A specific isoform of glial cell line-derived neurotrophic factor family receptor alpha 1 regulates RhoA expression and glioma cell migration.

摘要

Malignant gliomas are highly invasive neuroepithelial tumors where the tendency to invade and migrate away from the primary tumor mass is thought to be a leading cause of tumor recurrence and treatment failures. Autocrine signals produced by secreted factors that signal through receptors on the tumor are known to contribute to the invasiveness. Glial cell line-derived neurotrophic factor and GDNF family receptor alpha 1 (GFRalpha1) are over-expressed in human gliomas. We have previously reported that human gliomas express high levels of GFRalpha1b, an alternatively spliced isoform of GFRalpha1. However, the functional significance of GFRalpha1b in glioma behaviors is currently unknown. In this study, we have designed isoform-specific small-interfering RNA to knockdown the highly homologous GFRalpha1a or GFRalpha1b isoform efficiently in malignant C6 glioma cells. Unexpectedly, the knockdown of GFRalpha1b but not GFRalpha1a induced cell elongation and inhibited C6 cell migration and invasion in vitro. In addition, GFRalpha1b was found to regulate the expression of RhoA small GTPase, which was required for migration of C6 cells. The decreases in RhoA expression and cell migration after GFRalpha1b knockdown were attenuated by small-interfering RNA -resistant GFRalpha1b but not GFRalpha1a, further demonstrating the specific role of GFRalpha1b in glioma migration. Interestingly, the knockdown of NCAM but not receptor tyrosine kinase Ret resulted in the reduction of RhoA expression and C6 cell migration. Taken together, these unanticipated results indicate that GFRalpha1b is involved in glioma migration through glial cell line-derived neurotrophic factor -GFRalpha1b-NCAM signaling complex and modulation of RhoA expression.