TSPAN12 Is a Norrin Co-receptor that Amplifies Frizzled4 Ligand Selectivity and Signaling

Publication date: 27 June 2017
Source:Cell Reports, Volume 19, Issue 13
Author(s): Maria B. Lai, Chi Zhang, Jianli Shi, Verity Johnson, Lavan Khandan, John McVey, Michael W. Klymkowsky, Zhe Chen, Harald J. Junge
Accessory proteins in Frizzled (FZD) receptor complexes are thought to determine ligand selectivity and signaling amplitude. Genetic evidence indicates that specific combinations of accessory proteins and ligands mediate vascular β-catenin signaling in different CNS structures. In the retina, the tetraspanin TSPAN12 and the ligand norrin (NDP) mediate angiogenesis, and both genes are linked to familial exudative vitreoretinopathy (FEVR), yet the molecular function of TSPAN12 remains poorly understood. Here, we report that TSPAN12 is an essential component of the NDP receptor complex and interacts with FZD4 and NDP via its extracellular loops, consistent with an action as co-receptor that enhances FZD4 ligand selectivity for NDP. FEVR-linked mutations in TSPAN12 prevent the incorporation of TSPAN12 into the NDP receptor complex. In vitro and in Xenopus embryos, TSPAN12 alleviates defects of FZD4 M105V, a mutation that destabilizes the NDP/FZD4 interaction. This study sheds light on the poorly understood function of accessory proteins in FZD signaling.

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Teaser

Lai et al. study the role of tetraspanin12 in the norrin receptor complex, which mediates canonical frizzled4 signaling in retinal angiogenesis and is involved in familial exudative vitreoretinopathy. Using mutational approaches, cell-based assays, and in vivo experiments, the authors show that tetraspanin12 stabilizes norrin/frizzled4 complexes and increases ligand selectivity of frizzled4.


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