Ewing's Sarcoma Resistance to Immunity and Radiation

描述（由申请人提供）：尤文氏肉瘤是一种非常痛苦的骨癌（更罕见的是软组织癌），多发于儿童和青少年。尽管接受了手术、化疗和放疗，许多尤因氏肉瘤患者还是无法存活，特别是如果癌症已经转移。复发性尤文氏肉瘤倾向于表现出对化疗和放疗的耐药性，这推动了包括免疫疗法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消灭，并且这种癌症逃避的机制尚不清楚，尽管有报道称主要组织相容性复合体（MHC） I类分子的表达下调，以及MHC I类表达降低与生存率低的相关性。由于MHC I类分子的功能是将抗原（包括癌症相关抗原）呈递给细胞毒性T淋巴细胞，因此减少其表面表达可能导致免疫逃逸。我们试图描述与尤文氏肉瘤细胞避免免疫识别相关的细胞变化，研究MHC分子和淀粉样蛋白前体样蛋白2 （APLP2）在这一过程中的作用。APLP2是一个普遍表达的蛋白家族成员，该蛋白家族还包括淀粉样蛋白前体蛋白（APP）和神经系统限制性淀粉样蛋白前体样蛋白1 （APLP1）。APLP2以跨膜形式存在于细胞表面，β -分泌酶对其进行裂解，产生约12kda的c端片段。我们的新数据表明，Ewing肉瘤细胞系中APLP2的表达升高会降低MHC I类分子的表面表达。放疗后，APLP2表达相对较低的Ewing肉瘤细胞表面MHC I类表达增加，而APLP2表达较高的Ewing肉瘤亚群则没有增加。在我们的初步实验中，我们还证明了辐照Ewing肉瘤细胞后，APLP2减少了G2/M的细胞周期阻滞，并降低了亚g1 DNA含量的细胞比例（表明凋亡）。根据我们的初步数据，我们的中心假设是APLP2促进了

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.