Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.
PLoS One. 2011 Apr 26;6(4):e19279. doi: 10.1371/journal.pone.0019279.
While the role of canonical (β-catenin-mediated) Wnt signaling in hematolymphopoiesis has been studied extensively, little is known of the potential importance of non-canonical Wnt signals in hematopoietic cells. Wnt4 is one of the Wnt proteins that can elicit non-canonical pathways. We have previously shown that retroviral overexpression of Wnt4 by hematopoietic cells increased thymic cellularity as well as the frequency of early thymic progenitors and bone marrow hematopoietic progenitor cells (HPCs). However, the molecular pathways responsible for its effect in HPCs are not known.
METHODOLOGY/PRINCIPAL FINDINGS: Here we report that Wnt4 stimulation resulted in the activation of the small GTPase Rac1 as well as Jnk kinases in an HPC cell line. Jnk activity was necessary, while β-catenin was dispensable, for the Wnt4-mediated expansion of primary fetal liver HPCs in culture. Furthermore, Jnk2-deficient and Wnt4 hemizygous mice presented lower numbers of HPCs in their bone marrow, and Jnk2-deficient HPCs showed increased rates of apoptosis. Wnt4 also improved HPC activity in a competitive reconstitution model in a cell-autonomous, Jnk2-dependent manner. Lastly, we identified Fz6 as a receptor for Wnt4 in immature HPCs and showed that the absence of Wnt4 led to a decreased expression of four polarity complex genes.
CONCLUSIONS/SIGNIFICANCE: Our results establish a functional role for non-canonical Wnt signaling in hematopoiesis through a pathway involving Wnt4, Fz6, Rac1 and Jnk kinases.
虽然经典（β-连环蛋白介导的）Wnt 信号在造血中的作用已被广泛研究，但对于非经典 Wnt 信号在造血细胞中的潜在重要性知之甚少。Wnt4 是能够引发非经典途径的 Wnt 蛋白之一。我们之前已经表明，通过造血细胞过表达逆转录病毒 Wnt4 可增加胸腺细胞的细胞数量以及早期胸腺祖细胞和骨髓造血祖细胞（HPC）的频率。然而，其在 HPC 中产生作用的分子途径尚不清楚。
方法/主要发现：在这里，我们报告说 Wnt4 刺激导致小 GTPase Rac1 以及 HPC 细胞系中的 Jnk 激酶的激活。Jnk 活性对于 Wnt4 介导的原代胎肝 HPC 在培养中的扩增是必需的，而β-连环蛋白是可有可无的。此外，Jnk2 缺陷型和 Wnt4 半合子小鼠的骨髓中 HPC 数量较少，Jnk2 缺陷型 HPC 的凋亡率增加。Wnt4 还以细胞自主、Jnk2 依赖的方式改善了竞争性重建模型中的 HPC 活性。最后，我们确定了 Fz6 作为不成熟 HPC 中 Wnt4 的受体，并表明 Wnt4 的缺失导致四个极性复合物基因的表达降低。
结论/意义：我们的研究结果确立了非经典 Wnt 信号在造血中的功能作用，该途径涉及 Wnt4、Fz6、Rac1 和 Jnk 激酶。
