Structural and functional analysis of the amphioxus IGFBP gene uncovers ancient origin of IGF-independent functions.
Structural and functional analysis of the amphioxus IGFBP gene uncovers ancient origin of IGF-independent functions.
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DOI：
10.1210/en.2013-1201
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发表时间：
2013-07
期刊：
影响因子：
4.8
通讯作者：
Jianfeng Zhou;J. Xiang;Shicui Zhang;C. Duan
中科院分区：
文献类型：
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作者：
Jianfeng Zhou;J. Xiang;Shicui Zhang;C. Duan
IGF 在调节脊椎动物发育、生长、繁殖和衰老中发挥着关键作用。在细胞外液中，IGF 受到 IGF 结合蛋白 (IGFBP) 家族的结合和调节。尽管所有已知的 IGFBP 都是分泌蛋白，但也有一些存在于细胞核中并具有不依赖于 IGF 的活性。这些不同的生物行为模式何时以及如何进化尚不清楚。在这项研究中，我们鉴定并分析了文昌鱼的 IGFBP 基因。文昌鱼与现代脊椎动物有共同的祖先，其历史可以追溯到 5.2 亿年前。文昌鱼 IGFBP 具有脊椎动物 IGFBP 的所有主要结构特征。系统发育分析将其置于 IGFBP 谱系中的基础位置。配体印迹分析表明文昌鱼IGFBP 不与IGF-I 或-II 结合。然而，将其 Phe70 改为 Leu 足以将其转化为功能性 IGF 结合剂。在培养细胞中进行测试时，文昌鱼 IGFBP 定位于细胞核，这归因于其 L 结构域中的 2 个冗余核定位序列。此外，文昌鱼 IGFBP N 端结构域具有很强的转录激活活性。文昌鱼 IGFBP 在斑马鱼胚胎中的强制表达导致背侧化表型。这一行动需要核国产化。这些结果表明 IGFBP 的核定位和转录激活活性是古老的功能，并且 IGF 结合功能可能是在进化后期通过机会性功能获得性突变获得的。
IGFs play key roles in regulating vertebrate development, growth, reproduction, and aging. In extracellular fluids, IGFs are bound and regulated by a family of IGF-binding proteins (IGFBPs). Although all known IGFBPs are secreted proteins, some are also found in the nucleus and possess IGF-independent activities. When and how these distinct modes of biological actions have evolved is unknown. In this study, we identified and analyzed an IGFBP gene from amphioxus. Amphioxus shares a common ancestor with the modern vertebrate lineage that dates back to more than 520 million years ago. The amphioxus IGFBP shares all major structural characteristics of vertebrate IGFBPs. Phylogenetic analyses place it in a basal position in the IGFBP lineage. Ligand blot analysis reveals that amphioxus IGFBP does not bind to IGF-I or -II. Changing its Phe70 into Leu, however, is sufficient to convert it into a functional IGF binder. When tested in cultured cells, amphioxus IGFBP is localized in the nucleus, and this is attributed to 2 redundant nuclear localization sequences in its L domain. Furthermore, the amphioxus IGFBP N-terminal domain has strong transcriptional activation activity. Forced expression of amphioxus IGFBP in zebrafish embryos results in dorsalized phenotypes. This action requires nuclear localization. These results suggest that the nuclear localization and transcription activation activity of IGFBPs are ancient functions and the IGF-binding function may have been acquired by opportunistic gain-of-functional mutations later in evolution.