Section of Cell and Developmental Biology, University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093-0349, USA.
Dev Biol. 2010 Oct 1;346(1):1-10. doi: 10.1016/j.ydbio.2010.06.024. Epub 2010 Jun 28.
Analysis of diverse signaling systems has revealed that one important level of control is regulation of membrane trafficking of ligands and receptors. The activities of some ligands are also regulated by whether they are membrane bound or secreted. In Drosophila, several morphogenetic signals that play critical roles in development have been found to be subject to such regulation. For example, activity of the Hedgehog (Hh) is regulated by Raspberry, which palmitoylates Hh. Similarly, the palmitoylases Porcupine and Raspberry increase the activities of Wingless (Wg) and the EGF-ligand Spitz (Spi), respectively. In contrast to its vertebrate homologues, which have typical N-terminal signal sequences, the precursor form of Drosophila Hh contains an internal type-II secretory signal motif. The Short Gastrulation (Sog) protein is another secreted Drosophila protein that contains a type-II signal and differs from its vertebrate ortholog Chordin which contains a standard signal peptide. In this study, we examine the regulation of Sog secretion and regulation by dHIP14, the ortholog of a mammalian palmitoylase first identified as Huntington Interacting Protein (HIP). We show that dHIP14 binds to Sog and that Sog is palmitoylated. In S2 cells, dHIP14 promotes secretion of Sog as well as stabilizing a membrane associated form of Sog. We examined the requirement for candidate cysteine residues in the N-terminal predicted cytoplasmic domain of Sog and find that Cys27, one of two adjacent cysteines (Cys27 and Cys28), is essential for the full activity of dHIP14 and its effect on Sog. Finally, we find that dHIP14 promotes the activity of Sog in vivo. These studies highlight the growing importance of lipid modification in regulating signaling at the level of ligand production and localization.
对各种信号转导系统的分析表明，一个重要的调控水平是配体和受体的膜运输调控。一些配体的活性也受到它们是否结合在膜上或分泌的影响。在果蝇中，已经发现几种在发育中起关键作用的形态发生信号受到这种调节。例如，Hedgehog（Hh）的活性受到 Raspberry 的调节，Raspberry 对 Hh 进行棕榈酰化。同样，棕榈酰酶 Porcupine 和 Raspberry 分别增加 Wingless（Wg）和 EGF 配体 Spitz（Spi）的活性。与具有典型 N 端信号序列的脊椎动物同源物不同，果蝇 Hh 的前体形式含有内部 II 型分泌信号基序。Short Gastrulation（Sog）蛋白是另一种分泌型果蝇蛋白，它含有 II 型信号，与含有标准信号肽的脊椎动物同源物 Chordin 不同。在这项研究中，我们研究了 Sog 分泌的调节以及 dHIP14 的调节，dHIP14 是一种首先被鉴定为 Huntington 相互作用蛋白（HIP）的哺乳动物棕榈酰酶的同源物。我们表明 dHIP14 与 Sog 结合，并且 Sog 被棕榈酰化。在 S2 细胞中，dHIP14 促进 Sog 的分泌，并稳定 Sog 与膜相关的形式。我们检查了 Sog 预测的细胞质 N 端候选半胱氨酸残基的要求，并发现两个相邻半胱氨酸（Cys27 和 Cys28）之一的 Cys27 对于 dHIP14 的全部活性及其对 Sog 的影响是必不可少的。最后，我们发现 dHIP14 在体内促进 Sog 的活性。这些研究强调了脂质修饰在调节配体产生和定位水平的信号转导方面的重要性日益增加。
