Fbxo45 Binds SPRY Motifs in the Extracellular Domain of N-Cadherin and Regulates Neuron Migration during Brain Development

ABSTRACT

Several events during the normal development of the mammalian neocortex depend on N-cadherin, including the radial migration of immature projection neurons into the cortical plate. Remarkably, radial migration requires the N-cadherin extracellular domain but not N-cadherin-dependent homophilic cell-cell adhesion, suggesting that other N-cadherin-binding proteins may be involved. We used proximity ligation and affinity purification proteomics to identify N-cadherin-binding proteins. Both screens detected MycBP2 and SPRY domain protein Fbxo45, two components of an intracellular E3 ubiquitin ligase. Fbxo45 appears to be secreted by a nonclassical mechanism, not involving a signal peptide and not requiring transport from the endoplasmic reticulum to the Golgi apparatus. Fbxo45 binding requires N-cadherin SPRY motifs that are not involved in cell-cell adhesion. SPRY mutant N-cadherin does not support radial migration in vivo. Radial migration was similarly inhibited when Fbxo45 expression was suppressed. The results suggest that projection neuron migration requires both Fbxo45 and the binding of Fbxo45 or another protein to SPRY motifs in the extracellular domain of N-cadherin.

KEYWORDS:

• F-box proteins
• cadherin signaling
• cell migration
• neural development

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SUPPLEMENTAL MATERIAL

Supplemental material is available online only.

ACKNOWLEDGMENTS

We are very grateful to Barry Gumbiner and Kojo S. J. Elenitoba-Johnson for helpful discussions and for sharing reagents. We thank the staff of Fred Hutch Shared Resources, especially Phil Gafken, Yuko Ogata, David McDonald, Lena Schroeder, and Julio Vazquez, for proteomics and imaging; Alexander (Sasha) Strait for technical assistance; and members of the Cooper laboratory for encouragement.

This work was supported by grants R01 NS080194 and GM109463 from the U.S. Public Health Service and grants J.0129.15, J.0179.16, and T.0243.18 from the FNRS. FHCRC imaging and proteomics laboratories are supported by grant P01 CA015704 from the U.S. Public Health Service.

Y.N., E.C.-J., E.K., H.C., Y.J., and J.A.C. performed experiments. Y.N. and J.A.C. wrote and revised the manuscript with input from Y.J.