Dek overexpression in murine epithelia increases overt esophageal squamous cell carcinoma incidence

Esophageal cancer occurs as either squamous cell carcinoma (ESCC) or adenocarcinoma. ESCCs comprise almost 90% of cases worldwide, and recur with a less than 15% five-year survival rate despite available treatments. The identification of new ESCC drivers and therapeutic targets is critical for improving outcomes. Here we report that expression of the human DEK oncogene is strongly upregulated in esophageal SCC based on data in the cancer genome atlas (TCGA). DEK is a chromatin-associated protein with important roles in several nuclear processes including gene transcription, epigenetics, and DNA repair. Our previous data have utilized a murine knockout model to demonstrate that Dek expression is required for oral and esophageal SCC growth. Also, DEK overexpression in human keratinocytes, the cell of origin for SCC, was sufficient to cause hyperplasia in 3D organotypic raft cultures that mimic human skin, thus linking high DEK expression in keratinocytes to oncogenic phenotypes. However, the role of DEK over-expression in ESCC development remains unknown in human cells or genetic mouse models. To define the consequences of Dek overexpression in vivo, we generated and validated a tetracycline responsive Dek transgenic mouse model referred to as Bi-L-Dek. Dek overexpression was induced in the basal keratinocytes of stratified squamous epithelium by crossing Bi-L-Dek mice to keratin 5 tetracycline transactivator (K5-tTA) mice. Conditional transgene expression was validated in the resulting Bi-L-Dek_K5-tTA mice and was suppressed with doxycycline treatment in the tetracycline-off system. The mice were subjected to an established HNSCC and esophageal carcinogenesis protocol using the chemical carcinogen 4-nitroquinoline 1-oxide (4NQO). Dek overexpression stimulated gross esophageal tumor development, when compared to doxycycline treated control mice. Furthermore, high Dek expression caused a trend toward esophageal hyperplasia in 4NQO treated mice. Taken together, these data demonstrate that Dek overexpression in the cell of origin for SCC is sufficient to promote esophageal SCC development in vivo.

食管癌主要分为食管鳞状细胞癌（esophageal squamous cell carcinoma, ESCC）与腺癌。其中食管鳞状细胞癌占全球食管癌病例的近90%，即便接受现有治疗手段，其五年生存率仍不足15%且易复发。鉴定新的ESCC驱动基因与治疗靶点，对改善患者预后至关重要。本研究基于癌症基因组图谱（The Cancer Genome Atlas, TCGA）数据，发现人类DEK癌基因在食管鳞状细胞癌中存在显著上调表达。DEK是一种染色质结合蛋白，在基因转录、表观遗传调控、DNA修复等多种核内过程中发挥重要作用。我们此前的研究利用小鼠敲除模型证实，Dek表达对口腔和食管鳞状细胞癌的生长不可或缺。此外，在鳞状细胞癌的起源细胞——人类角质形成细胞中过表达DEK，足以在模拟人体皮肤的三维器官型筏式培养中诱发增生，从而将角质形成细胞中DEK的高表达与致癌表型建立关联。然而，DEK过表达在食管鳞状细胞癌发生发展中的具体作用，在人类细胞或遗传工程小鼠模型中仍未明确。为明确Dek过表达在体内的生物学效应，我们构建并验证了一种四环素响应型Dek转基因小鼠模型，命名为Bi-L-Dek。通过将Bi-L-Dek小鼠与角蛋白5四环素反式激活因子（keratin 5 tetracycline transactivator, K5-tTA）小鼠杂交，我们在复层鳞状上皮的基底角质形成细胞中诱导了Dek过表达。我们对杂交获得的Bi-L-Dek_K5-tTA小鼠的条件性转基因表达进行了验证，该系统属于四环素关闭（tet-off）表达体系，其转录活性可被多西环素（doxycycline）处理有效抑制。我们采用已建立的头颈部鳞状细胞癌（head and neck squamous cell carcinoma, HNSCC）及食管癌化学诱导方案，对小鼠给予化学致癌物4-硝基喹啉-1-氧化物（4-nitroquinoline 1-oxide, 4NQO）处理。结果显示，与经多西环素处理的对照组小鼠相比，Dek过表达显著促进了肉眼可见的食管肿瘤发生。此外，在经4NQO处理的小鼠中，高表达Dek还呈现出诱导食管增生的趋势。综上，本研究数据证实，在鳞状细胞癌的起源细胞中过表达Dek，足以在体内促进食管鳞状细胞癌的发生发展。