Assembly of type IV neuronal intermediate filaments in nonneuronal cells in the absence of preexisting cytoplasmic intermediate filaments.
We report here on the in vivo assembly of alpha-internexin, a type IV neuronal intermediate filament protein, in transfected cultured cells, comparing its assembly properties with those of the neurofilament triplet proteins (NF-L, NF-M, and NF-H). Like the neurofilament triplet proteins, alpha-internexin coassembles with vimentin into filaments. To study the assembly characteristics of these proteins in the absence of a preexisting filament network, transient transfection experiments were performed with a non-neuronal cell line lacking cytoplasmic intermediate filaments. The results showed that only alpha-internexin was able to self-assemble into extensive filamentous networks. In contrast, the neurofilament triplet proteins were incapable of homopolymeric assembly into filamentous arrays in vivo. NF-L coassembled with either NF-M or NF-H into filamentous structures in the transfected cells, but NF-M could not form filaments with NF-H. alpha-internexin could coassemble with each of the neurofilament triplet proteins in the transfected cells to form filaments. When all but 2 and 10 amino acid residues were removed from the tail domains of NF-L and NF-M, respectively, the resulting NF-L and NF-M deletion mutants retained the ability to coassemble with alpha-internexin into filamentous networks. These mutants were also capable of forming filaments with other wild-type neurofilament triplet protein subunits. These results suggest that the tail domains of NF-L and NF-M are dispensable for normal coassembly of each of these proteins with other type IV intermediate filament proteins to form filaments.
Ching
G Y
GY
Department of Pathology, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Liem
R K
RK
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism*; D007382:Intermediate Filaments / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D016900:Neurofilament Proteins / Q000737:chemistry / Q000378:metabolism*; D009474:Neurons / Q000737:chemistry / Q000378:metabolism; D014162:Transfection; D014746:Vimentin / Q000378:metabolism
D002352:Carrier Proteins; D007381:Intermediate Filament Proteins; D016900:Neurofilament Proteins; D014746:Vimentin; C046643:alpha-internexin; C044882:neurofilament protein L