Transactivation of the ApoCIII promoter by ATF-2 and repression by members of the Jun family.
Transactivation of the ApoCIII promoter by ATF-2 and repression by members of the Jun family.
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ATF-2 对 ApoCIII 启动子的反式激活和 Jun 家族成员的抑制。
DOI：
10.1021/bi9804176
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Kardassis,D
中科院分区：
文献类型：
--
作者：
Hadzopoulou-Cladaras,M;Lavrentiadou,SN;Zannis,VI;Kardassis,D
先前的研究表明，细胞因子如肿瘤坏死因子-α刺激信号转导通路，包括转录因子ATF-2和Jun，抑制HepG2细胞的apoCIII启动子活性。在本研究中，DNase I足迹分析证实ATF-2保护apoCIII启动子中的三个区域。apoCIII增强子中的一个区域（- 747/ - 726）位于先前鉴定的足迹I内，并且与Sp1（- 764/ - 742）和HNF-4（- 736/ - 714）的结合位点有重叠边界。另外两个区域代表新的足迹，被指定为D/E（- 219/ - 199）和B/C（- 102/ - 75）。B/C区与先前鉴定的包含HNF-4结合位点（- 87/ - 63）的足迹B重叠。在HepG2细胞中共转染实验表明，ATF-2可将−890/+24 apoCIII启动子转激活1.6倍。此外，近端D/E（- 219/ - 199）和远端I (- 747/ - 726) ATF-2结合位点的突变使apoCIII启动子强度分别降低到对照的33%和9%，表明ATF-2是apoCIII基因转录的正调节因子。ATF-2和HNF-4表达质粒共转染导致apoCIII启动子的加性反激活。此外，携带ATF-2结合位点D/E和I突变的apoCIII启动子构建体被HNF-4有效地反激活，这表明这两个因素独立地影响了apoCIII启动子的强度。Jun家族成员（c-Jun， JunB和JunD）对−890/+24 apoCIII启动子活性产生剂量依赖性抑制。在最小AdML启动子前含有apoCIII增强子的合成启动子也被Jun抑制。相反，缺少增强子区域的apoCIII启动子片段被Jun反激活。研究结果表明，Jun的同型二聚体或Jun与其他AP-1亚基的异源二聚体可能通过干扰apoCIII增强子的功能而导致了所观察到的抑制。在ATF-2和HNF-4存在的情况下，Jun对apoCIII基因的抑制可以逆转，这表明ATF2和Jun/ATF-2异源二聚体可能对apoCIII基因的转录产生积极影响，而Jun的同源二聚体或其他AP-1成员的异源二聚体则相反。这些发现表明Jun家族成员和ATF-2参与信号转导通路在肝源细胞基础或诱导apoCIII启动子活性中的作用。
It was shown previously that cytokines such as tumor necrosis factor-α that stimulate signal transduction pathways involving transcription factors ATF-2 and Jun repress apoCIII promoter activity in HepG2 cells. In the present study, DNase I footprinting analysis established that ATF-2 protected three regions in the apoCIII promoter. One region (−747/−726) present in the apoCIII enhancer is within the previously identified footprint I and has overlapping boundaries with the binding sites of Sp1 (−764/−742) and HNF-4 (−736/−714). The other two regions represent new footprints and have been designated D/E (−219/−199) and B/C (−102/−75). The B/C region overlaps with the previously identified footprint B which contains an HNF-4 binding site (−87/−63). Cotransfection experiments in HepG2 cells showed that ATF-2 transactivated the −890/+24 apoCIII promoter 1.6-fold. In addition, mutations in the proximal D/E (−219/−199) and distal I (−747/−726) ATF-2-binding sites reduced the apoCIII promoter strength to 33 and 9% of control, respectively, indicating that ATF-2 is a positive regulator of apoCIII gene transcription. Cotransfections with ATF-2 and HNF-4 expression plasmids resulted in additive transactivation of the apoCIII promoter. Furthermore, apoCIII promoter constructs bearing mutations in the D/E and I ATF-2 binding sites were efficiently transactivated by HNF-4, suggesting that these two factors contribute independently to the apoCIII promoter strength. Members of the Jun family (c-Jun, JunB, and JunD) caused a dose-dependent inhibition of the −890/+24 apoCIII promoter activity. A synthetic promoter containing the apoCIII enhancer in front of the minimal AdML promoter was also repressed by Jun. In contrast, apoCIII promoter segments lacking the enhancer region were transactivated by Jun. The findings suggest that homodimers of Jun or heterodimers of Jun with other AP-1 subunits could be responsible for the observed repression by interfering with the function(s) of the apoCIII enhancer. Repression by Jun could be reversed in the presence of ATF-2 and HNF-4, suggesting that ATF2 and possibly Jun/ATF-2 heterodimers exert a positive effect on apoCIII gene transcription, as opposed to Jun homodimers or heterodimers with other AP-1 members. These findings suggest a role for members of the Jun family and ATF-2 that participate in signal transduction pathways in basal or induced apoCIII promoter activity in cells of hepatic origin.