Coexistence of desmin and the fibroblastic intermediate filament subunit in muscle and nonmuscle cells: identification and comparative peptide analysis.

Abstract

Extraction of chicken embryo fibroblasts (CEF) or baby hamster kidney (BHK) cells with 1% Triton X-100 and 0.6 M KCl leaves an insoluble cytoskeletal residue composed primarily of the 52,000 MW, subunit of intermediate filaments (F-IFP). In addition, CEF cytoskeletons exhibit a minor component with MW of 50,000, identified as .alpha.-desmin, 1 of the 2 major isoelectric variants of the intermediate filament subunit from smooth muscle. BHK cytoskeletons contain the 50,000 MW mammalian desmin variant. Cytoskeletons prepared from chicken embryonic myotubes contain F-IFP and both .alpha.- and .beta.-desmin. Apparently 2 distinct 10-nm filament subunits coexist in a single cell. One-dimensional peptide analysis of F-IFP and desmin from avian and mammalian cells reveals significant interspecies homology, as well as homology between F-IFP and desmin from the same species. Peptide analyses of 32P-labeled intermediate filament subunits suggest that there is considerable similarity in the phosphorylation sites of these proteins. F-IFP and desmin might be evolutionally related.