Tpl2 in Intestinal Tumorigenesis

描述(申请人提供)：在逆转录病毒诱导的啮齿动物淋巴瘤和乳房腺癌中，编码Tpl2激酶的原癌基因被前病毒整合激活。在这里，我们提出了Tpl2在肠上皮细胞中也作为肿瘤抑制基因发挥作用的证据。为了确定Tpl2在Apcmin诱导的肿瘤发生中的作用，我们将Apcmin突变与Tpl2-/-遗传背景进行了交叉。与预期相反，与Tpl2+/+/Apcmin/+小鼠相比，Tpl2-/-/Apcmin/+小鼠的肠道息肉数量增加了5倍，肿瘤形成速度显著加快。相对于Tpl2+/+/Apcmin/+小鼠，Tpl2-/-/Apcmin/+小鼠的息肉数量较多，这表明Tpl2消融促进了肿瘤的启动。由于导致肿瘤发生的最早的基因改变是APC基因座的杂合性缺失(LOH)，因此Tpl2消融促进了杂合性缺失。这可能是由几种机制引起的。一种可能性是，Tpl2消融增加了可能成为LOH靶点的肠道干细胞的数量。鉴于Wnt途径促进干细胞的循环，我们假设Tpl2消融可能通过刺激Wnt信号而导致干细胞数量的增加。然而，这里的研究表明，尽管Tpl2有可能抑制几种类型的上皮细胞中的Wnt信号，但Tpl2消融并不增加肠隐窝中的干细胞数量。进一步的研究表明，Tpl2消融促进了肠道炎症，这也是已知的刺激肿瘤启动的因素。对炎症原因的搜索发现，Tpl2消融导致Paneth细胞缺陷，其特征是编码抗菌肽的基因显著下调。同样的研究发现，抑制可能通过Tpl2转导的TLR信号，刺激巨噬细胞中典型的Wnt途径的活性，并降低Tpl2-/-小鼠肠黏膜中IL-10的水平。然而，Tpl2的作用可能并不局限于肿瘤的启动。我们的初步数据确实提供了强有力的证据，证明Tpl2消融也可能有助于肿瘤形成的晚期。TPL2消融可能通过靶向Wnt通路或其他相互作用的通路来调节APC消融诱导的肿瘤细胞生物学。或者，它可能靶向Akt和mTOR，正如我们最近对人结肠癌细胞株的研究所表明的那样。本申请中提出的工作将集中在Tpl2在APC突变诱导的肠道肿瘤发生中对LOH前和LOH后事件的调节中的作用。 公共卫生相关性：我们的初步数据，在人类遗传学研究的背景下解释，表明Tpl2基因敲除小鼠是炎症性肠病(IBD)的优秀动物模型。同样的数据提供了炎症和癌症之间的强烈联系。因此，TPL2消融模型为从机制上解决IBD和结直肠癌的病理生理学以及为这些疾病的治疗干预确定新的靶点提供了一个有价值的工具。

DESCRIPTION (provided by applicant): The proto-oncogene encoding the Tpl2 kinase is activated by provirus integration in retrovirus-induced rodent lymphomas and mammary adenocarcinomas. Here, we present evidence that Tpl2 also functions as a tumor suppressor gene in the intestinal epithelia. To determine the role of Tpl2 in Apcmin-induced tumorigenesis, we crossed the Apcmin mutation into the Tpl2-/- genetic background. Contrary to expectation, Tpl2-/-/ Apcmin/+ mice exhibited a 5-fold increase in the number of intestinal polyps and a significant acceleration in tumorigenesis relative to their Tpl2+/+/Apcmin/+ littermates. The high number of polyps in Tpl2-/-/ Apcmin/+, relative to Tpl2+/+/Apcmin/+ mice suggested that Tpl2 ablation promotes tumor initiation. Since the earliest genetic change responsible for tumor initiation is the loss of heterozygocity (LOH) in the APC locus, it follows that Tpl2 ablation promotes LOH. This could be caused by several mechanisms. One possibility is that Tpl2 ablation increases the number of intestinal stem cells that may be the targets of LOH. Given that the Wnt pathway promotes the cycling of stem cells, we hypothesized that Tpl2 ablation may cause an increase in stem cell numbers, by stimulating Wnt signaling. Studies presented here however showed that, although Tpl2 has the potential to inhibit Wnt signaling in several types of epithelial cells, Tpl2 ablation does not increase the number of stem cells in the intestinal crypts. Further studies revealed that Tpl2 ablation promotes intestinal inflammation, which is also known to stimulate tumor initiation. A search for the causes of inflammation revealed that Tpl2 ablation causes a Paneth cell defect, characterized by significant downregulation of genes encoding antimicrobial peptides. The same search revealed that inhibition of TLR signals that may be transduced via Tpl2, stimulates the activity of the canonical Wnt pathway in macrophages and that the levels of IL-10 in the intestinal mucosa of Tpl2-/- mice are decreased. The role of Tpl2 however, may not be restricted to tumor initiation. Our preliminary data indeed provide strong evidence that Tpl2 ablation may also contribute to the late stages of oncogenesis. Tpl2 ablation may modulate the biology of tumor cells induced by the ablation of APC by targeting the Wnt pathway, or perhaps other interacting pathways. Alternatively, it may target Akt and mTOR, as suggested by our recent studies on human colon carcinoma cell lines. Work proposed in this application will focus on the role of Tpl2 in the regulation of pre-LOH and post-LOH events in intestinal tumorigenesis induced by APC mutations. PUBLIC HEALTH RELEVANCE: Our preliminary data, interpreted in the context of genetic studies in humans, indicate that the Tpl2 knockout mouse is an excellent animal model for inflammatory bowel disease (IBD). The same data provide a strong link between inflammation and cancer. The Tpl2 ablation model therefore, provides a valuable tool to mechanistically address the pathophysiology of IBD and colorectal cancer and to identify new targets for therapeutic intervention in these diseases.