Regulation of TGF-β superfamily signaling by two separable domains of glypican LON-2 inC. elegans

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Regulated intercellular signaling is critical for the normal development and maintenance of multicellular organisms. Glypicans have been shown to regulate signaling by TGF-βs, hedgehogs and Wnts in several cellular contexts. Glypicans comprise a conserved family of heparan sulfated, glycosylphosphatidylinositol (GPI)-linked extracellular proteins. The structural complexity of glypicans may underlie their functional complexity. In a recent study,31we built on previous findings that one of the twoC. elegansglypicans, LON-2, specifically inhibits signaling by the TGF-β super-family member DBL-1. We tested the functional requirements of LON-2 protein core components and post-translational modifications for LON-2 activity. We provide the first evidence that two parts of a glypican can independently regulate TGF-β superfamily signaling in vivo: the N-terminal furin protease product and a C-terminal region containing heparan sulfate attachment sites. Furthermore, we show a protein-protein interaction motif is crucial for LON-2 activity in the N-terminal protein core, suggesting that LON-2 acts by serving as a scaffold for DBL-1 and an RGD-binding protein. In addition, we demonstrate specificity of glypican function by showingC. elegansGPN-1 does not functionally substitute for LON-2. This work reveals a molecular foundation for understanding the complexity and specificity of glypican function.

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