Studies of mechanisms of antibody formation. III. Effects of 5-bromodeoxyuridine upon normal and neoplastic B-lymphocyte function

The role of calmodulin in the regulation of human lymphocyte activation

Calmodulin (Cam) was isolated from normal and from transformed human lymphocytes by affinity chromatography on CAPP-Sepharose 4B, followed by chromatofocusing. In the presence of Ca2+, lymphocyte Cam migrated as a single protein on 2-DE, and was located on the same position as Cam extracted from dog brain and rat testis; its MW was 17,500, with a pI of 3.9. In the presence of Ca2+, lymphocyte Cam stimulated activator-depleted dog brain phosphodiesterase; this effect was inhibited by trifluoperazine (TFP) or by EGTA. By the RIA technique, the EGTA-soluble Cam content of resting lymphocytes constituted 0.58% of the total protein; the total Cam was comparable to the content of other major proteins in lymphocytes, such as actin, tubulin, and intermediate filament protein. The amount of Cam per cell and the rate of incorporation of L-[35S]methionine into Cam increased after mitogen-induced transformation. Immunofluorescence labeling of normal, mitogen-transformed, and EBV-genome-positive lymphocytes with affinity-purified anti-Cam antibodies showed bright fluorescence in the region of the Golgi apparatus, as well as diffuse cytoplasmic but scant nuclear staining. Similar patterns were observed in T suppressor, T helper, and B cells. Normal lymphocytes cultured in the presence of 2 X 10(-5) M TFP remained viable, but failed to undergo blastogenic transformation after stimulation with allogeneic cells, concanavalin A (Con A), or pokeweed mitogen (PWM). The same concentration of TFP inhibited the replication of EBV-genome-positive and of leukemia cells. Exposure of natural killer cells or allospecific killer cells to this concentration of TFP inhibited the effector phase of killing in a dose-dependent manner. In the presence of lower concentrations of TFP (0.25-1.0 X 10(-5) M) strong MLC responses were inhibited, while weak reactions were markedly amplified. A similar effect was not observed in lymphocytes stimulated into blastogenesis by lectins, suggesting that different Cam-dependent secondary messenger(s) may be involved in the blastogenic responses evoked by alloantigenic determinants. The amplification of weak MLC responses by 0.25-1.0 X 10(-5) M TFP constitutes the first biological illustration of the capacity of a Cam-binding agent to enhance as well as to inhibit cellular activation. The paradoxical effect may have been a consequence of a shift in the relative concentrations of the four known molecular Cam X Ca2+ conformers. The results are also consistent with the suggested capacity of Cam X Ca2+ conformers to activate different enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

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

Lactoperoxidase iodination and two-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 two 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 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.

Deoxyribonucleoside triphosphate pools and differential thymidine sensitivities of cultured mouse lymphoma and myeloma cells

The effects of various concentrations of thymidine on DNA synthesis and deoxyribonucleoside triphosphate contents of a highly thymidine-sensitive cultured mouse lymphoma cell line (WEHI-7) and a relatively resistant mouse myeloma cell line (HPC-108) have been studied by 32P-labelling techniques. DNA synthesis in the myeloma cells was inhibited by thymidine at concentrations of 10(-3) M or greater, while DNA synthesis in the lymphoma cells was inhibited by concentrations 30-fold lower, consistent with the 25-fold difference between the two cell lines in sensitivity to growth inhibition by thymidine. Thymidine caused marked elevation of the dTTP and dGTP pools, slight elevation or no change in the dATP pool and a marked decrease in the dCTP pool in cells of both lines. The greater resistance of HPC-108 cells to thymidine inhibition was related to the finding that they normally contained a much higher concentration of dCTP than did the WEHI-7 cells. Pool size measurements on thymidine-treated (10(-4) M) cells of an additional seven sensitive lymphoma and six relatively resistant myeloma cell lines indicated that in all 15 lines studied, with one exception, a critical concentration of dCTP of about 32 nmol per ml of cell volume was required for the maintenance of normal rates of DNA synthesis. The dCTP content found normally in the lymphoma cells was only a little above this concentration. Amongst the myeloma lines, three contained similarly low levels of dCTP, but were more resistant to thymidine inhibition probably because of their inefficient production of dTTP from thymidine. Cells of the other four myeloma lines (including HPC-108) normally contained much higher dCTP concentrations. The mechanism of thymidine action was explained by reference to the known allosteric properties of ribonucleotide reductase.