Liu Yan, Rubin Boris, Bodine Peter V N, Billiard Julia
Women's Health & Musculoskeletal Biology, Wyeth Research, Collegeville, Pennsylvania 19426, USA.
J Cell Biochem. 2008 Oct 1;105(2):497-502. doi: 10.1002/jcb.21848.
Wnts are secreted glycoproteins that control vital biological processes, including embryogenesis, organogenesis and tumorigenesis. Wnts are classified into several subfamilies depending on the signaling pathways they activate, with the canonical subfamily activating the Wnt/beta-catenin pathway and the non-canonical subfamily activating a variety of other pathways, including the Wnt/calcium signaling and the small GTPase/c-Jun NH2-terminal kinase pathway. Wnts bind to a membrane receptor Frizzled and a co-receptor, the low-density lipoprotein receptor related protein. More recently, both canonical and non-canonical Wnts were shown to bind the Ror2 receptor tyrosine kinase. Ror2 is an orphan receptor that plays crucial roles in skeletal morphogenesis and promotes osteoblast differentiation and bone formation. Here we examine the effects of a canonical Wnt3a and a non-canonical Wnt5a on the signaling of the Ror2 receptor. We demonstrate that even though both Wnt5a and Wnt3a bound Ror2, only Wnt5a induced Ror2 homo-dimerization and tyrosine phosphorylation in U2OS human osteoblastic cells. Furthermore, Wnt5a treatment also resulted in increased phosphorylation of the Ror2 substrate, 14-3-3beta scaffold protein, indicating that Wnt5a binding causes activation of the Ror2 signaling cascade. Functionally, Wnt5a recapitulated the Ror2 activation phenotype, enhancing bone formation in the mouse calvarial bone explant cultures and potentiating osteoblastic differentiation of human mesenchymal stem cells. The effect of Wnt5a on osteoblastic differentiation was largely abolished upon Ror2 down-regulation. Thus we show that Wnt5a activates the classical receptor tyrosine kinase signaling cascade through the Ror2 receptor in cells of osteoblastic origin.
Wnt 是分泌型糖蛋白，可控制重要的生物学过程，包括胚胎发生、器官发生和肿瘤发生。根据其激活的信号通路，Wnt 被分为几个亚家族，其中经典亚家族激活 Wnt/β-连环蛋白通路，非经典亚家族激活多种其他通路，包括 Wnt/钙信号通路和小 GTP 酶/c-Jun NH2 末端激酶通路。Wnt 与膜受体卷曲蛋白（Frizzled）和共受体低密度脂蛋白受体相关蛋白结合。最近，经典和非经典 Wnt 均被证明可与 Ror2 受体酪氨酸激酶结合。Ror2 是一种孤儿受体，在骨骼形态发生中起关键作用，并促进成骨细胞分化和骨形成。在此我们研究经典 Wnt3a 和非经典 Wnt5a 对 Ror2 受体信号传导的影响。我们证明，尽管 Wnt5a 和 Wnt3a 都能结合 Ror2，但只有 Wnt5a 在 U2OS 人成骨细胞中诱导 Ror2 同源二聚化和酪氨酸磷酸化。此外，Wnt5a 处理还导致 Ror2 底物 14-3-3β支架蛋白的磷酸化增加，表明 Wnt5a 结合导致 Ror2 信号级联的激活。在功能上，Wnt5a 重现了 Ror2 激活表型，增强了小鼠颅骨外植体培养中的骨形成，并增强了人间充质干细胞的成骨细胞分化。Ror2 下调后，Wnt5a 对成骨细胞分化的影响基本消除。因此，我们表明 Wnt5a 通过成骨细胞来源细胞中的 Ror2 受体激活经典受体酪氨酸激酶信号级联。
