Actin changes in normal human and rat leukocytes and in transformed human leukocytic cells

The DNase I inhibition assay was used for the determination of the relative amounts of monomeric and total actin in normal human peripheral blood lymphocytes, normal Sprague-Dawley rat peritoneal leukocytes, and 6 transformed human cell lines of lymphoid and myeloid origins. In the normal lymphocytes and leukocytes, greater than 50% of the total actin was monomeric. In contrast, only 1 of the 6 transformed lines had greater than 50% of its actin in the monomeric form. In the other 5 lines, the percentage of actin in the monomeric form ranged from 23 to 39%. The normal lymphocytes, peritoneal leukocytes, and 2 of the transformed cell lines (CEM and K562) were examined in greater detail. The total actin (as a percentage of the total protein) was found to be much lower in the transformed cell lines than it was in the normal lymphocytes. The total amount of actin in the normal rat leukocytes was very similar to the amount in the normal human lymphocytes. In addition to these differences between the normal and transformed human cells, treatment of the normal lymphocytes with mitogenic doses of concanavalin A was found to significantly reduce the amount of monomeric actin in the cells. Similar treatment of the transformed cells produced no significant reduction in the monomeric actin.