ALUMINUM TREATMENT OF INTACT NEUROBLASTOMA-CELLS ALTERS NEUROFILAMENTSUBUNIT PHOSPHORYLATION, SOLUBILITY, AND PROTEOLYSIS

Addition of 400 mu M AlCl3 to the culture medium for 72 h has been pre viously shown to induce perikaryal whorls of intermediate-sized filame nts in intact mouse NB2a/d1 neuroblastoma cells. Immunoblot analyses d emonstrated that in vivo treatment of cells with aluminum induced the de novo appearance of extensively phosphorylated NF-H isoforms in cyto skeletons of undifferentiated cells and increased levels of these isof orms in differentiated cells. Neurofilament subunits isolated from int act cells treated with aluminum were resistant to dephosphorylation in vitro by alkaline phosphatase and to in vitro degradation by endogeno us calcium-dependent protease(s). These alterations were accompanied b y a greater tendency of neurofilaments to form insoluble aggregates af ter isolation. These findings demonstrate direct effects of aluminum o n neurofilament subunits within intact neuronal cells similar to those previously demonstrated following in vitro exposure of isolated neuro filaments to aluminum.