内质网蛋白ERp44在食管鳞癌放化疗敏感性中的作用及其分子机制

Concurrent chemoradiotherapy is an important strategy for esophageal squamous cell carcinoma (ESCC) treatment. However, the sensitivities of ESCC to chemo- and (or) radio- therapy are heterogeneous, and the mechanisms underlying ESCC drug resistance or radiation tolerance have not been fully understood. In our previous work, we identified a protein, endoplasmic reticulum protein 44 (ERp44), which showed increased expression in drug resistant ESCC cells in comparison with sensitive cells, and expression of ERp44 in ESCC tissues could predict the treatment effect and prognosis of patients, who received concurrent chemoradiotherapy. Our preliminary data showed that in ESCC cells, cells' sensitivity to cisplatin was changed by modifying ERp44 expression, ERp44 could affect ABCG2 protein expression, and the ER Ca2+ channel IP3R inhibitor could reverse the increase of cisplatin sensitivity induced by ERp44 knock-down. It is hypothesized that ERp44 might regulate ER protein maturation and expression or Ca2+ related apoptosis activation, so as to affect cancer drug resistance or radiation tolerance. In this study, we plan to verify the role of ERp44 in ESCC chemo- and (or) radio- resistance by both in vitro and in vivo studies, and further explore the underlying molecular mechanisms. The study would provide an alternative mechanism to understand the ESCC drug and radiation resistance, and lay foundation for identifying useful predictive molecular markers.

同期放化疗是食管鳞癌治疗的重要手段，但食管鳞癌放化疗敏感性存在异质性，其分子机制未完全阐明。本课题组首次报道内质网蛋白ERp44在食管鳞癌耐药细胞表达较亲代敏感细胞增高；且食管鳞癌组织ERp44高表达提示同期放化疗疗效较差及预后不良。前期预实验发现：食管鳞癌细胞中，改变ERp44表达水平可影响细胞对顺铂敏感性；ERp44可影响耐药相关蛋白ABCG2表达；内质网钙通道抑制剂可逆转ERp44表达敲除引起的顺铂敏感性增高。据此推测ERp44可能调控经内质网分泌途径的蛋白质的表达或钙相关凋亡通路的激活，从而影响肿瘤放化疗敏感性。为证实这一假说，我们将通过细胞转染、放化疗敏感性检测、动物模型、免疫组化等，从分子-细胞-动物三个层次，观察ERp44表达改变对食管鳞癌放化疗敏感性影响并探讨其分子机制。本课题将从新的视角阐明食管鳞癌放化疗耐受的机制，为寻找食管鳞癌放化疗敏感性预测的有效分子标志物奠定基础。

同期放化疗是食管鳞癌治疗的重要手段，但食管鳞癌放化疗敏感性存在异质性，其分子机制未完全阐明。我们在本研究中发现，内质网蛋白ERp44在食管鳞癌耐药细胞表达较亲代敏感细胞表达增高；且食管鳞癌组织中ERp44高表达提示同期放化疗疗效较差及预后不良；然而，肿瘤组织中ERp44表达水平与单纯手术食管鳞癌患者预后无显著相关性。并且，我们通过体外细胞及体内动物实验证实，改变ERp44表达水平可影响细胞对顺铂的敏感性：敲除ERp44表达后，食管鳞癌对顺铂的敏感性增高；过表达ERp44则降低细胞对顺铂的敏感性；但ERp44表达水平改变对细胞增殖、放射敏感性及其他化疗药物（如泰素、诺维本）等物显著影响。为进一步了解ERp44影响食管鳞癌细胞顺铂敏感性的机制，我们检测了顺铂作用下内质网应激相关蛋白的表达情况，结果发现，顺铂处理可显著升高食管鳞癌细胞GRP78，caspase-4, XBP-1s, p-eIF-2a和p-Akt的表达水平，提示内质网应激相关通路被激活；并且，ERp44敲除可进一步促进内质网应激的发生。据此，我们认为，ERp44表达敲除可能通过促进内质网应激的发生，从而使食管鳞癌细胞对顺铂敏感。