Myosin is a component of the cell surface of cultured cells

Antisera to myosin from mouse L929 cells, mouse uterus, and rabbit skeletal muscle, were prepared in goats. Each antiserum shows specific reaction by immunodiffusion only to the myosin against which it was prepared. Antiserum against L cell myosin agglutinates L929 cells and shows surface localization in unfixed cells by indirect immunofluorescence. This reaction is prevented by immunoabsorption with L cell myosin, but not by absorption with mouse uterine or rabbit skeletal muscle myosins. Elution of the antibody from L cell myosin antiserum that absorbs to fixed L cells yields antibody reactive to L cell myosin in immunodiffusion. At the ultrastructural level, surface localization is also evident with a peroxidase bridge immunocytologic method as a uniform distribution of surface label. Antiserum against L cell myosin also shows localization on the surface of other cells of rodent origin (3T3 4, NRK, MNRK, KNRK, and MEF) and HeLa cells, but not with some other cells of human origin (ALL and WI38). The reactivity with antibody of the plasma membrane myosin is unaffected by trypsin treatment or fixation with 0.5-2.0% formalin. These results strongly suggest that myosin in cultured nonmuscle cells is a component of the plasma membrane, a finding of possible significance in studying the mechanisms regulating the motility, morphology, and growth of these cells.