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  • Title: Autophagy and Ubiquitin-Mediated Proteolytic Degradation of PML/Rarα Fusion Protein in Matrine-Induced Differentiation Sensitivity Recovery of ATRA-Resistant APL (NB4-LR1) Cells: in Vitro and in Vivo Studies.
    Author: Wu D, Shao K, Zhou Q, Sun J, Wang Z, Yan F, Liu T, Wu X, Ye B, Huang H, Zhou Y.
    Journal: Cell Physiol Biochem; 2018; 48(6):2286-2301. PubMed ID: 30114705.
    Abstract:
    BACKGROUND/AIMS: Although the cure rate of acute promyelocytic leukemia (APL) has exceeded 90%, the relapse/refractory APL that resistant to all-trans retinoic acid (ATRA) or ATO was still serious concern. Matrine (MAT) could improve the differentiation ability of ATRA-resistant APL cells. This study aimed to explore how the APL-specific fusion protein was degraded in ATRA-resistant APL with the application of MAT and ATRA. METHODS: ATRA-sensitive (NB4) and ATRA-resistant (NB4-LR1) cell lines were used. Nitroblue tetrazolium reduction assay and flow cytometry were used to detect the differentiation ability. The activity of ubiquitin-proteasome and autophagy-mediated pathways in both cells treated with ATRA with or without MAT were compared in protein and mRNA level (Western blot analysis, qRT-PCR), the Fluorescent substrate Suc-LLVY-AMC detection was used to detect the activity of proteasome, and electron microscope for observing autophagosome. MG 132(proteasome inhibitor), rapamycin (autophagy activator), hydroxychloroquine (lysosomal inhibitor) and STI571 [retinoic acid receptor alpha (RARα) ubiquitin stabilizer] were used as positive controls. The effect of MAT was observed in vivo using xenografts. RESULTS: MAT improved the sensitivity of NB4-LR1cells to ATRA treatment, which was consistent with the expression of PML-RARα fusion protein. MAT promoted the ubiquitylation level in NB4-LR1. MG 132 induced the decrease in RARα in both cell lines, and hampered the differentiation of NB4 cells. MAT also promoted the autophagy in NB4-LR1 cells, with an increase in microtubule-associated protein 1 light chain3 (LC3)-II and LC3-II/LC3-I ratio and exhaustion of P62. The expression of LC3II increased significantly in the MAT and ATRA + MAT groups in combination with lysosomal inhibitors. A similar phenomenon was observed in mouse xenografts. MAT induced apoptosis and differentiation. CONCLUSIONS: Autophagy and ubiquitin-mediated proteolytic degradation of PML/RARα fusion protein are crucial in MAT-induced differentiation sensitivity recovery of NB4-LR1 cells.
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