amanitins and Lymphoma

During the course of B lymphocyte differentiation into immunoglobulin secreting cells the abundance of mRNA for the heavy chain of secreted IgM (microS) increases dramatically. In order to understand the regulatory events responsible for the selective increase in micS mRNA we have looked for transcriptional alterations of VDJC mu gene segments as well as changes in the relative stability of microM and microS mRNA in BCL1 lymphoma cells which can be stimulated to increase the expression of microS mRNA. These experiments showed that although the transcriptional level of the mu gene locus is not preferentially augmented after stimulation, an alteration in the sites of polymerase termination is a significant factor contributing to the higher microS to microM ratio. This switch is dependent on new RNA synthesis. In addition, although the half-life of microS mRNA is not selectively increased, stimulation of the cells does result in a specific enhancement of the half-lives of both species of mu mRNA, which accounts for the higher steady state levels of total mu message.

Topics: Amanitins; B-Lymphocytes; Genes, Immunoglobulin; Immunoglobulin M; Immunoglobulin mu-Chains; Lymphocyte Activation; Lymphoma; Receptors, Antigen, B-Cell; RNA, Messenger; Transcription, Genetic; Tumor Cells, Cultured

A covalent conjugate of an alpha-amanitin azo derivative and a monoclonal immunoglobulin G to the Thy 1.2 antigen on murine T lymphocytes was synthesized. The conjugate was 375- to 750-fold more inhibitory to murine T lymphoma S49.1 cells than the unconjugated derivative. At 0.7 X 10(-7) to 1.5 X 10(-7) M and at 4 X 10(-7) M amanitin equivalents, the conjugate inhibited protein synthesis in S49.1 cells by 50 percent and 80 to 96 percent, respectively. At these concentrations, mutant Thy l-deficient S49 cells and other murine lymphoma lacking Thy l altogether or carrying Thy 1.1 antigens were unaffected. This result demonstrated the potential for targeting amanitin to specific cell types.

Topics: Amanitins; Amino Acids; Animals; Antibodies; Antibodies, Monoclonal; Antigens, Surface; Cells, Cultured; Clone Cells; Hybrid Cells; Immunoglobulin G; Lymphoma; Membrane Proteins; Mice; Neoplasms, Experimental; T-Lymphocytes; Thy-1 Antigens