RET signaling

RET contains a cadherin-related motif and a cysteine-rich domain in the extracellular domain. It is the receptor for members of the glial cell-derived neurotrophic factor (GDNF) family of ligands, GDNF, neurturin (NRTN), artemin (ARTN), and persephin (PSPN), which form a family of neurotrophic factors. To stimulate RET, these ligands need a glycosylphosphatidylinositol (GPI)-anchored co-receptor, collectively termed GDNF family receptor-alpha (GFRA). The four members of this family have different, overlapping ligand preferences. GFRA1, GFRA2, GFRA3, and GFRA4 preferentially bind GDNF, NRTN, ARTN and PSPN, respectively (Jing et al. 1996, 1997, Creedon et al. 1997, Baloh et al. 1997, 1998, Masure et al. 2000). The GFRA co-receptor can come from the same cell as RET, or from a different cell. When the co-receptor is produced by the same cell as RET, it is termed cis signaling. When the co-receptor is produced by another cell, it is termed trans signaling. Cis and trans activation has been proposed to diversify RET signaling, either by recruiting different downstream effectors or by changing the kinetics or efficacy of kinase activation. Whether cis and trans signaling has significant differences in vivo is unresolved. Different GDNF family members could activate similar downstream signaling pathways since all GFRAs bind to and activate the same tyrosine kinase and induce coordinated phosphorylation of the same four RET tyrosines (Tyr905, Tyr1015, Tyr1062, and Tyr1096) with similar kinetics. However the exact RET signaling pathways in different types of cells and neurons remain to be determined.