<p>Glioblastoma multiforme (GBM) is the most common form of primary brain tumor in humans. Its aggressive and infiltrative growth into the brain, and, at best, only partial sensitivity to radiotherapy and chemotherapy, renders it extremely difficult to treat and survival remains dismal. </p><p>Growth factors, such as platelet-derived growth factor (PDGF) and epidermal growth factor (EGF), and their corresponding receptors are seen in glioma tissue, suggesting the presence of autocrine stimulatory loops. <i>PDGFB</i> and a mutated EGF receptor were also identified as cellular homologues of two oncoviruses, thereby indicating a role in tumorigenesis. This thesis presents a brain tumor model in mice, developed using a <i>PDGFB</i> coding retrovirus to induce overexpression of PDGF-B in neonatal mouse brain. Immature tumors, with histological characteristics of primary brain tumors developed at relatively high frequencies. Mice injected with a non-coding retrovirus did not develop tumors, indicating the crucial role of PDGF stimulation in this system. Tumor cells were also shown to continue to depend on PDGF stimulation when cultured <i>in vitro</i>. </p><p>In human glioblastomas, growth factor receptor signaling is present in conjunction with defects in cell cycle arrest pathways. When the <i>PDGFB</i>-virus model was used with <i>p53</i> or <i>Ink4a-Arf</i> deficient mice, tumors arose with shorter latency and higher frequency. Loss of <i>p53</i> or <i>Ink4a-Arf</i> seemed to facilitate signaling through the PI3K/Akt pathway. Thus, a functional role for the co-existence of p53 loss of function and PDGF signaling in a subset of gliomas is presented. </p><p>Human GBM samples were collected and analyzed with respect to expression and activation of the EGFR and PDGFRα. Most tumors expressed the both receptors at moderate to high levels, but high activation of either receptor seemed mutually exclusive.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-3445 |
| Date | January 2003 |
| Creators | Hesselager, Göran |
| Publisher | Uppsala University, Department of Genetics and Pathology, Uppsala University Library |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, 0282-7476 ; 1250 |
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