Shc1 cooperates with Frs2 and Shp2 to recruit Grb2 in FGF-induced lens development.

Abstract

Fibroblast growth factor (FGF) signaling elicits multiple downstream pathways, most notably the Ras/MAPK cascade facilitated by the adaptor protein Grb2. However, the mechanism by which Grb2 is recruited to the FGF signaling complex remains unresolved. Here we showed that genetic ablation of FGF signaling prevented lens induction by disrupting transcriptional regulation and actin cytoskeletal arrangements, which could be reproduced by deleting the juxtamembrane region of the FGF receptor and rescued by Kras activation. Conversely, mutations affecting the Frs2-binding site on the FGF receptor or the deletion of Frs2 and Shp2 primarily impact later stages of lens vesicle development involving lens fiber cell differentiation. Our study further revealed that the loss of Grb2 abolished MAPK signaling, resulting in a profound arrest of lens development. However, disrupting the Grb2 binding site on Shp2 or abrogating Shp2 phosphatase activity only modestly influenced FGF signaling, whereas mutating the presumed Shp2 dephosphorylation site on Grb2 did not impede MAPK signaling in lens development, indicating that Shp2 is only partially responsible for Grb2 recruitment. In contrast, we observed that FGF signaling is required for the phosphorylation of the Grb2-binding sites on Shc1 and the deletion of Shc1 exacerbates the lens vesicle defect caused by Frs2 and Shp2 deletion. These results reveal that Shc1 collaborates with Frs2 and Shp2 to target Grb2 in FGF signaling.