Experimental studies on glioma cell motility and proliferation

Abstract: Glioma is a malignant primary brain tumor associated with short patient survival. Various growth factors and cytoskeletal proteins are correlated to glioma progression. In this thesis the effects of transforming growth factor alpha (TGFα) and glial fibrillary acidic protein (GFAP) were studied.TGF-α is a potent mitogen that belongs to the epidermal growth factor (EGF) family. It binds to and activates the EGFR, which is a receptor tyrosine kinase. Glioma cell line U-1242 MG was transfected with human TGF-α cDNA in a tetracycline regulated system, to carry out in vitro and in vivo studies. TGF-α induced glioma cell motility via EGFR activation independent of cell density which implied a "private" autocrine TGF-α /EGFR loop. It was found that the binding of TGFα to the EGFR occurs in compartments that are not completely accessible to an extra-celularly added antibody.Nude mice were injected subcutaneously with the TGF-α inducible and control cells. TGF-α- inducible cells developed into the largest tumors, and i.p. administration of an EGFR-tyrosine kinase inhibitor significantly reduced the sizes of these tumors. Results indicate that an active TGF-α /EGFR autocrine loop leads to increased tumor growth in vivo.The intracellular effects of EGFR activation associated with glioma cell motility and ruffling have been investigated. Two major EGFR-signaling pathways, MAP kinase and phosphoinositide 3 kinase (PI3 kinase), were tested by using specific inhibitors. Results showed that the EGFR downstream pathway diverges. Inhibition of MAP kinase only affects motility, while inhibition of PI3 kinase can affect both motility and cell morphology.The GFAP studies were performed on two glioma cell lines, U-1242 MG and U-251 MG sp 3A which were transfected with a human GFAP cDNA. The effects of GFAP were studied on crude cultures as well as at single cell level. Results show that GFAP expression leads to inhibition of cell motility and proliferation and to a change in cell morphology.