Ross I L, Dunn T L, Yue X, Roy S, Barnett C J, Hume D A
Centre for Molecular Biology and Biotechnology, University of Queensland, Australia.
Oncogene. 1994 Jan;9(1):121-32.
The expression of mRNA encoding the DNA-binding protein PU.1 (Spi-1) is restricted to B lymphocytes and macrophages. The role of PU.1 in tissue-specific transcriptional regulation in the two cell types was examined by co-transfection of a PU.1 expression plasmid with vectors containing B cell (IgH enhancer) or macrophage-specific (c-fms) transcription control elements. Cotransfection of the PU.1 expression plasmid in MOPC31C B cells trans-repressed the IgH enhancer but trans-activated the c-fms promoter. The latter was insufficient to overcome a block to transcription elongation that determines macrophage-specific c-fms gene expression. In the macrophage line RAW264, PU.1 had no effect on the c-fms promoter, but trans-repressed the activity of a c-fms reporter plasmid containing the transcription attenuator. The effects of PU.1 in both cell types were distinct from those of c-ets-2, a related factor, which trans-activated the c-fms promoter in both B cells and macrophages but also repressed the IgH enhancer. PU.1 was shown to be one of several nuclear proteins that bound a critical cis-acting element of the IgH enhancer, microB, but analysis of nuclear extracts of a wide range of B cell and macrophage lines demonstrated a strong correlation between macrophage phenotype and nuclear PU.1 expression. The data suggest that differences in nuclear PU.1 expression and function between macrophages and B cells may play a role in lineage divergence.
编码DNA结合蛋白PU.1（Spi-1）的mRNA的表达仅限于B淋巴细胞和巨噬细胞。通过将PU.1表达质粒与含有B细胞（IgH增强子）或巨噬细胞特异性（c-fms）转录控制元件的载体共转染，研究了PU.1在这两种细胞类型的组织特异性转录调控中的作用。在MOPC31C B细胞中共转染PU.1表达质粒可反式抑制IgH增强子，但反式激活c-fms启动子。后者不足以克服决定巨噬细胞特异性c-fms基因表达的转录延伸阻滞。在巨噬细胞系RAW264中，PU.1对c-fms启动子无影响，但反式抑制含有转录衰减子的c-fms报告质粒的活性。PU.1在两种细胞类型中的作用不同于相关因子c-ets-2，后者在B细胞和巨噬细胞中均反式激活c-fms启动子，但也抑制IgH增强子。已证明PU.1是与IgH增强子的关键顺式作用元件microB结合的几种核蛋白之一，但对多种B细胞和巨噬细胞系的核提取物分析表明，巨噬细胞表型与核PU.1表达之间存在很强的相关性。数据表明，巨噬细胞和B细胞之间核PU.1表达和功能的差异可能在谱系分化中起作用。
