S1P lyase in colon cancer

描述（由申请人提供）：膳食鞘脂（如鞘氨醇和神经酰胺）可促进肠上皮细胞更新，并已证明可预防小鼠肠道肿瘤发生。然而，肠细胞摄取的鞘氨醇可以被致癌酶SphK 1磷酸化，产生鞘氨醇-1-磷酸（S1 P），这是一种抑制细胞凋亡并促进炎症、转化和致癌的促有丝分裂脂质。因此，饮食中的鞘脂在结肠癌中是一把双刃剑。阐明它们在致癌作用中的特定作用是开发基于鞘脂的策略以降低结肠癌风险的必要的第一步。S1 P被酶S1 P裂解酶（SPL）不可逆地降解，该酶在肠上皮细胞和肠粘膜的其他细胞区室中高度表达。我们先前表明SPL在ApcMin/+小鼠腺瘤和人结肠癌中下调。我们现在发现SPL在氧化偶氮甲烷/葡聚糖硫酸钠（AOM/DSS）治疗的小鼠中发展的肿瘤中也下调。因此，SPL下调是肠肿瘤的共同特征。我们产生了肠道特异性SPL基因敲除小鼠（SPLGutKO），并证明了肠细胞SPL表达的丧失促进了ApcMin/+小鼠的肿瘤发生，并增强了AOM/DSS治疗小鼠的结肠炎、肠细胞增殖和肿瘤发病率。SPL表达的丧失与STAT 3的活化增加有关，STAT 3是炎症、致癌和肿瘤细胞与肿瘤微环境或“小生境”之间相互作用的关键调节因子。STAT 3作为转录因子与许多mRNA和microRNA靶标一起起作用。STAT 3也被证明可以调节线粒体功能。重要的是，我们发现STAT 3的抑制阻止了SPL破坏促进AOM/DSS和异种移植模型系统中肿瘤发生的能力。除了这些发现之外，我们最近还发现了一个名为sphingadienes（SD）的大豆源性鞘脂家族，该家族在小鼠中具有化学预防作用。SD促进肠上皮细胞更新，抑制STAT 3，WNT和AKT信号通路，重要的是，诱导SPL在结肠癌细胞系中的表达。我们的累积研究结果使我们提出了我们的中心假设，即：SPL下调通过影响肠上皮细胞和肿瘤生态位的其他细胞区室的STAT 3依赖性机制促进结肠癌发生。我们进一步提出，SD作为一种解毒剂SPL下调逆转它及其相关的影响结肠炎症和癌变。为了验证我们的假设，我们设计了四个具体目标：1）阐明S1 P如何促进细胞转化和肿瘤发生; 2）阐明SPL在调节肿瘤生态位中的作用; 3）确定SPL下调是否促进由促炎饮食诱导的肠道肿瘤发生; 4）测试SD是否可以逆转SPL下调及其在肠道肿瘤发生期间的相关作用。在实现这些目标的过程中，我们应该实现我们的两个主要目标：阐明SPL在结肠癌中的生物学，并开发通过重新激活SPL起作用的化学预防策略。

DESCRIPTION (provided by applicant): Dietary sphingolipids such as sphingosine and ceramide promote enterocyte turnover and have been shown to protect against intestinal tumorigenesis in mice. However, sphingosine taken up by enterocytes can be phosphorylated by the oncogenic enzyme SphK1, generating sphingosine-1-phosphate (S1P), a mitogenic lipid that inhibits apoptosis and promotes inflammation, transformation and carcinogenesis. Thus, dietary sphingolipids represent a double-edged sword in colon cancer. Elucidating their specific roles in carcinogenesis is a necessary first step to developing sphingolipid-based strategies to lower colon cancer risk. S1P is irreversibly degraded by the enzyme S1P lyase (SPL) which is highly expressed in enterocytes and other cellular compartments of the gut mucosa. We showed previously that SPL is downregulated in ApcMin/+ mouse adenomas and human colon cancers. We now show that SPL is also downregulated in tumors that develop in azoxymethane/dextran sodium sulfate (AOM/DSS)-treated mice. Thus, SPL downregulation is a common feature of intestinal neoplasia. We generated gut-specific SPL knockout mice (SPLGutKO) and demonstrated that loss of enterocyte SPL expression promotes tumorigenesis in ApcMin/+ mice and enhances colitis, enterocyte proliferation and tumor incidence in AOM/DSS-treated mice. Loss of SPL expression was associated with increased activation of STAT3, a critical regulator of inflammation, carcinogenesis and interactions between tumor cells and the tumor microenvironment or "niche". STAT3 acts as a transcription factor with many mRNA and microRNA targets. STAT3 has also been shown to regulate mitochondrial functions. Importantly, we found that inhibition of STAT3 prevented the ability of SPL disruption to promote tumorigenesis in AOM/DSS and xenograft model systems. In addition to these findings, we recently identified a family of soy-derived sphingolipids called sphingadienes (SDs) with chemopreventive action in mice. SDs promote enterocyte turnover, inhibit STAT3, WNT and AKT signaling pathways and, importantly, induce SPL expression in colon cancer cell lines. Our cumulative findings have led us to propose our central hypothesis, which states that: SPL downregulation promotes colon carcinogenesis through STAT3-dependent mechanisms that influence intestinal epithelial cells and other cellular compartments of the tumor niche. We further propose that SDs serve as an antidote to SPL downregulation by reversing it and its associated effects on colon inflammation and carcinogenesis. To test our hypothesis, we have devised four Specific Aims: 1) To clarify how S1P promotes cell transformation and tumorigenesis; 2) To elucidate the role of SPL in modulating the tumor niche; 3) To establish whether SPL downregulation promotes intestinal tumorigenesis induced by a pro-inflammatory diet; 4) To test whether SDs can reverse SPL downregulation and its associated effects during intestinal tumorigenesis. In accomplishing these aims, we should achieve our two major goals: to elucidate the biology of SPL in colon cancer, and to develop chemopreventive strategies that work by reactivation of SPL.