UC San Diego

Apoptosis (programmed cell death) was first described 40 years ago, and has been the subject of active study for the past 20 years. Discovery of death stimuli, death receptors, and downstream signals in the mechanisms for apoptosis has provided information for the design of treatment strategies for various cancers. The cell line used for this study, S49, is a murine lymphoma derived from immature T lymphocytes. Studies of apoptosis in S49 lymphona cells, in particular in response to increases in glucocorticoid and the second messenger cAMP, may serve as a basis for the design of drugs for the treatment of lymphoma or leukemia cancer patients. The focus of efforts in this thesis was on the protein Bim, a pro-apoptotic member of the Bcl family, which initiates downstream signals that lead to cell death. My studies involved the use of double transgenic rtTA/tetO-Bim S49 cell lines to conditionally express Bim with doxycycline treatment. The results show that increased expression of Bim in response to doxycycline is sufficient to trigger S49 cell apoptosis. In addition, studies conducted with S49 cells with plasmid insert that produces Bim short hairpin RNAs show that Bim is necessary for cAMP/PKA- and glucocorticoid-induced apoptosis. Thus, expression of Bim appears to be necessary and sufficient to induce apoptosis in S49 cells, and the PKA and glucocorticoid pathways converged upstream or at the point of induction in Bim expression. The results thus define the mechanism for the killing of S49 cells by cAMP/PKA and glucocorticoids