砷剂诱导核内LC3参与蛋白酶体途径降解PML-RARa融合蛋白新机制研究

目前利用三氧化二砷的毒性治疗急性早幼粒白血病（APL）已成为血液学的研究热点，研究发现三氧化二砷可通过降解APL特征性PML/RARa融合蛋白起到治疗作用。关于此融合蛋白的降解，现存在两种不同的学说，即自噬溶酶体和蛋白酶体途径。本课题组前期结果显示，PML/RARa融合蛋白与自噬溶酶降解途径无因果无关，但发现核内LC3参与泛素-蛋白酶体途径来降解PML/RARa融合蛋白。本项目拟进一步深入展开砷和核内LC3对PML蛋白的降解和调控机理，明确回答以下三个问题：细胞核内LC3在PML/RARa融合蛋白降解过程中的具体机理；核内LC3与PML蛋白的相互作用的位点；自噬发生与PML蛋白降解无因果关系。本课题组已取得切实可靠的研究数据，突破LC3仅参与溶酶体降解途径的理论束缚，率先提出核内LC3可能参与蛋白酶体的降解过程，阐明三氧化二砷治疗急性早幼粒白血病过程中PML/RARa 蛋白降解的确切机理。

Arsenic trioxide (As2O3) has been demonstrated to be one of the most effective therapeutic agents for patient with acute promyelocytic leukemia (APL), and the possible explanations for arsenic trioxide induced the cells differentiation is that As2O3 directly targeted PML-RARa fusion protein, resulted in initiating PML-RARa oncoprotein degradation. Regarding the mechanism of PML-RARa fusion protein degradation, two different pathways has been identified; one is a lysosomal degradation pathway (autophagy) and another is a proteasomal degradation pathway. In our preliminary experiment, we have clearly found that degradation of PML-RARa fusion protein in NB4 cells is not dependent on a lysosomal degradation pathway, but dependent on the proteasomal degradation pathway. Surprisingly, we first time found that nuclear LC3 is necessary protein for proteasomal degradation, because LC3 is normally thought to be a key factor for lysosomal degradation. Given these discovery, the interesting new results call into questions why nuclear LC3 is involved in proteasomal degradation. In order to reveal the molecular mechanism, we using three cell lines to determine the PML protein degradation by using the transfection or knock down the target genes by exposure to arsenic compounds. In fact, we trying to answer the following issues; (1) what is the role of nuclear LC3 for PML-RARa fusion protein degradation, (2) which steps is necessary for nuclear LC3 involvement during the PML protein degradation, (3) degradation of PML-RARa protein is not resulted by induction of autophagy (but proteasomal degradation). Our results are expected to explain the exact mechanism of PML-RARa fusion protein degradation, and it will improve the life span of APL patients after treatment of arsenic in near future.