GDNF-induced cell signaling and neurite outgrowths are differentially mediated by GFRalpha1 isoforms

Glial cell line-derived neurotrophic factor (GDNF) transduces signal and promotes neurite outgrowths in diverse neurons through the interactions of GDNF family receptor alpha 1 (GFRα1) and other co-receptors including Ret receptor tyrosine kinase and NCAM. GFRα1 is alternatively spliced into two isoforms, GFRα1a and GFRα1b, with five amino acids difference. In this study, we found that both GFRα1a and GFRα1b were expressed in various human tissues. Interestingly, when stimulated with GDNF, GFRα1a but not GFRα1b promoted neurite outgrowth in neuroblastoma cells through the activations of ERK1/2, Rac1 and Cdc42. Remarkably, in cells co-expressing GFRα1a and GFRα1b, GDNF inhibited neurite outgrowths. The inhibitory activity of GFRα1b was dependent on RhoA and ROCK activation. Furthermore, GFRα1b but not GFRα1a activated Rho and various ROCK downstream effectors LIMK1/2, cofilin and MLC2. This study demonstrates the hitherto unrecognized roles of GFRα1 isoforms in the activation of distinct signaling pathways and in neurite outgrowths.