Characterization of two highly phosphorylated cytoskeleton-associated proteins, pp58 and pp60, in tumoricidal murine peritoneal macrophages and their comparison with vimentin

Two TX-insoluble cytoskeleton-associated proteins, pp58 and pp60, become highly phosphorylated in tumoricidal murine peritoneal macrophages. Results suggest that pp58 (pI 5.00) is phosphovimentin because it is highly insoluble in TX, shares the same mol. wt as vimentin, has a more acidic isoelectric point than vimentin, is phosphorylated primarily at serine, and generates the same V-8 protease peptide map as vimentin. pp60 generates at slightly different peptide map than pp58 and has a slightly less acidic isoelectric point (pI 5.02) than pp58 (pI 5.00), but is similar to pp58 by being highly insoluble in TX and being phosphorylated primarily at serine residues. Pulse-chase experiments demonstrate that pp58 is not a precursor to or breakdown product of pp60, or vice versa because they show similar rates of [32P]-phosphate incorporation and turnover.