Nerve growth factor-induced stimulation of alpha-aminoisobutyric acid uptake in PC12 cells: relationship to plasma membrane receptor occupancy

Characterization of two neuroblastoma cell lines expressing recombinant nerve growth factor receptors

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 of fos oncogene expression, and did not efficiently internalize NGF. LAN5 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 of fos oncogene, 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 of fos oncogene expression correlated with expression of high-affinity NGFRs, the putative second factor may also limit NGF responsiveness.

Neurotrophic activity in the central and peripheral nervous systems of the cat. Effects of injury

Neurotrophic activity for ciliary ganglion neurons in culture was found in both central and peripheral nervous system of the cat. The activity found in extracts of spinal cord supported the survival of 100% of the test neurons during 24 h and was characterized by a slope of -56 +/- 13 in the linear portion of the dose-response curve. Sciatic nerve extract supported the survival of only 60% of the test neurons; it dose-response curve had a slope of -20 +/- 4. Extracts of meninges, spinal rootlets, dorsal root ganglia and muscle supported 100% of the test neurons; two slopes were observed in their dose-response curves, which coincided with those of spinal cord and sciatic nerve dose-response curves. The two different slopes may correspond to two different active molecules, tentatively denominated I and II, having distinct distributions in the assayed tissues. In the spinal cord, both direct injury and deafferentation led to increases in neurotropic activity. In the peripheral nervous system, transections leading to death of dorsal root ganglion neurons or to degeneration of their axons were accompanied by decreases in activity II. Activity I in dorsal roots and dorsal root ganglia was unaffected by injury and may be associated with non-neuronal cells or extracellular matrix components.

Nerve growth factor does not activate Na+/H+ exchange in PC12 pheochromocytoma cells

We have reexamined the possible role of the Na+/H+ antiport in the cellular response by PC12 pheochromocytoma cells to nerve growth factor (NGF). In contrast to previous reports, we observe no activation of Na+/H+ exchange in these cells, using a very sensitive assay based on the measurement of cytoplasmic pH with dimethylfluorescein dextran (Rothenberg et al., J. Biol. Chem., 258:4883-4809, 1983). Our measurements indicate that the PC12 pheochromocytoma cells, under all conditions tested, show a high rate of Na+/H+ exchange. The discrepancy between these observations and previous experiments could be due to differences in cells in different laboratories, but also to changes in cell adhesion induced by NGF. We describe conditions where intracellular pH and rates of Na+ uptake can be measured reliably in PC12 cells with adequate controls for cell adhesion. We conclude that activation of Na+/H+ exchange is neither sufficient nor required for the differentiation of PC12 cells induced by NGF.