Cismasiu Valeriu B, Duque Javier, Paskaleva Elena, Califano Danielle, Ghanta Sailaja, Young Howard A, Avram Dorina
Center for Cell Biology and Cancer Research, Albany Medical College, 47 New Scotland Avenue, Albany, NY 12208, U.S.A.
Biochem J. 2009 Jan 15;417(2):457-66. doi: 10.1042/BJ20080925.
BCL11B is a transcriptional regulator with an important role in T-cell development and leukaemogenesis. We demonstrated recently that BCL11B controls expression from the IL (interleukin)-2 promoter through direct binding to the US1 (upstream site 1). In the present study, we provide evidence that BCL11B also participates in the activation of IL-2 gene expression by enhancing NF-kappaB (nuclear factor kappaB) activity in the context of TCR (T-cell receptor)/CD28-triggered T-cell activation. Enhanced NF-kappaB activation is not a consequence of BCL11B binding to the NF-kappaB response elements or association with the NF-kappaB-DNA complexes, but rather the result of higher translocation of NF-kappaB to the nucleus caused by enhanced degradation of IkappaB (inhibitor of NF-kappaB). The enhanced IkappaB degradation in cells with increased levels of BCL11B was specific for T-cells activated through the TCR, but not for cells activated through TNFalpha (tumour necrosis factor alpha) or UV light, and was caused by increased activity of IkappaB kinase, as indicated by its increase in phosphorylation. As BCL11B is a transcription factor, we investigated whether the expression of genes upstream of IkappaB kinase in the TCR/CD28 signalling pathway was affected by increased BCL11B expression, and found that Cot (cancer Osaka thyroid oncogene) kinase mRNA levels were elevated. Cot kinase is known to promote enhanced IkappaB kinase activity, which results in the phosphorylation and degradation of IkappaB and activation of NF-kappaB. The implied involvement of Cot kinase in BCL11B-mediated NF-kappaB activation in response to TCR activation is supported by the fact that a Cot kinase dominant-negative mutant or Cot kinase siRNA (small interfering RNA) knockdown blocked BCL11B-mediated NF-kappaB activation. In support of our observations, in the present study we report that BCL11B enhances the expression of several other NF-kappaB target genes, in addition to IL-2. In addition, we provide evidence that BCL11B associates with intron 2 of the Cot kinase gene to regulate its expression.
BCL11B是一种转录调节因子，在T细胞发育和白血病发生中起重要作用。我们最近证明，BCL11B通过直接结合US1（上游位点1）来控制IL（白细胞介素）-2启动子的表达。在本研究中，我们提供证据表明，在TCR（T细胞受体）/CD28触发的T细胞活化过程中，BCL11B还通过增强NF-κB（核因子κB）活性参与IL-2基因表达的激活。增强的NF-κB活化不是BCL11B与NF-κB反应元件结合或与NF-κB-DNA复合物缔合的结果，而是由IkappaB（NF-κB抑制剂）降解增强导致NF-κB向细胞核更高易位的结果。在BCL11B水平升高的细胞中，增强的IkappaB降解对通过TCR活化的T细胞具有特异性，但对通过TNFα（肿瘤坏死因子α）或紫外线活化的细胞则不然，并且是由IkappaB激酶活性增加引起的，这通过其磷酸化增加得以表明。由于BCL11B是一种转录因子，我们研究了TCR/CD28信号通路中IkappaB激酶上游基因的表达是否受BCL11B表达增加的影响，发现Cot（大阪甲状腺癌原癌基因）激酶mRNA水平升高。已知Cot激酶可促进增强的IkappaB激酶活性，从而导致IkappaB的磷酸化和降解以及NF-κB的活化。Cot激酶显性阴性突变体或Cot激酶siRNA（小干扰RNA）敲低可阻断BCL11B介导的NF-κB活化，这一事实支持了Cot激酶在BCL11B介导的对TCR活化的NF-κB活化中的潜在参与。为支持我们的观察结果，在本研究中我们报告，除IL-2外，BCL11B还增强了其他几个NF-κB靶基因的表达。此外，我们提供证据表明，BCL11B与Cot激酶基因的内含子2缔合以调节其表达。
