The Role of CD95 as a Tumor Promoter

描述（由申请人提供）：死亡受体CD 95（APO-1/Fas）最为人所知的是其细胞凋亡诱导活性，其涉及将衔接分子FADD和引发剂半胱天冬酶募集到受体的细胞内死亡结构域。尽管其具有凋亡潜力，但大多数人肿瘤对CD 95配体的细胞毒性作用是难治的。这是由于抗凋亡基因的上调、CD 95凋亡信号通路组分的功能性消除、CD 95的突变或下调。相反，在许多癌症患者和接受化疗的患者中，CD 95配体（CD 95 L）水平升高，无论是在血清中还是在肿瘤本身中。这主要被认为是一种免疫逃逸机制，以消除浸润淋巴细胞。我们最近发现，CD 95 L诱导增加的运动性和侵袭性的多重凋亡抵抗肿瘤细胞。CD 95的参与触发了多种信号传导途径的激活，其中3种-NF-κ B、Erkl/2和半胱天冬酶-8的激活-被发现有助于CD 95的这种新活性。我们还报道了野生型和突变型CD 95的组合表达，这是在CD 95死亡结构域携带杂合突变的人类肿瘤中常见的情况，完全阻断了凋亡信号传导，但允许完全激活非凋亡途径。我们假设，抗凋亡肿瘤细胞上的CD 95作为肿瘤促进受体发挥作用，并且在CD 95的一个等位基因中获得点突变将肿瘤抑制因子CD 95转化为肿瘤促进因子。此外，我们假设在癌症患者中发现的CD 95 L浓度增加可能有助于肿瘤致瘤性增加。为了在体外和体内测试这些假设，我们提出了以下三个具体目标：具体目标1：确定CD 95诱导肿瘤发生途径的机制。具体目标2：鉴定和表征调节CD 95促肿瘤活性的CD 95诱导基因。具体目的3：检测化疗药物是否能诱导耐药肿瘤细胞的侵袭性。我们的研究可能提供通过阻断CD 95 L的活性、致瘤信号通路或响应于CD 95刺激而激活的致瘤基因来抵消CD 95的新致瘤活性的方法。

DESCRIPTION (provided by applicant): The death receptor CD95 (APO-I/Fas) is best known for its apoptosis inducing activity which involves recruitment of the adaptor molecule FADD and initiator caspases to the intracellular death domain of the receptor. Despite its apoptotic potential most human tumors are refractory to the cytotoxic effects of CD95 ligand. This is due either to upregulation of antiapoptotic genes, functional elimination of CD95 apoptosis signaling pathway components, mutation or downregulation of CD95. In contrast, CD95 ligand (CD95L) levels are elevated in many cancer patients and in patients receiving chemotherapy, either systemically in the serum or within the tumor itself. This has mainly been viewed as an immune escape mechanism to eliminate infiltrating lymphocytes. We recently found that CD95L induces increased motility and invasiveness in multiple apoptosis resistant tumor cells. Engagement of CD95 triggered activation of multiple signaling pathways, 3 of which - activation of NF-kappaB, Erkl/2 and caspase-8 - were found to contribute to this novel activity of CD95. We also reported that the expression of a combination of wild-type and mutant CD95, a situation frequently found in human tumors carrying a heterozygous mutation in the death domain of CD95, completely blocks apoptosis signaling but allows full activation of nonapoptotic pathways. We hypothesize that CD95 on apoptosis resistant tumor cells functions as a tumor promoting receptor and that acquiring a point mutation in one allele of CD95 converts the tumor suppressor CD95 into a tumor promotor. Furthermore we hypothesize that increased concentrations of CD95L found in cancer patients can contribute to increased tumorigenicity of tumors. To test these hypotheses in vitro and in vivo we propose the following three specific aims: Specific Aim 1: Determine the mechanism by which CD95 induces tumorigenic pathways. Specific Aim 2: Identify and characterize the CD95 induced genes that regulate CD95's tumor promoting activities. Specific Aim 3: Test whether chemotherapeutic drugs can induce invasiveness of drug resistant tumor cells. Our studies may provide the means to counteract the novel tumorigenic activities of CD95 by either blocking the activity of CD95L, the tumorigenic signaling pathways, or the tumorigenic genes activated in response to CD95 stimulation.