Differences among 100-A filamentilament subunits from different cell types.

Abstract

The protein subunit of 100 .ANG. filaments constitutes approximately 50% of the cytoskeleton protein of chick fibroblasts. In addition to the 43,000 dalton protein (constitutive actin) common to all cell types, fibroblast cytoskeletons contain a 58,000 dalton protein likely to be the 100 .ANG. filament subunit, but smooth muscle contains, instead, a 55,000 dalton protein. Additional differences among 100 .ANG. filaments are shown by immunofluorescence, using antibodies against chick fibroblast 58,000 dalton component (anti-F58K) and against chick brain 100 .ANG. filament subunits (anti-BF). Anti-F58K binds to 100 .ANG. filaments in chick fibroblasts, presumptive myoblasts, chondroblasts, pigment cells and neurons, but not to 100 .ANG. filaments in mouse or human fibroblasts. This antibody stains cables of 100 .ANG. filaments induced by sequentially treating cells with cytochalasin B and Colcemid. Anti-BF binds only to neurofilaments and not to 100 .ANG. filaments of other cell types studied. Absorption of antibodies with purified subunits from gizzard 100 .ANG. filaments eliminates binding of anti-F58K to the filaments of all cell types but does not diminish binding of anti-BF to neurofilaments. Various Ig[immunoglobulin]Gs also bind nonspecifically to induced cables of 100 .ANG. filaments. The problem of nonspecific binding of labeled antibodies and the problem of cell and species specificity of the 100 .ANG. filaments, is discussed.