Differential immunoreactivity and Ca2+-dependent degradation of vimentin in human fibroblasts and fibrosarcoma cells.

Immunostaining of normal human fibroblasts with a monoclonal antibody (MAb) (V22AC12) revealed typical cytoplasmic arrays of vimentin filaments in both mitotic and interphase cells. In human A8387 fibrosarcoma cells and SV40-virus-transformed human fibroblasts, the same antibody showed positivity only in mitotic cells and in interphase cells only after treatment of the fixed cells with alkaline phosphatase. Upon immunoblotting with the MAb, an Mr 57,000 vimentin polypeptide was seen in normal fibroblasts. In fibrosarcoma cells the same polypeptide was revealed by this antibody only after treatment with alkaline phosphatase. The Mr 57,000 vimentin polypeptide was a major cytoskeletal protein in both fibroblasts and fibrosarcoma cells. Inclusion of Ca2+ into the cytoskeleton extraction medium brought about a somewhat increased degradation of vimentin in fibroblasts. In fibrosarcoma cells, such treatment caused a quantitative disappearance of the Mr 57,000 protein with a concomitant appearance of 3 distinct, low-molecular-weight degradation products in the detergent-soluble fraction. Another Ca2+-induced change in the polypeptide profile of fibrosarcoma cells was the disappearance of the Mr 240,000 non-erythroid alpha-spectrin and the concomitant appearance of a prominent Mr 140,000 degradation product. Inclusion of proteolysis inhibitors in the Ca2+-supplemented extraction medium inhibited degradation of both vimentin and alpha-spectrin polypeptides. The results suggest differences in the composition of the cytoskeletons of normal fibroblasts and fibrosarcoma cells, manifested in the differential Ca2+-susceptibility of vimentin and non-erythroid alpha-spectrin. Results with MAb V22AC12 suggest that differential phosphorylation of vimentin could account for at least part of this difference.