BASIC FIBROBLAST GROWTH-FACTOR IS A NEUROTROPIC FACTOR IN GT1 GONADOTROPIN-RELEASING-HORMONE NEURONAL CELL-LINES

Basic fibroblast growth factor (bFGF) plays an important role in devel opment of the central nervous system and is neurotropic for a variety of neurons. In this study, we investigated whether bFGF is neurotropic for GT1 GnRH neuronal cell lines and if these cells express functiona l FGF receptors (FGFRs). The GT1 cell lines generated by genetically t argeted tumorigenesis display highly differentiated properties of GnRH neurons. Addition of 2 and 10 ng/ml bFGF increased neurite outgrowth of GT1-7 cells and resulted in a significant increase of GT1 cell surv ival in serum-free medium. However, bFGF had no effect on [H-3]thymidi ne incorporation at 24 or 48 h. RNase protection assays using riboprob es specific for murine FGFRs 1-3 showed that GT1 cells express FGFRs 1 and 3 but not 2. Occupancy of FGFRs with 10 ng/ml bFGF stimulated the sustained tyrosine phosphorylation of both the 42- and 44-kilodalton mitogen-activated protein kinases (MAPKs) for up to 6 h as shown by We stern blot analysis. In addition, phosphorylation of the MAPKs was ass ociated with enzyme activation as shown by an in-gel MAPK assay. GT1-1 and GT1-7 cells also express messenger RNA for bFGF, although the lev el of bioactive bFGF synthesized by GT1 cells appears suboptimal becau se GT1 cells can further respond to exogenously added bFGF. Thus, we h ave demonstrated that bFGF is a neurotropic factor in GT1 GnRh neurona l cell lines, raising the possibility that bFGF may play a role in the neurobiology of GnRH neurons.