Two isoforms of the Notch antagonist Hairless are produced by differential translation initiation
Two isoforms of the Notch antagonist Hairless are produced by differential translation initiation
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DOI：
10.1073/pnas.242596699
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发表时间：
2002-11-26
影响因子：
11.1
通讯作者：
Preiss, A
中科院分区：
文献类型：
--
作者：
Maier, D;Nagel, AC;Preiss, A
Notch信号通路控制细胞分化，包括所有高等后生动物（包括苍蝇和人）的增殖和细胞死亡。通过激活的Notch的信号转导涉及CSL组的转录调节因子。Notch信号需要严格调节，在果蝇中，它们被无毛（H）蛋白拮抗。H通过将果蝇CSL蛋白（无毛抑制因子[Su（H）]）从转录激活因子转化为抑制因子，同时招募辅抑制因子dCtBP或Groucho之一来沉默Notch靶基因的活性。H蛋白的计算分子量约为110 kDa，除了两个辅阻遏物结合区外，还含有几个功能区。然而，尽管没有选择性剪接的迹象，但在整个发育过程中观察到两种无毛蛋白亚型H-p120和H-p150。在这里，我们表明，较小的亚型来自内部核糖体进入位点（IRES）的ORF。IRES在异源测定中具有活性，并含有必需的保守结构元件。两种无毛同种型在体内具有残余活性，然而，与两者的组合相比，其降低，这意味着两种蛋白质同种型对于WT功能是必需的。在幼虫组织中，这两种亚型的翻译受细胞周期调节：而H-p150亚型在间期翻译，H-p120在有丝分裂期间富集。因此，在整个细胞周期中任一H同种型的存在允许有效抑制Notch调节的细胞增殖。
The Notch-signaling pathway controls cellular differentiation, including proliferation and cell death in all higher metazoans (including flies and men). Signal transduction through activated Notch involves the CSL group of transcriptional regulators. Notch signals need to be tightly regulated, and in Drosophila they are antagonized by the Hairless (H) protein. H silences the activity of Notch target genes by transforming the Drosophila CSL protein, Suppressor of Hairless [Su(H)], from a transcriptional activator into a repressor while recruiting one of the corepressors dCtBP or Groucho. The H protein has a calculated molecular mass of approximate to110 kDa and contains several functional domains apart from the two small corepressor-binding domains. However, although there is no indication for alternative splicing, two Hairless protein isoforms, H-p120 and H-p150, are observed throughout development. Here, we show that the smaller isoform derives from an internal ribosome entry site (IRES) within the ORF. The IRES is active in a heterologous assay and contains an essential, conserved structural element. The two Hairless isoforms have residual activity in vivo which is, however, reduced compared to a combination of both, which implies that both protein isoforms are necessary for WT function. In larval tissues, translation of the two isoforms is cell-cycle regulated: whereas the H-p150 isoform is translated during interphase, H-p120 is enriched during mitosis. Thus, the presence of either H isoform throughout the cell cycle allows efficient inhibition of Notch-regulated cell proliferation.