Fuerer Christophe, Nostro M Cristina, Constam Daniel B
From the Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences (SV), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland and.
McEwen Centre for Regenerative Medicine, University Health Network, Toronto, Ontario M5G 1L7, Canada.
J Biol Chem. 2014 Jun 20;289(25):17854-71. doi: 10.1074/jbc.M114.550301. Epub 2014 May 5.
The TGFβ family member Nodal is central to control pluripotent stem cell fate, but its use as a stem cell differentiation factor is limited by low specific activity. During development, Nodal depends on growth and differentiation factor (Gdf)-1 and on the shared co-receptor Cryptic to specify visceral left-right axis asymmetry. We therefore asked whether the functionality of Nodal can be augmented by Gdf1. Because Nodal and Gdf1 coimmunoprecipitate each other, they were predicted to form heterodimers, possibly to facilitate diffusion or to increase the affinity for signaling receptors. Here, we report that Gdf1 suppresses an unexpected dependence of Nodal on serum proteins and that it is critically required for non-autonomous signaling in cells expressing Cryptic. Nodal, Gdf1, and their cleaved propeptides copurified as a heterodimeric low molecular weight complex that stimulated Activin receptor (Acvr) signaling far more potently than Nodal alone. Although heterodimerization with Gdf1 did not increase binding of Nodal to Fc fusions of co-receptors or Acvr extracellular domains, it was essential for soluble Acvr2 to inhibit Nodal signaling. This implies that Gdf1 potentiates Nodal activity by stabilizing a low molecular weight fraction that is susceptible to neutralization by soluble Acvr2. Finally, in differentiating human ES cells, endodermal markers were more efficiently induced by Nodal·Gdf1 than by Nodal, suggesting that Nodal·Gdf1 is an attractive new reagent to direct stem cell differentiation.
转化生长因子β（TGFβ）家族成员Nodal对于控制多能干细胞命运至关重要，但其作为干细胞分化因子的应用受到低比活性的限制。在发育过程中，Nodal依赖生长和分化因子（Gdf）-1以及共享的共受体Cryptic来确定内脏左右轴的不对称性。因此，我们询问Gdf1是否可以增强Nodal的功能。由于Nodal和Gdf1相互共免疫沉淀，预计它们会形成异二聚体，可能是为了促进扩散或增加对信号受体的亲和力。在这里，我们报告Gdf1抑制了Nodal对血清蛋白的意外依赖性，并且它对于表达Cryptic的细胞中的非自主信号传导至关重要。Nodal、Gdf1及其切割的前肽作为一种异二聚体低分子量复合物共纯化，该复合物刺激激活素受体（Acvr）信号传导的能力比单独的Nodal强得多。尽管与Gdf1异二聚化并没有增加Nodal与共受体或Acvr细胞外结构域的Fc融合蛋白的结合，但它对于可溶性Acvr2抑制Nodal信号传导至关重要。这意味着Gdf1通过稳定易被可溶性Acvr2中和的低分子量部分来增强Nodal活性。最后，在分化的人类胚胎干细胞中，与单独的Nodal相比，Nodal·Gdf1更有效地诱导了内胚层标记物，这表明Nodal·Gdf1是一种有吸引力的用于指导干细胞分化的新试剂。
