Nerve growth factor changes G protein levels and localization in PC12 cells

Abstract

Growth cones at the growing tips of developing neurites contain the machinery to transmit information from receptors to a variety of intracellular enzymes and ion channels. In order to understand how signals are transmitted across the membrane, we asked whether the multiplicity of signalling pathways in the growth cone is reflected by the diversity of G proteins found in this organelle. Our immunohistochemical analysis indicated that growth cones of differentiated PC12 cells contain at least 4 α G protein subunits, 3 that are pertussis toxin substrates (α₀, α_i−1, α_i−2) and 1 that is not (α_q). In addition to localization in the neurites and growth cones, α₀, α_i−1, α_i−2, and α_q were detected in intracellular perinuclear structures. We also analyzed the temporal change in G proteins in PC12 cells differentiated by treatment with nerve growth factor (NGF). Time course experiments have shown that α₀ and β proteins coordinately increase after 2 days of treatment with NGF, reach a maximum at 4 days, and remain elevated. In contrast to α₀, α_i−2 reached a peak at 4 days, then declined to almost the basal level by day 7 of treatment with NGF. These data indicated that the levels of α₀, α_i−2, and β are differentially regulated during NGF‐induced neuronal differentiation in PC12 cells. The α₀ protein was highly concentrated at the tips of the growth cones before the cellular level of α₀ had increased appreciably, suggesting that the α subunits are translocated during the first stage of neurite development. In addition, not every neural process has the same high level of α₀, suggesting that G proteins may help define the specialized functions of particular neurites within a single cell.