Bois-Joyeux B, Denissenko M, Thomassin H, Guesdon S, Ikonomova R, Bernuau D, Feldmann G, Danan J L
Centre de Recherche sur l'Endocrinologie Moléculaire et le Développement, CNRS, UPR 1511, Meudon, France.
J Biol Chem. 1995 Apr 28;270(17):10204-11. doi: 10.1074/jbc.270.17.10204.
The effects of a phorbol ester (TPA) and of members of the Jun and Fos oncoprotein family on the activity of the rat alpha-fetoprotein (AFP) promoter were checked by using transient expression experiments in HepG2 hepatoma cells. TPA blocked the activity of the rat AFP promoter in a dose-dependent manner. Overexpression of c-Jun specifically repressed the rat AFP promoter but not the albumin promoter. JunB and JunD were poorer inhibitors. c-Fos expression did not potentiate the negative effect of Jun. The Jun-induced repression does not require binding of c-Jun to the AFP promoter. DNase 1 footprinting experiments did not display any high affinity binding site for Jun on the AFP promoter. Integrity of the c-Jun DNA binding domain is not required for the c-Jun protein to block the AFP promoter. The N-terminal part of Jun, which contains the activating domain, is responsible for the repression as shown by using Jun-Gal4 chimera. Jun likely exerts its negative control on the AFP promoter via protein-protein interactions with a not yet identified trans-activating factor within the -134 to +6 region or with a component of the general machinery of transcription. Jun proteins can thus be key intermediates in regulatory cascades which result in the differential modulation of the AFP and albumin gene expression in the course of liver development and carcinogenesis.
通过在HepG2肝癌细胞中进行瞬时表达实验，检测了佛波酯（TPA）以及Jun和Fos癌蛋白家族成员对大鼠甲胎蛋白（AFP）启动子活性的影响。TPA以剂量依赖的方式阻断大鼠AFP启动子的活性。c-Jun的过表达特异性抑制大鼠AFP启动子，但不抑制白蛋白启动子。JunB和JunD是较弱的抑制剂。c-Fos的表达不会增强Jun的负面影响。Jun诱导的抑制作用不需要c-Jun与AFP启动子结合。DNase 1足迹实验未显示Jun在AFP启动子上有任何高亲和力结合位点。c-Jun蛋白阻断AFP启动子不需要其DNA结合结构域的完整性。如使用Jun-Gal4嵌合体所示，Jun包含激活结构域的N末端部分负责这种抑制作用。Jun可能通过与-134至+6区域内尚未鉴定的反式激活因子或与一般转录机制的一个组分进行蛋白质-蛋白质相互作用，对AFP启动子施加其负调控。因此，Jun蛋白可能是调节级联反应中的关键中间体，这些调节级联反应导致在肝脏发育和癌变过程中AFP和白蛋白基因表达的差异调节。
