Su G H, Ip H S, Cobb B S, Lu M M, Chen H M, Simon M C
Department of Medicine, University of Chicago, Illinois 60637, USA.
J Exp Med. 1996 Jul 1;184(1):203-14. doi: 10.1084/jem.184.1.203.
Spi-B and PU.1 are hematopoietic-specific transcription factors that constitute a subfamily of the Ets family of DNA-binding proteins. Here we show that contrary to previous reports, PU.1 and Spi-B have very different expression patterns. PU.1 is expressed at high levels in B cells, mast cells, megakaryocytes, macrophages, neutrophils, and immature erythroid cells and at lower levels in mature erythrocytes. PU.1 is completely absent from peripheral T cells and most T cell lines based on sensitive RT-PCR assays. In contrast, Spi-B is expressed exclusively in lymphoid cells and can be detected in early fetal thymus and spleen. In situ hybridizations of adult murine tissues demonstrate Spi-B mRNA in the medulla of the thymus, the white pulp of the spleen, and the germinal centers of lymph nodes. Spi-B expression is very abundant in B cells and both Spi-B mRNA and protein are detected in some T cells. In situ hybridization and Northern blot analysis suggest that Spi-B gene expression increases during B cell maturation and decreases during T cell maturation. Gel-retardation experiments show that Spi-B can bind to all putative PU.1 binding sites, but do not reveal any preferred Spi-B binding site. Finally, both PU.1 and Spi-B function as transcriptional activators of the immunoglobulin light-chain enhancer E lambda 2.4 when coexpressed with Pip (PU.1-interaction partner) in NIH-3T3 cells. Taken together, these data suggest that differences in patterns of expression between Spi-B and PU.1 distinguish the function of each protein during development of the immune system.
Spi-B和PU.1是造血特异性转录因子，它们构成了DNA结合蛋白Ets家族的一个亚家族。我们在此表明，与之前的报道相反，PU.1和Spi-B具有非常不同的表达模式。PU.1在B细胞、肥大细胞、巨核细胞、巨噬细胞、中性粒细胞和未成熟红细胞中高水平表达，而在成熟红细胞中低水平表达。基于灵敏的逆转录聚合酶链反应分析，外周T细胞和大多数T细胞系中完全不存在PU.1。相反，Spi-B仅在淋巴细胞中表达，并且在早期胎儿胸腺和脾脏中可检测到。成年小鼠组织的原位杂交显示，胸腺髓质、脾脏白髓和淋巴结生发中心中有Spi-B mRNA。Spi-B在B细胞中表达非常丰富，并且在一些T细胞中可检测到Spi-B mRNA和蛋白。原位杂交和Northern印迹分析表明，Spi-B基因表达在B细胞成熟过程中增加，而在T细胞成熟过程中减少。凝胶阻滞实验表明，Spi-B可以结合所有假定的PU.1结合位点，但未揭示任何优先的Spi-B结合位点。最后，当与Pip（PU.1相互作用伴侣）在NIH-3T3细胞中共表达时，PU.1和Spi-B均作为免疫球蛋白轻链增强子E lambda 2.4的转录激活因子发挥作用。综上所述，这些数据表明，Spi-B和PU.1表达模式的差异在免疫系统发育过程中区分了每种蛋白质的功能。
