| The research described in this thesis project evaluates the expression and functional significance of the nuclear receptor peroxisome proliferator activator receptor-gamma (PPAR-gamma) on B lineage cells. Normal mouse and human B cells and a variety of B lymphoma cells reflective of stages of B cell differentiation express PPAR-gamma mRNA, and by western blot analysis, the 67 kDa PPAR-gamma protein. Normal human B cells and B lymphomas were also found to express PPAR-gamma not only in the nucleus, but also in the cytoplasm, as determined by western blot analysis and immunohistochemistry. 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2), a PPAR-gamma agonist, has a dose-dependent anti-proliferative and cytotoxic effect on normal and malignant B cells as shown by [3H]-thymidine and 3-[4,5-dimethylthizol-2-yl]-2,5-diphenyltetrazolium bromide assays. Only PPAR-gamma agonists (thiazolidinediones), and not PPAR-alpha agonists, mimicked the effect of 15d-PGJ2 on B lineage cells, suggesting that the mechanism by which 15d-PGJ2 negatively affects B-lineage cells involves PPAR-gamma. The mechanism by which PPAR-gamma agonists induce cytotoxicity is via apoptosis, as shown by annexin V staining, morphology and TUNEL staining. Surprisingly, 15d-PGJ2 induced a massive increase in the MEK/ERK signaling pathway in B lineage cells. Pre-incubation with PGF 2alpha and a selective MAP kinase inhibitor, PD98059, blunted the 15d-PGJ2-induced MAP kinase activation of mouse and human B cells. Inhibition of 15d-PGJ2-induced MAP kinase activation rescued B lymphocytes from undergoing cell death in an apoptotic fashion. Therefore, the mechanism whereby 15d-PGJ2 interacts with B lymphocytes is MEK/ERK pathway dependent. PPAR-gamma agonists may serve as a counterbalance to the stimulating effects of other prostaglandins, namely PGE2, which promotes B cell differentiation. Finally, the use of prostaglandins such as 15d-PGJ2 and synthetic PPAR-gamma agonists to induce apoptosis in B lineage cells may lead to the development of novel therapies for autoimmune disease and certain cancers such as B cell lymphomas. |
