Aluminum Alters the Electrophoretic Properties of Neurofilament Proteins: Role of Phosphorylation State

Exposure of each of the three neurofilament proteins (NFPs) to AlCl 3 resulted in their failure to migrate into sodium dodecyl sulfate (SDS)‐containing gels. This effect was dependent on length of incubation (minimum, 2 h) and AlCl 3 concentrations (minimum, 50 μ M ) and was not reversed by 20% SDS, 6 M urea, freeze‐thawing, boiling, or extensive dialysis. The migration of vimentin and glial fibrillary acidic protein was not affected by AlCl 3 . The high‐molecular‐weight neurofilament subunit (NF‐H) entered SDS‐containing gels after exposure to aluminum lactate but migrated aberrantly as a long high‐molecular‐weight streak. Migration of the 160‐kDa α‐chymotryptic cleavage product of NF‐H, which contains the higher phosphorylated tail domain, was also prevented from migrating into SDS‐containing gels by AlCl 3 . Dephosphorylation of NF‐H and the middle‐molecular‐weight neurofilament subunit (NF‐M) eliminated these effects on gel migration. EDTA, EGTA, MgCl 2 , CaCl 2 , or FeCl 3 had no effect on NF‐H or NF‐M migration; furthermore, preincubation with, or simultaneous exposure to, CaCl 2 or FeCl 3 did not alter the effect of AlCl 3 . One interpretation of these results is that Al 3+ interacts with phosphate groups on extensively phosphorylated C‐terminal sidearms of NFPs, resulting in intermolecular cross‐linking. These findings demonstrate a direct effect of aluminum on NFPs and provide a possible mechanism for neurofilament accumulation in perikarya during aluminum intoxication.