Perez A, Kastner P, Sethi S, Lutz Y, Reibel C, Chambon P
Laboratoire de Génétique Moléculaire des Eucaryotes du CNRS, Unité 184 de Biologie Moléculaire et de Génie Génétique de l'INSERM, Faculté de Médecine, Strasbourg, France.
EMBO J. 1993 Aug;12(8):3171-82. doi: 10.1002/j.1460-2075.1993.tb05986.x.
Fusion proteins (named PMLRAR) between PML and the retinoic acid receptor alpha (RAR alpha) are generated as a result of the t(15;17) chromosomal translocation found in acute promyelocytic leukemia (APL). We show here that PMLRAR proteins exist in solution as stable homodimers whose formation is mediated by a presumptive coiled coil in the PML moiety. In contrast to RAR alpha, which requires heterodimerization with RXR for efficient DNA binding, PMLRAR homodimers can bind to target sequences in the absence of RXR, and the binding pattern of PMLRAR homodimeric complexes to directly repeated motif (DR) response elements with 1-5 bp spacers is different from that of RAR/RXR heterodimeric complexes. We show that the presence of RXR induces the formation of PMLRAR/RXR heteromeric complexes which bind to DNA via one RAR DNA binding domain (DBD) and one RXR DBD, like 'classical' RAR/RXR heterodimers. PMLRAR interaction with RXR occurs in solution and in transfected cultured Cos cells, and PMLRAR is able to sequester RXR efficiently in the cytoplasm, suggesting that dominant 'inactivation' of RXR may be a possible mechanism of action for PMLRAR. Accordingly, we show that PMLRAR can both prevent the binding of the vitamin D3 receptor (VDR) to a target sequence in vitro and inhibit vitamin D3-dependent activation of a VDR-responsive reporter gene in transfected cells. These results suggest that both the distinct DNA binding properties of PMLRAR homodimers and the sequestration of RXR by PMLRARs may contribute to the molecular mechanisms which underlie the pathogenesis of APL. We also report that RXR alpha transcripts are down-regulated by RA-treatment in promyelocytic cells.
在急性早幼粒细胞白血病（APL）中发现的t(15;17)染色体易位导致了早幼粒细胞白血病锌指蛋白（PML）与维甲酸受体α（RARα）之间的融合蛋白（命名为PMLRAR）的产生。我们在此表明，PMLRAR蛋白在溶液中以稳定的同二聚体形式存在，其形成由PML部分中假定的卷曲螺旋介导。与需要与维甲酸X受体（RXR）异二聚化才能有效结合DNA的RARα不同，PMLRAR同二聚体在没有RXR的情况下也能结合靶序列，并且PMLRAR同二聚体复合物与具有1 - 5个碱基对间隔的直接重复基序（DR）反应元件的结合模式与RAR/RXR异二聚体复合物不同。我们表明，RXR的存在诱导了PMLRAR/RXR异源复合物的形成，该复合物通过一个RAR DNA结合结构域（DBD）和一个RXR DBD与DNA结合，就像“经典”的RAR/RXR异二聚体一样。PMLRAR与RXR的相互作用发生在溶液中以及转染的培养Cos细胞中，并且PMLRAR能够在细胞质中有效地隔离RXR，这表明RXR的显性“失活”可能是PMLRAR的一种可能作用机制。因此，我们表明PMLRAR既能在体外阻止维生素D3受体（VDR）与靶序列的结合，又能在转染细胞中抑制VDR反应性报告基因的维生素D3依赖性激活。这些结果表明，PMLRAR同二聚体独特的DNA结合特性以及PMLRAR对RXR的隔离都可能有助于APL发病机制的分子机制。我们还报告说，在早幼粒细胞中，RA处理会下调RXRα转录本。
