López-Soto Alejandro, Quiñones-Lombraña Adolfo, López-Arbesú Rubén, López-Larrea Carlos, González Segundo
Departamento de Biología Funcional, Facultad de Medicina, Instituto Universitario de Oncología del Principado de Asturias, Universidad de Oviedo, Oviedo, Spain.
J Biol Chem. 2006 Oct 13;281(41):30419-30. doi: 10.1074/jbc.M604868200. Epub 2006 Aug 10.
Tumor cells expressing ligands of the NKG2D receptor stimulate anti-tumor immunity mediated by natural killer and T cells. In humans, NKG2D ligands (NKG2DL) are encoded by MIC and ULBP proteins. NKG2DL exhibit highly restricted expression in healthy tissues but are widely expressed in tumors. However, regulation of each NKG2DL differs substantially in different cancer cells. In this study, we characterized the mechanisms that regulate the expression of ULBP1. We show that the transcription of ULBP1 strictly depends on the binding of Sp1 and Sp3 to a CRE(1) site located in the ULBP1 minimal promoter. The mutation or deletion of this Sp1/Sp3 binding site abolished the transcription of ULBP1. It also diminished the transactivation of ULBP1 promoter by Sp3 overexpression, but not by Sp1, indicating that Sp3 is the main transcription factor that regulates ULBP1 through the CRE(1) site. Experiments in SL2 cells showed that the ULBP1 promoter was inactive in the absence of the Sp proteins and indicate that Sp3 is the essential activator of ULBP1 transcription, because the overexpression of Sp3 up-regulated its promoter activity > 500-fold. Additionally, we demonstrated that AP-2alpha repressed the expression of ULBP1 in HeLa cells by interfering with the binding of Sp3 and Sp1 to the ULBP1 promoter. These data indicate that Sp1, Sp3, and AP-2alpha may play an important role in the immunosurveillance against cancer. Finally, the definition of ULBP1 regulation may have implications for development of new therapeutic strategies against cancer cells.
表达NKG2D受体配体的肿瘤细胞可刺激由自然杀伤细胞和T细胞介导的抗肿瘤免疫。在人类中，NKG2D配体（NKG2DL）由MIC和ULBP蛋白编码。NKG2DL在健康组织中表达高度受限，但在肿瘤中广泛表达。然而，不同癌细胞中每种NKG2DL的调控存在很大差异。在本研究中，我们对调控ULBP1表达的机制进行了表征。我们表明，ULBP1的转录严格依赖于Sp1和Sp3与位于ULBP1最小启动子中的CRE(1)位点的结合。该Sp1/Sp3结合位点的突变或缺失消除了ULBP1的转录。它还减弱了Sp3过表达对ULBP1启动子的反式激活作用，但Sp1过表达则没有，这表明Sp3是通过CRE(1)位点调控ULBP1的主要转录因子。在SL2细胞中的实验表明，在没有Sp蛋白的情况下，ULBP1启动子无活性，这表明Sp3是ULBP1转录的必需激活因子，因为Sp3的过表达使其启动子活性上调了500倍以上。此外，我们证明AP-2α通过干扰Sp3和Sp1与ULBP1启动子的结合来抑制HeLa细胞中ULBP1的表达。这些数据表明，Sp1、Sp3和AP-2α可能在针对癌症的免疫监视中发挥重要作用。最后，ULBP1调控的定义可能对开发针对癌细胞的新治疗策略具有启示意义。
