NERVE GROWTH-FACTOR CHANGES G-PROTEIN LEVELS AND LOCALIZATION IN PC12CELLS

Growth cones at the growing tips of developing neurites contain the ma chinery to transmit information from receptors to a variety of intrace llular enzymes and ion channels. In order to understand how signals ar e transmitted across the membrane, we asked whether the multiplicity o f signalling pathways in the growth cone is reflected by the diversity of G proteins found in this organelle. Our immunohistochemical analys is indicated that growth cones of differentiated PC12 cells contain at least 4 alpha G protein subunits, 3 that are pertussis toxin substrat es (alpha(o), alpha(i-1), alpha(i-2)) and 1 that is not (alpha(q)). In addition to localization in the neurites and growth cones, alpha(o), alpha(i-1), alpha(i-2), and alpha(q) were detected in intracellular pe rinuclear structures. We also analyzed the temporal change in G protei ns in PC12 cells differentiated by treatment with nerve growth factor (NGF). Time course experiments have shown that alpha(o) and beta prote ins coordinately increase after 2 days of treatment with NGF, reach a maximum at 4 days, and remain elevated. In contrast to alpha(o), alpha (i-2) reached a peak at 4 days, then declined to almost the basal leve l by day 7 of treatment with NGF. These data indicated that the levels of alpha(o), alpha(i-2), and beta are differentially regulated during NGF-induced neuronal differentiation in PC12 cells. The alpha(o) prot ein was highly concentrated at the tips of the growth cones before the cellular level of alpha(o), had increased appreciably, suggesting tha t the alpha subunits are translocated during the first stage of neurit e development. In addition, not every neural process has the same high level of alpha(o), suggesting that G proteins may help define the spe cialized functions of particular neurites within a single cell.