P75 NERVE GROWTH-FACTOR RECEPTOR MODULATES P140(TRKA) KINASE-ACTIVITY, BUT NOT LIGAND INTERNALIZATION, IN PC12 CELLS

The biological activity of nerve growth factor (NGF) has been shown to be mediated by the p140(trkA) receptor tyrosine kinase, while the rol e of the p75 NGF receptor (p75(NGFR)) is Still unresolved. Here we hav e investigated the relative contribution of p140(trkA) and p75(NGFR) t o early consequences of NGF binding: ligand internalization, p140(trkA ) autophosphorylation, and tyrosine phosphorylation of Shc, phospholip ase C-gamma-1 (PLC(gamma-1)), and extracellular signal-regulated kinas es (ERKs). It was found that NGF internalization was neither prevented by blocking p140(trkA) activity using the protein kinase inhibitors m ethylthioadenosine, staurosporine, and K-252a, nor by inhibiting NGF b inding to p75(NGFR) with antibodies. However, when NGF binding to p140 (trkA) was reduced by the use of a synthetic peptide corresponding to amino acids 36-53 of human p140(trkA), internalization of NGF was decr eased. Thus, at least in PC12 cells, internalization appears to requir e binding of NGF to p140(trkA), but occurs irrespective of p140(trkA) kinase activity and ligand occupancy of p75(NGFR). The NGF triple muta nt Lys-32/Lys-34/Glu-35 to Ala, which has been demonstrated to bind to p140(trkA), but not to p75(NGFR), induced tyrosine phosphorylation mo re rapidly than wild-type NGF. Likewise, NGF-induced tyrosine phosphor ylation was accelerated when NGF binding to p75(NGFR) was prevented wi th REX-IgG. These findings indicate that NGF binding by p75(NGFR) may modulate NGF-induced p140(trkA) kinase activity. (C) 1994 Wiley-Liss, Inc.