Ceramide galactosyltransferase expression is regulated positively by Nkx2.2 and negatively by OLIG2
Ceramide galactosyltransferase expression is regulated positively by Nkx2.2 and negatively by OLIG2
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DOI：
10.1093/glycob/cwu042
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发表时间：
2014-10-01
期刊：
影响因子：
4.3
通讯作者：
Taniguchi, Naoyuki
中科院分区：
文献类型：
--
作者：
Okahara, Kyohei;Kizuka, Yasuhiko;Taniguchi, Naoyuki
髓磷脂是从少突胶质细胞或许旺细胞延伸的多层结构，在维持神经元功能中起关键作用，并且髓磷脂的损伤或损失引起脱髓鞘疾病，如多发性硬化症。为了精确排列髓鞘，需要半乳糖神经酰胺（GalCer）（髓鞘中的主要鞘糖脂）的表达。GalCer的合成以发育阶段特异性的方式严格限制在少突胶质细胞中。神经酰胺半乳糖基转移酶（CGT）是半乳糖苷酶生物合成的关键酶，在少突胶质细胞中表现出有限的表达，但其机制尚不清楚。基于我们的假设，即特定的少突胶质细胞谱系特异性转录因子调节CGT表达，我们共表达了一系列候选转录因子与人CGT启动子驱动荧光素酶在少突胶质细胞瘤细胞中的表达，以测量启动子活性。我们发现Nkx2.2强烈激活CGT启动子。此外，我们确定了一种新的抑制性DNA元件在CGT和OLIG2，少突胶质细胞特异性转录因子，作为该元件的结合蛋白的第一内含子。此外，OLIG2的过表达完全取消了Nkx2.2对CGT启动子活性的激活作用。CGT mRNA的表达也被Nkx2.2上调，但这种上调被OLIG2与Nkx2.2的共表达所抵消。我们的研究表明，CGT的表达是由负调节器OLIG2和正调节器Nkx2.2的平衡表达控制的，这为GalCer的表达如何以细胞类型和阶段特异性方式受到严格调节提供了新的见解。
Myelin, a multilamellar structure extended from oligodendrocytes or Schwann cells, plays a critical role in maintenance of neuronal function, and damage or loss of myelin causes demyelinating diseases such as multiple sclerosis. For precise alignment of the myelin sheath, there is a requirement for expression of galactosylceramide (GalCer), a major glycosphingolipid in myelin. Synthesis of GalCer is strictly limited in oligodendrocytes in a developmental stage-specific manner. Ceramide galactosyltransferase (CGT), a key enzyme for biosynthesis of GalCer, exhibits restricted expression in oligodendrocytes but the mechanism is poorly understood. Based on our assumption that particular oligodendrocyte-lineage-specific transcription factors regulate CGT expression, we co-expressed a series of candidate transcription factors with the human CGT promoter-driving luciferase expression in oligodendroglioma cells to measure the promoter activity. We found that Nkx2.2 strongly activated the CGT promoter. In addition, we identified a novel repressive DNA element in the first intron of CGT and OLIG2, an oligodendrocyte-specific transcription factor, as a binding protein of this element. Moreover, overexpression of OLIG2 completely canceled the activating effect of Nkx2.2 on CGT promoter activity. Expression of CGT mRNA was also upregulated by Nkx2.2, but this upregulation was cancelled by co-expression of OLIG2 with Nkx2.2. Our study suggests that CGT expression is controlled by balanced expression of the negative modulator OLIG2 and positive regulator Nkx2.2, providing new insights into how expression of GalCer is tightly regulated in cell-type-and stage-specific manners.