Xom Proteolysis During Early Vertebrate Embryogenesis

描述（由申请人提供）： 泛素介导的蛋白质水解在早期胚胎发生的信号转导中起着重要作用。早期发育途径的蛋白质水解失调通常导致成年后的肿瘤形成。因此，探索早期胚胎发生过程中的蛋白质水解提供了一个独特的机会，揭示相关的肿瘤发生机制。在我的K 08奖所涵盖的调查期间，我们发现Xom，BMP 4信号通路的同源框转录因子，在原肠胚形成开始时以阶段特异性方式降解。我们已经确定了Xom的破坏基序和对Xom稳定性重要的破坏基序的关键潜在磷酸化位点（Ser 140和Ser 144）。我们进一步表明SCF-β-TRCP最有可能是参与Xom降解的细胞E3泛素连接酶。非降解Xom的表达破坏背腹图案形成在早期爪蟾胚胎发育，表明在早期胚胎发育过程中调节蛋白水解的重要性。两个重要问题仍然存在：1）Xom在原肠胚形成前阶段是如何稳定的，以及2）在原肠胚形成开始时是什么开启了Xom蛋白水解。基于我们的初步研究，我们假设Xom破坏基序的磷酸化在早期发育期间确定Xom稳定性中起调节作用，并且丝氨酸/苏氨酸激酶在原肠胚形成开始时磷酸化Xom并触发Xom降解。我们建议通过以下具体目标来检验这一假设： 1)确定（Ser 140/144）磷酸化在Xom体外降解中的作用; 2)确定（Ser 140/144）磷酸化在体内Xom降解中的潜在调节作用; 3)鉴定在早期胚胎发生过程中磷酸化Xom的Ser 140/144的激酶。 这些问题的答案将提供证据的同源异型盒功能的稳定性是如何调节发育，这将承担重大意义，不仅了解胚胎发生的基本机制，而且广泛的疾病，如肿瘤的发病机制。

DESCRIPTION (provided by applicant): Ubiquitin-mediated proteolysis plays important roles in governing signaling during early embryogenesis. Dysregulation of proteolysis of early developmental pathways often results in tumor formation in adult life. Exploring proteolysis during early embryogenesis, therefore, offers a unique opportunity to unveil mechanisms pertinent to tumorigenesis. During the investigation covered by my K08 award, we found that Xom, a homeobox transcriptional factor of the BMP4 signaling pathway, was degraded in a stage-specific manner at the onset of gastrulation. We have identified the destruction motif of Xom and the critical potential phosphorylation sites (Ser140 and Ser144) of the destruction motif that are important for Xom stability. We have further shown that the SCF-beta-TRCP is most likely the cellular E3 ubiquitin ligase involved in Xom degradation. Expression of non-degradable Xom disrupts dorsoventral pattern formation during early Xenopus embryogenesis, indicating the importance of regulated proteolysis during early embryogenesis. Two important questions remains: 1) how is Xom stabilized during pre-gastrulation phase and 2) what turns on Xom proteolysis at the onset of gastrulation. Based on our preliminary studies, we hypothesized that phosphorylation of the Xom destruction motif plays a regulatory role in determining Xom stability during early development, and a serine/threonine kinase phosphorylates Xom at the onset of gastrulation and triggers Xom degradation. We propose to address the following specific aims to test this hypothesis: 1) Define the function of (Ser140/144) phosphorylation in Xom degradation in vitro; 2) Determine a potential regulatory role of (Ser140/144) phosphorylation in Xom degradation in vivo; 3) Identify the kinase that phosphorylates Ser140/144 of Xom during early embryogenesis. Answers to these questions will present the evidence of how stability of homeobox function is regulated developmentally, which will bear great implications for understanding not only the basic mechanism of embryogenesis but also a broad spectrum of diseases, such as pathogenesis of neoplasm.