R-spondins, Secreted Frizzled-Related Proteins and the Regulation of Wnt Signali

已知R-Spinins(RSPO)在各种环境中增强Wnt/β-catenin信号转导。这一途径的激活对胚胎发育和成人组织动态平衡的许多过程都是至关重要的。它是支持胚胎干细胞和多潜能祖细胞增殖的机制之一。β-连环蛋白途径的结构性激活在许多类型的癌症中都很常见，包括结直肠癌、肝细胞癌、乳腺癌、前列腺癌、肾癌、卵巢癌等。了解通过这一途径增强信号的Rspos等因子的特性，以及根据具体情况阻断或增强Wnt信号的SFRP-1等因子的性质，可能会带来更好的癌症诊断和治疗方法。此外，由于Wnt信号在胚胎发育和成人中具有多种功能，Rspos和sFRPs对其调控的了解增加可能会应用于其他疾病的治疗。重组蛋白处理的C57 MG小鼠乳腺上皮细胞的微阵列分析表明，Rsp2增强了很大比例依赖Wnt-3a的基因表达的变化。许多新的Wnt靶基因通过定量RT-PCR和免疫印迹被鉴定和验证，包括CXCR6，一个最近与乳腺癌转移有关的趋化因子受体。Rsp2和Wnt-3a联合诱导的基因表达的一些变化似乎不是由典型的Wnt/β-catenin/Tcf途径介导的，这表明其他机制与RSPO活性有关。用Rspo2和Wnt-1双转染C57 MG细胞，在三维Matrigel培养和Transwell实验中刺激细胞侵袭。侵袭性特征似乎不依赖于β-连环蛋白信号。皮下注射转Rspo2或Wnt-1表达载体的乳腺细胞在裸鼠体内产生肿瘤。Rspo2和Wnt-1的共表达导致肿瘤细胞表现出强烈的上皮-间充质转化表型，比Wnt-1转基因的模式更明显。最近的实验表明，SFRP-1在哺乳动物细胞中既是Wnt/β-catenin途径的正负调控因子。这种双相活动的机制基础正在积极研究中。一项合作研究表明，在与人类胚胎干细胞共培养时，某些饲养层提供的支持较差，这是由于SFRP-1的表达增加，并将其释放到条件培养液中。

R-spondins (Rspos) are known to potentiate Wnt/beta-catenin signaling in various settings. Activation of this pathway is critical for many processes during embryonic development and tissue homeostasis in the adult. It is one of the mechanisms that supports the proliferation of embryonic stem cells and multi-potential progenitor cells. Constitutive activation of the beta-catenin pathway is common in many types of cancers, including colorectal, hepatocellular, mammary, prostate, renal, ovary and others. Understanding the properties of factors such as the Rspos that enhance signaling through this pathway and factors like sFRP-1 that either block or potentiate Wnt signaling depending on the context could lead to better ways to diagnose and treat cancer. In addition, because Wnt signaling has many functions during embryonic development and in the adult increased knowledge of its regulation by Rspos and sFRPs could have applications in the treatment of other diseases.Microarray analysis of C57MG mouse mammary epithelial cells treated with recombinant proteins showed that Rspo2 potentiated a large percentage of Wnt-3a-dependent changes in gene expression. Many novel Wnt target genes were identified and validated by quantitative RT-PCR and immunoblotting, including CXCR6, a chemokine receptor recently implicated in breast cancer metastasis. Several changes in gene expression induced by the combination of Rspo2 and Wnt-3a did not appear to be mediated by the canonical Wnt/beta-catenin/TCF pathway, suggesting that other mechanisms were associated with Rspo activity. Double transfection of C57MG cells with Rspo2 and Wnt-1 stimulated cell invasiveness in three-dimensional Matrigel cultures as well as transwell assays. Invasive properties appeared to be independent of beta-catenin signaling. Subcutaneous injection of mammary cells transfected either with Rspo2 or Wnt-1 expression vectors produced tumors in nude mice. Co-expression of Rspo2 and Wnt-1 resulted in tumors with cells exhibiting a strong epithelial-mesenchymal transition phenotype, more pronounced than the pattern seen with the Wnt-1 transfectant.Recent experiments have shown that sFRP-1 is both a positive and negative regulator of the Wnt/beta-catenin pathway in mammalian cells. The mechanistic basis for this biphasic activity is under active investigation. A collaborative study demonstrated that the poor support afforded by certain feeder lines in co-culture with human embryonic stem cells was attributable to elevated expression and release of sFRP-1 into conditioned medium.