Tpl2 in Intestinal Tumorigenesis

描述（由申请人提供）：编码Tp 12激酶的原癌基因在逆转录病毒诱导的啮齿动物淋巴瘤和乳腺腺癌中被前病毒整合激活。在这里，我们提出的证据表明，Tp 12也作为一个肿瘤抑制基因在肠上皮细胞的功能。为了确定Tp 12在Apcmin诱导的肿瘤发生中的作用，我们将Apcmin突变交叉到Tp 12-/-遗传背景中。与预期相反，Tp 12-/-/ Apcmin/+小鼠相对于其Tp 12 +/+/Apcmin/+同窝出生的小鼠表现出肠息肉数量的5倍增加和肿瘤发生的显著加速。相对于Tp 12 +/+/Apcmin/+小鼠，Tp 12-/-/ Apcmin/+中的高息肉数量表明Tp 12消融促进肿瘤起始。由于负责肿瘤起始的最早遗传变化是APC基因座中杂合性的缺失（洛），因此Tp 12消融促进了洛。这可能是由几种机制引起的。一种可能性是Tp 12消融增加了可能是洛靶的肠干细胞的数量。鉴于Wnt途径促进干细胞的循环，我们假设Tpl 2消融可能通过刺激Wnt信号传导而引起干细胞数量的增加。然而，本文提出的研究表明，尽管Tp 12具有抑制几种类型的上皮细胞中的Wnt信号传导的潜力，但Tp 12消融不增加肠隐窝中干细胞的数量。进一步的研究表明，Tp 12消融促进肠道炎症，这也已知刺激肿瘤起始。对炎症原因的研究表明，Tp 12消融导致潘氏细胞缺陷，其特征在于编码抗微生物肽的基因的显著下调。相同的研究揭示，抑制可经由Tpl 2转导的TLR信号刺激巨噬细胞中经典Wnt途径的活性，并且Tpl 2-/-小鼠的肠粘膜中IL-10的水平降低。然而，Tpl 2的作用可能不限于肿瘤起始。我们的初步数据确实提供了Tp 12消融也可能有助于肿瘤发生的晚期阶段的有力证据。Tpl 2消融可以通过靶向Wnt途径或可能的其他相互作用途径来调节由APC消融诱导的肿瘤细胞的生物学。或者，它可以靶向Akt和mTOR，如我们最近对人结肠癌细胞系的研究所示。本申请中提出的工作将集中于Tp 12在APC突变诱导的肠肿瘤发生中的前LOH和后LOH事件的调节中的作用。 公共卫生相关性：在人类遗传研究的背景下解释的我们的初步数据表明，Tpl 2敲除小鼠是炎性肠病（IBD）的极好动物模型。同样的数据提供了炎症和癌症之间的强有力的联系。因此，Tpl 2消融模型提供了一种有价值的工具，用于机械地解决IBD和结肠直肠癌的病理生理学，并鉴定用于这些疾病中的治疗干预的新靶标。

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.