calcimycin and Leukemia-L5178

Fas-mediated cytotoxicity or activation-induced cell death (AICD) were analyzed and compared between a CD4+ cytotoxic T-cell clone (DB14) and a T-hybridoma (DBhy22) both of which bear the same T-cell antigen receptor (TCR) specific for p43-58 and restricted to I-Ab/d. DBhy22 expressed detectable FasL mRNA 4 h after activation through TCR and the expression of FasL mRNA reached a peak after 8 h of activation. The expression level of FasL mRNA was clearly associated with the level of Fas-mediated cytotoxicity and AICD seen after activation. On the other hand, FasL mRNA and FasL molecules were constitutively expressed in DB14 irrespective of the activation state. However, DB14 exhibited the Fas-mediated cytotoxicity only after activation. The present study suggests that Fas-mediated cytotoxicity requires not only FasL expression but also other activation signals.

Topics: Animals; Apoptosis; Calcimycin; Calcium; CD4-Positive T-Lymphocytes; Clone Cells; Coculture Techniques; Cytotoxicity, Immunologic; Fas Ligand Protein; fas Receptor; Gene Expression Regulation; Histocompatibility Antigens Class II; Hybridomas; Ion Transport; Ionophores; L Cells; Leukemia L5178; Lymphocyte Activation; Membrane Glycoproteins; Mice; Receptors, Antigen, T-Cell; RNA, Messenger; T-Lymphocytes, Cytotoxic; Th1 Cells; Tumor Cells, Cultured

We examined the response of L5178Y-S (radiosensitive, LY-S) and L5178Y-R (radioresistant, LY-R) lymphoblasts to X-irradiation with concomittant treatment with divalent cation ionophore, A23187 (3 h or 5 h, 5 micrograms/ml). Cells treated with A23187 alone progressed through the cell cycle more slowly than the untreated cells and their cloning efficiency was reduced. In both cell strains the ionophore prolonged duration of the postirradiation mitotic delay. Radiation-induced inhibition of DNA synthesis was reversed by A23187 in LY-S but not in LY-R cells. Cells subjected to the ionophore treatment survived X-irradiation in almost the same way as untreated cells, as if the effect of A23187 treatment were reversed by irradiation. There was also a reversion in the ion content: A23187 caused a marked increase in Na+ content and a decrease in K+ content, irradiation itself did not change the ion content, whereas in the A23187-treated cells it restored almost the same pattern as that found in the control cells. We found less Mg2+ ions in LY-S cells after treatment with A23187 and A23187 + X than in LY-R cells, in relation to untreated (control) cells. These observations point to the possible importance of ion transport for recovery from radiation damage.

Topics: Animals; Calcimycin; Cations; Cell Survival; DNA, Neoplasm; L Cells; Leukemia L5178; Mice; Radiation Tolerance