Integrins and Caspase 8 in Tumor Progression

描述（由申请人提供）：在之前的资助期内，我们在体内证明了caspase 8与未结合整合素的关联促进了细胞凋亡，并且在神经母细胞瘤中caspase 8或整合素的下调促进了肿瘤转移。在这些研究中，我们证实了细胞凋亡的作用，我们得出了一个矛盾的观察结果，即在凋亡抵抗细胞中，caspase 8的表达显著增强了整合素介导的体外迁移和体内转移。因此，本提案的总体目标是了解caspase 8的凋亡与非凋亡功能是如何被调节的。caspase 8作为caspase的启动物，可触发死亡受体、toll样受体和整合素下游的细胞凋亡。它的表达在侵袭性神经母细胞瘤和其他神经内分泌肿瘤中经常丢失。这促使临床策略寻求恢复或扩大其表达。然而，caspase 8并不足以导致细胞凋亡，而是需要下游的caspase级联。在凋亡受损的细胞中，我们提供的证据表明caspase 8的表达实际上具有促进肿瘤转移的功能。这个令人惊讶的结果值得重新考虑简单上调caspase 8是普遍有益的概念；相反，它可能会加剧疾病的进展。虽然已知caspase 8在免疫和血管室中的非凋亡功能，但caspase 8发挥这些功能的机制尚不清楚。在这里，我们提供的初步结果表明，在整合素连接后的局灶粘附接触中，增强的细胞迁移与caspase 8酪氨酸磷酸化和定位同时发生。本提案的AIM 1将表征粘附过程中磷酸化的特定caspase 8酪氨酸残基，并确定那些对迁移至关重要的残基。AIM 2将评估哪些酪氨酸残基影响caspase 8的催化和促凋亡活性，包括蛋白质与蛋白质的相互作用。最后，AIM 3将测试这些调节酪氨酸残基对体内疾病进展的影响。总之，这些研究的结果将揭示caspase 8调控的分子机制，这对抗转移治疗的发展很重要。

DESCRIPTION (provided by applicant): During the previous funding period, we demonstrated that caspase 8 association with unligated integrins in vivo promoted apoptosis, and that down-regulation of caspase 8 or integrins in neuroblastoma promoted tumor metastasis. Confirming the roll of apoptosis in these studies, we made the paradoxical observation that, among apoptosis-resistant cells, the expression of caspase 8 significantly enhanced integrin-mediated migration in vitro and metastasis in vivo. The overall goal of this proposal is therefore to understand how caspase 8 apoptotic vs nonapoptotic function is regulated. As an initiator caspase, caspase 8 triggers apoptosis downstream of death receptors, toll-like receptors and integrins. Its expression is frequently lost among aggressive neuroblastoma and other neuroendocrine tumors. This has prompted clinical strategies seeking to restore or amplify its expression. However, caspase 8 is not sufficient for apoptosis, but requires a compliant downstream caspase cascade. Among apoptosis-compromised cells, we provide evidence that caspase 8 expression actually functions to enhance tumor metastasis. This surprising result warrants reconsideration of the concept that simple upregulation of caspase 8 is universally beneficial; rather, it may exacerbate disease progression. While nonapoptotic functions of caspase 8 within the immune and vascular compartments are known, the mechanisms committing caspase 8 to these functions are not. Here, we provide preliminary results showing that enhanced cell migration occurs concurrent with caspase 8 tyrosine phosphorylation and localization in focal adhesion contacts following integrin ligation. AIM 1 of this proposal will characterize the specific caspase 8 tyrosine residues phosphorylated during adhesion, and identify those critical for migration. AIM 2 will evaluate which tyrosine residues influence caspase 8 catalytic and proapoptotic activities, including protein-protein interactions. Finally, AIM 3 will test the impact of these regulatory tyrosine residues on disease progression in vivo. Together, the results of these studies will reveal molecular mechanisms of caspase 8 regulation important for the development of anti-metastatic therapies. PUBLIC HEALTH RELEVANCE: The protein "caspase 8" is well known to be involved in programmed cell death, and its expression is suppressed among aggressive neuroendocrine tumors. However, caspase 8 can also promote cell migration, and we show that it actually enhances the spread of death-resisting cells, which may explain why it is frequently upregulated in carcinoma. This proposal seeks to understand the molecular mechanisms that control caspase 8 switching between these two roles.