Nature Biotechnology
15, 768 - 771 (1997)
doi:10.1038/nbt0897-768
Direct demonstration of MuSK involvement in acetylcholine receptor clustering through identification of agonist ScFvMing-Hong Xie1, Jean Yuan1, Camellia Adams1
& Austin Gurney*
1The Department of Molecular Biology, Genentech, Inc., 460 Pt. San Bruno Blvd. So., San Francisco, CA 94080.
*e-mail: nico@gene.com. MuSK is a tyrosine kinase localized to the postsynaptic surface of the neuromuscular junction. We have searched for modulators of MuSK function using a library of human single chain variable region antibodies (scFv) that can be displayed on M13 phage or expressed as soluble protein. A panel of 21 independent MuSK-specific scFv, identified in a screen for binding to MuSK-Fc immunoadhesin, were examined for ability to induce proliferation in a factor dependent cell line (Ba/F3) through a chimeric receptor, MuSK-Mpl. Four of the scFv induced a proliferative response, suggesting an ability to induce dimerization of MuSK. These scFv were also able to induce tyrosine phosphorylation of full-length MuSK and retained this ability when re-engineered to be expressed as authentic (and dimeric) human IgG molecules. Addition of agonist scFv to a cultured myotube cell line induced AChR clustering and tyrosine phosphorylation. These results provide direct evidence that MuSK activation is capable of triggering a key event in neuromuscular junction formation and further demonstrate that large libraries of phage-displayed scFv provide a robust method for generating highly specific agonist agents.
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