IKKβ磷酸化FOXJ1诱导其泛素化降解的新机制在调控胃黏膜肠上皮化生中的作用

Gastric intestinal metaplasia (IM) is one of the most important lesion in the transformation from atrophic gastritis to gastric carcinoma. Transcriptional factors have been considered to be pivotal during the development of chronic uncontrolled inflammation and IM. However, the underlying mechanism remains largely unknown. In general, IKKβ is regarded as a critical player in the progression of inflammation-cancer link. In the previous study, we found that the expression of FOXJ1 was significantly decreased in IM tissues and bile acids-stimulated GES-1 cells. In addition, the nuclear exclusion of FOXJ1 correlated with positive expression of IKKβ in IM. We also found that FOXJ1 was physically associated with IKKβ by coimmunoprecipitation analysis with lysates of bile acids-stimulated GES-1 cells. And serines 32/35 motifs in FOXJ1 were potential phosphorylation sites of IKKβ speculated by PhoshositePlus database and Scansite 4.0 software. It was also reported that IKKβ phosphorylated FOXO3a, with amino acid sequence similarities to the motifs in FOXJ1 which are highly conserved evolutionarily. As phosphorylation and ubiquitination are critical post-transcriptional modification of FOX transcription factors, we hypothesize that IKKβ phosphorylates and induces ubiquitin-mediated degradation of FOXJ1 in IM. In this study, we are going to explore the mechanism of IKKβ repressing FOXJ1 transactivation activity and the functions of IKKβ in IM through inhibiting FOXJ1 by organoid model for IM, and to verify the relationship between IKKβ and FOXJ1 in clinical IM tissues on a large scale. This study may deepen the understanding of the new function of IKKβ and FOXJ1, and provide new molecular markers for early warning of inflammation-tumor transformation in gastric cancer.

胃黏膜肠上皮化生是慢性萎缩性胃炎向胃癌转化的重要环节，转录因子调控的慢性不可控性炎症在其中起核心作用，其作用机制不清。IKKβ是炎症-肿瘤转化过程的关键分子。我们前期率先发现：FOXJ1在肠化生组织和胆汁酸刺激GES-1细胞中表达均显著下调；IKKβ和FOXJ1在肠化生组织中的表达呈负相关；IKKβ和FOXJ1可直接结合。进一步通过数据库和软件预测，结合文献，发现FOXJ1的丝氨酸32/35是IKKβ的潜在磷酸化位点。由于磷酸化修饰和泛素化降解是FOX蛋白转录活性的重要调控方式，据此推测：IKKβ通过磷酸化FOXJ1并介导其泛素化降解激活炎性通路，促进胃黏膜肠化生。本课题拟利用胃类器官模型，确定IKKβ通过抑制FOXJ1促进肠化生的功能，揭示IKKβ调控FOXJ1的新机制，并在临床大规模肠化生组织标本中验证。以期拓展对IKKβ和FOXJ1功能的新认识，为肠化生向胃癌转化提供新的预警分子。

胃黏膜肠上皮化生（intestinal metaplasia，IM）是慢性萎缩性胃炎向胃癌转化的关键环节，并显著增加胃癌的发病风险。胆汁酸反流形成的慢性炎症微环境是诱导IM的主要因素，也是诱导IM最重要的内源性因素。然而，连接炎症、IM与胃癌的分子网络在很大程度上仍是未知的。因此，深入研究胆汁酸反流如何破坏胃上皮稳态导致IM，对深化癌前疾病的认识，确定高风险人群，以及预警胃癌并早期干预具有重要意义。本课题研究发现，在Hp阴性IM患者组织中，相对于正常胃黏膜组织，对应IM中FOXJ1表达强度明显减弱，FOXJ1在正常胃黏膜中主要定位于胞核，而在IM组织中主要定位于胞浆，而且FOXJ1表达减弱与Hp阴性患者IM的进展相关；构建胆汁酸诱导的IM细胞/类器官模型，验证了FOXJ1通过抑制NF-κB信号通路抑制胆汁酸诱导的IM发生；进一步研究发现，IKKβ和FOXJ1在Hp阴性IM组织中的表达呈负相关，且IKKβ和FOXJ1的表达模式与IM进展相关；同时，IKKβ和FOXJ1可直接结合，FOXJ1的丝氨酸32/35是IKKβ的磷酸化位点，IKKβ通过磷酸化FOXJ1并通过泛素-蛋白酶体途径介导其降解，从而激活下游炎症通路，促进IM发生。本课题利用IM细胞/类器官模型，验证了IKKβ通过抑制FOXJ1促进IM的功能，揭示了IKKβ调控FOXJ1的新机制。本研究将有望拓展对IKKβ和FOXJ1新功能的认识，深化对IM分子机制的理解，使IKKβ和FOXJ1有可能成为干预IM、预警胃癌的新的切入点。