GGA3-mediated recycling of the RET receptor tyrosine kinase contributes to cell migration and invasion.

The RET receptor tyrosine kinase plays important roles in regulating cellular proliferation, migration, and survival in the normal development of neural crest derived tissues. However, aberrant activation of RET, through oncogenic mutations or overexpression, can contribute to tumourigenesis, regional invasion, and metastasis of several human cancers. RET is expressed as two main isoforms with unique C-terminal sequences that differ in protein interactions and subcellular trafficking in response to RET activation, and which also have distinct oncogenic potentials. The long isoform, termed RET51, is internalized from the membrane in response to stimulation by its ligand, GDNF, but is known to recycle back to the surface via RAB11 endosomes. However, the mechanisms regulating this process and its cellular effects have not been defined. Here, we show that recycling of RET51 requires a multicomponent complex that includes the endosomal-sorting protein GGA3, which mediates GDNF-dependent slow recycling of RET51 receptors to the plasma membrane. Our data show that the GRB2 adapter associates with RET51 through interactions with its C-terminal sequences, facilitating recruitment of active ARF6 and GGA3 interaction, and that depletion of GGA3 or ARF6 reduced RET51 recycling. Further, GGA3 knockdown accelerated RET51 degradation and also attenuated RET-mediated AKT activation. Finally, we showed that recycling of RET51 to the cell surface through association with GGA3 and ARF6 contributes to RET51-dependent cell motility, migration, and invasion. Our data establish RET recycling as a mechanism coordinating location and duration of RET signals in order to direct cell movement and invasion.