Apoptosis in cancer : regulation and prognostic value

For a tumor cell to propagate, it must survive extremely stressful conditions that would normally trigger the cell to die. Cancer cells however survive, probably due to evasion of the apoptotic cell death pathway. It follows that a detailed understanding of the regulation of the apoptotic pathways in cancer cells can improve the anti-cancer treatments. Part 1 of this thesis describes our in vitro studies regarding the regulation of apoptosis in melanoma cells, since melanoma is a form of cancer that is highly resistant to anti-cancer therapies. c-Myc enhances the apoptosis sensitivity of the cells. The protein Apaf-1 is not involved in this sensitivity. A yet unidentified serine protease plays an important role in the initiation of apoptosis upon DNA damage. Part 2 of this thesis describes our studies regarding both the regulation of apoptosis in rectal carcinoma and its prognostic value for rectal cancer patients. To evaluate the impact of (radiation-induced) tumor cell apoptosis on clinical outcome of cancer patients, the level of apoptosis have been determined in non-irradiated and irradiated rectal carcinoma samples. The level of tumor cell apoptosis is scored by immunohistochemical stainings of the carcinoma samples, and by measuring caspase-3 activity. Both studies show that high levels of apoptosis is associated with a low local recurrence risk. A genetic approach is used to identify factors that play a role in the regulation of apoptosis in rectal carcinoma in vivo. After evaluation two microarray procedures, the most convenient procedure is used to compare the gene expression profiles of tumors with high levels of apoptosis with low-apoptotic tumors. The difference in expression of several of the identified genes are confirmed on protein expression level by immunohistochemistry, and show two subsets of high-apoptotic tumors. These data suggest two different regulations of apoptosis in vivo. The prognostic value of one of the identified proteins, HLA-DR, has been studied in more detail and epithelial HLA-DR expression is significantly associated with lower recurrences and better survival for rectal cancer patients.LUMC / Geneeskund