COLOCALIZATION OF LOW-AFFINITY AND HIGH-AFFINITY NGF RECEPTORS ON PC12 CELLS, C6 GLIOMA-CELLS AND DORSAL-ROOT GANGLION NEURONS

The biological responsiveness of neural cells to nerve growth factor (NGF) appears to require expression and ligand binding to both the low-affinity NGF receptor (LNGFR) and the proto-oncogene product trk, the latter being a receptor tyrosine kinase. Immunolocalization of the LNGFR and the high-affinity component of the NGF receptor, trk (HNGFR) was studied by electron microscopic morphometric analysis on cultured PC12 pheochromocytoma cells, C6 glioma cells and neonatal rat dorsal root ganglia neurons using a double immunogold labeling technique. Two receptor-specific antibodies, anti-LNGFR monoclonal antibody 192-IgG and a polyclonal antibody against the 14 carboxy-terminal amino acids of the Trk protein, were utilized in conjunction with immunoglobulin conjugated to colloidal gold particles of different sizes. All cells treated with NGF (50 ng/ml) displayed significant colocalization of LNGFR/HNGFR-like immunoreactivity. Gold particles associated with LNGFR (LNGFR-like immunoreactivity) were frequently seen near 2 or 3 (or more) particles delineating the HNGFR on all cell surfaces. Positive Trk-like immunoreactivity (HNGFR) thus seems to localize in close proximity to LNGFRs in at least these cell types.