Aluminum alters the electrophoretic properties of neurofilament proteins: role of phosphorylation state.
Exposure of each of the three neurofilament proteins (NFPs) to AlCl3 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 AlCl3 concentrations (minimum, 50 microM) 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 AlCl3. 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 alpha-chymotryptic cleavage product of NF-H, which contains the higher phosphorylated tail domain, was also prevented from migrating into SDS-containing gels by AlCl3. Dephosphorylation of NF-H and the middle-molecular-weight neurofilament subunit (NF-M) eliminated these effects on gel migration. EDTA, EGTA, MgCl2, CaCl2, or FeCl3 had no effect on NF-H or NF-M migration; furthermore, preincubation with, or simultaneous exposure to, CaCl2 or FeCl3 did not alter the effect of AlCl3. One interpretation of these results is that Al3+ 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.
Shea
T B
TB
Laboratory for Cellular and Developmental Neurobiology, Mailman Research Center, McLean Hospital, Belmont 02178.
Beermann
M L
ML
Nixon
R A
RA
D000535:Aluminum / Q000494:pharmacology*; D000077410:Aluminum Chloride; D017607:Aluminum Compounds; D000818:Animals; D002712:Chlorides / Q000494:pharmacology*; D002918:Chymotrypsin / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D016900:Neurofilament Proteins / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation
D017607:Aluminum Compounds; D002712:Chlorides; D016900:Neurofilament Proteins; C044882:neurofilament protein L; C051774:neurofilament protein H; C061195:neurofilament protein M; D000077410:Aluminum Chloride; D000535:Aluminum; D002918:Chymotrypsin