Transcriptional regulation of CCR10 expression in plasma cells

CCR10已被报道在几乎所有分泌IgA的浆细胞中都有表达，而其配体CCL28在各种粘膜组织中广泛表达。因此，CCR10-CCL28系统很可能在常见的粘膜免疫系统中贡献了广泛的分泌IgA的浆细胞。在此，我们研究了CCR10在B细胞终末分化中的表达机制。据报道，经IL-21处理后活化的人CD19^B细胞可有效地分化为IGD^-CD38^浆细胞。即使IGD^-CD38^细胞不自发表达CCR10，但如果在1，25-二羟基维生素D3(1，25-(OH)_2D_3)的存在下诱导分化，相当一部分细胞会表达CCR10，1，25-(OH)_2D_3作为佐剂可促进常见的粘膜免疫反应。然而，我们观察到1，25-(OH)_2D_3对IgA细胞几乎没有增加。为了确定1，25-(OH)_2D_3诱导终末分化B细胞CCR10表达的转录机制，我们接下来对CCR10启动子进行了一系列分析。记者对一系列5‘端缺失的启动子片段和定点突变的启动子片段的分析表明，Ets-1近端的一个位点和上游的维生素D3反应元件(VDRE)对CCR10的表达至关重要。利用表达CCR10的骨髓瘤细胞系的核提取液进行NoShift转录因子结合分析，证实了Ets-1和1，25-(OH)_2D_3激活的维生素D3受体(VDR)与相应元件的特异性结合。总的来说，1，25-(OH)2D3在体外能有效地诱导IL-21诱导的人浆细胞CCR10的表达。此外，CCR10启动子被1，25-(OH)_2D_3激活的VDR和Ets-1协同激活。

CCR10 has been reported to be expressed by almost all IgA-secreting plasma cells, while its ligand CCL28 is widely expressed in various mucosal tissues. Thus, the CCR10-CCL28 system is likely to contribute a wide distribution of IgA-secreting plasma cells in the common mucosal immune system. Here we examined the mechanism of CCR10 expression in terminally differentiating B cells. As reported previously, activated human CD19^+ B cells treated with IL-21 efficiently differentiated into IgD^-CD38^+ plasma cells. Even though IgD^-CD38^+ cells did not spontaneously expressed CCR10, a substantial fraction turned to express CCR10 if the differentiation was induced in the presence of 1,25-dihydroxyvitamin D3 (1,25-(OH)_2D_3), which is known to promote common mucosal immune responses if used as an adjuvant. However, we observed little increases in IgA^+ cells by 1,25-(OH)_2D_3. To determine the transcriptional mechanism regulating 1,25-(OH)_2D_3-inducible expression of CCR10 in terminally differentiating B cells, we next carried out a series of analysis on the CCR10 promoter. The reporter assays involving a series of 5'-deleted promoter fragments and promoter fragments with site-directed mutations revealed that a proximal Ets-1 site and an upstream vitamin D3 response element (VDRE) were critical for CCR10 expression. The NoShift transcription factor binding assays using nuclear extracts from CCR10-expressing myeloma cell lines confirmed specific binding of Ets-1 and 1,25-(OH)_2D_3-activated vitamin D3 receptor (VDR) to the respective elements. Collectively, 1,25-(OH)2D3 efficiently induces CCR10 expression in IL-21-induced human plasma cells in vitro. Furthermore, the CCR10 promoter is cooperatively activated by 1,25-(OH)_2D_3-activated VDR and Ets-1.