Glial cell line-derived neurotrophic factor and neurturin inhibit neurite outgrowth and activate RhoA through GFRα2b, an alternatively spliced isoform of GFRα2

Abstract

The glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) belong to a structurally related family of neurotrophic factors. NTN exerts its effect through a multicomponent receptor system consisting of the GDNF family receptor α2 (GFRα2), RET, and/or NCAM (neural cell adhesion molecule). GFRα2 is alternatively spliced into at least three isoforms (GFRα2a, GFRα2b, and GFRα2c). It is currently unknown whether these isoforms share similar functional and biochemical properties. Using highly specific and sensitive quantitative real-time PCR, these isoforms were found to be expressed at comparable levels in various regions of the human brain. When stimulated with GDNF and NTN, both GFRα2a and GFRα2c, but not GFRα2b, promoted neurite outgrowth in transfected Neuro2A cells. These isoforms showed ligand selectivity in MAPK (mitogen-activated protein kinase) [ERK1/2 (extracellular signal-regulated kinase 1/2)] and Akt signaling. In addition, the GFRα2 isoforms regulated different early-response genes when stimulated with GDNF or NTN. In coexpression studies, GFRα2b was found to inhibit ligand-induced neurite outgrowth by GFRα2a and GFRα2c. Stimulation of GFRα2b also inhibited the neurite outgrowth induced by GFRα1a, another member of the GFRα. Furthermore, activation of GFRα2b inhibited neurite outgrowth induced by retinoic acid and activated RhoA. Together, these data suggest a novel paradigm for the regulation of growth factor signaling and neurite outgrowth via an inhibitory splice variant of the receptor. Thus, depending on the expressions of specific GFRα2 receptor spliced isoforms, GDNF and NTN may promote or inhibit neurite outgrowth through the multi-component receptor complex. Copyright © 2007 Society for Neuroscience.