Ubeda M, Wang X Z, Zinszner H, Wu I, Habener J F, Ron D
Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Mol Cell Biol. 1996 Apr;16(4):1479-89. doi: 10.1128/MCB.16.4.1479.
CHOP (GADD153) is a mammalian nuclear protein that dimerizes with members of the C/EBP family of transcriptional factors. Absent under normal conditions, CHOP is induced by the stress encountered during nutrient deprivation, the acute-phase response, and treatment of cells with certain toxins. The basic region of CHOP deviates considerably in sequence from that of other C/EBP proteins, and CHOP-C/EBP heterodimers are incapable of binding to a common class of C/EBP sites. With respect to such sites, CHOP serves as an inhibitor of the activity of C/EBP proteins. However, recent studies indicate that certain functions of CHOP, such as the induction of growth arrest by overexpression of the wild-type protein and oncogenic transformation by the TLS-CHOP fusion protein, require an intact basic region, suggesting that DNA binding by CHOP may be implicated in these activities. In this study an in vitro PCR-based selection assay was used to identify sequences bound by CHOP-C/EBP dimers. These sequences were found to contain a unique core element PuPuPuTGCAAT(A/C)CCC. Competition in DNA-binding assays, DNase 1 footprint analysis, and methylation interference demonstrate that the binding is sequence specific. Deletions in the basic region of CHOP lead to a loss of DNA binding, suggesting that CHOP participates in this process. Stress induction in NIH 3T3 cells leads to the appearance of CHOP-containing DNA-binding activity. CHOP is found to contain a transcriptional activation domain which is inducible by cellular stress, lending further support to the notion that the protein can function as a positively acting transcription factor. We conclude that CHOP may serve a dual role both as an inhibitor of the ability of C/EBP proteins to activate some target genes and as a direct activator of others.
CHOP（GADD153）是一种哺乳动物核蛋白，它与转录因子C/EBP家族的成员形成二聚体。在正常条件下不存在，CHOP在营养剥夺、急性期反应以及用某些毒素处理细胞时所遇到的应激情况下被诱导产生。CHOP的碱性区域在序列上与其他C/EBP蛋白有很大差异，并且CHOP-C/EBP异二聚体无法结合到一类常见的C/EBP位点。就这些位点而言，CHOP作为C/EBP蛋白活性的抑制剂。然而，最近的研究表明，CHOP的某些功能，如野生型蛋白过表达诱导生长停滞以及TLS-CHOP融合蛋白导致的致癌转化，需要完整的碱性区域，这表明CHOP与DNA的结合可能与这些活性有关。在本研究中，使用基于体外PCR的筛选试验来鉴定CHOP-C/EBP二聚体结合的序列。发现这些序列包含一个独特的核心元件PuPuPuTGCAAT(A/C)CCC。DNA结合试验中的竞争、DNase 1足迹分析和甲基化干扰表明这种结合具有序列特异性。CHOP碱性区域的缺失导致DNA结合能力丧失，表明CHOP参与了这一过程。NIH 3T3细胞中的应激诱导导致出现含CHOP的DNA结合活性。发现CHOP含有一个可被细胞应激诱导的转录激活结构域，这进一步支持了该蛋白可作为正向作用转录因子发挥功能的观点。我们得出结论，CHOP可能具有双重作用，既是C/EBP蛋白激活某些靶基因能力的抑制剂，又是其他一些靶基因的直接激活剂。
