Abstract:In earlier studies, a 75,000‐dalton glycoprotein (gp75) has been identified as a component of both low‐ and high‐affinity nerve growth factor (NGF) receptors (NGFRs). Using an amphoteric expression vector, we have introduced the cDNA encoding the human gp75 into two neuroblastoma cell lines. SHEP is a human neuroblastoma cell line that lacks most neuronal characteristics and does not express NGFRs. The transformant line SHEP/NGFR expressed a single affinity class of NGF binding sites, did not display NGF‐induced up‐regulation offosoncogene expression, and did not efficiently internalize NGF. LANS is a neuroblastoma cell line with neuronal characteristics, including expression of neurofilament and display of short neurites. This cell line expresses a small number of high‐affinity NGFRs but no detectable low‐affinity sites. The transformant line LAN5/NGFR expressed both high‐ and low‐affinity NGFRs, displayed NGF‐induced up‐regulation offosoncogene, and efficiently internalized NGF. The number of high‐affinity NGF binding sites was nearly the same for LAN5 and LAN5/NGFR, a finding suggesting that there is a limiting number of some separately coded factor or subunit that is required for high‐affinity NGFRs. Because NGF induction offosoncogene expression correlated with expression of high‐affinity NGFRs, the putative second factor may al