重点关注通过异常转录激活和microRNA依赖机制导致HCC中MDM 4-mRNA表达上调的机制。最后，我们将产生一种新的基于转座子的嵌合MDM 4小鼠模型，以评估MDM 4在原位环境中的促肿瘤发生功能和SJ-172550治疗（抑制p53-MDM 4相互作用）的体内功效。此外，MDM 4嵌合小鼠将作为一个有价值的工具，在体内分析的p53失调，在肝肿瘤的发展和它的串扰，以其他protumorigenic信号级联经常改变人肝癌。我们的分析可能揭示HCC中MDM 4失调的相关机制，评估新的治疗方法及其p53依赖性，这将是该项目进一步翻译发展的基础，并可能确定新的预测标记物，以有效靶向肿瘤治疗中的p53网络。

The tumor suppressor p53 encodes a transcription factor that is mutated in about 50% of all human tumors. Whereas the frequency of p53 mutations in HCCs is high in developing countries (>50%) due to exposure to exotoxins, it is low (<10-25%) in Western countries. We have previously demonstrated that the p53-interacting factor MDM4 is frequently upregulated in human HCCs. Thus, MDM4 dysregulation may complement for mutational inactivation of p53. On the other hand we observed a p53-independent MDM4 function, which might significantly affect the translation of targeting MDM4 into the treatment of human HCC patients. It is the aim of the project to characterize the p53-dependency of the protumorigenic MDM4 function using CRISPR/Cas9-mediated, specific knockout in vivo. Recently, the small molecule inhibitor XI-006 was described to suppress MDM4 transcription through a yet undefined mechanism. Therefore, we will focus on mechanisms resulting in upregulation of MDM4-mRNA expression in HCC by aberrant transcriptional activation and by microRNA-dependent mechanisms. Finally, we will generate a novel transposon-based chimeric MDM4 mouse model to evaluate the protumorigenic function of MDM4 in an orthotopic context and the efficacy of SJ-172550 treatment (inhibiting the p53-MDM4 interaction) in vivo. In addition, the MDM4 chimeric mice will serve as a valuable tool for in vivo analyses of p53 dysregulation in liver tumor development and its cross-talk to other protumorigenic signaling cascades frequently altered in human HCC. Our analyses may unravel relevant mechanisms underlying MDM4 dysregulation in HCC, evaluate new therapeutic approaches and their p53-dependency, which will be the basis for the further translational development of this project and may identify new predictive marker for efficiently targeting the p53 network in tumor therapy.