分化治疗作为疗效确切的肿瘤治疗方式已成功应用于白血病的临床治疗，但实体肿瘤的分化治疗进展缓慢，而目前骨肉瘤临床化疗疗效有限，亟需新的治疗策略。不少文献报道维甲酸可诱导骨肉瘤细胞分化，但临床疗效不佳。我们研究发现，RARa的低表达（原代样本高达70%）可能是影响骨肉瘤临床分化治疗敏感性的关键因素，如仅选择RARa高表达的骨肉瘤原代样本，维甲酸诱导分化的阳性率可从原来的30%提高到90%以上。本课题将在前期发现MDM2和E2F1可能参与调控RARa蛋白水平的基础上，进一步阐明泛素连接酶MDM2特异性介导RARa泛素化降解的分子机制，研究E2F1抑制RARa乙酰化修饰的作用及其对泛素化降解的影响，揭示RARa泛素化降解的调控网络，并探讨RARa/MDM2/E2F1作为选择骨肉瘤分化治疗适用人群分子标记物的可能性，寻找基于RARa降解机制的分化治疗新策略，故具有较高的理论意义和临床应用价值。

Differentiation therapy, which is now widely-used in the clinical treatment of acute myeloid leukemia, has held great promise in cancer therapy, but its clinical application in solid tumor is suspended. Since the chemotherapeutic effect in osteosarcoma is largely limited, novel strategies that seek to treat osteosarcoma are key avenues of investigation. Numerous experiments have shown that the differentiation agent ATRA could induce osteoblastic differentiation of osteosarcoma cells, suggesting that differentiation therapy may represent a novel therapeutic strategy for osteosarcoma, but the clinical response of osteosarcoma patients to ATRA is not ideal. We previously found that the lack of RARa expression might be the key factor involved in the sensitivity of osteosarcoma cells to differentiation therapy. If identifying osteosarcoma patients with high expression levels of RARa, the response rate to differentiation therapy could increase from 30% to 90%. Therefore, basing on our discovery that MDM2 and E2F1 cooperated to mediate RARa protein, we will investigate the role of MDM2 as E3 to regulate the degradation of RARa, and determine the effect of E2F1 on the acetylation of RARa and its degradation. In addition, we will not only evaluate the possibility of RARa/MDM2/E2F1 as novel biomarkers for the selection of osteosarcoma patients for differentiation therapy, but also provide new strategies for differentiation therapy based on the mechanisms involved in the degradation of RARa, in the hope to advance the understanding and development of differentiation therapy.