Field-Corbett Ciara, English Karen, O'Dea Shirley
Institute of Immunology, Biology Department, National University of Ireland Maynooth, Ireland.
Stem Cells. 2009 Mar;27(3):662-9. doi: 10.1634/stemcells.2008-0313.
While investigating the differentiation potential of bone marrow-derived cells, we previously demonstrated upregulated expression of the lung-related surfactant protein B (SP-B) gene in hematopoietic progenitor cells (HPCs) when they were cocultured with macerated lung tissue. During coculture, HPCs differentiated toward a dendritic-like myeloid cell phenotype (hematopoietic progenitor cell-derived dendritic-like cells [HPC-DCs]). However, immature dendritic cells (iDCs) cocultured under identical conditions did not express SP-B mRNA before or after coculture. We have now further examined the regulation of SP-B expression in HPC-DCs and iDCs. Of the transcription factors involved in SP-B gene expression, neither cell type expressed TTF-1, HNF3alpha, or HNF3beta, but both cell types expressed Sp1 and Sp3. Sp1 binding to the SP-B promoter was investigated in these cells. Three novel Sp1 binding motifs were identified in the mouse SP-B promoter. Using chromatin immunoprecipitation, it was demonstrated that Sp1 was bound to all three sites in HPC-DCs after coculture with lung tissue, but not in iDCs. We hypothesized that although genes from multiple lineages may be active in HPCs, gene silencing events, such as methylation, may subsequently occur to suppress expression of these genes in more mature myeloid cells, such as iDCs. Treatment with the demethylating agent 5-azacytidine resulted in expression of the SP-B gene in iDCs. These data indicate that tissue-specific transcription factors are not required to express the lung-related gene SP-B in hematopoietic progenitor cells. Furthermore, silencing events, such as methylation, may occur to suppress lung-related gene expression as progenitor cells become committed toward more mature hematopoietic cell phenotypes.
在研究骨髓来源细胞的分化潜能时，我们之前发现，造血祖细胞（HPCs）与研磨后的肺组织共培养时，肺相关表面活性蛋白B（SP-B）基因的表达上调。共培养期间，HPCs向树突状髓样细胞表型分化（造血祖细胞衍生的树突状细胞 [HPC-DCs]）。然而，在相同条件下共培养的未成熟树突状细胞（iDCs）在共培养前后均不表达SP-B mRNA。我们现在进一步研究了HPC-DCs和iDCs中SP-B表达的调控。在参与SP-B基因表达的转录因子中，两种细胞类型均不表达TTF-1、HNF3α或HNF3β，但都表达Sp1和Sp3。我们研究了这些细胞中Sp1与SP-B启动子的结合情况。在小鼠SP-B启动子中鉴定出三个新的Sp1结合基序。通过染色质免疫沉淀法证明，与肺组织共培养后，Sp1在HPC-DCs中与所有三个位点结合，但在iDCs中不结合。我们推测，尽管多个谱系的基因可能在HPCs中活跃，但随后可能会发生基因沉默事件，如甲基化，以抑制这些基因在更成熟的髓样细胞（如iDCs）中的表达。用去甲基化剂5-氮杂胞苷处理导致iDCs中SP-B基因的表达。这些数据表明，造血祖细胞中表达肺相关基因SP-B不需要组织特异性转录因子。此外，随着祖细胞向更成熟的造血细胞表型分化，可能会发生甲基化等沉默事件来抑制肺相关基因的表达。
