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 LNG FR and the high-affinity component of the NGF receptor, trk (HNGFR) wa s studied by electron microscopic morphometric analysis on cultured PC 12 pheochromocytoma cells, C6 glioma cells and neonatal rat dorsal roo t ganglia neurons using a double immunogold labeling technique. Two re ceptor-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 conj ugated to colloidal gold particles of different sizes. All cells treat ed with NGF (50 ng/ml) displayed significant colocalization of LNGFR/H NGFR-like immunoreactivity. Gold particles associated with LNGFR (LNGF R-like immunoreactivity) were frequently seen near 2 to 3 (or more) pa rticles delineating the HNGFR on ail cell surfaces. Positive Trk-like immunoreactivity (HNGFR) thus seems to localize in close proximity to LNGFRs in at least these cell types.