Institut National de la Santé et de la Recherche Médicale U.837, Centre Jean-Pierre Aubert, Institut pour la Recherche sur le Cancer de Lille and Université Lille Nord de France, UDSL, 59000 Lille, France.
Biochem J. 2011 Jul 1;437(1):75-88. doi: 10.1042/BJ20100829.
RhoH is a member of the Rho family of small GTP-binding proteins that lacks GTPase activity. Since RhoH is constantly bound by GTP, it is thought to be constitutively active and controlled predominantly by changes in quantitative expression. RhoH is produced specifically in haematopoietic cells and aberrant expression has been linked to various forms of leukaemia. Transcription of the RHOH gene is the first level at which the quantitative levels of the RhoH protein are regulated. Previous studies have demonstrated that RHOH gene transcription is initiated by three distinct promoter regions designated P1, P2 and P3 that define the 5' end of exons 1, 2 and 4 respectively. In the present study we report that the P3 promoter is largely responsible for RHOH gene transcription in the B-lymphocytic cell line Raji. The P3 promoter contains a minimal promoter region and a repressor region extending from -236 to +67 and +68 to +245 respectively, relative to the 5' end of exon 4. Chromatin immunoprecipitation demonstrated that two AP1 (activator protein 1) sites in the minimal promoter region bind JunD. When JUND is overexpressed, the endogenous RHOH gene is repressed; however, when JUND is inhibited, expression of endogenous RHOH is induced both in the Raji cell line and AML (acute myeloid leukaemia) cells. In the HCL (hairy cell leukaemia) cell line JOK-1, induction of RHOH increases expression of the α isoform of protein kinase C. This downstream target of RHOH is also induced in AML cells by JUND inhibition. Collectively, these data indicate that JunD is an inhibitor of RHOH gene expression.
RhoH 是 Rho 家族的小 GTP 结合蛋白成员，缺乏 GTP 酶活性。由于 RhoH 始终与 GTP 结合，因此被认为是组成性激活的，主要受定量表达变化的控制。RhoH 专门在造血细胞中产生，异常表达与各种形式的白血病有关。RHOH 基因的转录是调节 RhoH 蛋白定量水平的第一个层次。先前的研究表明，RHOH 基因转录由三个不同的启动子区域 P1、P2 和 P3 启动，分别定义了外显子 1、2 和 4 的 5' 端。在本研究中，我们报告 P3 启动子在 B 淋巴细胞系 Raji 中主要负责 RHOH 基因转录。P3 启动子包含一个最小启动子区域和一个从 -236 到 +67 以及从 +68 到 +245 延伸的抑制区域，相对于外显子 4 的 5' 端。染色质免疫沉淀表明，最小启动子区域中的两个 AP1（激活蛋白 1）位点与 JunD 结合。当 JUND 过表达时，内源性 RHOH 基因被抑制；然而，当 JUND 被抑制时，内源性 RHOH 的表达在 Raji 细胞系和 AML（急性髓系白血病）细胞中均被诱导。在 HCL（毛细胞白血病）细胞系 JOK-1 中，RHOH 的诱导增加了蛋白激酶 C 的α同工型的表达。RHOH 的这个下游靶标也被 JUND 抑制在 AML 细胞中诱导。总之，这些数据表明 JunD 是 RHOH 基因表达的抑制剂。
