Xi Z F, Russell M, Woodward S, Thompson F, Wagner L, Taetle R
Cancer Biology Program, University of Arizona, Tucson, USA.
Leukemia. 1997 Feb;11(2):212-20. doi: 10.1038/sj.leu.2400547.
The EVI-1 gene encodes a Zn finger, DNA binding protein previously detected in some acute myelogenous leukemias (AML) and myelodysplasias (MDS), but not in normal marrow or cord blood cells. Experimental studies suggest EVI-1 blocks cellular differentiation by binding to GATA-1 or other specific DNA sequences controlling gene expression, and may be involved in the pathogenesis of some AMLs. To further define potential roles for EVI-1 in leukemia pathogenesis, we studied its regulation in acute promyelocytic leukemias (APL). Seven of 11 APL cases expressed EVI-1 RNA detected by RNA PCR at diagnosis, and expression was detected in two additional cases after treatment with all-trans retinoic acid (ATRA). Two of four cases studied at relapse also expressed EVI-1 RNA. To investigate regulation of EVI-1 expression in APL, we examined its expression in the NB4 APL cell line. NB4 cells did not express EVI-1 under basal conditions, but expressed EVI-1 after ATRA-induced differentiation. When NB4 cells were exposed to ATRA and transferred to cultures with N,N'-hexamethylene-bis-acetamide (HMBA), differentiation occurred but EVI-1 RNA was not detected, indicating that EVI-1 expression was not required for terminal, NB4 differentiation. ATRA-resistant NB4 cells were obtained by continuous culture in gradually increasing concentrations of ATRA. These cells did not express markers of differentiation but continued to express EVI-1 for several weeks even after ATRA withdrawal. To assess whether expression of the APL PML-RAR alpha fusion gene alone was sufficient for ATRA induction of EVI-1, the PML-RAR alpha gene cDNA was expressed in U937 histiocytic lymphoma cells. ATRA treatment of PML-RAR alpha-transfected or control U937 cells did not induce EVI-1 expression. In conclusion, this study demonstrates the EVI-1 gene is consistently expressed in APL cells either constitutively or after ATRA treatment. ATRA represents the first biologically active agent shown to specifically regulate EVI-1 expression in blood cells. In contrast to previous studies in AML and MDS, the pattern of EVI-1 expression suggests it may facilitate rather than inhibit myeloid differentiation during ATRA treatment. However, effects of EVI-1 expression are likely to be complex, and expression in ATRA-resistant APL cells may indicate multiple roles for this gene.
EVI-1基因编码一种锌指DNA结合蛋白，该蛋白先前在一些急性髓性白血病（AML）和骨髓增生异常综合征（MDS）中被检测到，但在正常骨髓或脐血细胞中未被检测到。实验研究表明，EVI-1通过与GATA-1或其他控制基因表达的特定DNA序列结合来阻断细胞分化，并且可能参与某些AML的发病机制。为了进一步确定EVI-1在白血病发病机制中的潜在作用，我们研究了其在急性早幼粒细胞白血病（APL）中的调控情况。11例APL病例中有7例在诊断时通过RNA PCR检测到EVI-1 RNA表达，另外2例在接受全反式维甲酸（ATRA）治疗后检测到表达。4例复发时研究的病例中有2例也表达EVI-1 RNA。为了研究APL中EVI-1表达的调控，我们检测了其在NB4 APL细胞系中的表达。NB4细胞在基础条件下不表达EVI-1，但在ATRA诱导分化后表达EVI-1。当NB4细胞暴露于ATRA并转移至含N，N'-六亚甲基双乙酰胺（HMBA）的培养基中时，细胞发生分化，但未检测到EVI-1 RNA，这表明EVI-1表达并非NB4细胞终末分化所必需。通过在逐渐增加浓度的ATRA中连续培养获得了对ATRA耐药的NB4细胞。这些细胞不表达分化标志物，但即使在撤去ATRA后仍持续表达EVI-1达数周。为了评估单独的APL PML-RARα融合基因表达是否足以诱导ATRA诱导EVI-1表达，将PML-RARα基因cDNA在U937组织细胞淋巴瘤细胞中表达。对转染了PML-RARα的U937细胞或对照U937细胞进行ATRA处理均未诱导EVI-1表达。总之，本研究表明EVI-1基因在APL细胞中持续表达，无论是组成性表达还是在ATRA治疗后表达。ATRA是首个被证明能特异性调控血细胞中EVI-1表达的生物活性剂。与先前关于AML和MDS的研究不同，EVI-1的表达模式表明它在ATRA治疗期间可能促进而非抑制髓系分化。然而，EVI-1表达的影响可能很复杂，并且在对ATRA耐药的APL细胞中的表达可能表明该基因具有多种作用。
