Human glial cell line-derived neurotrophic factor receptor α4 is the receptor for persephin and is predominantly expressed in normal and malignant thyroid medullary cells

Glial cell line-derived neurotrophic factor (GDNF) family ligands signal through receptor complex consisting of a glycosylphosphatidylinositol-linked GDNF family receptor (GFR) ru subunit and the transmembrane receptor tyrosine kinase RET. The inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2), associated with different mutations in RET, is characterized by medullary thyroid carcinoma. GDNF signals via GFR alpha1, neurturin via GFR alpha2, artemin via GFR alpha3, whereas the mammalian GFR alpha: receptor for persephin (PSPN) is unknown. Here we characterize the human GFR alpha4 as the ligand-binding subunit required together with BET for PSPN signaling. Human and mouse GFR alpha4 lack the first Cys-rich domain characteristic of other GFRa: receptors. Unlabeled PSPN displaces I-125-PSPN from GFRA4-transfected cells, which express endogenous Ret. PSPN can be specifically cross-linked to mammalian GFR alpha4 and Ret, and is able to promote autophosphorylation of Ret in GFRA4-transfected cells. PSPN, but not other GDNF family ligands, promotes the survival of cultured sympathetic neurons microinjected with GFRA4. We identified different splice forms of human GFRA4 mRNA encoding for two glycosylphosphatidylinositol-linked and one putative soluble isoform that were predominantly expressed in the thyroid gland, Overlapping expression of RET and GFRA4 but not other GFRA mRNAs in normal and malignant thyroid medullary cells suggests that GFR alpha4 may restrict the MEN2 syndrome to these cells.