How KAI1/CD82 Suppresses Cancer Invasion and Metastasis

描述（申请人提供）：KAI1/CD82是实体瘤转移抑制因子。KAI1/CD82介导的转移抑制机制在很大程度上仍然是未知的。最近的研究表明，KAI1/CD82可诱导脂筏和tetraspanin富集微域（TEM）等膜微域的重组，减弱生长因子和整合素信号，抑制细胞的突缩。值得注意的是，我们还发现KAI1/CD82通过抑制癌细胞侵袭性来抑制癌症转移。因此，KAI1/CD82如何抑制癌细胞运动成为了解KAI1/CD82如何抑制癌症转移的突出问题。我们假设KAI1/CD82通过重组膜微域，从而减少突出和收缩过程以及外向内有丝分裂信号传导来抑制癌细胞的迁移和侵袭。为了阐明KAI1如何抑制肿瘤侵袭和转移，我们将首先对含KAI1/CD82的TEM进行结构和功能表征：1)鉴定CD82分子中将TEM与脂质层物理连接的结构元件；2)系统表征CD82阳性TEM的蛋白质和脂质成分；3)分析含CD82 TEM的转运和亚细胞定位。其次，我们将通过解决含cd82的TEM如何使膜弯曲和运输来确定含KAI1/ cd82的TEM调节细胞运动活动的机制。我们还将评估cd82诱导的膜曲率改变和转运的作用：1)膜运动活性，2)有丝分裂信号传导，3)cd82介导的癌症侵袭抑制。最后，我们将确定KAI1/CD82在体内抑制癌症侵袭的机制，通过解决i)细胞运动活性CD82在体内抑制癌症侵袭的机制，ii)与CD82在物理或功能上相关的蛋白质对CD82介导的癌症侵袭抑制的贡献；iii)上述分析的CD82特征是否对其在体内抑制肿瘤侵袭至关重要。总之，该研究将使我们能够i)了解KAI1/CD82如何作为膜微结构域的组织者调节细胞迁移、癌症侵袭和癌症转移；ii)揭示细胞运动和癌症转移的新机制，即膜曲率和运输调节侵袭和转移。通过对KAI1/CD82在体外和体内的深入机制研究，我们将对肿瘤的侵袭和转移有更全面的认识，最终使KAI1/CD82成为肿瘤侵袭和转移的诊断标志物和治疗靶点。

DESCRIPTION (provided by applicant): KAI1/CD82 is a metastasis suppressor of solid tumors. The mechanism of KAI1/CD82- mediated metastasis suppression still remains largely elusive. Recent studies indicate that KAI1/CD82 induces the reorganization of membrane microdomains such as lipid rafts and tetraspanin-enriched microdomain (TEM), attenuates growth factor and integrin signaling, and inhibits cell protrusion and retraction. Notably, we also found that KAI1/CD82 suppresses cancer metastasis by inhibiting cancer cell invasiveness. Thus, how KAI1/CD82 inhibits cancer cell movement becomes the outstanding question to understand how KAI1/CD82 suppresses cancer metastasis. We hypothesize that KAI1/CD82 inhibits cancer cell migration and invasion through re-organizing membrane microdomains and consequently reducing protrusive and retraction processes and the outside-in mitogenic signaling. To elucidate how KAI1 suppresses cancer invasion and metastasis, we will first carry out the structural and functional characterization of KAI1/CD82-containing TEM by i) identifying the structural element(s) in CD82 molecule that physically links TEM to lipid rafts, ii) systematically characterizing the protein and lipid components of CD82-positive TEM, and iii) analyze the trafficking and subcellular localization of CD82- containing TEM. Secondly, we will determine the mechanism by which KAI1/CD82-containing TEM regulates the cellular motile activities by addressing how CD82-containing TEM renders membrane curvature and trafficking. We will also assess the roles of CD82-induced alterations in membrane curvature and trafficking in i) membrane motile activities, ii) mitogenic signaling, and iii) CD82-mediated suppression of cancer invasion. Finally, we will determine the mechanism by which KAI1/CD82 inhibits cancer invasion in vivo by addressing i) through which cellular motile activity CD82 suppresses cancer invasion in vivo, ii) the contributions of the proteins physically or functionally associated with CD82 to CD82-mediated suppression of cancer invasion; and iii) whether the CD82 features analyzed above are crucial for its suppression of cancer invasion in vivo. Together, the proposed study will enable us to i) understand how KAI1/CD82 regulates cell migration, cancer invasion, and cancer metastasis as an organizer for membrane microdomains and ii) unveil a novel mechanisms by which cell motility and cancer metastasis are regulated, i.e., membrane curvature and trafficking regulates invasion and metastasis. From the in-depth in vitro and in vivo mechanistic study of KAI1/CD82, we will develop an integrated understanding of cancer invasion and metastasis, which will ultimately lead to the development of KAI1/CD82 into a diagnostic marker and therapeutic target for cancer invasion and metastasis.