Ying H, Chang J F, Parnes J R
Department of Medicine, Stanford University School of Medicine, CA 94305, USA.
J Immunol. 1998 Mar 1;160(5):2287-96.
CD72 is a 45-kDa glycoprotein that is predominantly expressed on cells of the B lineage, except for plasma cells. Its expression pattern is representative of many B cell-specific proteins, which are essential for B cell development and activation but are down-regulated after B cells become terminally differentiated plasma cells. We have examined the promoter region of the mouse CD72 gene to identify sequences responsible for this regulatory pattern. The CD72 gene does not have an obvious TATAA box. Primer extension assays identified multiple transcription initiation sites. Deletion analyses have identified the 255-bp minimal promoter required for tissue-specific and developmental stage-specific expression. DNase I footprinting analysis of the CD72 minimal promoter revealed three protected elements: FP I, FP II, and FP III. Sequences corresponding to FP I or III gave increased reporter gene activity specifically in B cells, but not in T cells or NIH-3T3 cells. Sequences corresponding to FP II gave increased reporter gene activity in mature B cells, but not in plasma cells or non-B cells. Electrophoretic mobility shift assays and DNase I protection analyses revealed that FP I was bound by the transcription factor PU.1/Spi-1. Transient reporter analyses with plasmid bearing the mutated PU.1 binding site showed that binding of PU.1 is necessary for the increase in CD72 promoter activity in B cells. These results suggest that the 255-bp CD72 promoter confers both tissue specificity and developmental stage specificity, and that the B cell and macrophage-specific transcription factor PU.1 is essential for regulating the tissue specificity of the mouse CD72 promoter.
CD72是一种45 kDa的糖蛋白，主要在B淋巴细胞系的细胞上表达，但浆细胞除外。其表达模式代表了许多B细胞特异性蛋白，这些蛋白对B细胞的发育和激活至关重要，但在B细胞终末分化为浆细胞后会下调。我们研究了小鼠CD72基因的启动子区域，以确定负责这种调控模式的序列。CD72基因没有明显的TATAA盒。引物延伸分析确定了多个转录起始位点。缺失分析确定了组织特异性和发育阶段特异性表达所需的255 bp最小启动子。对CD72最小启动子的DNase I足迹分析揭示了三个受保护元件：FP I、FP II和FP III。与FP I或III对应的序列在B细胞中特异性地增加了报告基因活性，但在T细胞或NIH-3T3细胞中没有。与FP II对应的序列在成熟B细胞中增加了报告基因活性，但在浆细胞或非B细胞中没有。电泳迁移率变动分析和DNase I保护分析表明，FP I被转录因子PU.1/Spi-1结合。用带有突变PU.1结合位点的质粒进行的瞬时报告分析表明，PU.1的结合对于B细胞中CD72启动子活性的增加是必要的。这些结果表明，255 bp的CD72启动子赋予了组织特异性和发育阶段特异性，并且B细胞和巨噬细胞特异性转录因子PU.1对于调节小鼠CD72启动子的组织特异性至关重要。
