Thyroid hormone (TH) is a critical regulator of cellular function and cell fate. The circulating TH level is relatively stable, while tissue TH action fluctuates according to cell type–specific mechanisms. Here, we focused on identifying mechanisms that regulate TH action through the type 2 deiodinase (D2) in glial cells. mRNA has an unusually long 3′UTR where we identified multiple putative MSI1 binding sites for Musashi-1 (MSI1), a highly conserved RNA-binding cell cycle regulator. Binding to these sites was confirmed through electrophoretic mobility shift assay. In H4 glioma cells, shRNA-mediated MSI1 knockdown increased endogenous D2 activity, whereas MSI1 overexpression in HEK293T cells decreased D2 expression. This latter effect could be prevented by the deletion of a 3.6 kb region of the 3′UTR of mRNA containing MSI1 binding sites. MSI1 immunoreactivity was observed in 2 mouse expressing cell types, that is, cortical astrocytes and hypothalamic tanycytes, establishing the anatomical basis for a potential interaction of mRNA and MSl1. Indeed, increased D2 expression was observed in the cortex of mice lacking MSI1 protein. Furthermore, MSI1 knockdown–induced D2 expression slowed down cell proliferation by 56% in primary cultures of mouse cortical astrocytes, establishing the functionality of the MSI1–D2–T3 pathway. In summary, mRNA is a target of MSI1 and the MSI1–D2–T3 pathway is a novel regulatory mechanism of astrocyte proliferation with the potential to regulate the pathogenesis of human glioblastoma.

中文翻译：

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Musashi-1-2型脱碘酶途径调节星形胶质细胞增殖


甲状腺激素（TH）是细胞功能和细胞命运的关键调节剂。循环 TH 水平相对稳定，而组织 TH 作用根据细胞类型特异性机制而波动。在这里，我们重点研究通过神经胶质细胞中的 2 型脱碘酶 (D2) 调节 TH 作用的机制。 mRNA 具有异常长的 3'UTR，我们在其中识别出 Musashi-1 (MSI1)（一种高度保守的 RNA 结合细胞周期调节因子）的多个假定 MSI1 结合位点。通过电泳迁移率变动测定证实与这些位点的结合。在 H4 神经胶质瘤细胞中，shRNA 介导的 MSI1 敲低增加了内源性 D2 活性，而 HEK293T 细胞中 MSI1 过表达则降低了 D2 表达。后一种效应可以通过删除含有 MSI1 结合位点的 mRNA 3'UTR 的 3.6 kb 区域来防止。在 2 种小鼠表达细胞类型（即皮质星形胶质细胞和下丘脑单胞细胞）中观察到 MSI1 免疫反应性，为 mRNA 和 MSl1 的潜在相互作用奠定了解剖学基础。事实上，在缺乏 MSI1 蛋白的小鼠皮层中观察到 D2 表达增加。此外，在小鼠皮质星形胶质细胞的原代培养物中，MSI1 敲低诱导的 D2 表达使细胞增殖减慢了 56%，从而建立了 MSI1-D2-T3 途径的功能。总之，mRNA是MSI1的靶标，MSI1-D2-T3通路是星形胶质细胞增殖的一种新的调节机制，具有调节人胶质母细胞瘤发病机制的潜力。