Study on transcriptional regulation in CD40 signaling.

CD 40信号传导在免疫应答中起重要作用。CD 40信号传导激活各种信号传导分子，例如转录因子NF-kB。然而，目前还没有阐明这些信号分子如何调节靶基因。目前还不清楚靶基因的产物如何参与免疫反应。以前，我们证明了CD 40信号降低了细胞周期抑制剂kip 1的mRNA水平。首先，我们讨论了CD 40信号转导抑制kip 1的分子机制。我们用3 T3细胞检测了kip 1基因启动子的活性，证明NF-κ B抑制kip 1启动子。此外，kip 1启动子中含有-581至-348的区域携带两个NF-kB识别序列，并且该区域中的启动子活性被NF-kB抑制。这表明该区域可能在CD 40介导的kip 1水平抑制中发挥作用。然而，即使NF-κ B位点突变，NF-κ B介导的抑制仍然发生。因此，NF-kB如何抑制该区域的启动子活性仍不清楚。接下来，我们评估了kip 1抑制在CD 40介导的B细胞增殖和存活中的作用。由于p27 kip 1抑制细胞周期进程中必不可少的CDKs，kip 1抑制可能在CD 40信号诱导的B细胞增殖中发挥作用。CD 40信号传导通过消除抗原受体介导的细胞凋亡来诱导包括B细胞系WEHI-231的B细胞的存活。当我们使用逆转录病毒载体在WEHI-231细胞中表达kip 1时，抗原受体连接的WEHI-231细胞的存活部分受损。这表明kip 1抑制是完全恢复抗原受体诱导的细胞凋亡所必需的。总之，kip 1抑制似乎涉及NF-κ B，并在B细胞的增殖和存活中起作用。

CD40 signaling plays an essential role in immune responses. CD40 signaling activates various signaling molecules such as the transcription factor NF-kB. However, it is not yet elucidated how these signaling molecules regulate the target genes. It is also not yet clear how the products of the target genes are involved in immune responses. Previously, we demonstrated that CD40 signaling reduces the mRNA level of the cell cycle inhibitor kip1. First, we addressed the molecular mechanisms for the repression of kip1 by CD40 signaling. We assessed the promoter activity of the kip1 gene by luciferace assay using 3T3 cells, and demonstrated that NF-kB repress the kip1 promoter. Further the region containing -581 to -348 in the kip1 promoter carry two NF-kB recognition sequences and the promoter activity in this region is suppressed by NF-kB. This suggests that this region may play a role in CD40-mediated suppression of the kip1 level. However, NF-kB-mediated suppression still occurs even if the NF-kB site is mutated. Thus, how NF-kB represses the promoter activity in this region is still unclear. Next, we assessed the role of kip1 repression in CD40-mediated B cell proliferation and survival. Since p27kip1 inhibits CDKs essential fur cell cycle progression, kip1 repression may play a role in B cell proliferation induced by CD40 signaling. CD40 signaling induces survival of the B cells including the B cell line WEHI-231 by abrogating antigen receptor-mediated apoptosis. When we expressed kip1 in WEHI-231 cells using a retrovirus vector, survival of antigen receptor-ligated WEHI-231 cells is partially impaired. This indicates that kip1 suppression is required for fully restore antigen receptor-induced apoptosis by CD40 signaling. Taken together kip1 repression appears to involve NF-kB and play a role in proliferation and survival of B cells.