cytochalasin-b and Lymphoma--B-Cell

The CD53 antigen is a member of the tetraspan family of proteins with unknown function. Stimulation of rat IR938F B-cell lymphoma cells with monoclonal antibody MRC OX44 (anti-rat CD53) triggered a homotypic adhesion reaction which reached a maximum effect at 24 hr. This effect occurred at 37 degrees C but not at 4 degrees C. Adhesion was prevented by removal of divalent cations, Ca2+ and Mg2+, with EGTA and EDTA as chelating agents. The adhesion induced by MRC OX44 was inhibited by cycloheximide and actinomycin D, suggesting that de novo protein synthesis was required for this effect. The addition of mAb WT1 against rat LFA-1 (CD11a) antigen had no effect on adhesion, suggesting that the cell-cell interaction is not mediated by the expression of LFA-1 antigen. The intracellular signals required to induce adhesion were inhibited by two tyrosine kinase inhibitors, genistein and piceatannol. Wortmannin, a selective inhibitor of phosphoinositide 3-kinase activity, completely blocked adhesion. Two protein kinase C inhibitors, H7 and bisindolylmaleimide, inhibited the adhesion, suggesting that part of the signal is mediated by PKC. Electron microscopy of aggregated cells showed that the interaction is localized to short membrane regions, where contact areas of higher density in opposing zones from both cells were detected. We postulate that there is a common adhesion mechanism that is modulated by several tetraspan family members and associated proteins. This adhesion structure might represent a novel form of cell communication among lymphoid cells.

Topics: Animals; Antigens, CD; Antigens, Differentiation, T-Lymphocyte; B-Lymphocytes; Cations, Divalent; Cell Adhesion; Cell Adhesion Molecules; Cell Communication; Cytochalasin B; Histocompatibility Antigens Class II; Humans; Lipopolysaccharides; Lymphocyte Function-Associated Antigen-1; Lymphoma, B-Cell; Membrane Glycoproteins; Phorbol Esters; Phosphatidylinositol 3-Kinases; Phosphotransferases (Alcohol Group Acceptor); Phosphotyrosine; Protein Kinase C; Protein-Tyrosine Kinases; Rats; Tetraspanin 25; Tumor Cells, Cultured; Tunicamycin

The cytochalasins are fungal metabolites that have previously been shown to have some chemotherapeutic potential. When various cell types are treated in vitro with both cytochalasin B and vincristine, the resultant DNA fragmentation is greater than the sum of that caused by each agent alone. The levels necessary to achieve this potentiation are obtainable in vivo. DNA fragmentation induced by cytochalasin E, an actin-specific agent, is potentiated by vincristine. Pretreatment of the mastocytoma line P815 with vincristine results in an enhancement of the ability of cytochalasin B to fragment DNA. These results indicate that cytochalasin B might be effective as a chemotherapeutic agent in the presence of vincristine.

Topics: Cytochalasin B; DNA Damage; DNA, Neoplasm; Drug Synergism; Humans; Lymphoma, B-Cell; Lymphoma, T-Cell; Mast-Cell Sarcoma; Vincristine