Dai J L, Turnacioglu K K, Schutte M, Sugar A Y, Kern S E
Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205-2196, USA.
Cancer Res. 1998 Oct 15;58(20):4592-7.
Dpc4 (Smad4) is implicated in mediation of signals from transforming growth factor (TGF) beta and related ligands, and wild-type Dpc4 mediates TGF-beta-stimulated gene transcription at specific DNA sequences bound by Dpc4 [Smad binding element (SBE)]. We characterized panels of DPC4 tumor mutations and cancer cell lines. Amino acid substitutions within the NH2-terminal third of Dpc4 weakened or ablated SBE-mediated gene regulation by a disruption of DNA binding. An interaction of the COOH-terminal end with the DNA-binding domain of Dpc4 was evident but was not required to explain the functional impairment produced by NH2-terminal DPC4 mutations. Both substitution and truncation mutations of the COOH-terminal half of DPC4 lacked the ability to regulate transcription while retaining the sequence-specific DNA-binding function, but through differing mechanisms. A modular domain to redistribute Dpc4 to the nuclear compartment allowed SBE-mediated transcriptional activation in a cell line having a TGF-1 receptor defect and was sufficient to restore SBE-mediated transactivation ability to COOH-terminal DPC4 missense mutants. Cells harboring DPC4 alterations had a universal impairment of the TGF-beta-stimulated SBE transcriptional response. These studies identify the loss of SBE-mediated gene regulation as a uniform outcome of the selection for DPC4 alterations during tumorigenesis. They raise the possibility of restoration of some Dpc4-associated transcriptional events in cancer cells through the targeted redistribution of wild-type and some missense mutant forms of Dpc4 to the nucleus.
Dpc4（Smad4）参与介导来自转化生长因子（TGF）β及相关配体的信号，野生型Dpc4在由Dpc4 [Smad结合元件（SBE）]结合的特定DNA序列处介导TGF-β刺激的基因转录。我们对DPC4肿瘤突变和癌细胞系进行了特征分析。Dpc4氨基末端三分之一内的氨基酸替换通过破坏DNA结合削弱或消除了SBE介导的基因调控。Dpc4羧基末端与DNA结合结构域之间的相互作用很明显，但并非解释氨基末端DPC4突变产生的功能损害所必需。DPC4羧基末端一半的替换和截短突变均缺乏调节转录的能力，同时保留序列特异性DNA结合功能，但机制不同。一个将Dpc4重新分布到核区室的模块化结构域在具有TGF-1受体缺陷的细胞系中实现了SBE介导的转录激活，并且足以恢复羧基末端DPC4错义突变体的SBE介导的反式激活能力。携带DPC4改变的细胞对TGF-β刺激的SBE转录反应普遍受损。这些研究确定SBE介导的基因调控丧失是肿瘤发生过程中DPC4改变选择的统一结果。它们提出了通过将野生型和一些错义突变形式的Dpc4靶向重新分布到细胞核来恢复癌细胞中一些与Dpc4相关的转录事件的可能性。
