Ewing's Sarcoma Resistance to Immunity and Radiation

描述(申请人提供)：尤文氏肉瘤是一种非常痛苦的骨癌(更罕见的是软组织癌)，侵袭儿童和青少年。尽管接受了手术、化疗和放射治疗，许多尤文氏肉瘤患者还是无法存活，特别是在癌症已经转移的情况下。复发的尤文氏肉瘤往往表现出对化疗和放射治疗的抵抗，这促使了包括免疫治疗在内的新疗法的发展。然而，一些尤文氏肉瘤细胞可以逃脱免疫系统的清除，这种肿瘤逃逸的机制尚不清楚，尽管有报道称主要组织相容性复合体(MHC)I类分子表达下调，并与MHC I类分子表达下降和生存不良有关。由于MHC I类分子的功能是将抗原(包括肿瘤相关抗原)呈递给细胞毒性T淋巴细胞，其表面表达的减少可能导致免疫逃避。我们试图表征与尤文氏肉瘤细胞相关的细胞变化，以避免免疫识别，研究MHC分子和淀粉样前体蛋白2(APLP2)在这一过程中的作用。APLP2是一个普遍表达的蛋白质家族成员，还包括淀粉样前体蛋白(APP)和神经系统限制性淀粉样前体蛋白1(APLP1)。APLP2以跨膜形式存在于细胞表面，被β-分泌酶切割后产生~12 kDa的C末端片段。我们的新数据表明，尤文肉瘤细胞系中APLP2的高表达降低了MHC I类分子的表面表达。放射治疗后，APLP2表达相对较低的尤文肉瘤细胞表面MHC-I类表达增加，但APLP2高表达的尤文肉瘤亚群没有。在我们的初步实验中，我们还证明了照射尤文肉瘤细胞后，APLP2减少了细胞周期停滞在G2/M期，并降低了亚G1DNA含量的细胞比例(表明发生了凋亡)。根据我们的初步数据，我们的中心假设是APLP2促进了 尤因肉瘤细胞。为了验证我们的中心假设，这项拟议项目的具体目标是(1)确定APLP2在尤文肉瘤细胞辐射前后对细胞毒性的抵抗中的作用，以及(2)确定APLP2对尤文肉瘤细胞的辐射抗性的贡献。总体而言，本申请中提出的研究有望为调节尤文肉瘤细胞生存的分子途径提供新的视角，包括逃避免疫和放射治疗。

DESCRIPTION (provided by applicant): Ewing's sarcoma is a very painful cancer of the bone (and, more rarely, soft tissue) that strikes children and adolescents. Despite treatment with surgery, chemotherapy, and radiation, many patients with Ewing's sarcoma do not survive, particularly if the cancer has metastasized. Recurrent Ewing's sarcoma tends to exhibit resistance to chemo- and radiotherapies, motivating the development of novel therapies, including immunotherapies. However, some Ewing's sarcoma cells can escape elimination by the immune system and the mechanisms underlying evasion by this cancer are poorly understood, although there have been reports of down-regulated expression of major histocompatibility complex (MHC) class I molecules, and correlation of decreased MHC class I expression and poor survival. Since the function of MHC class I molecules is to present antigens (including cancer-associated antigens) to cytotoxic T lymphocytes, reduction of their surface expression could cause immune evasion. We have sought to characterize cellular changes associated with Ewing's sarcoma cells that avoid immune recognition, investigating the roles of MHC molecules and amyloid precursor-like protein 2 (APLP2) in this process. APLP2 is a ubiquitously expressed member of a protein family that also includes amyloid precursor protein (APP) and the nervous system-restricted amyloid precursor-like protein 1 (APLP1). APLP2 is found in transmembrane form at the cell surface, and its cleavage by beta-secretases leads to the production of ~12 kDa C-terminal fragments. Our new data suggests that elevated expression of APLP2 in Ewing's sarcoma cell lines reduces surface expression of MHC class I molecules. Following treatment with radiation, the Ewing's sarcoma cells that had relatively low APLP2 expression had increased MHC class I expression at the cell surface, but APLP2- high Ewing's sarcoma sub-populations did not. In our preliminary experiments, we have also demonstrated that following irradiation of Ewing's sarcoma cells APLP2 reduces cell cycle arrest at G2/M and lowers the proportion of cells with sub-G1 DNA content (indicating apoptosis). On the basis of our preliminary data, our central hypothesis is that APLP2 facilitates the survival of Ewing's sarcoma cells. To test our central hypothesis, the Specific Aims of this proposed project are (1) to determine the role of APLP2 in resistance of Ewing's sarcoma cells, pre- and post-irradiation, to cytotoxicity, and (2) to determine the contribution of APLP2 to radiation resistanc by Ewing's sarcoma cells. Overall, the studies proposed in this application are expected to provide a new perspective on molecular pathways regulating Ewing's sarcoma cell survival, involving evasion of both immunity and radiotherapy.