Appearance of cytoskeletal components on the surface of leukemia cells and of lymphocytes transformed by mitogens and Epstein-Barr virus.

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Abstract
Lactoperoxidase iodination and 2-dimensional electrophoresis of the labeled proteins have demonstrated well-characterized cytoskeletal proteins (actin and tubulins) on the surface of human lymphocytes undergoing blastogenic transformation and of certain malignant human cells. Such proteins could not be detected on the surface of normal resting human lymphocytes. The most prominent cytoskeletal protein identified on the surface membrane of mitogen-transformed T and B lymphocytes was actin. In Epstein-Barr virus genome-positive Burkitt''s lymphoma and lymphoblastoid cell lines and in 2 leukemia cells, the major iodinated membrane protein components were actin and .alpha.1-, .alpha.2- and .beta.-tubulins. These proteins were firmly connected to the cytoplasmic skeleton and could not be removed by Triton X-100. Concurrent immunofluorescence studies with specific antibodies and F(ab'')2 fragments confirmed the appearance of cytoskeletal components on the surface of live and fixed lymphocytes, in parallel with the biochemical data, and indicated that such cytoskeletal proteins formed distinctive patterns on the cell surface, ranging from small patches to large projections. Five hour labeling with [35S]methionine indicates that all such cells released large quantities of labeled actin and tubulins into the culture medium. These materials were not readsorbed to the membrane surfaces of the cells.