Palmer G, Manen D, Bonjour J P, Caverzasio J
Division of Bone Diseases, WHO Collaborating Center for Osteoporosis and Bone Diseases, Department of Internal Medicine, University Hospital of Geneva, 24 rue Micheli-du-Crest, CH-1211 14, Geneva, Switzerland.
Gene. 2001 Nov 14;279(1):49-62. doi: 10.1016/s0378-1119(01)00747-8.
The Pit1 phosphate transporter is involved in regulated phosphate handling in bone forming cells. In this study, we compared the structure of the murine and human Pit1/PIT1 promoters and characterized cis-acting elements controlling Pit1/PIT1 expression. The Pit1/PIT1 promoter sequence and its location relative to the first transcribed exon are conserved and similar transcription factor binding sites are found at identical positions in mouse and human. Luciferase reporter gene assays in transiently transfected mouse ATDC5 chondrocytes and human SaOS-2 osteoblasts indicated that the activity of the mouse Pit1 promoter depends on several cis-acting elements, including ATF/CREB, Sp1 and AP-1 sites, an E-box and a TATA box. In contrast, the activity of the human promoter essentially requires a TATA-like sequence and one single Sp1 site. This Sp1 site binds Sp1, Sp3, as well as unidentified proteins present in SaOS-2 nuclear extracts and co-transfection experiments in SL2 cells indicate that Sp1 and Sp3 activate transcription from the human PIT1 promoter. These data suggest that, despite similarities in promoter structure, changes in the relative importance of conserved transcription factor binding sites cause species-dependent differences in Pit1 promoter function, which allow Sp1-related proteins to play a particularly important role in human.
Pit1磷酸转运蛋白参与成骨细胞中磷酸盐的调节处理。在本研究中，我们比较了小鼠和人类Pit1/PIT1启动子的结构，并对控制Pit1/PIT1表达的顺式作用元件进行了特征分析。Pit1/PIT1启动子序列及其相对于第一个转录外显子的位置是保守的，并且在小鼠和人类的相同位置发现了相似的转录因子结合位点。在瞬时转染的小鼠ATDC5软骨细胞和人类SaOS-2成骨细胞中进行的荧光素酶报告基因测定表明，小鼠Pit1启动子的活性取决于几个顺式作用元件，包括ATF/CREB、Sp1和AP-1位点、一个E盒和一个TATA盒。相比之下，人类启动子的活性基本上需要一个类TATA序列和一个单一的Sp1位点。这个Sp1位点结合Sp1、Sp3以及SaOS-2核提取物中存在的未鉴定蛋白质，并且在SL2细胞中的共转染实验表明Sp1和Sp3激活人类PIT1启动子的转录。这些数据表明，尽管启动子结构存在相似性，但保守转录因子结合位点相对重要性的变化导致Pit1启动子功能存在物种依赖性差异，这使得Sp1相关蛋白在人类中发挥特别重要的作用。
