Tubulin as a Major Cell Surface Protein in Human Lymphoid Cells of Leukemic Origin1

Surface-exposed proteins of vinblastine-sensitive human lymphoid cell line of leukemic origin (CCRF-CEM) were exam ined by the lactoperoxidase-catalyzed iodination and two-di mensional polyacrylamide gel electrophoresis methods. Spots which comigrate with bovine brain tubulin and rabbit muscle actin were prominently labeled in the whole membrane but not in the high-speed supernatant fraction of the disrupted cells. Mild trypsinization of labeled cells removed the iodinated tu bulin and actin without significantly affecting the protein stain ing pattern. Iodination of normal human lymphocytes resulted in no labeling of the tubulin or actin. The presence of surfaceexposed tubulin in this leukemic cell line suggests a possible mechanism for their enhanced sensitivity to the cytotoxic action of vinblastine.