Abstract
Monoclonal antibodies specific for neurofilament (NF) subunits or for vimentin filament (VF) protein were used to study nerve growth factor (NGF)-induced intermediate filament expression and organization in a rat pheochromocytoma cell line (PC12 cells). NGF induced increased amounts of NF subunits and VF protein, and they were, in part, differentially localized within PC12 cells. The relative expression of each of the NF subunits and of the VF protein was measured by an enzyme- linked immunosorbent assay which revealed that PC12 cells grown in the absence of NGF (PC12- cells) contained 3 times more VF than 68,000- dalton NF subunits and only barely detectable amounts of 150,000- and 200,000-dalton NF subunits. Exposure of these cells to NGF (PC12+ cells) increased the amount of 68,000-dalton NF subunits 8-fold, VF protein 3-fold, and 150,000- and 200,000-dalton NF subunits 2-fold. The ratio of VF to 68,000-dalton NF proteins in PC12- versus PC12+ cells decreased from 3.0 to 1.5. Both VF and 68,000-dalton NF subunits were arranged in juxtanuclear “ball-like” configurations and both were present in neurites of PC12+ cells. The distribution of 150,000- and 200,000-dalton NF subunits was diffuse with perinuclear stippling and only occasional, weakly fluorescent “balls.” After perturbation of the PC12 cell cytoskeleton, 68,000-dalton NF subunits and VF redistributed together and, thus, may exist as heteropolymers. Finally, the increased expression of NF and VF proteins was specific for NGF since they could not be induced by other hormones or “growth” factors. We conclude that PC12 cells constitute a model system for studies of NF and VF expression, assembly, and interactions.
