The Crucial Role of NR4A1 Dependent Apoptosis Induced By Fenretinide in Acute Myeloid Leukemia
Authors: Xiong Jie , Kuang Xingyi , Lu Tingting , Cheng Bingqing , Wei Danna , Li Xinyao , Wang Weili , Zhang Zhaoyuan , Wang Jishi 
Published: October 2019

Abstract
OBJECTIVE: NR4A1 is a member of the orphan nuclear receptor family, which is involved in biological processes such as cell proliferation, apoptosis, metabolism, and differentiation. The expression of NR4A1 is increased in a variety of solid tumors, which promotes oncogenesis and enhances the viability of tumor cells. However, in hematological malignancies, its expression is significantly lower than normal. Studies have shown that clearance of NR4A1 can lead to the progression of mice to acute myeloid leukemia, reducing the amount of NR4A gene expression can make mice progress to MDS / MPN, and even acute myeloid leukemia. This indicates that NR4A1 is an important tumor suppressor in acute myeloid leukemia. The present study was to investigate the effect of drug-induced NR4A1 expression on apoptosis in acute myeloid leukemia and its related mechanisms. The results suggested that NR4A1 may become a new target for the treatment of acute myeloid leukemia. METHODS: In vitro, on the one hand, bone marrow mononuclear cells from patients with newly diagnosed or relapsed acute myeloid leukemia were extracted as samples, and the expression of NR4A1 mRNA and protein was detected by Real-time PCR and Western blot. Acute myeloid leukemia cell lines HL60 and Kasumi-1 were tested for fenretinide activity and apoptosis, as well as NR4A1 and mitochondrial apoptosis pathway-related protein expression. We used siNR4A1 to knockdown NR4A1 expression and LMB to inhibit nuclear export, the apoptosis rate and apoptosis protein were detected. The mechanism of anti-apoptotic effect of NR4A1 was verified by western blot, immunofluorescence and co-immunoprecipitation. AML mice model were established and fenretinide was injected into the tail veins to observe the effects of NR4A1 expression on survival time, blood routine, bone marrow and important organs. Results: 1. NR4A1 expression in patients with acute myeloid leukemia was significantly higher than normal. 2. The expression of NR4A1 increased in a time- and concentration-dependent manner under the action of fenretinide. 3. After siNR4A1, the apoptosis of acute myeloid leukemia cells was significantly decreased, and the expression of apoptotic proteins was decreased. 4. The expression of apoptotic proteins was decreased after fenretinide combined with leptomycin treatment. After fenretinide treatment, the expression of NR4A1 was decreased in nuclear extracts, and the expression of mitochondrial extract was increased. After drug treatment, NR4A1 interacted with Bcl-2, and the bcl-2 BH3 domain in cytoplasm was exposed to play an anti-apoptotic effect. After successful modeling of AML mice, the survival rate of the fenretinide treatment group was significantly prolonged compared with the control group. The peripheral blood leukocytes, hemoglobin and platelet values were significantly different. The liver and spleen volume of the treatment group were significantly smaller than that of the control group. The mRNA and protein levels of NR4A1 in the spleen were significantly higher than those in the control group. Conclusion: The effect of fenretinide on acute myeloid leukemia cells induces NR4A1 expression and plays a pro-apoptotic effect. This apoptosis effect depends on the nuclear export of NR4A1. NR4A1 is located from the nucleus to the mitochondria, and binds to the Bcl-2 BH3 domain.
Key words: NR4A1, fenretinide, acute myeloid leukemia, apoptosis, nuclear export

Disclosures
No relevant conflicts of interest to declare.