Transcriptional regulation of CCR10 expression in plasma cells

据报道，CCR 10在几乎所有分泌IgA的浆细胞中表达，而其配体CCL 28在各种粘膜组织中广泛表达。因此，CCR 10-CCL 28系统可能在常见的粘膜免疫系统中贡献IgA分泌浆细胞的广泛分布。在这里，我们研究了终末分化B细胞中CCR 10表达的机制。如前所述，用IL-21处理的活化的人CD 19 ^+ B细胞有效地分化为IgD^-CD 38 ^+浆细胞。尽管IgD^-CD 38 ^+细胞并不自发表达CCR 10，但如果在1，25-二羟维生素D3（1，25-（OH）_2D_3）存在下诱导分化，则相当大一部分细胞转向表达CCR 10，已知1，25-（OH）_2D_3用作佐剂时可促进常见的粘膜免疫应答。然而，我们观察到伊加^+细胞在1，25-（OH）_2D_3作用下几乎没有增加。为了确定调节终末分化B细胞中1，25-（OH）_2D_3诱导的CCR 10表达的转录机制，我们接下来对CCR 10启动子进行了一系列分析。报道基因检测包括一系列5 '缺失的启动子片段和具有定点突变的启动子片段，揭示了近端Ets-1位点和上游维生素D3反应元件（VDRE）对CCR 10表达至关重要。用表达CCR 10的骨髓瘤细胞核提取物进行的NoShift转录因子结合试验证实了Ets-1和1，25-（OH）_2D_3激活的维生素D_3受体（VDR）与相应元件的特异性结合。总的来说，1，25-（OH）2D 3在体外有效诱导IL-21诱导的人浆细胞中的CCR 10表达。此外，CCR 10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.