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Abstract

Multiple myeloma (MM) is a hematological malignancy characterized by the clonal proliferation of mature plasma cells in the bone marrow. During the progression of the disease, post-germinal B-cells proliferate and expand rapidly. In some cases, high amounts of proteins (immunoglobulins) can be detected in blood or urine. Additionally, many patients suffer from an activation of osteoclasts (cells that resorb bone). Without therapy, patients survive 3-6 months, treatment with state-of-theart therapy prolongs the life expectation to 3-6 years. The progression of the disease depends on the microenvironment in the bone marrow, since MM cells migrate into the bone marrow (homing) leading to increased tumorangiogenesis promoting the vascularization of the tumor. My thesis is about the influence of Galectin-8 (Gal-8) on the interaction of MM with endothelial cells (EC). Gal-8 is a carbohydrate binding protein (lectin) that consists of two carbohydrate recognition domains (CRD) connected by a peptide linker. I was able to show that the content of the Gal-8 protein in the serum of MM patients is higher compared to healthy donors and that high expression of Gal-8 on mRNA level correlates with a poor prognosis. Using several in vitro approaches, I showed that Gal-8 binds both, MM and EC and has no effect on angiogenesis, but on homing of MM to EC. Recombinant Gal-8 enhances the binding of MM cells to EC is in static, as well as in shear stress conditions during the simulation of blood flow. Gal-8 conditioned MM supernatants were also capable of promoting adhesion. Gal-8 appears in two isoforms differing in the length of the linker peptide (S-short; L-long), the pro-adhesive effect is particularly stronger by the addition of the Gal-8L isoform. This effect might be explained by the formation of Gal-8 complexes. Although these processes have been assumed hypothetically, no experimental evidence exists. Using thermophoresis, I was now able to show that Gal-8L can form multimers. Interestingly, this happens without the addition of a carbohydrate ligand. These findings are in contrast to the existing interaction-models. The measurements show that Gal-8S and Gal-8L act differently in solution, this could have an impact on the biological activity of both isoforms.