Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Cell Signal. 2013 Jun;25(6):1468-75. doi: 10.1016/j.cellsig.2013.03.009. Epub 2013 Mar 19.
Frizzled receptors have long been thought to couple to G proteins but biochemical evidence supporting such an interaction has been lacking. Here we expressed mammalian Wnt-Frizzled fusion proteins in Saccharomyces cerevisiae and tested the receptors' ability to activate the yeast mitogen-activated protein kinase (MAPK) pathway via heterotrimeric G proteins. Our results show that Frizzled receptors can interact with Gαi, Gαq, and Gαs proteins, thus confirming that Frizzled functions as a G protein coupled receptor (GPCR). However, the activity level of Frizzled-mediated G protein signaling was much lower than that of a typical GPCR and, surprisingly, was highest when coupled to Gαs. The Frizzled/Gαs interaction was further established in vivo as Drosophila expressing a loss-of-function Gαs allele rescued the photoreceptor differentiation phenotype of Frizzled mutant flies. Together, these data point to an important role for Frizzled as a nontraditional GPCR that preferentially couples to Gαs heterotrimeric G proteins.
卷曲受体长期以来一直被认为与 G 蛋白偶联，但缺乏支持这种相互作用的生化证据。在这里，我们在酿酒酵母中表达了哺乳动物 Wnt-Frizzled 融合蛋白，并测试了受体通过异三聚体 G 蛋白激活酵母丝裂原活化蛋白激酶 (MAPK) 途径的能力。我们的结果表明，卷曲受体可以与 Gαi、Gαq 和 Gαs 蛋白相互作用，从而证实卷曲作为 G 蛋白偶联受体 (GPCR) 发挥作用。然而，卷曲介导的 G 蛋白信号转导的活性水平远低于典型的 GPCR，而且令人惊讶的是，与 Gαs 偶联时活性水平最高。在体内，Frizzled 与 Gαs 的相互作用进一步得到证实，因为表达功能丧失 Gαs 等位基因的果蝇挽救了 Frizzled 突变果蝇的光感受器分化表型。总之，这些数据表明卷曲作为一种非传统的 GPCR 发挥重要作用，其优先与 Gαs 异三聚体 G 蛋白偶联。
