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

已知 R-spondins (Rspos) 可在各种情况下增强 Wnt/β-catenin 信号传导。 该途径的激活对于胚胎发育和成人组织稳态过程中的许多过程至关重要。 它是支持胚胎干细胞和多能祖细胞增殖的机制之一。 β-连环蛋白途径的组成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。 了解通过该途径增强信号传导的 Rspos 等因子的特性，以及根据具体情况阻断或增强 Wnt 信号传导的 sFRP-1 等因子的特性，可能会带来更好的癌症诊断和治疗方法。 此外，由于 Wnt 信号在胚胎发育过程中具有多种功能，并且在成人中，增加对 Rspos 和 sFRP 对其调节的了解可能会在其他疾病的治疗中得到应用。对用重组蛋白处理的 C57MG 小鼠乳腺上皮细胞进行的微阵列分析表明，Rspo2 增强了大部分 Wnt-3a 依赖性基因表达变化。 通过定量 RT-PCR 和免疫印迹鉴定并验证了许多新的 Wnt 靶基因，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 组合诱导的基因表达的一些变化似乎不是由经典 Wnt/β-连环蛋白/TCF 途径介导的，这表明其他机制与 Rspo 活性相关。 用 Rspo2 和 Wnt-1 双转染 C57MG 细胞可刺激三维 Matrigel 培养物以及 Transwell 测定中的细胞侵袭性。 侵袭特性似乎与β-连环蛋白信号传导无关。 皮下注射用 Rspo2 或 Wnt-1 表达载体转染的乳腺细胞在裸鼠中产生肿瘤。 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 转染子的模式更明显。最近的实验表明，sFRP-1 是哺乳动物细胞中 Wnt/β-catenin 通路的正调节因子和负调节因子。 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，某些饲养层系在与人胚胎干细胞共培养中提供的支持较差，可归因于 sFRP-1 表达升高并释放到条件培养基中。

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.