FGF signal transduction in PC12 cells: comparison of the responses induced by endogenous and chimeric receptors.

Rat phaeochromocytoma (PC12) cells respond to many growth factors and produce different phenotypes, including neurite outgrowth. Receptor tyrosine kinases (RTK), which activate multiple signalling pathways in response to ligand binding, initiate many of these. One such family of receptors, the fibroblast growth factor receptor (FGFR), has four different members and expresses at least three of these in PC12 cells. A chimeric tyrosine kinase receptor, consisting of the extracellular domain of human plasma-derived growth factor receptor-beta (hPDGFR-beta) and the transmembrane and intracellular region of FGFR1 (designated PFR1), was constructed and was stably transfected into cloned PC12 cell lines. This chimera, which can be activated without stimulating endogenous RTK including other FGFR, induces neurite outgrowth in a PDGF-dependent manner. By altering the protocol for preparing the retroviral vectors, cells with a wide range of expression levels can be obtained. The amount of these chimeric receptors seems to correlate with the time and the intensity of response as observed in neurite outgrowth assays. Analysis of proteins implicated in FGFR1 signalling indicates that upon stimulation, a tyrosine phosphorylated protein designated FRS2 associates with SOS, Grb2 and the receptor. The chimeric receptor appears entirely similar to that observed for the stimulation of native PC12 cells with FGF2. These results support the view that FRS2 is the dominant FGFR1 signalling entity in PC12 cells.