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

已知r -连接蛋白（Rspos）在各种情况下增强Wnt/ β -连环蛋白信号传导。该通路的激活对胚胎发育和成人组织稳态的许多过程至关重要。它是支持胚胎干细胞和多潜能祖细胞增殖的机制之一。β -连环蛋白通路的组成性激活在许多类型的癌症中都很常见，包括结肠直肠癌、肝细胞癌、乳腺癌、前列腺癌、肾癌、卵巢癌等。了解通过该途径增强信号传导的Rspos等因子的特性，以及根据环境阻断或增强Wnt信号传导的sFRP-1等因子的特性，可能会找到更好的方法来诊断和治疗癌症。此外，由于Wnt信号在胚胎发育和成人过程中具有许多功能，因此增加对Rspos和sFRPs对其调节的了解可能会应用于其他疾病的治疗。重组蛋白处理的C57MG小鼠乳腺上皮细胞的微阵列分析显示，Rspo2增强了很大比例的wnt -3a依赖性基因表达变化。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CXCR6，一种最近与乳腺癌转移有关的趋化因子受体。Rspo2和Wnt-3a结合诱导的一些基因表达变化似乎并不是由典型的Wnt/ β -catenin/TCF途径介导的，这表明Rspo活性与其他机制有关。在三维基质培养和transwell实验中，Rspo2和Wnt-1双重转染C57MG细胞可刺激细胞侵袭性。侵袭特性似乎独立于β -连环蛋白信号传导。皮下注射转染了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-间质转化表型，比Wnt-1转染的模式更明显。最近的实验表明，在哺乳动物细胞中，sFRP-1既是Wnt/ β -catenin通路的正调控因子，也是负调控因子。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，某些饲养系与人胚胎干细胞共培养时支持能力差是由于sFRP-1在条件培养基中的表达和释放升高。

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.