Nerve growth factor in the nucleus: interaction with receptors on the nuclear membrane.

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Abstract
Cells of a continuous line of rat pheochromocytoma (PC12) were incubated with 125I-labeled .beta. nerve growth factor (.beta.NGF), and at given time intervals the cell nuclei were isolated by a procedure that used the detergent Triton X-100. NGF was detectable in the nucleus after 20 min and continued to accumulate in a linear fashion for several hours after the total binding to the cell had reached steady state. After 17 h at 37.degree. C, about 60% of the NGF bound to the cell was in the nucleus. NGF was not translocated to the nucleus at 4.degree. C. When nuclei were purified from PC12 cells and incubated with 125I-labeled .beta.NGF, specific binding sites were found. Binding was saturable and consistent with 2 sites: a high-affinity site with a Kd of 0.08 nM (.+-. 0.02 nM) and a lower-affinity site with a Kd of 9.0 nM (.+-. 2.0 nM). The receptors in the nucleus were shown to be localized to the nuclear membrane. Membrane-free chromatin did not bind NGF specifically. The translocation of NGF to the nucleus was accompanied by a commensurate decrease in the cell-surface binding capacity. In the nucleus the receptor capacities of both sites were increased when PC12 cells were grown in the presence of NGF.