Lefty Blocks a Subset of TGFβ Signals by Antagonizing EGF-CFC Coreceptors

Abstract

Members of the EGF-CFC family play essential roles in embryonic development and have been implicated in tumorigenesis. The TGFβ signals Nodal and Vg1/GDF1, but not Activin, require EGF-CFC coreceptors to activate Activin receptors. We report that the TGFβ signaling antagonist Lefty also acts through an EGF-CFC-dependent mechanism. Lefty inhibits Nodal and Vg1 signaling, but not Activin signaling. Lefty genetically interacts with EGF-CFC proteins and competes with Nodal for binding to these coreceptors. Chimeras between Activin and Nodal or Vg1 identify a 14 amino acid region that confers independence from EGF-CFC coreceptors and resistance to Lefty. These results indicate that coreceptors are targets for both TGFβ agonists and antagonists and suggest that subtle sequence variations in TGFβ signals result in greater ligand diversity.

Xenopus Lefty requires proprotein cleavage but not N‐linked glycosylation to inhibit nodal signaling

“…Xlefty L was the only isoform detected, however, when produced from embryonic cells and seems to be the inhibitory isoform in mesoderm induction assays. These findings lead to the conclusion that future biochemical experiments should be sure to employ the Xlefty L isoform in, for example, determining which region(s) of Xlefty binds to either the Nodal ligand or xCR1-3 to antagonize Nodal signaling (Chen and Shen, 2004;Cheng et al, 2004;Tanegashima et al, 2004). Additionally, determining the binding constants for the interaction of Xlefty L with xCR1-3 or Xnr ligands, by producing stable Xlefty L from an Xlefty mcs2 construct, may determine the level to which each mechanism contributes to the antagonism of Nodal signaling.…”

“…In P19 mouse embryonic carcinoma cells, however, human Lefty A proprotein has been reported to activate the MAPK pathway (Ulloa et al, 2001). Mechanistically, this result might be explained by the fact that Lefty molecules have been shown to associate physically with EGF-CFC family members (Chen and Shen, 2004;Cheng et al, 2004;Tanegashima et al, 2004) and that overexpression of FRL1/xCR1 in Xenopus tissues can activate MAPK (Yabe et al, 2003;Yokota et al, 2003). Thus, Xlefty engagement of EGF-CFC co-receptors might lead to MAPK activation.…”

“…Lefty, a divergent member of the TGF␤ family whose transcription is directly regulated by Nodal signaling, is one of the principal extracellular feedback inhibitors of Nodal signaling (Meno et al, 1996(Meno et al, , 1999Thisse and Thisse, 1999;Cheng et al, 2000;Tanegashima et al, 2000;Branford and Yost, 2002;Cha et al, 2006). The current understanding is that Lefty antagonizes Nodal signaling by binding to either the EGF-CFC cofactor directly, or by physically interacting with the Nodal ligand, thereby blocking Nodal-receptor interaction and inhibiting downstream signal transduction (Chen and Shen, 2004;Cheng et al, 2004;Tanegashima et al, 2004).…”

Activin/Nodal signalling before implantation: setting the stage for embryo patterning

“…They inhibit Nodal signalling by interacting with Nodal or with Cripto. Because Activin signals in a Cripto-independent fashion, it is not sensitive to inhibition by Lefty [14]. Activin is however antagonized by another secreted molecule, called Follistatin.…”

Antagonistic interactions in the zebrafish midline prior to the emergence of asymmetric gene expression are important for left–right patterning

“…Nodal is a transforming growth factor-beta (TGF-b) superfamily member that signals through serine/threonine kinase receptors to phosphorylate Smad2 and Smad3 (reviewed in [6,7]). This requires EGF-CFC proteins, such as that encoded by the zebrafish gene oneeyed pinhead (oep), which act as co-receptors for Nodal ligands [8][9][10][11]. Smad2 and Smad3 then interact with the co-Smad, Smad4, as well as transcription factors, such as FoxHI, to induce transcription of downstream targets [12][13][14][15][16][17][18].…”